Disposition and bioavailability of the beta 1-adrenoceptor antagonist talinolol in man

Extracorporeal treatment for poisoning to beta-adrenergic antagonists: systematic review and recommendations from the EXTRIP workgroup

BACKGROUND

β-adrenergic antagonists (BAAs) are used to treat cardiovascular disease such as ischemic heart disease, congestive heart failure, dysrhythmias, and hypertension. Poisoning from BAAs can lead to severe morbidity and mortality. We aimed to determine the utility of extracorporeal treatments (ECTRs) in BAAs poisoning.

METHODS

We conducted systematic reviews of the literature, screened studies, extracted data, and summarized findings following published EXTRIP methods.

RESULTS

A total of 76 studies (4 in vitro and 2 animal experiments, 1 pharmacokinetic simulation study, 37 pharmacokinetic studies on patients with end-stage kidney disease, and 32 case reports or case series) met inclusion criteria. Toxicokinetic or pharmacokinetic data were available on 334 patients (including 73 for atenolol, 54 for propranolol, and 17 for sotalol). For intermittent hemodialysis, atenolol, nadolol, practolol, and sotalol were assessed as dialyzable; acebutolol, bisoprolol, and metipranolol were assessed as moderately dialyzable; metoprolol and talinolol were considered slightly dialyzable; and betaxolol, carvedilol, labetalol, mepindolol, propranolol, and timolol were considered not dialyzable. Data were available for clinical analysis on 37 BAA poisoned patients (including 9 patients for atenolol, 9 for propranolol, and 9 for sotalol), and no reliable comparison between the ECTR cohort and historical controls treated with standard care alone could be performed. The EXTRIP workgroup recommends against using ECTR for patients severely poisoned with propranolol (strong recommendation, very low quality evidence). The workgroup offered no recommendation for ECTR in patients severely poisoned with atenolol or sotalol because of apparent balance of risks and benefits, except for impaired kidney function in which ECTR is suggested (weak recommendation, very low quality of evidence). Indications for ECTR in patients with impaired kidney function include refractory bradycardia and hypotension for atenolol or sotalol poisoning, and recurrent torsade de pointes for sotalol. Although other BAAs were considered dialyzable, clinical data were too limited to develop recommendations.

CONCLUSIONS

BAAs have different properties affecting their removal by ECTR. The EXTRIP workgroup assessed propranolol as non-dialyzable. Atenolol and sotalol were assessed as dialyzable in patients with kidney impairment, and the workgroup suggests ECTR in patients severely poisoned with these drugs when aforementioned indications are present.

Urinary Excretion of Nadolol as a Possible In Vivo Probe for Drug Interactions Involving P-Glycoprotein

Nadolol is a hydrophilic and nonselective β-adrenoceptor blocker with a bioavailability of 30%, relatively longer half-life, negligible metabolism, and predominant renal excretion. Previous studies have reported that nadolol is a substrate of P-glycoprotein, and the coadministration with itraconazole, a typical P-glycoprotein inhibitor, results in elevated plasma concentrations and cumulative urinary excretion of nadolol. In this study, we assessed whether measurements of urinary-excreted nadolol can be an alternative method of plasma pharmacokinetics for P-glycoprotein-mediated drug interactions in humans. We reanalyzed the pooled data set of plasma concentration and urinary excretion of nadolol from our previous clinical studies in a total of 32 healthy Japanese adults. The area under the plasma concentration-time curve from 0 to infinity (AUC_0-∞ ) of nadolol in individual subjects was significantly correlated with the maximum plasma concentration (r = 0.80, P < .01) and the cumulative amount excreted into urine (A_e ) at 4 (r = 0.51, P = .01), 8 (r = 0.63, P < .01), 24 (r = 0.75, P < .01), and 48 (r = 0.77, P < .01) hours. Significant correlations were also observed between the AUC and A_e during the same respective periods. In the drug interactions of nadolol with itraconazole, rifampicin, a well-known P-glycoprotein inducer, or grapefruit juice, there were significant correlations between the differences in AUC_0-48 and those in A_{e, 0-48} from the controls in individual subjects. These results suggest that the measurements of urinary excretion of nadolol can be employed as a sensitive and reliable alternative to plasma pharmacokinetics for the evaluation of P-glycoprotein-mediated drug interactions.

Evaluation of Self-Nanoemulsifying Drug Delivery Systems (SNEDDS) for Poorly Water-Soluble Talinolol: Preparation, in vitro and in vivo Assessment

Objective

The aim of this study was to investigate the in vitro and in vivo performance of self-nanoemulsifying drug delivery systems (SNEDDSs) of talinolol (TAL), a poorly water-soluble drug.

Methods

Self-nanoemulsifying drug delivery systems of TAL were prepared using various oils, non-ionic surfactants and/or water-soluble co-solvents and assessed visually/by droplet size measurement. Equilibrium solubility of TAL in the anhydrous and diluted SNEDDS was conducted to achieve the maximum drug loading. The in vitro dissolution experiments and human red blood cells (RBCs) toxicity test, ex vivo gut permeation studies, and bioavailability of SNEDDS in rats were studied to compare the representative formulations with marketed product Cordanum^® 50 mg and raw drug.

Results

The results from the characterization and solubility studies showed that SNEDDS formulations were stable with lower droplet sizes and higher TAL solubility. From the dissolution studies, it was found that the developed SNEDDS provided significantly higher rate of TAL release (>97% in 2.0 h) compared to raw TAL and marketed product Cordanum^®. The RBC lysis test suggested negligible toxicity of the formulation to the cells. The ex vivo permeability assessment and in vivo pharmacokinetics study of a selected SNEDDS formulation (F6) showed about four-fold increase in permeability and 1.58-fold enhanced oral bioavailability of TAL in comparison to pure drug, respectively.

Conclusion

Talinolol loaded SNEDDS formulations could be a potential oral pharmaceutical product with high drug-loading capacity, improved drug dissolution, increased gut permeation, reduced/no human RBC toxicity, and enhanced oral bioavailability.

Curcumin as an In Vivo Selective Intestinal Breast Cancer Resistance Protein Inhibitor in Cynomolgus Monkeys

To estimate the clinical impact of pharmacokinetic modulation via breast cancer resistance protein (BCRP), in vivo approaches in nonclinical settings are desired in drug development. Clinical observation has identified curcumin as a promising candidate for in vivo selective BCRP inhibition, in addition to several well known inhibitors, such as lapatinib and pantoprazole. This study aimed to confirm the inhibitory efficacy of curcumin on gastrointestinal BCRP function in cynomolgus monkeys and to perform comparisons with lapatinib and pantoprazole. Oral area under the plasma concentration-time curve (AUC) and bioavailability of well known BCRP (sulfasalazine and rosuvastatin), P-glycoprotein (fexofenadine, aliskiren, and talinolol), and CYP3A (midazolam) substrates were investigated in the presence and absence of inhibitors. Oral exposures of sulfasalazine and rosuvastatin were markedly elevated by curcumin with minimal changes in systemic clearance, whereas pharmacokinetic alterations after fexofenadine, aliskiren, and talinolol oral exposure were limited. Curcumin increased oral midazolam exposure without affecting systemic clearance, presumably owing to partial inhibition of intestinal CYP3A. Lapatinib increased the oral AUC for sulfasalazine to a greater extent than curcumin did, whereas pantoprazole had a smaller effect. However, lapatinib also exerted significant effects on fexofenadine, failed to selectively discriminate between BCRP and P-glycoprotein inhibition, and had an effect on oral midazolam exposure comparable with that of curcumin. Thus, pharmacokinetic evaluation in monkeys demonstrated that pretreatment with curcumin as an in vivo selective BCRP inhibitor was more appropriate than pretreatment with lapatinib and pantoprazole for the assessment of the impact of BCRP on gastrointestinal absorption in nonrodent models.

Low heritability in pharmacokinetics of talinolol: a pharmacogenetic twin study on the heritability of the pharmacokinetics of talinolol, a putative probe drug of MDR1 and other membrane transporters

BACKGROUND

Efflux transporters like MDR1 and MRP2 may modulate the pharmacokinetics of about 50 % of all drugs. It is currently unknown how much of the variation in the activities of important drug membrane transporters like MDR1 or MRP2 is determined by genetic or by environmental factors. In this study we assessed the heritability of the pharmacokinetics of talinolol as a putative probe drug for MDR1 and possibly other membrane transporters.

METHODS

Talinolol pharmacokinetics were investigated in a repeated dose study in 42 monozygotic and 13 same-sex dizygotic twin pairs. The oral clearance of talinolol was predefined as the primary parameter. Heritability was analyzed by structural equation modeling and by within- and between-subject variance and talinolol clearance was correlated with polymorphisms in MDR1, MRP2, BCRP, MDR5, OATP1B1, and OCT1.

RESULTS

Talinolol clearance varied approximately ninefold in the studied sample of healthy volunteers. The correlation of clearances between siblings was not significantly different for the monozygotic and dizygotic pairs. All data analyses consistently showed that variation of talinolol pharmacokinetics was mainly determined by environmental effects. Structural equation modeling attributed 53.5 % of the variation of oral clearance to common environmental effects influencing both siblings to the same extent and 46.5 % to unique environmental effects randomly affecting individual subjects. Talinolol pharmacokinetics were significantly dependent on sex, body mass index, total protein consumption, and vegetable consumption.

CONCLUSIONS

The twin study revealed that environmental factors explained much more of the variation in pharmacokinetics of talinolol than genetic factors.

TRIAL REGISTRATION

European clinical trials database number: EUDRA-CT 2008-006223-31. Registered 26 September 2008. ClinicalTrials.gov number: NCT01845194 .

Characterisation of selected active agents regarding pKa values, solubility concentrations and pH profiles by SiriusT3

The aim of this work was to determine pKa values and solubility properties of 34active agents using the SiriusT3 apparatus. The selected drug substances belong to the groups of ACE-inhibitors, β-blockers, antidiabetics and lipid lowering substances. Experimentally obtained pKa and intrinsic solubility values were compared to calculated values (program ACD/ChemSketch) and pKa values to published data as well. Solubility-pH profiles were generated to visualise the substance solubility over the gastrointestinal pH range. The relationship between the solubility characteristic of a substance, its bioavailability and categorisation according to the Biopharmaceutics Classification System (BCS) was examined as well. The results showed a good agreement between experimentally obtained, calculated and published pKa values. The measured and calculated intrinsic solubility values indicated several major deviations. All solubility-pH profiles showed the expected shape and appearance for acids, bases or zwitterionic substances. The obtained results for the pKa and solubility measurements of the examined active agents may help to predict their physicochemical behaviour in vivo, and to understand the bioavailability of the substances according to their BCS categorisation. The easy and reproducible determination of pKa and solubility values makes the SiriusT3 apparatus a useful tool in early stages of drug and formulation development.

Improved oral bioavailability of BCS class 2 compounds by self nano-emulsifying drug delivery systems (SNEDDS): the underlying mechanisms for amiodarone and talinolol

PURPOSE

Superior bioavailability of BCS Class 2 compounds incorporated into SNEDDS was previously reported. This study aims to elucidate the underlying mechanisms accountable for this phenomenon.

METHODS

SNEDDS of amiodarone (AM) and talinolol were developed. Pharmacokinetic parameters were assessed in vivo. Effect on intestinal permeability, P-gp efflux and toxicity was evaluated in vitro (Caco-2) and ex vivo (Ussing). Solubilization was assessed in vitro (Dynamic Lipolysis Model). Effect on intraenterocyte metabolism was evaluated using CYP3A4 microsomes.

RESULTS

Oral administration of AM-SNEDDS and talinolol-SNEDDS resulted in higher and less variable AUC and Cmax. In vitro, higher talinolol-SNEDDS Papp indicated Pgp inhibition. Lipolysis of AM-SNEDDS resulted in higher AM concentration in the fraction available for absorption. Incubation of AM-SNEDDS with CYP3A4 indicated CYP inhibition. SNEDDS didn't alter mannitol Papp and TEER. SNEDDS effect was transient.

CONCLUSIONS

Multiple mechanisms are accountable for improved bioavailability and reduced variability of Class-2 compounds by SNEDDS: increased solubilization, reduced intraenterocyte metabolism and reduced P-gp efflux. SNEDDS effect is reversible and doesn't cause intestinal tissue or cell damage. These comprehensive findings can be used for intelligent selection of drugs for which oral bioavailability will improve upon incorporation into SNEDDS, based on recognition of the drug's absorption barriers and the ability of SNEDDS to overcome them.

Characterization of multidrug resistance 1a/P-glycoprotein knockout rats generated by zinc finger nucleases

The development of zinc finger nuclease (ZFN) technology has enabled the genetic engineering of the rat genome. The ability to manipulate the rat genome has great promise to augment the utility of rats for biological and pharmacological studies. A Wistar Hannover rat model lacking the multidrug resistance protein Mdr1a P-glycoprotein (P-gp) was generated using a rat Mdr1a-specific ZFN. Mdr1a was completely absent in tissues, including brain and small intestine, of the knockout rat. Pharmacokinetic studies with the Mdr1a P-gp substrates loperamide, indinavir, and talinolol indicated that Mdr1a was functionally inactive in the blood-brain barrier and intestine in Mdr1a(-/-) rats. To identify possible compensatory mechanisms in Mdr1a(-/-) rats, the expression levels of drug-metabolizing enzyme and transporter-related genes were compared in brain, liver, kidney, and intestine of male and female Mdr1a(-/-) and control rats. In general, alterations in gene expression of these genes in Mdr1a(-/-) rats seemed to be modest, with more changes in female than in male rats. Taken together, our studies demonstrate that the ZFN-generated Mdr1a(-/-) rat will be a valuable tool for central nervous system drug target validation and determining the role of P-gp in drug absorption and disposition.

Validated HPLC method for quantitative determination of talinolol in rat plasma and application to a preclinical pharmacokinetic study

BACKGROUND

A simple HPLC-UV method with a high reproducibility and sensitivity for the determination of talinolol in rat plasma was developed in this study.

METHOD

After liquid-liquid extraction, the compounds were separated on a Vydac(®) C18 monomeric column (250 × 4.6 mm inner diameter × 5-µm particle size) using a mobile phase composed of acetonitrile and potassium dihydrogen phosphate buffer (34:66 v/v), delivered isocratically at a flow rate of 1.0 ml min(-1). Escitalopram was used as an internal standard. The chromatographic peak-area ratio, based on UV absorbency at 245 nm, was used for quantitative analysis.

RESULTS

Calibration standards with concentrations over the range of 10-1000 ng ml(-1) were validated for routine sample analysis to support pharmacokinetic studies with talinolol in rats. The intra- and inter-day precision studies showed good reproducibility with coefficients of variation of less than 11.49%. The developed method is simpler and more sensitive than previously reported methods.

DISCUSSION

The analytical sensitivity and accuracy of this assay were adequate for characterization of talinolol in rat plasma and the assay has been applied successfully to the in vivo kinetic study of talinolol in rats. After talinolol (10 mg kg(-1)) was given orally, the maximum concentration and the AUC(0-∞) were 341.8 ± 99.4 ng ml(-1) and 976.26 ± 173.37 ng h ml(-1), respectively. The oral bioavailability was approximately 52.14 ± 9.26%.

CONCLUSION

The advantages of our method are a small sample volume (200 µl), short analysis time (13.5 min) and a simple sample extraction and clean-up compared with multiple extraction and washing steps and a longer analysis time in previously published methods.

In vivo probes of drug transport: commonly used probe drugs to assess function of intestinal P-glycoprotein (ABCB1) in humans

Intestinal P-glycoprotein (P-gp, ABCB1) may significantly influence drug absorption and elimination. Its expression and function is highly variable, regio-selective and influenced by genetic polymorphisms, drug interactions and intestinal diseases. An in vivo probe drug for intestinal P-gp should a registered, safe and well tolerated nonmetabolized selective substrate with low protein binding for which P-gp is rate-limiting during absorption. Other P-gp dependent processes should be of minor influence. The mechanism(s) and kinetics of intestinal uptake must be identified and quantified. Moreover, the release properties of the dosage form should be known. So far, the cardiac glycoside digoxin and the ß₁-selective blocker talinolol have been used in mechanistic clinical studies, because they meet most of these criteria. Digoxin and talinolol are suitable in vivo probe drugs for intestinal P-gp under the precondition, that they are used as tools in carefully designed pharmacokinetic studies with adequate biometrically planning of the sample size and that several limitations are considered in interpreting and discussion of the study results.

Importance of P-glycoprotein for drug-drug interactions

P-glycoprotein (ABCB1) is one of the most extensively studied transporters regarding drug resistance and drug-drug interactions. P-glycoprotein is expressed in multiple key organs in drug disposition such as small intestine, blood-brain barrier, kidney, and liver. Therefore, P-glycoprotein mediated drug-drug interactions can occur at various organs and tissues. This chapter will mainly focus on drug-drug interactions that are mediated by the intestinal P-glycoprotein.During the last decade, many in vitro and in vivo studies reported that the induction or inhibition of P-glycoprotein can lead to drug-drug interactions. For instance, induction of the intestinal P-glycoprotein activity can cause reduced bioavailability of orally administered drugs and decreased therapeutic efficacy. On the other hand, the inhibition of the intestinal P-glycoprotein activity can lead to increased bioavailability, thus leading to an increased risk of adverse side effects.

Evaluation of in vivo P-glycoprotein phenotyping probes: a need for validation

Drug transporters are involved in clinically relevant drug-drug interactions. P-glycoprotein (P-gp) is an efflux transporter that displays genetic polymorphism. Phenotyping permits evaluation of real-time, in vivo P-gp activity and P-gp-mediated drug-drug interactions. Digoxin, fexofenadine, talinolol and quinidine are commonly used probe drugs for P-gp phenotyping. Although current regulatory guidance documents highlight methodologies for evaluating transporter-based drug-drug interactions, whether current probe drugs are suitable for phenotyping has not been established, and validation criteria are lacking. This review proposes validation criteria and evaluates P-gp probes to determine probe suitability. Based on these criteria, digoxin, fexofenadine, talinolol and quinidine have limitations to their use and are not recommended for P-gp phenotyping.

Species difference in the effect of grapefruit juice on intestinal absorption of talinolol between human and rat

Bioavailability of talinolol, a beta(1)-adrenergic receptor antagonist, was enhanced by coadministration with grapefruit juice (GFJ) in rats, whereas GFJ ingestion markedly reduced the absorption of talinolol in humans. Because our recent study indicated that the inhibitory effect of GFJ on organic anion-transporting polypeptide (Oatp)- and P-gp-mediated talinolol absorption depends on the concentration of naringin in ingested GFJ, the apparent inconsistent findings may be explained by the species difference in the affinity of naringin for OATP/Oatp and P-gp multidrug resistance 1 (MDR1/Mdr1) between humans and rats. Although human MDR1-mediated talinolol transport was not inhibited by 2000 microM naringin, naringin inhibited human OATP1A2-, rat Oatp1a5-, and rat Mdr1a-mediated talinolol transport with IC(50) values of 343, 12.7, and 604 microM, respectively, in LLC-PK1 cell and Xenopus laevis oocyte systems. Because the naringin concentration in commercially prepared GFJ was found to be approximately 1200 microM, these results suggested that GFJ would reduce the intestinal absorption of talinolol through inhibition of OATP1A2-mediated talinolol uptake in humans, whereas an increase of talinolol absorption is mainly through inhibition of Mdr1a-mediated efflux in rats. The rat intestinal permeability of talinolol measured by the in situ closed loop method was indeed significantly increased in the presence of GFJ, whereas a significant decrease was observed with 6-fold diluted GFJ, in which the naringin concentration was approximately 200 microM. The present study indicated that the species difference in the effect of GFJ on intestinal absorption of talinolol between humans and rats may be due to differences in the affinity of naringin for OATP/Oatp and MDR1/Mdr1 transporters between the two species.

Simulations of the nonlinear dose dependence for substrates of influx and efflux transporters in the human intestine

The purpose of this study was to develop simulation and modeling methods for the evaluation of pharmacokinetics when intestinal influx and efflux transporters are involved in gastrointestinal absorption. The advanced compartmental absorption and transit (ACAT) model as part of the computer program GastroPlus was used to simulate the absorption and pharmacokinetics of valacyclovir, gabapentin, and talinolol. Each of these drugs is a substrate for an influx or efflux transporter and all show nonlinear dose dependence within the normal therapeutic range. These simulations incorporated the experimentally derived gastrointestinal distributions of transporter expression levels for oligopeptide transporters PepT1 and HPT1 (valacyclovir); System L-amino acid transporter LAT2 and organic cation transporter OCTN1 (gabapentin); and organic anion transporter (OATP1A2) and P-glycoprotein (talinolol). By assuming a uniform distribution of oligopeptide transporter and by application of the in vitro K(m) value for valacyclovir, the simulations accurately reproduced the experimental nonlinear dose dependence. For gabapentin, LAT2 distribution produced simulation results that were much more accurate than OCTN1 distributions. For talinolol, an influx transporter distribution for OATP1A2 and the efflux transporter P-glycoprotein distributed with increasing expression in the distal small intestine produced the best results. The physiological characteristics of the small and large intestines used in the ACAT model were able to accurately account for the positional and temporal changes in concentration and carrier-mediated transport of the three drugs included in this study. The ACAT model reproduced the nonlinear dose dependence for each of these drugs.

Unexpected effect of concomitantly administered curcumin on the pharmacokinetics of talinolol in healthy Chinese volunteers

OBJECTIVE

To investigate the effect of concomitantly administered curcumin on the pharmacokinetics of the beta1 adrenoceptor blocker talinolol.

METHODS

The study was conducted in a self-controlled, two-period experiment with a randomized, open-labeled design, using 12 healthy volunteers and a wash out period of 1 week between the administration of a single oral dose of 50 mg talinolol and the concomitant administration of curcumin (300 mg day(-1) for 6 days) and a single oral dose of 50 mg talinolol on the seventh day. Concentrations of talinolol were measured in plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry. Non-compartmental analysis was used to characterize talinolol plasma concentration-time profiles, all pharmacokinetic parameters were calculated using DAS: (ver. 2.0) software, and comparisons of mean values were analyzed by the Wilcoxon signed rank test. Differences were considered to be significant at p < 0.05 (two-sided test).

RESULTS

The consumption of curcumin for 6 days reduced the area under the curve (AUC) from predose to infinity (AUC(0-infinity)) of talinolol from 1860.0 +/- 377.9 to 1246.0 +/- 328.2 ng x h mL(-1), the highest observed concentration values (C(max)) were significantly decreased from 147.8 +/- 63.8 to 106.4 +/- 39.9 ng mL(-1), and the CL/F was increased from 27.9 +/- 5.5 to 43.1 +/- 13.4 L x h(-1) (p < 0.05). There was no significant difference in sampling time for C(max) (t(max)) and elimination half-life (t(1/2)) values between the two periods (p > 0.05). The interindividual variability in AUC(0-60) and C(max) of talinolol was comparable in two study periods; the coefficient of variance (CV) of AUC(0-60) and C(max) was 26 and 40% after curcumin versus 21 and 43% after talinolol alone, respectively.

CONCLUSION

We suggest that the reduced bioavailability of talinolol is most probably due to the low intraluminal curcumin concentration, or possibly due to the upregulation of further ATP-binding cassette transporters, such as MRP2, in different tissues.

Induction of intestinal P-glycoprotein by St John's wort reduces the oral bioavailability of talinolol

St John's wort (SJW) is known to induce cytochrome P450 (CYP) 3A4 and P-glycoprotein through pregnane X-receptor activation. Our study evaluated the effects of long-term SJW administration on oral and intravenous pharmacokinetics of the nonmetabolized in vivo probe of P-glycoprotein, talinolol, in relation to intestinal P-glycoprotein expression. In a controlled, randomized study (N=9), the pharmacokinetics of oral (50 mg) and intravenous talinolol (30 mg) was determined before and after 12 days SJW (900 mg daily, Jarsin 300). Duodenal biopsies were taken and MDR1 genotypes assessed. SJW reduced the oral talinolol bioavailability by 25% (P=0.049) compared with water control. A 93% increase in oral clearance (P=0.177) and a 31% reduction in area under the serum concentration time curve (AUC; P=0.030) were observed. Renal and nonrenal clearance (CLNR), elimination half-life, peak serum drug concentration (Cmax), and time to reach Cmax were not significantly altered. After intravenous talinolol, SJW affected only CLNR (35% increase compared with water, P=0.006). SJW increased MDR1 messenger ribonucleic acid (mRNA) as well as P-glycoprotein levels in the duodenal mucosa. Subjects with the combined MDR1 genotype comprising 1236C>T, 2677G>T/A, and 3435C>T polymorphisms had lower intestinal MDR1 mRNA levels and displayed an attenuated inductive response to SJW as assessed by talinolol disposition. Long-term SJW decreased talinolol AUC with a corresponding increase in intestinal MDR1 expression, suggesting that SJW has a major inductive effect on intestinal P-glycoprotein. Interestingly, the magnitude of induction appeared to be affected by MDR1 genotype.

Role of pharmacogenetics of ATP-binding cassette transporters in the pharmacokinetics of drugs

Interindividual differences of drug response are an important cause of treatment failures and adverse drug reactions. The identification of polymorphisms explaining distinct phenotypes of drug metabolizing enzymes contributed in part to the understanding of individual variations of drug plasma levels. However, bioavailability also depends on a major extent from the expression and activity of drug transport across biomembranes. In particular efflux transporters of the ATP-binding cassette (ABC) family such as ABCB1 (P-glycoprotein, P-gp), the ABCC (multidrug resistance-related protein, MRP) family and ABCG2 (breast cancer resistance protein, BCRP) have been identified as major determinants of chemoresistance in tumor cells. They are expressed in the apical membranes of many barrier tissue such as the intestine, liver, blood-brain barrier, kidney, placenta, testis and in lymphocytes, thus contributing to plasma, liquor, but also intracellular drug disposition. Since expression and function exhibit a broad variability, it was hypothesized that hereditary variances in the genes of membrane transporters could explain at least in part interindividual differences of pharmacokinetics and clinical outcome of a variety of drugs. This review focuses on the functional significance of single nucleotide polymorphisms (SNP) of ABCB1, ABCC1, ABCC2, and ABCG2 in in vitro systems, in vivo tissues and drug disposition, as well as on the clinical outcome of major indications.

Simvastatin does not influence the intestinal P-glycoprotein and MPR2, and the disposition of talinolol after chronic medication in healthy subjects genotyped for the ABCB1, ABCC2 and SLCO1B1 polymorphisms

AIMS

To evaluate whether simvastatin influences (i) the intestinal expression of P-glycoprotein (P-gp) and MRP2, and (ii) the disposition of the beta(1)-selective blocker talinolol, a substrate of these transporter proteins.

METHODS

The disposition of talinolol after intravenous (30 mg) and single or repeated oral administration (100 mg daily) was monitored before and after chronic treatment with simvastatin (40 mg daily) in 18 healthy subjects (10 males, eight females, body mass index 19.0-27.0 kg m(-2)) genotyped for ABCB1, ABCC2 and SLCO1B1 polymorphisms. The steady-state pharmacokinetics of simvastatin was evaluated before and after repeated oral talinolol administration. The duodenal expression of ABCB1 and ABCC2 mRNA before and after simvastatin treatment was quantified using real-time reverse transcriptase-polymerase chain reaction (TaqMan.

RESULTS

Simvastatin did not influence the expression of duodenal ABCB1 and ABCC2. There was no significant pharmacokinetic interaction between simvastatin and talinolol. Duodenal ABCB1 mRNA content was significantly correlated with the AUC(0-infinity) (r = 0.627, P = 0.039) and C(max) (r = 0.718, P = 0.013) of oral talinolol. The ABCB1 and ABCC2 gene polymorphisms did not influence simvastatin and talinolol disposition. The half-life of the latter was significantly shorter in the nine carriers with a SLCO1B1*1b allele compared with the seven subjects with the wild-type SLCO1B1*1a/*1a genotype (12.2 +/- 1.6 h vs. 14.5 +/- 1.4 h, P = 0.01).

CONCLUSIONS

Simvastatin does not influence the intestinal expression of P-gp and MRP2 in man. There was no pharmacokinetic interaction between talinolol and simvastatin during their chronic co-administration to healthy subjects.

Expression and function of efflux drug transporters in the intestine

A variety of drug transporters expressed in the body control the fate of drugs by affecting absorption, distribution, and elimination processes. In the small intestine, transporters mediate the influx and efflux of endogenous or exogenous substances. In clinical pharmacotherapy, ATP-dependent efflux transporters (ATP-binding cassette [ABC] transporters) expressed on the apical membrane of the intestinal epithelial cells determine oral bioavailability, intestinal efflux clearance, and the site of drug-drug interaction of certain drugs. The expression and functional activity of efflux transporters exhibit marked interindividual variation and are relatively easily modulated by factors such as therapeutic drugs and daily foods and beverages. In this article, we will summarize the recent findings regarding the intestinal efflux transporters, especially P-glycoprotein (P-gp or human multidrug resistance gene [MDR] 1), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP).

MDR1 genotype do not influence the absorption of a single oral dose of 100 mg talinolol in healthy Chinese males

OBJECTIVE

We investigated the linkage between SNPs in exon 12 (C1236T), exon 21 (G2677T/A) and exon 26 (C3435T) of MDR1, and explored the effect of linked polymorphism on the absorption of talinolol after a single oral dose of 100 mg.

METHODS

The genotype of 192 healthy Chinese volunteers was determined using PCR-RFLP with respect to the MDR1 alleles of interest, C1236T, G2677T/A and C3435T. Linkage disequilibrium was analyzed using PHASE software. Consecutive eligible subjects received a single oral dose of 100 mg talinolol. Venous blood samples were taken at intervals up to 60 h post dose for HPLC analysis of plasma concentration of talinolol to obtain a pharmacokinetic profile.

RESULTS

Linkage disequilibrium existed between exon 21 (G2677T/A) and exon 26 (C3435T), exon 12 (C1236T) and exon 21 (G2677T/A), but not between exon 12 (C1236T) and exon 21 (G2677T/A). AUC (0,3 h), AUC (0, infinity), Cmax and Cmax/AUC (0, infinity), used as indices of talinolol absorption, were not significantly different between the genotype groups of 2677GG/3435TT, 2677TT/3435TT, 2677GT/3435CT and 2677AT/3435CT. For these 4 groups, AUC(0,3 h) were 436.8 +/- 50.1, 510.1 +/- 86.3, 466.1 +/- 77.8 and 437.2 +/- 73.4 (microg x h/l) and the Cmax/AUC (0, infinity) were 0.097 +/- 0.018, 0.093 +/- 0.022, 0.105 +/- 0.014 and 0.102 +/- 0.027 (h(-1)), respectively. (P > 0.05).

CONCLUSIONS

The linked MDR1 polymorphisms in exon 21 G2677T/A and exon 26 C3435T apparently did not contribute to the absorptive pharmacokinetics of a single oral dose of 100 mg talinolol.

The Talinolol Double-Peak Phenomenon Is Likely Caused by Presystemic Processing After Uptake from Gut Lumen

PURPOSE

Evaluation of the double-peak phenomenon during absorption of the beta(1)-selective blocker talinolol relative to paracetamol, which is well absorbed from all parts of the gut, and relative to vitamin A, which is absorbed via the lymphatic pathway.

METHODS

Talinolol was given with paracetamol and retinyl palmitate in fast-disintegrating, enteric-coated, and rectal soft capsules to 8 fasting male healthy subjects (21-29 years, 68-86 kg). To evaluate whether the talinolol double-peak is associated with processes of food absorption, a breakfast was served 1 h after administration of a fast disintegrating capsule.

RESULTS

Bioavailability of talinolol in enteric-coated and rectal capsules was significantly reduced by about 50% and 80%, respectively, despite unchanged bioavailability of paracetamol. Double-peaks appeared after 2-3 h and 4-6 h with talinolol given as fast-liberating capsules. Food increased the maximum concentrations significantly (223 +/- 76 microg/ml vs. 315 +/- 122 microg/ml, p < 0.05) and shifted the second peak of talinolol to shorter t(max) values (3.8 +/- 1.2 h vs. 2.1 +/- 0.6 h, p < 0.05), which was associated with faster absorption of retinyl palmitate. Pharmacokinetic model fits showed that about half of the oral talinolol dose given with and without meal is drained from the intestine via a presystemic storage compartment.

CONCLUSIONS

The double-peak phenomenon of talinolol is likely caused by a presystemic storage compartment, which represents the complex interplay of heterogeneous uptake and kick-back transport processes along the intestinal-hepatic absorption pathway.

The Role of P-Glycoprotein and Organic Anion-Transporting Polypeptides in Drug Interactions

The use of polytherapy in clinical practice necessitates an appreciation and understanding of the potential for drug interactions. Recent publications provide insight into the role of the active transport systems P-glycoprotein (P-gp) and human organic anion-transporting polypeptides (OATPs) in drug interactions. Active drug transporters influence the bioavailability of a number of drugs by controlling their movement into, and out of, cells. The active transport systems P-gp and OATP play an important role in drug elimination. The activity of these transport systems is controlled, in part, by genetic factors; however, drugs and foods also influence the activity of these systems. It appears that interference with P-gp or OATP, either as upregulation or inhibition, may affect plasma drug concentrations by altering intestinal absorption, proximal renal-tubular excretion or biliary excretion. Overall, the net bioavailability of a drug or substance is affected by the relative contributions of cellular efflux (P-gp) and influx (OATP) mechanisms and to what extent these systems are active during phases of uptake and absorption versus removal and excretion from the body. Many of the drugs and foods that affect active drug transport activity are known to interact with the cytochrome P450 enzyme system; therefore, the net effect of concomitant drug administration is complex. One must now consider the impact of metabolism (CYP-mediated drug biotransformation), P-gp-mediated drug efflux and OATP-mediated uptake when making assessments of drug absorption and distribution.

Effect of simulated intestinal fluid on drug permeability estimation across Caco-2 monolayers

Presently, the Caco-2 cell culture model is widely used during drug discovery and development as a predictive tool for the oral absorption of drug candidates. For transport experiments in the Caco-2 system, HBSS-like buffered salt solutions are commonly used, although different shortcomings have been associated with the use of these buffers. In this paper, we investigated the effect of using fasted state simulated intestinal fluid (FaSSIF) as potential biorelevant medium for the drug permeability estimation across Caco-2 monolayers. The transport characteristics of 19 model compounds were determined in the Caco-2 cell culture model in the presence of FaSSIF as compared to classic transport medium. A sigmoidal relation was obtained when the estimated P(app), s of the apical to basolateral transport were plotted versus the reported values of the fraction absorbed in man. Although no effect of FaSSIF as compared to classic transport medium (TM) was observed on the total predictability of the model, an impact was demonstrated (1) on the bi-directional transport of actively transported drugs (including talinolol, digoxin and doxorubicin), (2) on recovery and (3) on the solubility and permeability estimation of poorly water-soluble drugs. The observed differences may be attributed to a P-gp inhibitory effect of sodium taurocholate (NaTC), micellar encapsulation by the NaTC/lecithin mixed micelles and/or an increase of the solubility of lipophilic drugs. As the experimental conditions should mimic the physiological in vivo conditions, the use of FaSSIF as medium during Caco-2 experiments may improve the biorelevance of the model.

Different Dissolution Media Lead to Different Crystal Structures of Talinolol with Impact on Its Dissolution and Solubility

During the performance of dissolution tests with immediate and controlled-release talinolol tablets it was detected that the type of the buffer used as dissolution medium had a strong influence on the solubility and the dissolution behavior of the drug. It was proven that talinolol appeared in different crystal structures with strongly differing solubilities when pure water, acetate, or phosphate buffers were employed as dissolution media. The resulting crystal structures were characterized by means of light microscopy, differential scanning calorimetry, and X-ray powder diffraction. All methods were adjuvant to detect changes in talinolol crystal structures. The different solubility and dissolution properties of the talinolol salts or modifications may be viewed as a source for its incomplete and variable bioavailability. Furthermore, the food effect, described in the literature, that leads to a decrease in talinolol absorption, could be due to changes in the composition of gastrointestinal fluids leading to different talinolol crystal structures. Furthermore, it was detected that the addition of sodium chloride increases talinolol solubility and accelerates its dissolution from controlled-release tablets at concentrations between 0% and 1.25%, while an addition of sodium dodecylsulfate (SDS) as surfactant only had a solubility-improving effect at concentrations > 0.75%. At lower concentrations SDS decreased the solubility of talinolol and notably decelerated its release from controlled-release tablets.

Variability of intestinal expression of P-glycoprotein in healthy volunteers as described by absorption of talinolol from four bioequivalent tablets

The beta(1)-selective blocker talinolol is incompletely absorbed in man from an "absorption window" in the upper small intestine which is under control of P-glycoprotein. The following single dose, four-period, changeover study with 7 days washout in 36 healthy subjects (21 females, age 20-33 years) was designed to confirm bioequivalence of four marketed tablet formulations of talinolol with identical in vitro liberation and to deduce from the intrasubject and intersubject variability of talinolol pharmacokinetics on the variability of intestinal P-gp function. All point estimates of the primary criteria AUC(0-infinity) and C(max) for the comparison of the galenic forms were within 0.9-1.10. The 90% confidence intervals were entirely within the standard ranges of bioequivalence (0.80-1.25 for AUC(0-infinity), 0.70-1.43 for C(max)). The intra- and intersubject coefficients of variation for AUC(0-infinity) were 14.0% and 20.4-29.5%, respectively. In conclusion, the four talinolol tablets are bioequivalent in extent and rate of absorption. The low intrasubject variability of the AUC(0-infinity) after weekly administration of the tablets refers to a small intrasubject variability of the "absorption window" and elimination of talinolol that most likely depends on the expression of P-gp in the small intestine.

Apricot extract inhibits the P-gp-mediated efflux of talinolol

Within the framework of developing strategies to enhance the intestinal absorption of P-glycoprotein (P-gp) substrates, the modulatory effect of a standardized apricot extract on P-gp-related efflux carriers was investigated in the Caco-2 system, Ussing chambers and the rat in situ perfusion model using talinolol as a model substrate. Using the Caco-2 system, polarity in transport of talinolol could be observed, the absorptive transport being much lower than the secretory transport (P(app-abs) = 1.08 +/- 0.29 x 10(-6) cm/s and P(app-secr) = 11.74 +/- 0.80 x 10(-6) cm/s). Inclusion of apricot extract (1%) in the apical medium resulted in a statistically significantly diminished polarity (P(app-abs) = 4.88 +/- 0.96 x 10(-6) cm/s and P(app-secr) = 9.39 +/- 0.58 x 10(-6) cm/s, p < 0.05). In addition, the inhibitory effect of apricot extract on P-gp related efflux mechanisms was shown to be concentration (0% approximately 0.1% < 0.3% < 1%) and pH dependent. Experiments performed with the Ussing chambers resulted in similar observations. In the rat in situ perfusion model, inclusion of apricot extract (1%) in the perfusion medium resulted in a threefold increase of the amount of talinolol appearing in the collected blood compared to the reference condition (23.6 +/- 5.53 pmol/cm. min and 7.13 +/- 1.08 pmol/cm. min, respectively; p < 0.05). Coadministration of this standardized apricot extract might be a safe and useful strategy to enhance the intestinal absorption of P-gp substrates. The nature and structure of the compound(s) responsible for this inhibiting effect on P-gp-related efflux carriers remain to be elucidated, as well as the exact mechanism by which apricot extract exerts its inhibitory function.

A mechanistic approach to understanding the factors affecting drug absorption: a review of fundamentals

This article provides an overview of the patient-specific and drug-specific variables that can affect drug absorption following oral product administration. The oral absorption of any chemical entity reflects a complex spectrum of events. Factors influencing product bioavailability include drug solubility, permeability, and the rate of in vivo dissolution. In this regard, the Biopharmaceutics Classification System has proven to be an important tool for predicting compounds likely to be associated with bioavailability problems. It also helps in identifying those factors that may alter the rate and extent of drug absorption. Product bioavailability can also be markedly influenced by patient attributes such as the integrity of the gastrointestinal tract, physiological status, site of drug absorption, membrane transporters, presystemic drug metabolism (intrinsic variables), and extrinsic variables such as the effect of food or concomitant medication. Through an awareness of a drug's physicochemical properties and the physiological processes affecting drug absorption, the skilled pharmaceutical scientist can develop formulations that will maximize product availability. By appreciating the potential impact of patient physiological status, phenotype, age, gender, and lifestyle, dosing regimens can be tailored to better meet the needs of the individual patient.

Stereoselective disposition of talinolol in man

The disposition of the beta-blocking drug talinolol is controlled by P-glycoprotein in man. Because talinolol is marketed as a racemate, we reevaluated the serum-concentration time profiles of talinolol of a previously published study with single intravenous (30 mg) and repeated oral talinolol (100 mg for 14 days) before and after comedication of rifampicin (600 mg per day for 9 days) in eight male healthy volunteers (age 22-26 years, body weight 67-84 kg) with respect to differences in the kinetic profiles of the two enantiomers S(-) talinolol and R(+) talinolol. Additionally, the metabolism of talinolol in human liver microsomes was examined. After oral administration, S(-) talinolol was slightly less absorbed and faster eliminated than R(+) talinolol. The absolute bioavailabilty of the R(+) enantiomer of talinolol was slightly but significantly higher than of its S(-) enantiomer. Coadministration of rifampicin further intensified this difference in the disposition of R(+) and S(-) talinolol (p < 0.05). Formation of 4-trans hydroxytalinolol was the major metabolic pathway in human liver microsomes. All Cl(int) values of S(-) were higher than of R(+) talinolol; 0.1 microM ketoconazole inhibited the formation of all metabolites. In conclusion, the stereoselectivity of talinolol disposition is of minor importance, and most likely caused by presystemic biotransformation via CYP3A4. The less active R(+) talinolol might be suitable for phenotyping P-glycoprotein expression in man.

High speed determination of beta-receptor blocking agents in human urine by liquid chromatography/tandem mass spectrometry

Beta-receptor blocking agents are present on the international market in a huge variety. The International Olympic Committee prohibits the use of these drugs in several sport sections and doping control laboratories analyse urine samples of high-performance athletes with different techniques. Therefore, fast and reliable methods are required to enable a sensitive detection of many drugs and a high throughput of samples. In the present study a screening procedure is described using high speed liquid chromatography and multiple reaction monitoring to identify 32 beta-receptor blocking agents extracted from human urine. Urine specimens (blank urine samples, spiked urine samples and specimens of excretion studies) were hydrolysed, extracted and analysed within 7 min. Quasi-molecular ions (M(+) + H) of the beta-blockers are generated by means of an atmospheric pressure chemical ionization interface followed by collision-induced dissociation in a triple quadrupole mass spectrometer and subsequent detection of daughter ions. Proposals for the origin of common and individual secondary ions are presented.

Intestinal secretion of intravenous talinolol is inhibited by luminal R-verapamil

OBJECTIVE

To examine the secretion of the beta1-adrenergic receptor antagonist talinolol into the small intestine during its intravenous administration and to show the relevance of the P-glycoprotein-modulating drug verapamil for this secretory transport mechanism in humans.

METHODS

In six healthy volunteers the intestinal steady-state perfusion technique (triple lumen tubing system) was used for measuring the appearance of talinolol within the small intestine while the drug was infused intravenously. During four of the seven perfusions performed, the perfusion fluid was changed from a verapamil-free solution and talinolol appearance was measured while a R-verapamil-containing solution (565 micromol/L) was perfused.

RESULTS

Talinolol was transported into the intestinal lumen up to a concentration gradient between lumen and blood of about 5.5:1. While perfusing the small intestine with a verapamil-free solution, the intestinal secretion rate of talinolol ranged from 1.94 to 6.62 microg/min per 30 cm length of the intestine (median values). Perfusion of a R-verapamil-containing perfusion fluid resulted in lower secretion rates (0.59 to 3.71 microg/30 cm x min), corresponding to 29% to 56% of the values obtained without verapamil supplied intraluminally.

CONCLUSION

Intravenously administered talinolol is actively secreted into the human small intestine. This secretion is reduced by the intraluminal supply of the P-glycoprotein modulating drug R-verapamil. This gives further rationale for P-glycoprotein-mediated intestinal drug secretion as a cause for incomplete oral bioavailability and for drug interactions during intestinal absorption.

Direct demonstration of small intestinal secretion and site-dependent absorption of the beta-blocker talinolol in humans

OBJECTIVE

To examine the relevance of site-dependent small intestinal absorption for incomplete intestinal absorption of the poorly metabolized beta 1-adrenergic receptor antagonist talinolol.

METHODS

The intestinal steady-state perfusion technique (triple lumen tubing system with a 30 cm test segment) for intraluminal measurements was combined with simultaneous determination of talinolol serum concentrations. Dissolved talinolol was perfused over 160 minutes into different parts of the small intestine. The middle of the test segment was located between 25 and 235 cm beyond the teeth. Each of the six healthy subjects was studied twice with a proximal and a more distal site of perfusion to allow for comparisons within an individual subject.

RESULTS

The area under the curve for serum concentrations from 0 to 480 minutes [AUC(0-480 min)] and the maximum serum concentration after distal perfusions corresponded to only 15% to 73% and 7% to 90% of the proximal values, respectively. AUC decreased with increasing distance from the teeth. The mean amount of talinolol absorbed from the test segment per unit time (intestinal transport rate) corresponds to only one-tenth of the amount of drug offered to the test segment (perfusion rate). There was a direct correlation between the perfusion rate of talinolol and its transport rate for both regions and in all subjects investigated. However, to achieve the same transport rate in the distal region a higher perfusion rate is required, compared to the proximal small intestine. At perfusion rates lower than 600 micrograms/min, net secretion of talinolol into the intestinal lumen occurred against a steep concentration gradient blood: lumen of about 1:4200.

CONCLUSION

Talinolol oral bioavailability of 55% is due to a low absorption rate and a decrease of absorption capabilities along the small intestine. Net absorption of talinolol is reduced by the involvement of active intestinal secretion.