Serum Concentrations of Losartan Metabolites Correlate With Improved Physical Function in a Pilot Study of Prefrail Older Adults

Losartan is an oral antihypertensive agent that is rapidly metabolized to EXP3174 (angiotensin-subtype-1-receptor blocker) and EXP3179 (peroxisome proliferator-activated receptor gamma [PPARγ] agonist), which was shown in animal studies to reduce inflammation, enhance mitochondrial energetics, and improve muscle repair and physical performance. We conducted an exploratory pilot study evaluating losartan treatment in prefrail older adults (age 70-90 years, N = 25). Participants were randomized to control (placebo) or treatment (daily oral losartan beginning at 25 mg per day and increasing every 8 weeks) for a total of 6 months. Fatigue, hyperkalemia, and hypotension were the most observed side effects of losartan treatment. Participants in the losartan group had an estimated 89% lower odds of frailty (95% confidence interval [CI]: 18% to 99% lower odds, p = .03), with a 0.3-point lower frailty score than the placebo group (95% CI: 0.01-0.5 lower odds, p = .04). Frailty score was also negatively associated with serum losartan and EXP3179 concentrations. For every one standard deviation increase in EXP3179 (ie, 0.0011 ng/μL, based on sample values above detection limit) and EXP3174 (ie, 0.27 ng/μL, based on sample values above detection limit), there was a 0.0035 N (95% CI: 0.0019-0.0051, p < .001) and a 0.0027 N (95% CI: 0.00054-0.0043, p = .007) increase in average knee strength, respectively.

ABCB1 c.2677G>T/c.3435C>T diplotype increases the early-phase oral absorption of losartan

Losartan has been shown to be a substrate of the drug-efflux transporter MDR1, encoded by the ABCB1 gene. ABCB1 c.2677G>T and c.3435C>T variants are known to be associated with reduced expression and function of P-glycoprotein (P-gp). We investigated the effects of ABCB1 diplotype on the pharmacokinetics of losartan. Thirty-eight healthy Korean volunteers with different ABCB1 diplotypes [c.2677G> T and c.3435C>T; carriers of GG/CC (n = 13), GT/CT (n = 12) and TT/TT (n = 13) diplotype] were recruited and administered a single 50 mg oral dose of losartan potassium. Losartan and its active metabolite E-3174 samples in plasma and urine were collected up to 10 and 8 h after drug administration, respectively, and the concentrations of both samples were determined by HPLC method. Significant differences were observed in C_max of losartan and losartan plus E-3174 (Lo + E) among the three diplotype groups (both P < 0.01). However, the power of the performed test is less than the desired power (0.800). The t_max of losartan and E-3174 in three diplotype groups were also significantly different (both P < 0.01). The AUC values of Lo + E were significantly different among the three diplotype groups until 6 h after losartan administration (P < 0.01). On the contrary, AUC at the periods of 8-10 h and 10 h-infinity of Lo + E were significantly lower in the TT/TT group than in the GG/CC group. Urinary excretion of losartan until 4 h after losartan administration in the TT/TT group was higher than that of the GG/CC group. These results suggest that c.2677G>T/c.3435C>T diplotypes of ABCB1 may significantly increase the early-phase absorption of losartan, but not the total absorption.

Effect of Hibiscus sabdariffa and Zingiber officinale on the antihypertensive activity and pharmacokinetic of losartan in hypertensive rats

The present study aimed to determine the effect of Hibiscus sabdariffa and Zingiber officinale on antihypertensive activity and pharmacokinetic of losartan in hypertensive rats.Hypertension was induced in rats by oral administration of L-NAME (40 mg/kg per day). Pharmacodynamics and pharmacokinetics of losartan were evaluated without and with herbal treatment in hypertensive rats.Treatment of hypertensive rats with investigated herbs substantially reduced systolic blood pressure (SBP), and diastolic blood pressure (DBP) of rats. Treatment of rats (n = 5) with L-NAME plus H. sabdariffa plus losartan and L-NAME plus Z. officinale plus losartan reduced SBP by 16.20% and 14.88% and DBP by 14.82% and 17.52% respectively after 12 h, as compared to L-NAME alone treated rats. In a pharmacokinetic study, the Cmax and AUC0-t of losartan in L-NAME plus H. sabdariffa plus losartan and L-NAME plus Z. officinale plus losartan treated rats was increased by 0.7, 1.99 and 1.51, 3.00 fold respectively in comparison to the Cmax and AUC0-t obtained for L-NAME plus losartan treated group. In conclusion, both the investigated herbs significantly increased the antihypertensive effect and plasma concentration of losartan in L-NAME induced hypertensive rats. The current study predicted that the herb-drug interaction between H. sabdariffa-losartan and Z. officinale-losartan could occur; hence these results in rats may warrant further studies in humans, either in humans or in in vitro human liver microsomes.

Evaluation of potential herbal-drug interactions of a standardized propolis extract (EPP-AF®) using an in vivo cocktail approach

ETHNOPHARMACOLOGICAL RELEVANCE

Propolis has been employed extensively in many cultures since ancient times as antiseptic, wound healing, anti-pyretic and others due to its biological and pharmacological properties, such as immunomodulatory, antitumor, anti-inflammatory, antioxidant, antibacterial, antiviral, antifungal, antiparasite activities. But despite its broad and traditional use, there is little knowledge about its potential interaction with prescription drugs.

AIM OF THE STUDY

The main objective of this work was to study the potential herbal-drug interactions (HDIs) of EPP-AF® using an in vivo assay with a cocktail approach.

MATERIALS AND METHODS

Subtherapeutic doses of caffeine, losartan, omeprazole, metoprolol, midazolam and fexofenadine were used. Sixteen healthy adult volunteers were investigated before and after exposure to orally administered 125 mg/8 h (375 mg/day) EPP-AF® for 15 days. Pharmacokinetic parameters were calculated based on plasma concentration versus time (AUC) curves.

RESULTS

After exposure to EPP-AF®, it was observed decrease in the AUC^0-∞ of fexofenadine, caffeine and losartan of approximately 18% (62.20 × 51.00 h.ng/mL), 8% (1085 × 999 h.ng/mL) and 13% (9.01 × 7.86 h.ng/mL), respectively, with all 90% CIs within the equivalence range of 0.80-1.25. On the other hand, omeprazole and midazolam exhibited an increase in AUC^0-∞ of, respectively, approximately 18% (18.90 × 22.30 h.ng/mL) and 14% (1.25 × 1.43 h.ng/mL), with the upper bounds of 90% CIs slightly above 1.25. Changes in pharmacokinetics of metoprolol or its metabolite α-hydroxymetoprolol were not statistically significant and their 90% CIs were within the equivalence range of 0.80-1.25.

CONCLUSIONS

In conclusion, our study shows that EPP-AF® does not clinically change CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A activities, once, despite statistical significant, the magnitude of the changes in AUC values after EPP-AF® were all below 20% and therefore may be considered safe regarding potential interactions involving these enzymes. Besides, to the best of our knowledge this is the first study to assess potential HDIs with propolis.

Interaction of pseudoephedrine and azithromycin with losartan: Spectroscopic, dissolution and permeation studies

This study aims at investigating the potential effect of selected cationic drugs (azithromycin (AZN) and pseudoephedrine sulfate (PSD) on the dissolution profile and intestinal permeation of losartan potassium (LOS) that might occur due to ion pair salt formation. DSC, FT-IR and ¹H NMR indicated the formation of ion pair salts between LOS and each of AZN and PSD. Based on NMR chemical shifts calculations, utilizing specialized software, the most likely structures of the salt were proposed and revealed interesting structural features. The obtained ion pair products were shown to have lower aqueous solubilities (water and phosphate buffer pH 6.8) and higher apparent partition coefficient values compared to the parent compound. Neither of the cations affected the dissolution of LOS tablet (Cozaar® 100 mg) in the studied media (HCl pH 1.2 and phosphate buffer pH 6.8). Interestingly, AZN significantly increased the dissolution of LOS in phosphate buffer pH 4.5 (f₂ = 33), and an explanation based on distinguished association pattern between AZN and LOS (CH/π) was offered. Employing permeation test across Caco-2 cells monolayer, the apparent permeability coefficient (Papp) of LOS increased significantly (from 0.9 × 10^-5 cm/s to 1.8 × 10^-5 cm/s) in the presence of the selected cations. Therefore, while the employed cationic drugs were not shown to form ion pair salts under the in-vitro dissolution conditions, they may still participate in significant in-vivo interaction with LOS.

Effects of Ginkgo leaf tablets on the pharmacokinetics of losartan and its metabolite EXP3174 in rats and its mechanism

CONTEXT

Ginkgo leaf tablets (GLTs) and losartan are often simultaneously used for the treatment of hypertension in Chinese clinics. However, the herb-drug interaction between GLT and losartan is still unknown.

OBJECTIVE

This study investigates the effects of GLT on the pharmacokinetics of losartan and its metabolite EXP3174 in rats and its potential mechanism.

MATERIALS AND METHODS

The pharmacokinetic profiles of losartan and EXP3174 of orally administered losartan (10 mg/kg) with or without GLT pretreatment (80 mg/kg/day for 10 days) in Sprague-Dawley rats were determined. In vitro, the effects of GLT on the metabolic stability of losartan were investigated with rat liver microsomes.

RESULTS

The C_max (1.22 ± 0.25 vs 1.85 ± 0.37 μg/mL) and the AUC_(0-t) (6.99 ± 1.05 vs 11.94 ± 1.79 mg·h/L) of losartan increased significantly (p < 0.05) with GLT pretreatment, while the C_max (1.05 ± 0.19 vs 0.72 ± 0.12 μg/mL) of EXP3174 decreased significantly (p < 0.05) compared to the control. The t_1/2 of losartan was prolonged significantly from 3.94 ± 0.62 to 4.75 ± 0.52 h (p < 0.05). The metabolic stability of losartan was increased from 37.4 min to 59.6 min with GLT pretreatment.

DISCUSSION AND CONCLUSIONS

The results indicate that GLT might increase the plasma concentration of losartan and decrease the concentration of EXP3174 through inhibiting the metabolism of losartan.

Formulation and in vitro evaluation of directly compressed controlled release tablets designed from the Co-precipitates

Controlled release dosage forms provide sustained therapeutics effects for prolonged period of time and improve patient compliance. In present study, controlled release co-precipitates of Metoprolol Tartrate and Losartan Potassium were prepared by solvent evaporation method using polymers such as Eudragit RL 100 and Carbopol 974PNF and controlled release tablets were directly compressed into tablets. In-vitro dissolution of controlled release co-precipitates were performed by USP Method-II (paddle method) and tablets were evaluated by USP Method-I (rotating basket method) in phosphate buffer (PH 6.8) using pharma test dissolution apparatus. The temperature was maintained constant at 37±1.0°C and the rotation speed of paddle and basket was kept constant at 100rpm. Drug release mechanisms were determined by applying Power Law kinetic model. The difference and similarity of dissolution profiles test formulations with reference standards were also determined by applying difference factor (f₁) and similarity factor (f₂). The results showed that the controlled release co-precipitates with polymer Eudragit RL 100 of both the drug extended the drug release rates for 10 hours and those having polymer Carbopol 974P NF extended the drug release rates for 12 hours. The controlled release tablets prepared from controlled release co-precipitates extended the drugs release up to 24 hours with both the polymers. The drug was released by all tests anomalous non fickian mechanism except F1 and F5 do not follow Power Law. The f₁ and f₂ values obtained were not in acceptable limits except F15 whose values were in acceptable limits. It is concluded from the present study that polymers (Eudragit RL 100 and Carbopol 974P NF) can be efficiently used in development of controlled release dosage forms having predictable kinetics.

Repeated administration of Sailuotong, a fixed combination of Panax ginseng, Ginkgo biloba, and Crocus sativus extracts for vascular dementia, alters CYP450 activities in rats

BACKGROUND

Sailuotong (SLT) is a standard Chinese preparation made from extracts of Panax ginseng (ginseng), Ginkgo biloba (ginkgo), and Crocus sativus (saffron). Preliminary clinical trials and animal experiments have demonstrated that SLT could improve cognition of vascular dementia (VD).

PURPOSE

To avoid incident drug-drug interaction which is easily encountered in patients of VD, the potential influence of SLT on main drug-metabolic cytochromes P450 enzymes (CYP450) was investigated.

METHOD

A "cocktail probes" approach was employed to evaluate the activities of CYP450. A rapid and selective analysis method was developed to examine 5 CYP probe drugs and their specific metabolites in plasma by using online SPE followed by a single LC-MS/MS run. After pretreatment for 2 weeks with SLT, ginseng, gingko, saffron or water (control), a cocktail solution containing caffeine, losartan, omeprazole, dextromethorphan and midazolam was given to rats orally. The plasma was obtained at different time intervals and then measured for the concentration of probes and their metabolites using developed SPE-LC-MS/MS method. Activity of five isozymes was estimated by comparing plasma pharmacokinetics of substrates and their metabolites (caffeine/paraxanthine for CYP1A2, losartan/E-3174 for CYP2C11, omeprazole/5-hydroxyl omeprazole for CYP2C6, dextromethorphan/dextrophan for CYP2D2 and midazolam/1-hydroxyl midazolam for CYP3A1/2) between control and drug treatment groups.

RESULT

Compared with control group, repeated administration of SLT induced CYP1A2 by enhancing AUC _paraxanthine / AUC _caffeine to144%. The influence is attributed to its herbal component of ginseng to a large extent. Meanwhile, metabolic ability towards losartan was significantly elevated in SLT and gingko group by 31% and 25% respectively, indicating weak induction of CYP2C11 in rats. The analysis on probes of omeprazole and dextromethorphan showed a lack of influence on CYP 2C6 and CYP2D2 in all treated groups. In terms of CYP3A1/2, SLT decreased AUC ratio of 1-hydroxyl midazolam to midazolam by 39% and extended the half-life of midazolam apparently. Besides, significantly decreased systematic exposure of midazolam suggested the inhibition on metabolism of CYP3A1/2 is likely secondary to the interaction on absorption at intestinal level. The inhibition of SLT on CYP3A was likely attributed to ginseng and gingko cooperatively.

CONCLUSION

Further observation on herb-drug interaction should be considered during clinical application of SLT.

Pharmacogenetic approach to losartan in Marfan patients: a starting point to improve dosing regimen?

BACKGROUND

Losartan is under evaluation for managing Marfan patients with aortic root dilatation. Cytochrome P450 (CYP) enzymes convert losartan to E3174 active metabolite. The aim of this study is to describe the distribution of CYP2C9*2, CYP2C9*3, CYP3A4*22 and CYP3A5*3 defective alleles, according to losartan tolerance in paediatric Marfan patients.

METHODS

We genotyped 53 paediatric Marfan patients treated with losartan. The rate of aortic root dilatation was evaluated using the delta z-score variation. Differences in tolerated losartan daily doses with respect to CYP metabolic classes were assessed through the Kruskal-Wallis test.

RESULTS

The losartan daily dose spans from 0.16 to 2.50 mg/kg (median 1.10 mg/kg). As we expect from the pharmacokinetics pathway, we observe highest tolerated dose in CYP2C9 poor metabolisers (median 1.50 mg/kg, interquartile range 1.08-1.67 mg/kg); however, this difference is not statistically significant.

CONCLUSIONS

The optimal dose of angiotensin receptor blocker is not known, and no data are available about losartan pharmacogenetic profile in Marfan syndrome; we have proposed a strategy to tackle this issue based on evaluating the major genetic polymorphisms involved in the losartan conversion into active carboxylic acid metabolite. Further studies are needed to support the use of genetic polymorphisms as predictors of the right dose of losartan.

Effects of berberine on the pharmacokinetics of losartan and its metabolite EXP3174 in rats and its mechanism

CONTEXT

Losartan and berberine (BBR) are often simultaneously used for the treatment of senile diabetic nephropathy in clinics. However, the potential herb-drug interaction between losartan and BBR is unknown.

OBJECTIVE

This study investigates the influence of BBR on the pharmacokinetics of losartan and EXP3174, and investigates the effects of BBR on the metabolic stability of losartan.

MATERIALS AND METHODS

The pharmacokinetic profiles losartan and EXP3174 of orally administered losartan (10 mg/kg) with and without pretreatment with BBR (20 mg/kg) within 24 h were determined in Sprague-Dawley rats. The inhibitory effects of BBR on the metabolic stability of losartan were investigated using rat liver microsomes.

RESULTS

The C_max (1.26 ± 0.37 versus 1.96 ± 0.45 mg/L) and the AUC_(0-t) (8.25 ± 0.89 versus 12.70 ± 1.42 mg h/L) of losartan were significantly (p < 0.05) increased by BBR compared to the control, while the C_max (0.97 ± 0.15 versus 0.77 ± 0.06 mg/L) of EXP3174 was significantly decreased compared to the control (p < 0.05). The T_max of losartan was prolonged from 0.41 ± 0.12 to 0.52 ± 0.18 h, but the difference was not significant. However, the T_max of EXP3174 was decreased significantly (p < 0.05) from 8.14 ± 0.36 to 3.33 ± 0.28 h. The metabolic stability of losartan was increased from 37.4 to 59.6 min.

DISCUSSION AND CONCLUSION

We infer that BBR might increase the plasma concentration of losartan and decrease the concentration of EXP3174 through inhibiting the activity of CYP3A4 or CYP2C9.

Effects of salvianolic acid B and tanshinone IIA on the pharmacokinetics of losartan in rats by regulating the activities and expression of CYP3A4 and CYP2C9

Losartan (LST) is a common chemical drug used to treat high blood pressure and reduce the risk of stroke in certain people with heart disease. Danshen, prepared from the dried root and rhizome of Salvia miltiorrhiza Bunge, has been widely used for prevention and treatment of various cardiovascular and cerebrovascular diseases. There are more than 35 formulations containing Danshen indexed in the 2010 Chinese Pharmacopoeia, which are often combined with LST to treat cardiovascular and cerebrovascular diseases in the clinic. The effects of the two major components of Danshen, salvianolic acid B (SA-B) and tanshinone IIA (Tan IIA), on the pharmacokinetics of losartan and its metabolite, EXP3174, in rats were investigated by liquid chromatography coupled with mass spectrometry (LC-MS). Male Sprague-Dawley rats were randomly assigned to 3 groups: LST, LST+SA-B and LST+Tan IIA, and the main pharmacokinetic parameters were estimated after oral administration of LST, LST+SA-B and LST+Tan IIA. It was found that there are significant differences in the pharmacokinetic parameters among the three groups: Cmax, t1/2, AUC, AUMC in the LST+SA-B group was smaller than those in group LST, while larger in group LST+Tan IIA. Further, the effects of SA-B and Tan IIA on the metabolism of losartan was also investigated using rat liver microsomes in vitro. The results indicated that SA-B can induce the metabolism of LST, while Tan IIA can inhibit the metabolism of LST in rat liver microsomes in vitro by regulating activities of CYP450 enzymes. In addition, the effect of SA-B and Tan IIA on CYP3A4 and CYP2C9 expression was studied in Chang liver cells by western-blotting and Real-time PCR. It was concluded that the two components of Danshen, SA-B and Tan IIA have different influences on the metabolism of LST: SA-B can obviously speed up the metabolism of LST by inducing CYP3A4/CYP2C9 activities and expression, however, Tan IIA can slow down the metabolism of LST by inhibiting CYP3A4/CYP2C9 activities.

Negligible Pharmacokinetic Interaction of Red Ginseng and Losartan, an Antihypertensive Agent, in Sprague-Dawley Rats

Red ginseng (RG) is one of the top selling herbal medicines in Korea, but is not recommended in hypertensive patients. In this study, the pharmacokinetic (PK) interaction between RG and losartan, an antihypertensive drug, was examined. RG was orally administered for 2 wk to male Sprague-Dawley (S-D) rats at either control (0), 0.5, 1, or 2 g/kg/d for 2 wk. After the last administration of RG and 30 min later, all animals were treated with 10 mg/kg losartan by oral route. In addition, some S-D rats were administered RG orally for 21 d at 2 g/kg followed by losartan intravenously (iv) at 10 mg/kg/d. Post losartan administration, plasma samples were collected at 5, 15, and 30 min and 1, 1.5, 2, 3, 6, 12, and 24 h. Plasma concentrations of losartan and E-3174, the active metabolite of losartan, were analyzed by a high-pressure liquid chromatography-tandem mass spectrometer system (LC-MS/MS). Oral losartan administration showed dose-dependent pharmacokinetics (PK) increase with time to maximum plasma, but this was not significant between different groups. There was no significant change in tmax with E-3174 PK. With iv losartan, pharmacokinetics showed elevation of area under the plasma concentration-time curve from time zero extrapolated to infinitity. There was not a significant change in AUCinf with E-3174 PK. Therefore, RG appeared to interfere with biotransformation of losartan, as RG exerted no marked effect on E-3174 PK in S-D rats. Data demonstrated that oral or iv treatment with losartan in rats pretreated with RG for 2 wk showed that losartan PK was affected but E-3174 PK remained unchanged among different dose groups. These results suggested that RG induces negligible influence on losartan and E-3174 PK in rats.

[EVALUATION OF THE PHARMACOKINETIC INTERACTION OF AFOBAZOLE WITH CYP2C9 ENZYME DRUG SUBSTRATE OF CYTOCHROME P450]

We have studied the pharmacokinetics of drug-marker of cytochrome P450 isoenzyme CYP2C9 (losartan) and its metabolite E-3174 after subchronic oral administration of afobazole in doses 5 and 25 mg/kg in rats. The metabolic ratio (MR) of E-3174/Losartan was calculated. The pharmacokinetic parameters of losartan and its metabolite on the background of 4-day afabazole administration 5 mg/kg dose were not significantly different from analogous values calculated for the control group of rats. Therefore, afobazole in the effective anxiolytic dose did not change the MR value of metabolized P450 isoform. A five-fold dose increase in the afobazole dose led to significant difference in pharmacokinetic parameters, including A UC0-t, Cmax, Kel, t1/2el, MRT, CL/F, and Vd/F of losartan and AUC0-T, Cmax, and Tmax of E-3174. These findings are indicative of the induction of CYP2C9 isoenzyme by afobazole.

Effects of licochalcon A on the pharmacokinetics of losartan and its active metabolite, EXP-3174, in rats

Losartan and licochalcon A interact with cytochrome P-450 (CYP) enzymes and P-glycoprotein (P-gp), and the increase in the use of health supplements may result in licochalcon A being taken concomitantly with losartan to treat or prevent cardiovascular diseases as a combination therapy. The effect of licochalcon A, a natural flavonoid, on the pharmacokinetics of losartan and its active metabolite, EXP-3174, was investigated in rats. Pharmacokinetic parameters of losartan and EXP-3174 were determined after oral administration of losartan (9 mg/kg) to rats in the presence or absence of licochalcon A (0.5, 2.5 and 10 mg/kg). The effect of licochalcon A on P-glycoprotein (P-gp) as well as CYP3A4 and 2C9 activities was also evaluated. Licochalcon A inhibited CYP3A4 and CYP2C9 enzyme activities with 50% inhibition concentrations (IC50) of 2.0 and 0.1 microM, respectively. In addition, licochalcon A significantly enhanced the cellular accumulation of rhodamine-123 in a concentration-dependent manner in MCF-7/ADR cells overexpressing P-gp. The pharmacokinetic parameters of losartan were significantly altered by licochalcon A. Licochalcon A (2.5 mg/kg or 10 mg/kg) increased AUC0-infinity of losartan by 33.4-63.2% and Cmax of losartan by 34.0-62.8%. The total body clearance (CL/F) was significantly decreased (2.5 mg/kg, p < 0.05; 10 mg/kg, p < 0.01) by licochalcon A. Consequently, the absolute bioavailability of losartan in the presence of licochalcon A increased significantly (2.5 mg/kg, p < 0.05; 10 mg/kg, p < 0.01) compared to that in the control group. The relative bioavailability (R.B.) of losartan was 1.15- to 1.63-fold greater than that of the control group. However, there was no significant change in Tmax and t1/2 of losartan in the presence of licochalcon A. Licochalcon A (10 mg/kg) increased the AUC0-infinity of EXP-3174 but this was not significant. Furthermore, concurrent use of licochalcon A (10 mg/kg) significantly decreased the metabolite-parent AUC ratio (M.R.) by 20%, suggesting that licochalcon A inhibited the CYP-mediated metabolism of losartan to its active metabolite, EXP-3174. In conclusion, the enhanced oral bioavailability of losartan in the presence of licochalcon A may mainly result from decreased P-gp-mediated efflux transporter in the small intestine and from the inhibition of CYP 3A- and CYP2C9-mediated metabolism in the small intestine and liver and/or from the reduction of total body clearance of losartan by licochalcon A.

Tamoxifen Inhibits Cytochrome P450 2C9 Activity in Breast Cancer Patients

Tamoxifen has been reported to potentiate the anticoagulant effect of warfarin and also to increase the plasma level of phenytoin, which are mainly metabolized by CYP2C9. The aim of this study was to determine the influence of tamoxifen on CYP2C9 activity in vivo in humans. Thirteen breast cancer patients who would start tamoxifen following cytotoxic chemotherapy were enrolled in the study. A single oral dose of 25 mg losartan was given to the patients 2 days before and 2 weeks after starting tamoxifen therapy. Losartan and E3174 in 8-hour urine samples were measured by HPLC. Tamoxifen significantly increased the average urinary losartan/E3174 ratio from 0.73 (CI 95% = 0.15 - 2.30) to 1.66 (CI 95% = 0.68 - 5.20), after 2 weeks of treatment (p = 0.002). Tamoxifen inhibited CYP2C9 activity in breast cancer patients within two weeks of its administration. The inhibition of CYP2C9 activity may be a possible explanation for the drug-drug interaction of tamoxifen with CYP2C9 substrates.

Inhalation delivery of Telmisartan enhances intratumoral distribution of nanoparticles in lung cancer models

The purpose of the present study was to evaluate the effect of Telmisartan (Tel) and Losartan (Los) on nanoparticle intratumoral distribution and anticancer effects in lung cancer. A549 lung tumor cells were orthotopically and metastatically administered to Nu/nu mice. Fluorescent polystyrene nanoparticles (FPNPs, size ~200 nm) beads were used to study their intratumoral distribution after Tel and Los treatments. Animals were administered with FPNPs and after 2h, FPNPs intratumoral distribution was studied by fluorescent microscopy. Tel (~1.12 mg/kg) and Los (~4.5mg/kg) were administered by inhalation delivery at alternative days for 4 weeks to tumor bearing animals. Collagen-1, transforming growth factor beta 1 (TGF-β1), cleaved caspase-3, Vimentin and E-Cadherin expressions were studied by western blotting. To correlate the AT1 receptor blockage to anticancer effects, VEGF levels and microvessel densities (MVD) were quantified. Los and Tel treated group resulted in the 5.33 and 14.33 fold increase respectively in the FPNPs intratumoral distribution as compared to the controls. Tel treatment attenuated 2.23 and 1.70 fold Collagen 1 expression compared to untreated control and Los groups, respectively. Further, in Tel and Los treated groups, the TGF-β1 active levels were significantly (p<0.05) decreased. Tel (at four times less dose) was 1.89 and 1.92 fold superior in anticancer activity to Los respectively in A549 orthotopic and metastatic tumor models (p<0.05) when given by inhalation route. Tel, by virtue of its dual pharmacophoric nature could be an ideal candidate for combination therapy to improve the nanoparticle intratumoral distribution and anticancer effects.

Drug-Disease Interactions: Losartan Effect Is Not Downregulated by Rheumatoid Arthritis

Inflammatory conditions, such as rheumatoid arthritis, reduce response to calcium channel and beta-adrenergic antagonists but not the angiotensin II type 1 receptor (AT(1)R) antagonist valsartan. Inflammation also reduces clearance of some drugs or active metabolite, thereby reducing response. Active (n = 14) and controlled rheumatoid arthritis (n = 12) and healthy subjects (n = 12) received losartan (100 mg). Blood pressures were measured, and samples were taken for pharmacokinetic and inflammatory mediator concentration determination. Active disease significantly increased arthritic index, nitric oxide, and Creactive protein. Although no between-group difference in plasma losartan concentration-time curves was observed, concentrations of the active metabolite, EXP 3174, were significantly reduced by arthritis. This, however, was not accompanied by reduced clinical response. One subject produced no detectable concentrations of EXP 3174 likely due to insufficient CYP2C9 activity. Despite reduced concentrations of the active metabolite, AT1R antagonists potency does not appear to be reduced by inflammation.

Comparative Study of Taste Disturbance by Losartan and Perindopril in Healthy Volunteers

The aim of this study was to compare the degree of taste disturbance by losartan, an angiotensin II receptor blocker, with that of perindopril, an angiotensin-converting enzyme inhibitor. Perindopril erbumine (2 mg), losartan potassium (25 mg), or vehicle was given to Japanese volunteers (n = 7) for 14 days in a randomized, placebo-controlled, 3-way crossover design with a 14-day washout period. Gustometry by filter-paper test and electrogustometry were performed before and at the end of each trial. Plasma renin activity (PRA) and serum and salivary zinc concentrations were measured. One subject dropped out because of a perindopril-induced dry cough, but no one claimed a taste disturbance. Detection thresholds of 4 basic tastes (sweet, salty, sour, and bitter) by the paper-disc test and electrogustometry were significantly worsened, and plasma renin activity was elevated by the drugs, whereas the deteriorating effects of 2 drugs did not significantly differ. These drugs did not affect zinc concentrations in plasma and saliva. It was concluded that losartan and perindopril similarly alter taste sensitivity during repeated dosing of the drugs.

[Relationship between warfarin dosing and activity of CYP2C9 assessed by the content of losartan and its metabolite E-3174 in the urine of patients with mechanical prosthetic heart valves]

We evaluated effect of activity of cytochrome P450 CYP2C9 on maintenance doses of warfarin in 33 patients with implanted artificial heart valves. Losartan test was used for measurement of concentration of active metabolite E-3174 in urine. Concentration of E-3174 below 2500 ng/ml in patients with genotype CYP2C981/*1 with sensitivity 87% and specificity 66% predicted requirement of low doses (< 5 mg/day) of warfarin in the late postoperative period (odds ratio 14, 95% confidence interval 1.135 to 172.75).

[In vivo study of the pharmacokinetic interaction of afobazole and losartan (cytochrome CYP2C9 substrate)]

The influence of afobazole on isoenzyme CYP2C9 production in rats was studied using losartan as the marker drug. Single dose of losartan was administered orally without afobazole in a dose of 30 mg/kg and in the same single (30 mg/kg) on the background of 3- and 4-day administration of afobazole in a dose of 5, 25, 75, 100, and 125 mg/kg. At 5 mg/kg (effective dose for anxiolytic effect), afobazole did not cause any induction/inhibition effect on CYP2C9 isoenzyme. A multiple increase in afobazole dose was manifested by a moderate induction effect. The maximum induction effect of afobazole was achieved in a dose of 75 mg/kg. At doses above 75 mg/kg, the induction effect of afobazole was less pronounced.

[Pharmacokinetic drug interactions by herbal drugs: Critical evaluation and clinical relevance]

Pharmacokinetic herb-drug interactions are caused by an induction or inhibition of cytochrome P450 (CYP) enzymes or transporters e.g. P-glycoprotein. St. John's wort extracts containing hyperforin increase the expression of CYP-enzymes and P-glycoprotein mainly in the gut and liver which leads to a clinically relevant decrease of the bioavailability of CYP and P-glycoprotein substrates. Contrarily, the bioactivation of the prodrug losartan is reduced by milk thistle extracts which is due to an inhibition of CYP2C9. However, the 15 % reduction of the bioavailability of the active metabolite E-3174 is clinically not relevant. Also, minor changes in drug bioavailability observed in clinical studies for valerian, echinacea, ginkgo and hawthorne are clinically not relevant, although in vitro studies point to drug interactions in vivo. Since for herbal extracts a positive in vitro - in vivo correlation regarding the impact on drug bioavailability is rare, results from in vitro studies should be carefully interpreted.

Pharmacokinetics of a losartan potassium released from a transdermal therapeutic system for the treatment of hypertension

Monolithic transdermal therapeutic systems (TTS) were developed for sustained antihypertensive effect of losartan potassium using the polymers Eudragit E 100 and polyvinyl pyrrolidone VA 64. The developed formulations (polymeric films) were evaluated for physical characteristics, ex vivo (histopathology) and in vivo (pharmacokinetic studies). Pharmacokinetic parameters, such as C(max), t(max), and AUC were estimated. The transdermal formulation in the present study was found to enhance the relative bioavailability of losartan potassium by 2.2 times with reference to an oral delivery. The increased bioavailability might be due to elimination of hepatic first pass metabolism. Thus, the transdermal formulation F3E with polymeric composition of Eudragit E 100 and polyvinyl pyrrolidone VA 64 (5:3) was found to provide prolonged steady state concentrations of losartan potassium with minimal fluctuations and improved bioavailability.

Effect of soy extract administration on losartan pharmacokinetics in healthy female volunteers

BACKGROUND

osartan is metabolized by CYP2C9 and CYP3A4 to an active metabolite, E-3174, which has greater antihypertensive activity than the parent compound. Soy extract has been shown to be an activator of CYP2C9 and CYP3A4 in vitro. Coadministration of soy extract and losartan may therefore alter the pharmacokinetics of losartan and E-3174.

OBJECTIVE

To determine whether, when losartan was used in combination with soy extract, a significant pharmacokinetic interaction would be observed in healthy female volunteers.

METHODS

Eighteen healthy Chinese female volunteers were recruited. In an open-label, 2-phase study, losartan 50 mg was given to each subject, with and without soy extract. Plasma concentrations of losartan and E-3174 were determined by liquid chromatography-tandem mass spectrometry for 12 and 24 hours, respectively. On day 8 through day 21 of the study, following a 7-day washout period, each subject consumed two 1000-mg Genistein Soy Complex tablets orally after meals, twice daily, for 14 days. On day 22, all volunteers received losartan 50 mg and blood samples were collected again.

RESULTS

All subjects completed the study, without adverse drug effects. Over the 14-day pretreatment period, soy extract did not significantly influence the pharmacokinetics of losartan or E-3174. The ratio of the area under the curve of the drug and metabolite after losartan administration, with and without soy extract ingestion, was 0.21 +/- 0.05 and 0.23 +/- 0.05 (mean +/- SD), respectively. The difference was not statistically significant (p = 0.22).

CONCLUSIONS

Our data indicate that a significant interaction between soy extract and losartan is unlikely to occur in females.

Inhibitory Effect of Valproic Acid on Cytochrome P450 2C9 Activity in Epilepsy Patients

Drug interactions constitute a major problem in the treatment of epilepsy because drug combinations are so common. Valproic acid is a widely used anticonvulsant drug with a broad therapeutic spectrum. Case reports suggest interaction between valproic acid and other drugs metabolized mainly by cytochrome P450 isoforms. The aim of this study was to evaluate the inhibitory effect of valproic acid on cytochrome P450 2C9 (CYP2C9) activity by using losartan oxidation as a probe in epilepsy patients. Patients were prescribed sodium valproate (mean 200 mg/day for the first week and 400 mg/day in the following period) according to their clinical need. A single oral dose of 25 mg losartan was given to patients before and after the first dose, first week and 4 weeks of valproic acid treatment. Losartan and E3174, the CYP2C9-derived carboxylic acid metabolite of losartan in 8 hr urine were assayed by using high pressure liquid chromatography. Urinary losartan/E3174 ratio did not change significantly on the first day (0.9, 0.3-3.5; median, range), and first week (0.6, 0.2-3.8; median, range), while a significant increase was observed after 4 weeks of valproic acid treatment (1.1, 0.3-5.7; median, range) as compared to that of measured before valproic acid administration (0.6, 0.1-2.1; median, range) (P = 0.039). The degree of inhibition was correlated with the steady-state plasma concentrations of valproic acid (r(2) = 0.70, P = 0.04). The results suggest an inhibitory effect of valproic acid on CYP2C9 enzyme activity in epilepsy patients at steady state. The risk of pharmacokinetic drug-drug interactions should be taken into account during concomitant use of valproic acid and CYP2C9 substrates.

Release modulating hydrophilic matrix systems of losartan potassium: Optimization of formulation using statistical experimental design

The aim of the present research work was to systemically device a model of factors that would yield an optimized sustained release dosage form of an anti-hypertensive agent, losartan potassium, using response surface methodology by employing a 3-factor, 3-level Box-Behnken statistical design. Independent variables studied were the amount of the release retardant polymers - HPMC K15M (X(1)), HPMC K100M (X(2)) and sodium carboxymethyl cellulose (X(3)). The dependent variables were the burst release in 15 min (Y(1)), cumulative percentage release of drug after 60 min (Y(2)) and hardness (Y(3)) of the tablets with constraints on the Y(2)=31-35%. Statistical validity of the polynomials was established. In vitro release and swelling studies were carried out for the optimized formulation and the data were fitted to kinetic equations. The polynomial mathematical relationship obtained Y(2)=32.91-2.30X(1)-5.69X(2)-0.97X(3)-0.41X(1)X(2)+0.21X(1)X(3)-0.92X(1)(2)-1.89X(2)(2) (r(2)=0.9944) explained the main and quadratic effects, and the interactions of factors influencing the drug release from matrix tablets. The adjusted (0.9842) and predicted values (0.9893) of r(2) for Y(2) were in close agreement. Validation of the optimization study indicated high degree of prognostic ability of response surface methodology. Tablets showed an initial burst release preceding a more gradual sustained release phase following a non-fickian diffusion process. The Box-Behnken experimental design facilitated the formulation and optimization of sustained release hydrophilic matrix systems of losartan potassium.

Bioequivalence study of two losartan formulations administered orally in healthy male volunteers

The bioavailability of a new losartan preparation (2-butyl-4-chloro-1-[p-(o-1H-tetrazol-5-ylphenyl)benzyl]imidazole-5-methanol monopotassium salt, CAS 114798-26-4) was compared with the reference preparation of the drug in 24 healthy male volunteers, aged between 19 and 32. The open, randomized, single-blind two-sequence, two-period crossover study design was performed. Under fasting conditions, each subject received a single oral dose of 100 mg losartan as a test or reference formulation. The plasma concentrations of losartan and its active metabolite were analyzed by a rapid and sensitive HPLC method with UV detection. The pharmacokinetic parameters included AUC0-36h, AUC0-infinity, Cmax, t1/2, and Ke. Values of AUC0-infinity demonstrate nearly identical bioavailability of losartan from the examined formulations. The AUC0-infinity of losartan was 2019.92+/-1002.90 and 2028.58+/-837.45 ng x h/ml for the test and reference formulation, respectively. The AUC0-infinity of the metabolite was 10851.52+/-4438.66 and 11041.18 +/-5015.81 ng x h/ml for test and reference formulation, respectively. The maximum plasma concentration (Cmax) of losartan was 745.94+/-419.75 ng/ml for the test and 745.74+/-329.99 ng/ml for the reference product and the Cmax of the metabolite was 1805.77+/-765.39 and 1606.22 +/-977.22 ng/ml for the test and reference product, respectively. No statistical differences were observed for Cmax and the area under the plasma concentration-time curve for both losartan and its active metabolite. 90 % confidence limits calculated for Cmax and AUC from zero to infinity (AUC0-infinity) of losartan and its metabolite were included in the bioequivalence range (0.8-1.25 for AUC). This study shows that the test formulation is bioequivalent to the reference formulation for losartan and its main active metabolite.

AT1 receptors and the actin cytoskeleton during angiotensin II treatment

BACKGROUND

The response of proximal convoluted tubules (PCTs) to angiotensin II is mediated by specific type 1 receptors found on both apical and basolateral surface membrane cells. After ligand association with type 1 receptors, different signaling pathways are triggered and determine changes in fluid absorption (Jv). The presence of AT1 and actin cytoskeleton, which are directly related to Jv, can undergo changes in distribution based on the actions of AngII and losartan.

METHODS

Using a microperfusion technique and immunohistochemistry analysis, we investigated the basolateral action in PCTs, of AngII and/or losartan on Jv in rabbits, with regard to AT1 and actin cytoskeleton.

RESULTS

AngII increased Jv, while in contrast, losartan and combined AngII + losartan led to its decrease. AngII did not change fluorescence intensity of AT1 receptors on tubular membranes, while losartan and AngII + losartan demonstrated a slight increase after treatment. On the other hand, AngII increased the fluorescence intensity of actin cytoskeleton, while losartan induced a decrease. AngII + losartan led actin cytoskeleton having a higher fluorescence intensity than in the control group.

CONCLUSIONS

In the present study, we demonstrated that treatment of the basolateral side of PCT cells with AngII and losartan could lead to changes in absorptive tubular function. Important alterations were detected in AT1 receptor fluorescence on the luminal and basolateral membranes, and changes in F-actin cytoskeleton were verified by fluorescence following these protocols.

The effect of AST-120 on the single-dose pharmacokinetics of losartan and losartan acid (E-3174) in healthy subjects

AST-120 is an orally administered adsorbent used to slow the progression of chronic kidney disease (CKD). This was a randomized, open-label, 5-way crossover study to assess the effect of AST-120 on the pharmacokinetics of losartan and its active metabolite (E-3174) in healthy subjects. Losartan (100 mg) was administered alone under fasting (A) and fed (B) conditions, and results were compared when AST-120 (3 g thrice daily for 2 days) was administered 60 minutes after (C), 30 minutes prior to (D), and 30 minutes after (E) losartan. Plasma concentrations of losartan and E-3174 were assayed by high-performance liquid chromatography with mass spectrometry detection. Under fed conditions, treatment C had no significant effect on the AUC(0-t) and Cmax of losartan and E-3174. Treatments D and E resulted in a marked decrease in Cmax of losartan and E-3174. Therefore, administration of AST-120 60 minutes after losartan under fed conditions may be preferred over other dosing regimens for CKD patients.

Amodiaquine, its desethylated metabolite, or both, inhibit the metabolism of debrisoquine (CYP2D6) and losartan (CYP2C9) in vivo

OBJECTIVE

To study the extent of in vivo inhibition by the antimalarial drug amodiaquine, its active metabolite N-desethylamodiaquine, or both, of the metabolism of four probe drugs of the enzymes CYP2D6, CYP2C19, CYP2C9 and CYP1A2.

METHODS

Twelve healthy Swedish volunteers received a cocktail of four probe drugs (debrisoquine, omeprazole, losartan and caffeine) to determine their baseline metabolic capacities. After a washout period, they received a 600 mg oral dose of amodiaquine hydrochloride; and 2-3 h later the cocktail was administered again. One week after the intake of amodiaquine, the subjects received the cocktail a third time. The levels of probe drugs and their metabolites as well as amodiaquine and its metabolite were determined by HPLC.

RESULTS

Plasma levels of amodiaquine and N-desethylamodiaquine could be followed in all subjects for 6 h and 28 days, respectively. Among the 12 subjects, a 3-fold variation in amodiaquine AUC and a 2-fold variation in N-desethylamodiaquine AUC, were observed. The CYP2D6 and CYP2C9 activities of the subjects were measured by debrisoquine and losartan phenotyping tests, respectively. There were significant mean increases in debrisoquine metabolic ratio (MR) between baseline and the second cocktail [MR(2 h)-MR(baseline) 1.426 (95% confidence interval 1.159, 1.755), P=0.002; ANOVA, Fisher LSD test] and in mean losartan MR between baseline and the second cocktail [MR(2 h)-MR(baseline) 1.724 (95% confidence interval 1.076, 2.762), P=0.026; ANOVA, Fisher LSD test]. The effects on CYP2D6 and CYP2C9 activities subsided within a week after intake of amodiaquine as tested by the phenotyping cocktail. The changes in omeprazole MRs and caffeine MRs were not statistically significant between any of the study phases.

CONCLUSION

A single dose of amodiaquine decreased CYP2D6 and CYP2C9 activities significantly compared to baseline values. Amodiaquine has the potential to cause drug-drug interactions and should be further investigated in malarial patients treated with drug combinations containing amodiaquine.

Effects of a fenofibrate/losartan combination on the plasma concentration and urinary excretion of purine bases

OBJECTIVE

To assess the effects of a combination of fenofibrate and losartan on the plasma concentrations and urinary excretion of purine bases in healthy male subjects.

METHODS

5 healthy males participated in a fenofibrate plus losartan combination study. The plasma concentrations and urinary excretion of purine bases (hypoxanthine, xanthine, uric acid) were measured before and after administrations of losartan (100 mg o.d.) alone for 2 weeks, losartan and fenofibrate together for 2 weeks and fenofibrate (300 mg o.d.) alone for 2 weeks, which were given consecutively over a 6-week period.

RESULTS

Losartan alone significantly reduced the serum uric acid concentration and increased uric acid excretion, whereas the combination of losartan and fenofibrate reduced serum uric acid concentrations further with a concomitant increased uric acid excretion. Fenofibrate alone also reduced plasma uric acid concentration with an increase in urinary excretion, although the effect was weak when compared with the combination treatment. The plasma concentrations and urinary excretion of oxypurines remained unchanged throughout the entire study.

CONCLUSION

A combination of fenofibrate and losartan demonstrated an additive urate-lowering effect which may be beneficial in the treatment of patients with gout and hypertriglyceridemia.

Comparative bioavailability of two losartan formulations in healthy human volunteers after a single dose administration

OBJECTIVE

To compare the bioavailability of two potassic losartan immediate release tablet (50 mg) formulations (Losartan from Laboratórios Cristália Ltd., Brazil, as a test formulation and Cozaar from Merck Sharp & Dohme Farmacêutica Ltd., Brazil, as a reference formulation) in 25 volunteers of both sexes.

MATERIAL AND METHODS

The study was conducted in an open, randomized, 2-period crossover design and a 1-week washout period. Plasma samples were obtained over a 24-hour interval. The concentrations of losartan and its active metabolite losartan acid were analyzed by combined reversed phase liquid chromatography and tandem mass spectrometry (LC-MS-MS) with negative ion electrospray ionization using a selected ion monitoring method. From the losartan and losartan acid plasma concentrations vs. time curves the following pharmacokinetic parameters were obtained: AUClast, AUC0-inf and Cmax.

RESULTS

The geometric mean and respective 90% confidence interval (CI) of Losartan/Cozaar losartan percent ratios were 92.9% (82.2-105.0%) for Cmax, 99.0% (92.5-105.9%) for AUClast, and 99.1% (92.7-105.8%) for AUC0-inf. Furthermore, the geometric mean and respective 90% CI of Losartan/Cozaar losartan acid percent ratios were 98.5% (91.5-106.0%) for Cmax, 97.9% (93.3 102.7%) for AUClast, and 98.1% (93.6-102.9%) for AUC0-inf.

CONCLUSION

Since the 90% CI for Cmax, AUClast and AUC0-inf were within the 80-125% interval proposed by the US Food and Drug Administration, it was concluded that the potassic losartan immediate release 50 mg tablet was bioequivalent to the Cozaar immediate release 50 mg tablet, according to both the rate and extent of absorption. While there were no significant differences in the bioequivalence assessed by either losartan or losartan acid, future bioequivalence studies on losartan may be performed by quantifying losartan alone as the parent compounds are more discriminative.

Clinical pharmacokinetics of losartan

Losartan is the first orally available angiotensin-receptor antagonist without agonist properties. Following oral administration, losartan is rapidly absorbed, reaching maximum concentrations 1-2 hours post-administration. After oral administration approximately 14% of a losartan dose is converted to the pharmacologically active E 3174 metabolite. E 3174 is 10- to 40-fold more potent than its parent compound and its estimated terminal half-life ranges from 6 to 9 hours. The pharmacokinetics of losartan and E 3174 are linear, dose-proportional and do not substantially change with repetitive administration. The recommended dosage of losartan 50 mg/day can be administered without regard to food. There are no clinically significant effects of age, sex or race on the pharmacokinetics of losartan, and no dosage adjustment is necessary in patients with mild hepatic impairment or various degrees of renal insufficiency. Losartan, or its E 3174 metabolite, is not removed during haemodialysis. The major metabolic pathway for losartan is by the cytochrome P450 (CYP) 3A4, 2C9 and 2C10 isoenzymes. Overall, losartan has a favorable drug-drug interaction profile, as evidenced by the lack of clinically relevant interactions between this drug and a range of inhibitors and stimulators of the CYP450 system. Losartan does not have a drug-drug interaction with hydrochlorothiazide, warfarin or digoxin. Losartan should be avoided in pregnancy, as is the case with all other angiotensin-receptor antagonists. When given in the second and third trimester of pregnancy, losartan is often associated with serious fetal toxicity. Losartan is a competitive antagonist that causes a parallel rightward shift of the concentration-contractile response curve to angiotensin-II, while E 3174 is a noncompetitive "insurmountable" antagonist of angiotensin-II. The maximum recommended daily dose of losartan is 100mg, which can be given as a once-daily dose or by splitting the same total daily dose into two doses. Losartan reduces blood pressure comparably to other angiotensin-receptor antagonists. Losartan has been extensively studied relative to end-organ protection, with studies having been conducted in diabetic nephropathy, heart failure, post-myocardial infarction and hypertensive patients with left ventricular hypertrophy. The results of these studies have been sufficiently positive to support a more widespread use of angiotensin-receptor antagonists in the setting of various end-organ diseases. Losartan, like other angiotensin-receptor antagonists, is devoid of significant adverse effects.

Inhibitory Effect of 5-Fluorouracil on Cytochrome P450 2C9 Activity in Cancer Patients

Drug interactions have been reported between 5-fluorouracil and cytochrome P450 2C9 (CYP2C9) substrates, S-warfarin and phenytoin. This study was performed to determine the influence of 5-fluorouracil on cytochrome P450 2C9 (CYP2C9) activity in colorectal cancer patients (n=17) receiving 5-fluorouracil. Losartan was used as a marker to assess CYP2C9 activity. Losartan and its CYP2C9 dependent metabolite, E-3174, were determined in urine. The ratios of urinary losartan/E-3174 before and after the 5-fluorouracil treatment were compared for each patient. Genotyping was performed to detect the CYP2C9*2 and CYP2C9*3. At the end of the first cycle of 5-fluorouracil, losartan/E-3174 ratio was increased by 28.0% compared to the pre-treatment values (P=0.15). In five patients recruited for phenotyping after three 5-fluorouracil cycles, the metabolic ratio was increased significantly by 5.3 times (P=0.03). The results suggest that in most patients 5-fluorouracil inhibited CYP2C9 activity. This inhibition was more pronounced when the total administered dose increased. This finding may help explain the mechanism of interaction between 5-fluorouracil and CYP2C9 substrates.

Losartan Metabolite EXP3179 Activates Akt and Endothelial Nitric Oxide Synthase via Vascular Endothelial Growth Factor Receptor-2 in Endothelial Cells

Background— Recent studies suggest that angiotensin type 1 receptor (AT1R) blockers have vascular protective effects beyond blood pressure lowering. Because of the importance of endothelial nitric oxide synthase (eNOS) in vascular and platelet function, we hypothesized that losartan and its metabolites would stimulate eNOS and its upstream activators Akt and phosphatidylinositol 3-kinase (PI3K).

Methods and Results— Losartan is metabolized into EXP3174 (AT1R-blocking metabolite) and EXP3179 (no AT1R-blocking properties). Treatment of endothelial cells (ECs) with losartan and both metabolites stimulated phosphorylation of Akt and eNOS in the absence of angiotensin II. However, the magnitude for EXP3179 was much greater than EXP3174, and the EC 50 was significantly lower (−logEC 50 , 8.2±0.1 versus 5.4±0.2 mol/L), suggesting an AT1R-independent effect. Inhibiting PI3K or vascular endothelial growth factor receptor 2 (VEGFR2) tyrosine phosphorylation abrogated EXP3179-induced eNOS phosphorylation. In endothelium of intact rat aorta, EXP3179 also stimulated Akt and eNOS phosphorylation. VEGFR2 activation was shown to be calcium and Src family kinase dependent by use of specific drug inhibitors and dominant negative kinase transfection. EXP3179 significantly inhibited tumor necrosis factor α–induced apoptosis by ≈60% (from 30.1±5.8% to 12.2±2.0% TUNEL-positive cells), which was abolished by pretreatment with the PI3K inhibitor LY294002. Cleaved caspase-3 was suppressed by 48% with EXP3179.

Conclusions— The losartan metabolite EXP3179 stimulates eNOS phosphorylation and suppresses tumor necrosis factor α–induced EC apoptosis by activating the VEGFR2/PI3K/Akt pathway.

Pharmacophore, Drug Metabolism, and Pharmacokinetics Models on Non-Peptide AT1, AT2, and AT1/AT2Angiotensin II Receptor Antagonists

About 20 non-peptide angiotensin II receptor antagonists are in various stages of clinical development. Different modeling approaches were used to predict the pharmacophoric requirements for AT(1) (angiotensin II receptor subtype 1) affinity. However, to our knowledge, none was used to predict both the selectivity toward AT(1) and AT(2) (angiotensin II receptor subtype 2) receptor subtypes. In this paper, partial least squares discriminant analysis is applied to derive the chemical features guiding AT(1) and AT(2) selectivity or mixed AT(1)/AT(2) receptor binding. The method can be used to modulate AT(1) versus AT(2) selectivity. Concerns that unopposed stimulation of the AT(2) receptor might produce adverse effects initiated a search for new balanced antagonists. Moreover, it can serve as a fast filtering procedure in database searches. Finally, some relevant pharmacokinetics and metabolic properties of the database of 53 compounds are calculated using the VolSurf and MetaSite software to allow the simultaneous characterization of pharmacodynamic and pharmacokinetics properties of the chemical space of angiotensin II receptor antagonists.

Valsartan for the treatment of heart failure

Heart failure (HF) still has a discouraging prognosis. Therapeutic strategies aim to reduce mortality as well as slow the progression of the disease, improve symptoms and reduce the frequency of hospital admission. Activation of the renin-angiotensin-aldosterone system (RAAS) is a hallmark of several cardiocirculatory diseases, including HF. Drugs for evidence-based therapy of HF are angiotensin-converting enzyme inhibitors (ACEIs), beta-blockers and aldosterone antagonists. A promising alternative is a more complete action on the RAAS through selective blockade of the angiotensin type 1 (AT(1)) receptors, taking into account not only physiopathological issues but also pharmacological, experimental and clinical data. The effect of valsartan, an orally-active, selective antagonist of AT(1) receptors, on the outcome in patients with chronic and symptomatic HF was evaluated in a large-scale, international, placebo-controlled clinical study, the Valsartan in Heart Failure Trial (Val-HeFT). In this study, overall mortality was similar in the valsartan and placebo groups (19.7 and 19.4%, respectively). However, valsartan, in addition to recommended therapy of HF including an ACEI, significantly reduced the combined end point of mortality and morbidity, with a significant reduction in the risk of hospitalisation, paralleled by improvements in New York Heart Association (NYHA) functional class, signs and symptoms and quality of life. Valsartan also improved left ventricular anatomy and function and significantly reduced neurohormonal activation. These results were confirmed and extended by the CHARM trial, where the benefits of candesartan were proved not only in all 7599 patients with HF, but also in the 2548 given an ACEI, the 2028 not given an ACEI and in the 3023 patients with an ejection fraction of > 40%. In conclusion, the first choice for HF remains an ACEI with a beta-blocker, but two new options are emerging. In patients intolerant to ACEI, the combination of valsartan or candesartan with a beta-blocker is proposed, whereas an ACEI with either valsartan or candesartan can be considered in patients intolerant to or with contraindications to beta-blockers.

Losartan

Losartan (Cozaar) is an angiotensin AT1 receptor antagonist. It is approved in numerous countries for the treatment of hypertension and has been approved in the UK, the US and several European countries for stroke risk reduction in patients with hypertension and left ventricular hypertrophy (LVH). Losartan is recommended for use alone or with hydrochlorothiazide, but it can also be administered with other antihypertensive medications. In patients with hypertension, losartan effectively lowers blood pressure and also leads to regression of LVH. In the large, well designed LIFE (Losartan Intervention For Endpoint reduction in hypertension) study in patients with hypertension and LVH, losartan was more effective than atenolol in reducing the composite primary endpoint of cardiovascular (CV) mortality, stroke or myocardial infarction (MI). This was mainly due to a significant 25% reduction in the risk of stroke in the losartan group. Losartan recipients also had a significantly lower incidence of new-onset diabetes mellitus compared with atenolol recipients. Similar benefits were observed in several patient subgroups from the LIFE study, but not in the subgroup of Black patients. Losartan is well tolerated and is a cost effective alternative to atenolol in the setting of stroke reduction. Comparative data on clinical outcomes in hypertensive patients for losartan versus other antihypertensive agents would be of interest. Nonetheless, in addition to its established antihypertensive and end organ effects, the LIFE study indicates that, with the possible exception of Black patients, losartan can reduce the risk of stroke in patients with hypertension and LVH.

Significance of Angiotensin II Receptor Blocker Lipophilicities and Their Protective Effect against Vascular Remodeling

Although the lipophilicities of the various angiotensin II receptor blockers (ARBs) are very different, the relationship between lipophilicity and the protective effect against vascular remodeling is unclear. In this study, we compared the protective effects of a highly lipophilic ARB, telmisartan, and an ARB with low lipophilicity, losartan, on vascular function and oxidative stress in stroke-prone spontaneously hypertensive rats (SHR-SP). SHR-SP received oral placebo, 1 mg/kg telmisartan, or 10 mg/kg losartan for 2 weeks. The blood pressure (BP) in SHR-SP was significantly higher than that in Wistar-Kyoto (WKY) rats before treatment, and the BP was reduced equally in telmisartan- and losartan-treated SHR-SP compared to placebo-treated SHR-SP. Acetylcholine-induced vasorelaxation in isolated carotid arteries was significantly weaker in SHR-SP than in WKY rats, but in both telmisartan- and losartan-treated SHR-SP, acetylcholine-induced vasorelaxation was significantly higher than in placebo-treated SHR-SP. Moreover, acetylcholine-induced vasorelaxation in telmisartan-treated rats was significantly stronger than in losartan-treated SHR-SP. The expression of the endothelial nitric oxide synthase gene was significantly higher in telmisartan- and losartan-treated rats than in placebo-treated SHR-SP, and was significantly higher in telmisartan-treated rats than in losartan-treated rats. In contrast, the expression of the NAD(P)H oxidase subunit p22phox gene in telmisartan-treated SHR-SP was significantly lower than that in losartan-treated SHR-SP. Immunohistochemistry showed that angiotensin II expression in the aorta was significantly lower in telmisartan-treated SHR-SP than in losartan-treated SHR-SP. In conclusion, a highly lipophilic ARB, telmisartan, may be useful for preventing NAD(P)H oxidase activity, and thereby for conferring vascular protection.

Comparative pharmacokinetics of two tablet formulations of Losartan: bioequivalence assessment

The pharmacokinetic profiles of two brands of losartan 50 mg tablets were compared in 24 healthy adult volunteers after a single oral dose in a randomized cross-over study. The study was conducted at the ACDIMA Center for Bioequivalence & Pharmaceutical Studies, Amman, Jordan. The reference (Cozaar, MSD, The Netherlands) and test (Blosart, Julphar, UAE) products were administered to fasting volunteers. Blood samples were collected at specified time intervals, and the plasma separated and analysed for losartan and its active metabolite (losartan carboxylic acid) using a validated HPLC method with fluorescence detection. Pharmacokinetic parameters AUC(0-t), AUC(0-alpha), C(max), T(max), T(1/2), elimination rate constant, MRT, Cl/F and Vss/F were determined from plasma concentration-time profiles of both formulations and found to be in good agreement with reported values. Three parameters (AUC(0-t), AUC(0-alpha), and C(max)) were compared statistically to evaluate the bioequivalence between the two brands, using statistical modules recommended by the FDA. Analysis of variance (ANOVA) did not show any significant difference between the two formulations and 90% confidence intervals fell within the acceptable range (80%-125%) for bioequivalence. Based on these statistical inferences it was concluded that the two formulations exhibited comparable pharmacokinetic profiles and that Julphar's Blosart is bioequivalent to Cozaar of MSD, The Netherlands.

Drug interactions with the potential to prevent prodrug activation as a common source of irrational prescribing in hospital inpatients

OBJECTIVE

Our objective was to investigate the frequency of potential drug-drug interactions between the prodrugs losartan, codeine, and tramadol and drugs known to inhibit their activation in hospitalized patients.

METHODS

The frequency of coadministration between losartan and well-established cytochrome P450 (CYP) 2C9 inhibitors, as well as codeine and tramadol and CYP2D6 inhibitors, was studied by use of data from a university hospital medication database. The study population comprised all patients treated in internal medicine, pulmonary medicine, oncology, and neurology wards (105,533 treatment periods and 65,526 patients) between July 1, 1996, and June 30, 2002 (6 years).

RESULTS

Every fifth patient receiving losartan, codeine, or tramadol was concomitantly taking another drug that has the potential to inhibit the activation of these drugs. During the 6-year time period, 1999 patients were exposed to a potential interaction. Interactions occurred more commonly in internal medicine wards (odds ratio, 2.3; 95% confidence interval, 2.1-2.5) and in women (odds ratio, 1.5; 95% confidence interval, 1.4-1.7).

CONCLUSIONS

Coadministration of drugs that potentially result in inhibition of prodrug activation present a common and unrecognized source of irrational prescribing.

Losartan: in the reduction of stroke risk in patients with hypertension and left ventricular hypertrophy

Losartan binds selectively to the angiotensin II subtype 1 receptor, blocking the activity of angiotensin II. Losartan 50-100 mg/day was compared with atenolol 50-100 mg/day in patients with essential hypertension and left ventricular hypertrophy (LVH) [n = 9,193] in the randomized, double-blind Losartan Intervention For Endpoint reduction in hypertension (LIFE) study. Two substudies compared these drugs in patients with diabetes mellitus (n = 1,195) or isolated systolic hypertension (ISH) [n = 1326]. The target BP (<140/90 mm Hg) was achieved in approximate, equals 45% of losartan and atenolol recipients in the LIFE study. Significant regression of LVH occurred with losartan versus atenolol in the LIFE study, as well as in the diabetes mellitus and ISH substudies. In the LIFE study, although BP reduction was similar for the two treatments, the risk of a cardiovascular event (the composite of cardiovascular death, stroke, and myocardial infarction; primary endpoint), stroke, or new-onset diabetes mellitus was significantly lower with losartan than with atenolol. Losartan was generally well tolerated in patients with hypertension and LVH in the LIFE study. Significantly fewer losartan than atenolol recipients discontinued treatment because of adverse events, drug-related adverse events, or serious, drug-related adverse events.

Combination of losartan and hydrochlorothiazide: in vivo bioequivalence

Two trials were performed in different groups of volunteers with the aim to compare the bioavailability of 50 mg losartan tablets (Sarvas as test and an originator product as reference formulation; study 1) and losartan/hydrochlorothiazide (50 mg/12.5 mg) (CAS 124750-99-8/CAS 58-93-5) combined formulations (Sarvastan as test and an originator product as reference formulation; study 2), respectively. Each study was conducted according to an open, randomized, single-dose, two-period cross-over design in 24 healthy volunteers with a wash-out period from 7 to 14 days. Blood samples were taken up to 36 h in the first study and up to 48 h in the second study. Concentrations of losartan and its principal active metabolite, i.e. E3174, as well as hydrochlorothiazide were determined by HPLC or LC-MS-MS, respectively. In the first study, the 90% confidence interval for intra-individual ratios of AUC0-t and Cmax of losartan were between 0.91 and 1.03 (AUC0-t) as well as between 0.87 and 1.19 (Cmax), and thus within the acceptance ranges. The 90% confidence interval for intra-individual ratios of AUC0-t, and Cmax of E3174 were between 0.90 and 1.13 for AUC0-t, and between 0.97 and 1.14 for Cmax. In the second study, i.e. after administration of combined losartan/hydrochlorothiazide formulations, the 90% confidence interval for intra-individual ratios of AUC0-t and Cmax of losartan were between 0.90 and 1.04 (AUC0-t) as well as between 0.86 and 1.20 (Cmax). Similarly to the parent compound, no significant differences of bioavailability parameters of E3174 between the two studied formulations were found. The 90% confidence interval for intra-individual ratios of AUC0-t and Cmax of hydrochlorothiazide were between 0.89 and 0.98 (AUC0-t) as well as between 0.82 and 1.00 (Cmax). In the light of the present studies it can be concluded that the losartan as well as losartan/hydrochlorothiazide test formulations are bioequivalent to the respective reference formulations.

Functional impact of CYP2C9*5, CYP2C9*6, CYP2C9*8, and CYP2C9*11 in vivo among black Africans*1

Background and aim Previous data indicate that the urinary losartan/E-3174 ratio is a marker for cytochrome P450 (CYP) 2C9 activity in vivo. The functional impact of CYP2C9*5, *6, *8, and *11 polymorphisms in vivo has not been investigated previously in humans.

METHODS

A single oral dose of losartan (25 mg) was given to 19 Beninese subjects with CYP2C9*1/*1 (n = 9), *1/*5 (n = 1), *1/*6 (n = 1), *1/*8 (n = 2), *1/*11 (n = 3), *5/*6 (n = 1), *5/*8 (n = 1), and *8/*11 (n = 1) genotypes. Concentrations of losartan and its active metabolite E-3174 were determined in urine from 0 to 8 hours by HPLC. The losartan/E-3174 metabolic ratio was used as a measure of losartan oxidation in vivo.

RESULTS

The urinary losartan/E-3174 ratio in the various genotypes was as follows: 1.85 +/- 2.4 (mean +/- SD) for CYP2C9*1/*1, 14.6 for CYP2C9*1/*5, 4.2 for CYP2C9*1/*6, 188 for CYP2C9*5/*6, 11.6 for CYP2C9*5/*8, 0.44 +/- 0.13 (mean +/- SD) for CYP2C9*1/*8, 2.2 for CYP2C9*8/*11, and 5.72 +/- 4.5 (mean +/- SD) for CYP2C9*1/*11. Compared with the CYP2C9*1/*1 genotypes, the losartan/E-3174 ratio was significantly different in the CYP2C9*5 allele carriers (CYP2C9*1/*5, CYP2C9*5/*8, and CYP2C9*5/*6 genotypes) (P =.01, Mann-Whitney) but was not different in CYP2C9*1/*8 (P =.16) and CYP2C9*1/*11 (P =.11) carriers. The urinary losartan/E-3174 ratio of the single CYP2C9*1/*6 subject was higher than the 95% confidence interval of the mean of the CYP2C9*1/*1 group (0.0-3.7), whereas the metabolic ratio of the CYP2C9*8/*11 carrier was inside the 95% confidence interval of the means of the CYP2C9*1/*1 and CYP2C9*1/*11 groups (0.0-18).

CONCLUSIONS

The CYP2C9*5 and *6 alleles are associated with decreased enzyme activity in vivo compared with the wild-type variant, whereas the CYP2C9*8 and *11 variants did not appear to have large in vivo effects.

Effect of the single CYP2C9*3 allele on pharmacokinetics and pharmacodynamics of losartan in healthy Japanese subjects

OBJECTIVE

Losartan is metabolized to the active carboxylic acid metabolite EXP3174 by CYP2C9. In this study, we determined the effects of the single CYP2C9*3 variant on the pharmacokinetics and pharmacodynamics of losartan.

METHODS

Seven healthy Japanese subjects ( CYP2C9*1/*1, n=4 and CYP2C9*1/*3, n=3) were phenotyped with a single dose of losartan (25 mg). Blood and urine samples were collected and assayed for losartan and EXP3174. Blood pressure and pulse rate were also measured using a sphygmomanometer.

RESULTS

The maximum plasma concentration of EXP3174 was significantly (P<0.05) lower in the CYP2C9*1/*3 (n=3) group than in the CYP2C9*1/*1 (n=4) group. Diastolic blood pressure in the CYP2C9*1/*1 group, but not that in the CYP2C9*1/*3 group except for at 6 h and 8 h, was reduced from 1.5 h to 12 h compared with the baseline level. Systolic blood pressure in the CYP2C9*1/*1 group, but not that in the CYP2C9*1/*3 group, was reduced from 1 h to 12 h compared with the baseline level. The metabolic ratio (MR) of EXP3174 concentration to the losartan concentration in plasma at 6 h post-dosing and the 4-h to 8-h urinary EXP3174/losartan MR were significantly lower in the CYP2C9*1/*3 group than in the CYP2C9*1/*1 group. The plasma 6-h MR and the 4-h to 8-h urinary MR were significantly (P<0.05) correlated with the plasma AUC ratio (AUC(EXP3174)/AUC(losartan)), with Spearman rank correlation coefficients of 0.75 and 0.89, respectively.

CONCLUSION

The single CYP2C9*3 variant reduces the metabolism of losartan and its hypotensive effect. Plasma MR, as well as urine MR, may be useful for phenotyping assays of CYP2C9 activity.

Increased Plasma Concentration of Natriuretic Peptides by Selective β1-Blocker Bisoprolol

Beta-blocker therapy has been shown to be associated with an increase in the plasma concentration of A-type natriuretic peptide (ANP). Whether the plasma concentration of B-type natriuretic peptide (BNP), which is mainly derived from ventricular tissue, is also increased and whether this increase is caused by increased production or decreased metabolism by down-regulation of the natriuretic peptide-clearance receptor remains to be established. In a double-blind crossover study effects of 8 weeks' treatment of bisoprolol,10 mg once daily, and losartan, 50 mg once daily, on plasma concentrations of ANP, BNP, and N-terminal (Nt)-ANP and ambulatory blood pressure (ABP) were measured in 24 hypertensive patients. With bisoprolol plasma concentrations of ANP and BNP increased (P < 0.001) by 93 +/- 88% (mean +/- SD) and 148 +/- 117%, whereas these parameters did not change with losartan. Nt-ANP, which is not metabolized by the NP clearance receptor, increased by 83 +/- 45%, and increments in ANP and Nt-ANP were related (r =0.77, P < 0.001). The decrease in ABP was greater with bisoprolol than with losartan. Monotherapy with bisoprolol, but not with losartan, is associated with substantial increments in plasma concentrations of ANP, Nt-ANP, and BNP. As the magnitude of the increase in ANP and Nt-ANP was comparable, the beta-blocker-induced increase in NPs is not likely to be explained by a decrease in NP clearance receptor density.

[Therapeutic interchange between angiotensin II receptor blockers in institutionalized elderly patients. Implimenting a protocol]

OBJECTIVE

To assess the effectiveness of a therapeutic interchange protocol for angiotensin II receptor blockers (ARB's) in the maintenance of blood pressure levels for institutionalized elderly patients diagnosed with hypertension.

METHODS

A new protocol was discussed by the Pharmacy and Therapeutics Committee, and its implementation by the Pharmacy Department was authorized. The protocol specifies equivalent doses between drugs and the patients' clinical follow-up. Criteria used in the assessment includes: need to change dosage for an ARB included in the Pharmacotherapeutic Guide, and blood pressure changes after drug interchange.

RESULTS

In the absence of hepatic insufficiency, the protocol may replace the standard doses of any drugs within this group with losartan 50 mg daily. If needed, the dose of losartan may be increased to 100 mg daily divided into two doses. Eighteen patients, which represent 10% of all interchange operations carried out by the Pharmacy Department, were included in this study. Blood pressures both before and after the interchange process show no major differences between them. Only two patients required an increase in the dose of losartan.

CONCLUSION

The implementation of a therapeutic interchange protocol as agreed upon by the Pharmacy and Therapeutics Committee allows the clinical follow-up of patients and therefore facilitates an evaluation of the process. This ARB interchange protocol, as suggested for the institutionalized elderly population setting, has proven effective in maintaining anti-hypertensive activity.

Pharmacokinetics, safety, and antihypertensive efficacy of losartan in combination with hydrochlorothiazide in hypertensive patients with renal impairment

The pharmacokinetics and pharmacodynamics of 7 days of treatment with losartan 50 mg/hydrochlorothiazide 12.5 mg were evaluated in 14 patients with normal renal function and in 12 patients with mild to moderate renal impairment. The efficacy of losartan 50 mg/hydrochlorothiazide 12.5 mg titrated to losartan 100 mg/hydrochlorothiazide 25 mg was examined in 32 hypertensive patients with mild to moderate renal impairment who were treated for 12 weeks. Safety was assessed in both studies by the incidence of adverse experiences. After 7 days of treatment, the AUC for losartan, E-3174, and hydrochlorothiazide was slightly higher in patients with mild to moderate renal impairment, but the reduction in blood pressure (BP) after 7 days was not different between the two groups. The final (week 12) mean reductions in trough sitting diastolic and systolic BP were 15.0 +/- 7.1 mmHg (p < 0.01) and 20.8 +/- 16.7 mmHg (p < 0.01), respectively. There were no observed increases in drug-related adverse experiences in either study. Overall, the combination of losartan/hydrochlorothiazide was effective in lowering blood pressure and was well tolerated in patients with mild to moderate renal impairment.