A validated method for simultaneous quantification of four antiretrovirals in dried blood spot and plasma using LC-MS/MS: Application to efavirenz therapeutic drug monitoring in pregnant patients

INTRODUCTION

The specific physiological background induced by pregnancy leads to significant changes in maternal pharmacokinetics, suggesting potential variability in plasma concentrations of antiretrovirals. Pregnant HIV patients exposed to subtherapeutic doses, particularly in the last trimester of the pregnancy, have higher chances to transmit the infection to their children. Therefore, the therapeutic drug monitoring of antiretrovirals in HIV pregnant patients would be of great value.

OBJECTIVES

This study aimed to develop and validate a sensitive liquid chromatograph tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of efavirenz, raltegravir, atazanavir, and ritonavir in dried blood spots (DBS) and plasma.

DESIGN AND METHODS

The analytes were extracted from the DBS punch and plasma with a mixture of methanol:zinc sulfate 200 mM (50:50, v/v) and 100 % methanol, respectively. For the chromatographic separation a Shim-pack® C18, 4.6 mm × 150 mm, 5 μm column was used. Detection was performed in a 3200-QTRAP® mass spectrometer, with a run time of 6 min.

RESULTS

The assay was linear in the range of 15-1,000 ng/mL for raltegravir, 50-10,000 ng/mL for both atazanavir and ritonavir, 50-5,000 ng/mL for efavirenz. Precision and accuracy at these concentrations were less than 15 % for all analytes. Raltegravir, atazanavir, and ritonavir were stable for seven days at 23 °C and 40 °C, whereas efavirenz was stable for twenty-four hours at the same conditions.

CONCLUSIONS

The method was successfully applied to quantify efavirenz in DBS samples obtained from HIV-1 infected pregnant volunteers under antiretroviral therapy. The concentrations of efavirenz in DBS and plasma were comparable according to Passing-Bablok regression and Bland-Altman analysis.

High efavirenz levels but not neurofilament light plasma levels are associated with poor neurocognitive functioning in asymptomatic HIV patients

The aim of this study is to assess the effect of efavirenz exposure on neurocognitive functioning and investigate plasma neurofilament light (Nfl) as a biomarker for neurocognitive damage. Sub-analysis of the ESCAPE-study, a randomised controlled trial where virologically suppressed, cognitively asymptomatic HIV patients were randomised (2:1) to switch to rilpivirine or continue on efavirenz. At baseline and week 12, patients underwent an extensive neuropsychological assessment (NPA), and serum efavirenz concentration and plasma Nfl levels were measured. Subgroups of elevated (≥ 4.0 mg/L) and therapeutic (0.74 to< 4.0 mg/L) baseline efavirenz concentration were made. Differences between these groups in baseline NPA Z-scores and in delta scores after efavirenz discontinuation were assessed. Nfl level was measured using an ELISA analysis using single molecule array (Simoa) technology. Correlation of plasma NFL with NPA Z-scores was evaluated using a linear mixed model. The elevated group consisted of 6 patients and the therapeutic group of 48. At baseline, the elevated group showed lower composite Z-scores (median - 1.03; IQR 0.87 versus 0.27; 0.79. p 0.02). This effect was also seen on the subdomains verbal (p 0.01), executive functioning (p 0.02), attention (p < 0.01) and speed (p 0.01). In the switch group, the elevated group improved more on composite scores after discontinuing efavirenz (mean 0.58; SD 0.32 versus 0.22; 0.54, p 0.15). No association between plasma Nfl and composite Z-score was found. High efavirenz exposure is associated with worse cognitive functioning compared with patients with therapeutic concentrations. Plasma Nfl is not a suitable biomarker to measure cognitive damage in this group.

A Thorough QT Study of the Combination Glecaprevir + Pibrentasvir on Cardiac Repolarization in Healthy Subjects

PURPOSE

Fixed-dose combination glecaprevir (GLE) 300 mg + pibrentasvir (PIB) 120 mg is an orally administered once daily antiviral regimen approved for the treatment of hepatitis C virus (HCV) infection. The objective of this study was to evaluate the potential for cardiac repolarization following GLE + PIB administration in healthy adults.

METHODS

This placebo- and active-controlled, randomized, single-dose, 4-period, 4-sequence crossover study enrolled 48 healthy subjects. The doses of GLE 400 mg + PIB 120 mg were selected to provide exposures comparable to those with the doses that are therapeutic in the HCV-infected population, GLE 300 mg + PIB 120 mg. The doses of GLE 600 mg + PIB 240 mg were selected to provide supratherapeutic exposures without exceeding the exposures of the GLE + PIB maximal tolerated doses. Moxifloxacin 400 mg (active control/open label) was used for confirming the sensitivity of the ECG assay in detecting QTc prolongation. Time-matched plasma concentrations and triplicate ECGs were obtained on treatment days -1 and 1. The primary end point was time-matched, placebo-corrected, baseline-adjusted Fridericia-corrected QT interval (ΔΔQTcF). Pharmacokinetic-pharmacodynamic analyses characterized the relationship between GLE and PIB plasma concentrations and ΔΔQTcF using a linear regression model and linear mixed-effects model. Findings from categorical analyses of ECG-interval data were also summarized. Tolerability was evaluated through adverse-events monitoring, physical examination including vital sign measurements, ECGs, and laboratory tests.

FINDINGS

A total of 48 subjects (22 women [46%], 26 men [54%]), were enrolled in the study, and 47 subjects completed all 4 periods. None of the subjects had a change from baseline in QTcF interval of >30 msec or an absolute QTcF interval of >450 msec. Peak ΔΔQTcF values observed at 5 h postdose (T_max) were 2.9 msec (upper 95% confidence limit, 4.9 msec) with the therapeutic dose and 3.1 msec (upper 95% confidence limit, 5.1 msec) with the supratherapeutic dose, with both upper 95% confidence limits well below the 10-msec threshold. Assay sensitivity was confirmed by peak ΔΔQTcF in the positive control (12.8 ms at 2 h postdose). No statistically significant GLE or PIB concentration-dependent effects on ΔΔQTcF were observed. Headache and skin irritation from ECG electrodes were the most commonly reported AEs. No clinically significant vital sign measurements, ECG findings, or laboratory measurements were observed. There were no patterns of T- and U-wave morphologic abnormalities.

IMPLICATIONS

The fixed-dose combination regimen of GLE/PIB does not prolong the QTc interval. ClinicalTrials.gov identifier.

Dosage Optimization of Efavirenz Based on a Population Pharmacokinetic-Pharmacogenetic Model of HIV-infected Patients in Thailand

PURPOSE

Efavirenz exhibits high interindividual variability in plasma concentrations, leading to unpredictable efficacy and toxicity. Polymorphism of CYP2B6 516G > T has been found to predominantly contribute to efavirenz variability. However, dosage recommendations incorporating CYP2B6 516G > T polymorphism have not been investigated in the Thai population. This study aimed to develop a population model of the pharmacokinetic properties of efavirenz, and to investigate the impact of patients' characteristics and CYP2B6 516G > T polymorphism on the pharmacokinetic properties of efavirenz. Model-based simulations were performed to provide genotype-based dosage optimization in a Thai population.

METHODS

Plasma efavirenz concentrations measured at 12 h post-dose in 360 Thai HIV-infected patients with and without tuberculosis were analyzed by the nonlinear mixed-effects modeling approach. A 1-compartment model with first-order absorption and elimination was used for describing the pharmacokinetic properties of efavirenz.

FINDINGS

The allele frequency of CYP2B6 516G > T was 34.17%. The efavirenz oral clearance were 11.9, 8.0, and 2.8 L/h in patients weighing 57 kg and having the CYP2B6 516 GG, 516 GT, and 516 TT genotypes, respectively. The use of rifampicin increased efavirenz oral clearance by 28%. The results from the simulations suggest that efavirenz dosages of 400, 300, and 100 mg once daily in Thai HIV mono-infected patients, and 800, 600, and 200 mg once daily in HIV/tuberculosis co-infected patients carrying CYP2B6 516 GG, 516 GT, and 516 TT, respectively.

IMPLICATION

The results from this study provide a rationale for efavirenz dose adjustment based on CYP2B6 516G > T polymorphism in Thai HIV-infected patients, which could help to improve treatment outcomes in this population. ClinicalTrials.gov identifier: NCT01138267.

Influence of a herbal preparation on the pharmacokinetics of highly active antiretroviral therapy drugs in rats

Shenlin Fuzheng Capsule (SLFZC) is a herbal preparation used for HIV/AIDS in Guangxi, China. This study was designed to evaluate the influence of SLFZC on the pharmacokinetics of highly active antiretroviral therapy (HAART) drugs, zidovudine (3'-azido-3'-deoythymidine, AZT), 2',3'-dideoxy-3'-thiacytidine (3TC) and efavirenz (EFV). Thirty-six male SD rats were divided into three groups. Group A was given a combination of AZT, 3TC and EFV (AZT/3TC/EFV). Group B rats were given AZT/3TC/EFV simultaneously with SLFZC. Group C rats were given AZT/3TC/EFV 2h prior to SLFZC. Blood samples were collected at fixed time intervals. Plasma concentration of each antiretroviral drug was tested for calculation of pharmacokinetic parameters. There was significant difference among groups with respect to t1/2 for AZT (F=3.371, P<0.05), but the Student-Newman-Keuls (SNK) pairwise multiple comparison procedure showed no statistical differences in all pairwise comparisons (P>0.05). There were no significant differences among groups in terms of C_max, T _max, AUC_0-12h and CL for AZT, and t_1/2, C_max, T_max, AUC_0-12h and CL for 3TC and EFV, respectively. The results indicate that SLFZC has little impact on pharmacokinetic properties of AZT, 3TC and EFV.

Gas chromatography/negative chemical ionization mass spectrometry of transfluthrin in rat plasma and brain

RATIONALE

Transfluthrin is a relatively non-toxic rapid-acting synthetic pyrethroid insecticide. It is widely used in household and hygiene products. A sensitive and accurate bioanalytical method is required for quantification of its concentration in plasma and its potential target organ, the brain for studies to assess its health effects and toxicokinetics in mammals.

METHODS

The samples were prepared by liquid-liquid extraction. Gas chromatography mass spectrometry (GC/MS) analysis was performed for the determination of transfluthrin in biological samples with an overall method run time of 15 min. Transfluthrin was quantified using selected-ion monitoring (SIM) in the negative chemical ionization (NCI) mode. Chromatographic separation was achieved using a Zebron® ZB5-MS GC column operating with 1 mL/min constant flow helium. Cis-Permethrin was used as the internal standard.

RESULTS

The method was validated to be precise and accurate within the linear range of 1.0-400.0 ng/mL in plasma and 4.0-400.0 ng/mL in brain homogenate, based on a 100 μL sample volume for both matrices. This method was applied to samples following administration of a 10 mg/kg oral dose to male adult rats. The plasma concentrations were observed to be 11.70 ± 5.69 ng/mL and brain concentrations 12.09 ± 3.15 ng/g when measured 2 h post-dose.

CONCLUSIONS

A rapid GC/NCI-MS method was demonstrated to be sensitive, specific, precise and accurate for the quantification of transfluthrin in rat plasma and brain. The optimized method was successfully used to quantify the rat plasma and brain concentrations of transfluthrin 2 h after the oral dosing of Sprague-Dawley rats.

Novel Roflumilast analogs as soft PDE4 inhibitors

PDE4 inhibitors are of high interest for treatment of a wide range of inflammatory or autoimmune diseases. Their potential however has not yet been realized due to target-associated side effects, resulting in a low therapeutic window. We herein report the design, synthesis and evaluation of novel PDE4 inhibitors containing a γ-lactone structure. Such molecules are designed to undergo metabolic inactivation when entering circulation, thereby limiting systemic exposure and reducing the risk for side effects. The resulting inhibitors were highly active on both PDE4B1 and PDE4D2 and underwent rapid degradation in human plasma by paraoxonase 1. In contrast, their metabolites displayed markedly reduced permeability and/or on-target activity.

Simultaneous quantitation of IC87114, roflumilast and its active metabolite roflumilast N-oxide in plasma by LC-MS/MS: application for a pharmacokinetic study

A sensitive and reliable high-performance liquid chromatography-mass spectrometry (LC-MS/MS) was developed and validated for simultaneous quantification IC87114, roflumilast (RFM), and its active metabolite roflumilast N-oxide (RFN) using tolbutamide as an internal standard. The analytes were extracted by using liquid-liquid extraction and separated on a reverse phase C(18) column (50 mm × 3 mm i.d., 4.6 µ) using methanol: 2 mM ammonium acetate buffer, pH 4.0 as mobile phase at a flow rate 1 mL/min in gradient mode. Selective reaction monitoring was performed using the transitions m/z 398.3 > 145.9, 403.1 >186.9, 419.1 > 187.0 and 271.1 > 155.0 to quantify quantification IC87114, RFM, RFN and tolbutamide, respectively. The method was validated over the concentration range of 0.1-60 ng.mL(-1) for RFM and RFN and 6 to 2980 ng.mL(-1) for IC87114. Intra- and inter-day accuracy and precision of validated method were within the acceptable limits of <15% at all concentrations. Coefficients of correlation (r(2) ) for the calibration curves were >0.99 for all analytes. The quantitation method was successfully applied for simultaneous estimation of IC87114, RFM and RFN in a pharmacokinetic drug-drug interaction study in Wistar rats.

The oral, once-daily phosphodiesterase 4 inhibitor roflumilast lacks relevant pharmacokinetic interactions with inhaled budesonide

This open-label, randomized, 3-period crossover study evaluated the pharmacokinetic interaction potential of roflumilast and budesonide following repeated coadministration to healthy male subjects (N = 12). Treatments consisted of oral roflumilast 500 mug, once daily, orally inhaled budesonide 800 mug, twice daily, and concomitant administration of both treatments for 7 days each. Roflumilast and roflumilast N-oxide in plasma and budesonide serum levels were measured by specific assays. Geometric mean test/reference ratios of steady-state pharmacokinetic parameters were evaluated by analysis of variance. Safety and tolerability were monitored. Pharmacokinetic parameters of roflumilast, roflumilast N-oxide, and budesonide after coadministration of roflumilast and budesonide were similar to those after mono-treatment. Compared with budesonide and roflumilast mono-treatments, slightly lower maximum serum/plasma concentration (C(max)) and area under the curve (AUC) values of roflumilast N-oxide and budesonide (ranging from -8% to -16%) were observed with combined treatment. All test/reference ratios were within predefined equivalence acceptance ranges for roflumilast AUC (0.80, 1.25) and C(max) (0.70, 1.43) and for roflumilast N-oxide and budesonide AUC and C(max) (all 0.67, 1.50). Coadministration of roflumilast and budesonide did not alter the steady-state disposition of each other and did not affect safety and tolerability of either drug.

Effect of fluvoxamine on the pharmacokinetics of roflumilast and roflumilast N-oxide

OBJECTIVE

To investigate the effects of steady-state dosing of fluvoxamine, an inhibitor of cytochrome P450 (CYP) 1A2 and CYP2C19, on the pharmacokinetics of roflumilast, an oral, once-daily phosphodiesterase 4 (PDE4) inhibitor and its pharmacodynamically active metabolite roflumilast N-oxide.

METHODS

In an open-label, non-randomised, one-sequence, two-period, two-treatment crossover study, 14 healthy subjects received a single oral dose of roflumilast 500 microg on study day 1. After a 6-day washout period, repeated doses of fluvoxamine 50 mg once daily were given from days 8 to 21. On day 15, roflumilast 500 microg and fluvoxamine 50 mg were taken concomitantly. Percentage ratios of test/reference (reference: roflumilast alone; test: roflumilast plus steady-state fluvoxamine) of geometric means and their 90% confidence intervals for area under the plasma concentration-time curve, maximum plasma concentration (roflumilast and roflumilast N-oxide) and plasma clearance of roflumilast were calculated.

RESULTS

Upon co-administration with steady-state fluvoxamine, the exposure to roflumilast as well as roflumilast N-oxide increased by a factor of 2.6 and 1.5, respectively. Roflumilast plasma clearance decreased by a factor of 2.6, from 9.06 L/h (reference) to 3.53 L/h (test). The combined effect of fluvoxamine co-administration on roflumilast and roflumilast N-oxide exposures resulted in a moderate (i.e. 59%) increase in total PDE4 inhibitory activity.

CONCLUSION

Co-administration of roflumilast and fluvoxamine affects the disposition of roflumilast and its active metabolite roflumilast N-oxide most likely via a potent dual pathway inhibition of CYP1A2 and CYP2C19 by fluvoxamine. The exposure increases observed for roflumilast N-oxide are suggested to be attributable to CYP2C19 co-inhibition by fluvoxamine and thus, are not to be expected to occur when roflumilast is co-administered with more selective CYP1A2 inhibitors.

The G196A polymorphism of the brain-derived neurotrophic factor gene and the antidepressant effect of milnacipran and fluvoxamine

Prediction of the response to different classes of antidepressants has been an important matter of concern in the field of psychopharmacology. The purpose of the present study was to investigate whether the G196A polymorphism of the brain-derived neurotrophic factor (BDNF) gene is associated with the antidepressant effect of milnacipran, a serotonin norepinephrine reuptake inhibitor, and fluvoxamine, a selective serotonin reuptake inhibitor. The subjects of our previous study of milnacipran (n = 80) and fluvoxamine (n = 54) were included in the present study. Severity of depression was assessed with the Montgomery Asberg depression rating scale (MADRS). Assessments were carried out at baseline and at 1, 2, 4 and 6 weeks of treatment. Polymerase chain reaction was used to determine allelic variants. In all subjects receiving milnacipran or fluvoxamine, the G/A genotype of the BDNF G196A polymorphism was associated with a significantly better therapeutic effect in the MADRS scores during this study. When milnacipran and fluvoxamine-treated subjects were analysed independently, the G/A genotype group showed greater reduction of MADRS scores than other genotype groups, irrespective of which antidepressant was administered. These results suggest that the BDNF G196A polymorphism in part determines the antidepressant effect of both milnacipran and fluvoxamine.

Steady-state pharmacokinetics of roflumilast and roflumilast N-oxide in patients with mild and moderate liver cirrhosis

BACKGROUND

Roflumilast and its primary N-oxide metabolite are targeted phosphodiesterase 4 (PDE4) inhibitors with similar in vivo potency. Roflumilast is being developed for the treatment of inflammatory airway diseases such as chronic obstructive pulmonary disease and asthma.

OBJECTIVE

To investigate the effects of mild and moderate liver cirrhosis on the steady-state pharmacokinetics of roflumilast and roflumilast N-oxide.

METHODS

Patients with mild (n = 8, Child-Pugh A) and moderate (n = 8, Child-Pugh B) liver cirrhosis and healthy subjects (n = 8) matched with patients with cirrhosis with regard to sex, age and bodyweight received oral roflumilast 250 microg once daily for 14 days. Blood samples were collected for 24 hours after the last dose on day 14. Steady-state plasma concentrations of roflumilast and roflumilast N-oxide were determined using a validated high-performance liquid chromatography with tandem mass spectrometry assay. The pharmacokinetics were compared between groups using ANOVA.

RESULTS

In patients with liver cirrhosis, the average total exposure (area under the plasma concentration-time curve from 0 to 24 hours [AUC(24)]) of roflumilast was approximately 51% (Child-Pugh A) and 92% (Child-Pugh B) higher than in healthy subjects. In contrast, roflumilast maximum plasma concentration (C(max)) was unaltered in Child-Pugh A patients and was increased by 27% in Child-Pugh B patients. Changes in the AUC(24) of roflumilast N-oxide were less distinct, with 24% and 41% increases and corresponding C(max) increases of 26% and 40% in Child-Pugh A and B patients, respectively, compared with healthy subjects. Overall, changes in average potency-corrected exposure to the sum of the free fractions of both compounds were estimated to result in approximately 26% and 46% increases in total PDE4 inhibitory capacity (tPDE4i) in Child-Pugh A and B patients, respectively, relative to healthy subjects. Roflumilast was well tolerated.

CONCLUSIONS

Mild and moderate liver cirrhosis resulted in distinct alterations of exposure to roflumilast but only in modest alterations of exposure to roflumilast N-oxide. The integrated exposure-weighted assessment of the observed pharmacokinetic changes of roflumilast and roflumilast N-oxide (tPDE4i) indicates modest average exposure increases to the sum of both compounds. These findings and the favourable tolerability profile suggest that roflumilast can be safely used in patients with mild and moderate liver cirrhosis without special precautions or dose adjustment.

L-454,560, a potent and selective PDE4 inhibitor with in vivo efficacy in animal models of asthma and cognition

Type 4 phosphodiesterases (PDE4) inhibitors are emerging therapeutics in the treatment of a number of chronic disorders including asthma, chronic obstructive pulmonary disease (COPD) and cognitive disorders. This study delineates the preclinical profile of L-454,560, which is a potent, competitive and preferential inhibitor of PDE4A, 4B, and 4D with IC50 values of 1.6, 0.5 and 1.2 nM, respectively. In contrast to the exclusive binding of cilomilast and the preferential binding of roflumilast to the PDE4 holoenzyme state (Mg2+-bound form), L-454,560 binds to both the apo-(Mg2+-free) and holoenzyme states of PDE4. The intrinsic enzyme potency for PDE4 inhibition by L-454,560 also results in an effective blockade of LPS-induced TNFalpha formation in whole blood (IC50 = 161 nM) and is comparable to the human whole blood potency of roflumilast. The cytokine profile of inhibition of L-454,560 is mainly a Th1 profile with significant inhibition of IFNgamma and no detectable inhibition of IL-13 formation up to 1 microM. L-454,560 was also found to be efficacious in two models of airway hyper-reactivity, the ovalbumin (OVA) sensitized and challenged guinea pig and the ascaris sensitized sheep model. Furthermore, L-454560 was also effective in improving performance in the delayed matching to position (DMTP) version of the Morris watermaze, at a dose removed from that associated with potential emesis. Therefore, L-454,560 is a novel PDE4 inhibitor with an overall in vivo efficacy profile at least comparable to roflumilast and clearly superior to cilomilast.

Roflumilast, a once-daily oral phosphodiesterase 4 inhibitor, lacks relevant pharmacokinetic interactions with inhaled salbutamol when co-administered in healthy subjects

OBJECTIVE

Roflumilast is an oral, once-daily phosphodiesterase 4 inhibitor under investigation for the treatment of chronic obstructive pulmonary disease and asthma. In clinical practice, the drug is likely to be co-administered with inhaled bronchodilating beta2-adrenoceptor agonists. Therefore, this study investigated the pharmacokinetic characteristics of roflumilast and its pharmacodynamically active metabolite roflumilast N-oxide when co-administered with orally inhaled salbutamol in healthy subjects.

METHODS

In this open, randomized clinical study, 12 healthy male subjects received repeated doses of oral roflumilast 500 microg once daily, orally inhaled salbutamol 200 microg 3 times daily, and a combination of both drugs over 7 days according to a 3-period, changeover design with 14 days washout between treatments.

RESULTS

Co-administration of roflumilast and salbutamol did not markedly change roflumilast or roflumilast N-oxide disposition. Point estimates (90% confidence intervals) of area under the curve from 0-24 h (AUC 0-24) and maximum plasma concentration in steady state (Cmax,ss) for roflumilast with salbutamol versus roflumilast alone were 1.05 (0.94, 1.17) and 0.97 (0.84, 1.10); the respective point estimates (90% confidence intervals) for AUC 0-24 and Cmax,ss of roflumilast N-oxide were 0.98 (0.91, 1.06) and 0.98 (0.92, 1.03). Roflumilast co-administration did not alter the pharmacokinetics of steady state salbutamol. The respective point estimates (90% confidence intervals) for AUC 0-6 and Cmax,ss of salbutamol with roflumilast versus salbutamol alone were 1.10 (0.99, 1.21), 1.08 (0.91, 1.28). The combination of both drugs was well tolerated.

CONCLUSION

There were no relevant pharmacokinetic interactions between roflumilast and salbutamol at therapeutically effective doses.

Investigation of a potential food effect on the pharmacokinetics of roflumilast, an oral, once-daily phosphodiesterase 4 inhibitor, in healthy subjects

This open, randomized, single-dose crossover study investigated effects of a high-fat meal on the pharmacokinetics of roflumilast and its major active N-oxide metabolite. Twelve healthy subjects received oral roflumilast 500 microg (2 x 250 microg) after overnight fasting and after breakfast. Blood was sampled up to 54 hours for pharmacokinetic profiling of roflumilast and N-oxide. Geometric mean ratios (fed/fasted) for point estimates (PE) and 90% confidence intervals (CI) were calculated for AUC(0-last), AUC(0-infinity), and C(max) of both compounds. After the meal, roflumilast C(max) (PE, 0.59; 90% CI, 0.49-0.70) was modestly reduced; N-oxide C(max) (PE, 0.95; 90% CI, 0.90-1.01) was unchanged. Roflumilast t(max) was delayed in fed state (2.0 +/- 0.4 hours) versus fasted state (1.0 +/- 0.2 hours); N-oxide t(max) was unaltered. No significant food effect on roflumilast AUC(0-last) (PE, 1.04; 90% CI, 0.90-1.21), AUC(0-infinity) (PE, 1.12; 90% CI, 1.00-1.25), and respective N-oxide AUCs (PE, 0.91; 90% CI, 0.79-1.04; PE, 0.99; 90% CI, 0.92-1.06) occurred. Because roflumilast N-oxide is the major contributor to roflumilast's overall pharmacologic effects, these findings suggest that roflumilast can be taken with or without food.

Dose-proportional intraindividual single- and repeated-dose pharmacokinetics of roflumilast, an oral, once-daily phosphodiesterase 4 inhibitor

The dose-proportional, intraindividual, single- and repeated-dose pharmacokinetics of roflumilast, an oral, once-daily phosphodiesterase 4 inhibitor under investigation for chronic obstructive pulmonary disease and asthma, was investigated in healthy subjects. In an open, randomized, 2-period, 2-sequence crossover study, 15 subjects received immediate-release tablets of roflumilast 250 or 500 microg as single (day 1) and as repeated, once-daily doses for 8 days (days 5-12). Dose-adjusted point estimates and 90% confidence intervals of test (500 microg)/reference (250 microg) ratios for AUC and Cmax of roflumilast and its pharmacologically active N-oxide metabolite after single and repeated dosing were all within the standard equivalence acceptance range (0.80, 1.25) indicating dose proportionality. The pharmacokinetic properties of both roflumilast dosage forms provide clinically relevant evidence of predictable, intraindividual total (AUC) and maximum (Cmax) exposure of roflumilast and roflumilast N-oxide. Repeated oral dosing with roflumilast 250 and 500 microg once daily was well tolerated.

Lack of a pharmacokinetic interaction between steady-state roflumilast and single-dose midazolam in healthy subjects

AIMS

The aim of this study was to investigate the effects of roflumilast, an investigational PDE4 inhibitor for the treatment of COPD and asthma, on the pharmacokinetics of the CYP3A probe drug midazolam and its major metabolites.

METHODS

In an open, randomized (for midazolam treatment sequence) study, 18 healthy male subjects received single doses of midazolam (2 mg oral and 1 mg i.v., 1 day apart) alone, repeated doses of roflumilast (500 microg once daily for 14 days) alone, and repeated doses of roflumilast together with single doses of midazolam (2 mg oral and 1 mg i.v., 1 day apart).

RESULTS

A comparison of clearance and peak and systemic exposure to midazolam following administration of roflumilast indicated no effect of roflumilast dosed to steady state on the pharmacokinetics of midazolam. Point estimates (90% CI) were 0.97 (0.84, 1.13) for the AUC of i.v. midazolam and 0.98 (0.82, 1.17) for that of oral midazolam with and without roflumilast.

CONCLUSIONS

Therapeutic steady state concentrations of roflumilast and its N-oxide do not alter the disposition of the CYP3A substrate midazolam in healthy subjects. This finding suggests that roflumilast is unlikely to alter the clearance of drugs that are metabolized by CYP3A4.

Preclinical evaluation of 2,2,3,3-tetramethylcyclopropanecarbonyl-urea, a novel, second generation to valproic acid, antiepileptic drug

2,2,3,3-Tetramethylcyclopropanecarbonylurea (TMCU) is an amide derivative of a tetramethylcyclopropyl analogue of valproic acid (VPA), one of the leading antiepileptic drugs. Structural considerations used in the design of TMCU aimed to enhance the anticonvulsant potency of VPA and to prevent its two life-threatening side effects; i.e., teratogenicity and hepatotoxicity. The anticonvulsant activity of TMCU was evaluated in the MES, scMet, 6-Hz, scBic and scPic tests, and also in the hippocampal kindling model of partial seizures and lamotrigine-resistant amygdala kindling model of therapy-resistant seizures. Minimal motor impairment was determined using the rotorod test in mice and the positional sense test, muscle tone test, and gait and stance test in rats. The antinociceptive effect of TMCU was evaluated in the mouse formalin model of acute-tonic pain. The molecular mechanisms of action of TMCU were investigated in electrophysiological studies using the whole-cell patch-clamp technique. Teratogenicity studies were performed in a SWV/Fnn-mouse model of VPA-induced teratogenicity. TMCU hepatotoxicity was evaluated following 1-week intraperitoneal and oral administration of 50, 250 and 500 mg/kg doses to rats. In the hepatotoxicity study the blood levels of TMCU were evaluated at day 1 and day 7 of the treatment. TMCU mutagenicity was evaluated in the Ames test.

Lack of pharmacokinetic interaction when switching from fluoxetine to milnacipran

The lack of a therapeutic effect or unsupportable side-effects can lead to substitution of one antidepressant by another. The present study investigated potential modifications to the pharmacokinetic profile of milnacipran at steady-state when it is substituted for fluoxetine without any washout period. The open-label, multiple dose, three-period study was carried out in 12 evaluable healthy volunteers. A reference period (period 1) comprising a 3.5-day treatment with milnacipran at 50 mg b.i.d. was followed, after a 5-10-day washout, by 3 weeks of administration of 20 mg fluoxetine once daily (period 2), immediately followed by a further 3.5 days of administration of milnacipran at 50 mg b.i.d. (period 3). Blood samples collected at each period were analysed for milnacipran, N-dealkyl milnacipran, fluoxetine and norfluoxetine. Potential drug-drug interactions were evaluated by comparing milnacipran pharmacokinetic parameters between periods 1 and 3. A steady-state of fluoxetine and its metabolite was effectively reached by the end of the 3-week period. A steady-state of milnacipran was reached on day 2 of both periods 1 and 3. Trough concentrations of milnacipran were 66 and 65 ng/ml before and after the fluoxetine administration period, respectively. Cmax values were 226 and 248 ng/ml. When comparing the kinetic parameters of milnacipran before and after fluoxetine treatment, all the 90% confidence intervals were in the 20% range. No significant difference in the adverse events of milnacipran was observed before or after fluoxetine administration.

Response Rate Obtained Using Milnacipran Depending on the Severity of Depression in the Treatment of Major Depressive Patients

Milnacipran--a new specific serotonin and noradrenaline reuptake inhibitor--is as effective as tricyclic antidepressants and exhibits a higher remission rate for major depressive patients than selective serotonin reuptake inhibitors. However, the effectiveness of milnacipran for severe major depressive patients had not been studied adequately. The study included 96 Japanese patients who fulfilled the DSM-IV criteria for the diagnosis of major depressive disorders and whose score on the Montgomery-Asberg Depression Rating Scale (MADRS) was 21 or higher. Of these, 16 patients were excluded because 10 did not complete the study, and 6 showed poor compliance. Finally, 80 patients were included. We defined patients with a baseline MADRS score of > or = 31 points as "severe" (n = 25). The remaining patients were classified as "moderate" (31 > MADRS score > or = 25, n = 30) and "mild" (MADRS score < 25, n = 25) using the median score of those patients as the cutoff. Milnacipran was administered twice daily for 6 weeks. The initial total dose was 50 mg/d; after a week it was increased to 100 mg/d. The response rates were 72%, 70%, and 44% in the "severe," "moderate," and "mild," respectively. No significant differences were found between "severe" and the "moderate"; however, significant differences were observed between "severe" and "mild" and "moderate" and "mild." These results demonstrated that milnacipran is almost equally effective in "severe" and "moderate." This study suggested that milnacipran has a reliable antidepressant effect in treating severe and moderate major depressive patients.

Lack of Interaction of Milnacipran with the Cytochrome P450 Isoenzymes Frequently Involved in the Metabolism of Antidepressants

OBJECTIVE

To compare the pharmacokinetics of milnacipran in extensive metabolisers (EMs) and poor metabolisers (PMs) of sparteine and mephenytoin, and to assess the influence of multiple administrations of milnacipran on the activity of cytochrome P450 (CYP) isoenzymes through its own metabolism and through various probes, namely CYP2D6 (sparteine/dextromethorphan), CYP2C19 (mephenytoin), CYP1A2 (caffeine) and CYP3A4 (endogenous 6-beta-hydroxy-cortisol excretion).

METHODS

Twenty-five healthy subjects, 12 EMs for both sparteine/dextromethorphan and mephenytoin, nine EMs for mephenytoin and PMs for sparteine/dextromethorphan (PM(2D6)) and four PMs for mephenytoin and EMs for sparteine/dextromethorphan (PM(2C19)) were administered milnacipran as a single 50 mg capsule on day 1 followed by a 50 mg capsule twice daily for 7 days. The pharmacokinetics of milnacipran and its oxidative metabolites were assessed after the first dose (day 1) and after multiple administration (day 8), and were compared for differences between CYP2D6 and CYP2C19 PMs and EMs. Metabolic tests were performed before (day -2), during (days 1 and 8) and after (day 20) milnacipran administration.

RESULTS

Milnacipran steady state was rapidly achieved. Metabolism was limited: approximately 50% unchanged drug, 30% as glucuronide and 20% as oxidative metabolite (mainly F2800 the N-dealkyl metabolite). Milnacipran administration to PM2D6 and PM2C19 subjects did not increase parent drug exposure or decrease metabolite exposure. Milnacipran oxidative metabolism is not mediated through CYP2D6 or CYP2C19 polymorphic pathways nor does it significantly interact with CYP1A2, CYP2C19, CYP2D6 or CYP3A4 activities.

CONCLUSION

Limited reciprocal pharmacokinetic interaction between milnacipran and CYP isoenzymes would confer flexibility in the therapeutic use of the drug when combined with antidepressants. Drug-drug interaction risk would be low, even if the combined treatments were likely to inhibit CYP2D6 and CYP2C19 isoenzyme activities.

Prediction of antidepressant response to milnacipran by norepinephrine transporter gene polymorphisms

OBJECTIVE

With a multitude of antidepressants available, predictors of response to different classes of antidepressants are of considerable interest. The purpose of the present study was to determine whether norepinephrine transporter gene (NET) and serotonin transporter gene (5-HTT) polymorphisms are associated with the antidepressant response to milnacipran, a dual serotonin/norepinephrine reuptake inhibitor.

METHOD

Ninety-six Japanese patients with major depressive disorder were treated with milnacipran, 50-100 mg/day, for 6 weeks. Severity of depression was assessed with the Montgomery-Asberg Depression Rating Scale. Assessments were carried out at baseline and at 1, 2, 4, and 6 weeks of treatment. The method of polymerase chain reaction was used to determine allelic variants.

RESULTS

Eighty patients completed the study. The presence of the T allele of the NET T-182C polymorphism was associated with a superior antidepressant response, whereas the A/A genotype of the NET G1287A polymorphism was associated with a slower onset of therapeutic response. In contrast, no influence of 5-HTT polymorphisms on the antidepressant response to milnacipran was detected.

CONCLUSIONS

The results suggest that NET but not 5-HTT polymorphisms in part determine the antidepressant response to milnacipran.

Determination of milnacipran, a serotonin and noradrenaline reuptake inhibitor, in human plasma using liquid chromatography with spectrofluorimetric detection

Milnacipran is an antidepressant drug belonging to the class of serotonin and noradrenaline reuptake inhibitors. A sensitive high performance liquid chromatographic during the development method coupled with a fluorimetric detection was set up, validated and then used routinely of the drug. After liquid-liquid extraction, milnacipran and its internal standard were analyzed by reversed-phase liquid chromatography (LC). The drug was derivatized with fluorescamine for fluorescence detection. The identity of the liquid chromatography peaks was controlled using mass spectrometry. The assay linearity was validated up to 1000 ng/ml. The limit of quantification was set at 5 ng/ml. Precision values (relative standard deviations) were lower than 5.4%, whereas the mean accuracy was higher than 95%. The extraction recoveries were higher than 70% for both milnacipran and the internal standard. In clinics, the LC-fluorescence method was routinely used to investigate the pharmacokinetics of milnacipran in patients and proved to be robust and capable of quantifying milnacipran in plasma for at least 36 h (four- to five-fold the elimination half-life).

Associations between baseline plasma MHPG (3-methoxy-4-hydroxyphenylglycol) levels and clinical responses with respect to milnacipran versus paroxetine treatment

The purpose of this study was to investigate the effects of milnacipran and paroxetine on plasma levels of catecholamine metabolites, and we attempted to elucidate the differences between the mechanisms of these drugs in catecholaminergic neurons. In depressed patients, we investigated the relationships among pretreatment levels of catecholamine metabolites, the changes in plasma catecholamine metabolite levels before and after administration of milnacipran or paroxetine, and clinical response to these drugs. Responders to milnacipran showed lower pretreatment levels of plasma 3-methoxy-4-hydroxyphenylglycol (pMHPG) than did nonresponders to milnacipran; there was also a positive correlation between changes in pMHPG levels and percent improvement of the score on the 17-item Hamilton Rating Scale for Depression (HRSD). On the other hand, responders to paroxetine showed higher pretreatment levels of pMHPG than did nonresponders to paroxetine, and a negative correlation was observed between changes in pMHPG levels and percent improvement of the HRSD score. However, a significant difference was not observed in the pretreatment plasma level of homovanillic acid between responders and nonresponders to treatment with milnacipran or paroxetine. These results suggest that there is an association between baseline pMHPG levels and clinical responses with respect to milnacipran versus paroxetine treatment.

Milnacipran plasma levels and antidepressant response in Japanese major depressive patients

The relationship between antidepressant effects and plasma levels of milnacipran was studied in 49 cases of major depression without psychotic features during 6 weeks of milnacipran treatment. The daily dose of milnacipran was 50 mg/day for the first week, and up to 100 mg/day thereafter. Depressive symptoms were evaluated by the Montgomery and Asberg depression rating scale (MADRS) before treatment and at 1, 2, 4 and 6 weeks after the beginning of this study. Thirty-four patients (69.4%) were responders (defined as a 50% or greater decrease in the baseline MADRS score). Significant differences of MADRS scores were seen from 1 week after the beginning of this study (p=0.004, unpaired t-test) between responders and nonresponders. The mean plasma milnacipran level of responders, 82.0 +/- 29.4 ng/ml, was similar to that of non-responders, 78.6+/-23.1 ng/ml; there was no significant difference between responders and nonresponders. Neither a significant linear nor a curvilinear relationship was obtained between the final MADRS score and the plasma levels of milnacipran. Although there was no significant relationship between the plasma levels of milnacipran and the antidepressant response, milnacipran should be considered an efficacious agent in the treatment of major depressive patients.

Blood concentration of milnacipran in a case of a fatal automobile accident

A fatal automobile accident involving milnacipran and ethyl alcohol is reported. The drug was identified and quantitated in blood by high-performance liquid chromatography-diode-array detection. The concentration of milnacipran in peripheral blood was 3.15 microg/mL exceeded 10.5 times the therapeutic concentration. The blood ethyl alcohol level was 1.3 g/L.

Hemodynamic, antiischemic, and neurohumoral effects of tedisamil and atenolol in patients with coronary artery disease

Clinical drawbacks of beta-blocker treatment in stable angina have motivated researchers to provide alternative heart-rate-lowering agents, such as tedisamil, which additionally exerts antiischemic and antiarrhythmic effects by blockade of cellular repolarizing K+ currents. Forty-eight patients with stable angina pectoris were investigated (doubleblind, randomized, parallel grouped) comparing the hemodynamic, antiischemic, metabolic and neurohumoral effects of tedisamil 100 mg b.i.d. and atenolol 50 mg b.i.d. after a single dose and over 6 days of treatment. Tedisamil and atenolol produced a decrease in heart rate both at rest [day 1:-13.6 versus - 15.4 bpm; day 6: - 14.8 versus - 22.2 bpm, resp.; p > 0.05] and exercise [day 1: - 9.1 versus - 18.3 bpm; p = 0.001; day 6: - 12.0 versus - 24.8 bpm, resp.; p = 0.001], while anginal threshold increased. Cardiac output decreased with tedisamil and atenolol at rest [day 1: -1.01 versus -1.19 l/min; p > 0.05; day 6: - 0.86 versus - 1.10 l/min, resp.; p > 0.05] and exercise [day 1: - 0.82 versus - 1.28 l/min; p > 0.05; day 6: - 0.65 versus - 2.68 l/min, resp.; p = 0.03], while stroke volume remained unchanged. Right atrial pressure changed during exercise only: it decreased with tedisamil (-1.7 mmHg) and increased with atenolol (+ 3.7 mmHg) (p < .001). Mean pulmonary capillary wedge pressures decreased both at rest (- 0.5 mmHg) and exercise (- 6.9 mmHg) in the tedisamil group but tended to increase with atenolol on day 6 of treatment [rest: + 1.7; exercise: + 3.7 mmHg) (p = 0.03). Arterial pressure decreased under atenolol treatment only. Exercise-induced plasma norepinephrine levels were reduced by tedisamil (- 93 pg/ml) but elevated by atenolol (+ 172 pg/ml) (p = 0.001). As compared to atenolol, tedisamil produced a prolongation of QTc interval [+ 31 versus 8 ms] at initial values of 0.408 +/- 0.018 s with PQ and QRS remaining unaltered. In patients with stable angina, tedisamil (100 mg b.i.d.) as compared to atenolol (50 mg b.i.d.) generated similar hemodynamic, neurohumoral and antiischemic effects. The antiischemic efficacy of tedisamil, as measured by ST segment depression and angina threshold, was comparable to that of atenolol.

Inhibition of prostaglandin-induced intestinal secretion by igmesine in healthy volunteers

BACKGROUND & AIMS

Igmesine, a final sigma ligand, has been shown to inhibit intestinal secretion and diarrhea in animal models. The purpose of this study was to measure the inhibitory effect of igmesine on basal and prostaglandin E2 (PGE2)-induced jejunal secretion in normal volunteers.

METHODS

Jejunal absorption of water and electrolytes was measured with a three-lumen open-segment perfusion method in 16 volunteers. A double-blind crossover study was performed involving intraluminal infusion of PGE2 after oral administration of placebo or igmesine at two doses.

RESULTS

PGE2 induced net secretion of water and electrolytes (P < 0.01 vs. basal conditions). The effect of PGE2 on water and electrolytes was not changed by 25 mg of igmesine but was suppressed by 200 mg of igmesine. This effect lasted at least 3 hours after a single oral dose. Igmesine at a dose of 200 mg also produced a significant decrease in basal rates of water and electrolyte absorption.

CONCLUSIONS

Igmesine, a final sigma ligand, inhibits PGE2-induced intestinal secretion in normal humans. Evaluating the drug in chronic diarrheas may be of interest.

Antifibrillatory efficacy of long-term tedisamil administration in a postinfarcted canine model of ischemic ventricular fibrillation

The electrophysiologic and antifibrillatory properties of tedisamil (KC-8857) were studied in vivo in a conscious canine model of sudden cardiac death. Male mongrel dogs were anesthetized, and surgical anterior myocardial infarction was induced by a 2-h occlusion, with reperfusion of the left anterior descending coronary artery. Three to five days after infarction, dogs were subjected to programmed electrical stimulation (PES) to identify those at risk for ischemia-induced ventricular fibrillation. Previous studies documented that dogs with a significant anterior-wall infarction develop ventricular tachycardia in response to PES and are at an increased risk for sudden cardiac death on imposition of a transient ischemic event in a region remote from the infarct-related artery. PES-inducible animals were randomized to either oral placebo or oral tedisamil treatment (3 mg/kg, b.i.d for 4 days, Group 1, n = 8). Control animals received empty gelatin capsules (Group 2, n = 8). The effective refractory period and QTc interval were unchanged after 3 days of oral placebo or tedisamil dosing. Arrhythmic activity after drug administration was not observed in dogs treated with tedisamil. PES induction of ventricular tachycardia was reduced significantly in the tedisamil-treated group (100% inducible before drug vs. 9% inducible after drug; p < 0.05). In the sudden-cardiac-death protocol, tedisamil reduced the incidence of lethal ischemic arrhythmias developing in response to acute posterolateral myocardial ischemia. Tedisamil-treated animals exhibited a 100% compared with a 25% survival rate in the control group (p < 0.05). Anterior-wall infarct size, expressed as a percentage of the left ventricle, did not differ between groups: Group 1 = 20 +/- 1%; Group 2 = 22 +/- 1%. Our findings suggest that tedisamil might be useful in the prevention of malignant ventricular arrhythmias in myocardial ischemic injury.

Pharmacokinetic analysis and antiepileptic activity of tetra-methylcyclopropane analogues of valpromide

PURPOSE

The described structure pharmacokinetic pharmacodynamic relationships (SPPR) study explored the utilization of tetramethylcyclopropane analogues of valpromide (VPD), or tetramethylcyclopropane carboxamide derivatives of valproic acid (VPA) as new antiepileptics.

METHODS

The study was carried out by investigating the pharmacokinetics in dogs and pharmacodynamics (anticonvulsant activity and neurotoxicity) of the following three cyclopropane analogues of VPD: 2,2,3,3-tetramethylcyclopropane carboxamide (TMCD), N-methyl TMCD (M-TMCD) and N-[(2,2,3,3-tetramethylcyclopropyl)carbonyl]-glycinamide (TMC-GLD).

RESULTS

The three investigated compounds showed a good anticonvulsant profile in mice and rats due to the fact that they were metabolically stable VPD analogues which were not biotransformed to their nonactive acid, 2,2,3,3-tetramethylcyclopropane carboxylic acid (TMCA). M-TMCD was metabolized to TMCD and TMC-GLD underwent partial biotransformation to its glycine analogue N-[(2,2,3,3-tetramethylcyclopropyl)carbonyl]-glycine (TMC-GLN). Unlike TMC-GLN, the above mentioned amides had low clearance and a relatively long half life.

CONCLUSIONS

In contrast to VPD which is biotransformed to VPA, the aforementioned cyclopropane derivatives were found to be stable to amide-acid biotransformation. TMCD and M-TMCD show that cyclic analogues of VPD, like its aliphatic isomers, must have either two substitutions at the beta position to the carbonyl, such as in the case of TMCD, or a substitution in the alpha and in the beta positions like in the VPD isomer, valnoctamide (VCD). This paper discusses the antiepileptic potential of tetramethylcyclopropane analogues of VPD which are in animal models more potent than VPA and may be non-teratogenic and non-hepatotoxic.

Diphencyprone is not detectable in serum or urine following topical application

Diphencyprone is a potent contact sensitizer in widespread use for treatment of alopecia areata. It is currently not known whether this compound is absorbed following topical application. This is important, since little is known regarding potential toxicity. We therefore analysed serum and urine samples following application of at least 0.5 ml of a 1% solution of diphencyprone to the scalp of patients under treatment for alopecia areata. Serum samples were obtained over 8 h following treatment and 24-h urine collections were performed. The threshold for detection was 2 ng, and the assay gave an accurate linear response for samples of serum and urine containing known concentrations of diphencyprone. Blood and/or urine samples were obtained from a total of 18 subjects. Diphencyprone was not detected in any sample of serum or urine from the subjects. These data suggest that diphencyprone is not absorbed following application to the skin.

Acute electrophysiological effects of intravenous milnacipran, a new antidepressant agent

Milnacipran is a new antidepressant agent selected from a series of cycloproprane derivatives. The aim of this study was to investigate the acute electrophysiological effects and the tolerance of intravenous administration of this drug in 10 patients without any abnormality as shown in an electrophysiological study done for various complaints. Milnacipran was given over a 30-min period at doses of 0.2 mg/kg (2 patients), 0.4 mg/kg (2 patients) and 0.8 mg/kg (6 patients). The most significant alterations observed in this study were increases in heart rate (average of maximal increase: +19.5% at 50 min, P = 0.06) and systolic blood pressure (average of maximal increase: +21.5% at 10 min, P < 0.005), and decreases in the functional refractory period of the atrium (-3%, P < 0.05), the atrioventricular node (-9%, P < 0.005) and the effective refractory period of the right ventricle (-10.8%, P < 0.05) at 50 min. The sinus node function was improved in nine patients but depressed in one patient with previous slight baseline sinus node alterations. Milnacipran being devoid of both anticholinergic and monoamine oxidase inhibition activities, these alterations could be related to inhibition of noradrenaline uptake leading to an increase of adrenergic activities. No other ECG or electrophysiological parameters were significantly altered. Five of the 10 patients reported transient nausea, four of them for the highest dosage (0.8 mg/kg) and at the moment of peak of milnacipran plasma level. In conclusion, electrophysiological effects of intravenous milnacipran are negligible. These findings differ from those, well described in the literature, for imipramine-like antidepressant agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of imipenem and cilastatin after their simultaneous administration to the elderly

The pharmacokinetics of imipenem and cilastatin were studied in a group of six healthy elderly male volunteers following the combined intravenous administration of 500 mg imipenem and 500 mg cilastatin sodium as either single or multiple (6 hourly for 6 days) 20 min constant-rate infusions. The pharmacokinetics of both imipenem and cilastatin in the elderly were similar to those of young individuals with mild renal failure (Verpooten et al., 1984). There was no change in the pharmacokinetics of either species with time following multiple-dosing. Correlations existed between total clearance and the glomerular filtration-rate (51Cr-EDTA) for both imipenem and cilastatin.

Pharmacokinetic studies of imipenem/cilastatin in elderly patients

Six patients, aged between 68 and 83 years, with glomerular filtration rates (GFR) between 31 and 80 ml/min received imipenem/cilastatin as treatment for acute lower respiratory tract infection. A combination of 500 mg of both agents was administered, 6-hourly, intravenously over 30 min. After a minimum of four doses, blood specimens were obtained for assay of imipenem and cilastatin concentrations by HPLC. Pharmacokinetic parameters were calculated from the results. The mean half life was 1.6 h for imipenem and 2.1 h for cilastatin, values similar to those reported for patients with moderate renal impairment. Elimination constant, clearance and AUC significantly correlated with GFR but not with age. No accumulation was observed.

High-performance liquid chromatographic determination of cilastatin in biological fluids

Cilastatin, a dehydropeptidase-I inhibitor, is coadministered with the beta-lactam antibiotic imipenem. The described procedure was developed for quantification of cilastatin in human plasma and urine. The assay involved sample purification on a C18 extraction cartridge, reversed-phase high-performance liquid chromatography with post-column derivatization and fluorescence detection. Standard curves were linear from 0.75 to 75.0 micrograms/ml in plasma and from 2.5 to 200.0 micrograms/ml in urine. Intra-day mean coefficients of variation at concentrations within the standard curve range were 4.2 +/- 2.4% and 3.1 +/- 1.7% in plasma and urine, respectively. The inter-day coefficients of variation for analyses of cilastatin in plasma (1.0 and 50.5 micrograms/ml) were less than 10% after 31 days of analysis while those for urine (5.0 and 74.1 micrograms/ml) were less than 11% after 44 days of analysis. The limits of reliable detection were 0.75 and 2.5 micrograms/ml in plasma and urine, respectively. This procedure met the sensitivity and specificity requirements for the analysis of samples from clinical pharmacokinetic studies.

[Fundamental and clinical studies on imipenem/cilastatin sodium in the field of obstetrics and gynecology]

Fundamental and clinical studies on imipenem/cilastatin sodium (MK-0787/MK-0791) were carried out and the results obtained were summarized below. The transfer of MK-0787/MK-0791 into female genital organ tissues was found to be satisfactory. The transfer of MK-0787/MK-0791 into umbilical arterial blood, umbilical venous blood and amniotic fluid was relatively good. A dose of 1,000 mg/1,000 mg per day of MK-0787/MK-0791 was given to each of 6 gynecology patients for 5-22 days and satisfactory clinical effect was obtained in 5 patients out of 6 patients. No notable side effects or abnormal laboratory findings were observed except for a moderate in elevation in S-GOT/S-GPT in 1 case.

[A study on the penetration of imipenem/cilastatin sodium into the female genital tissues]

A new carbapenem antibiotic, imipenem/cilastatin sodium (MK-0787/MK-0791), was administered by intravenous drip infusion at a dose level of 500 mg/500 mg to 30 patients who underwent total abdominal hysterectomy for uterine myomas with or without benign ovarian tumors. The uterine arteries were clamped bilaterally at 0.25, 0.5, 1, 2, 3, 4, 6 and 8 hours after administration, and plasma samples and uterine tissues were taken for measurements of MK-0787 by bioassay and MK-0791 by HPLC. The measured values were analyzed using a two-compartment open model. Maximum concentrations of MK-0787 at 0.5 hour after the start of intravenous drip infusion were 98.5 micrograms/ml in the antecubital vein, 100.1 micrograms/ml in the uterine artery, 26.5 micrograms/g in the oviduct, 21.2 micrograms/g in the ovary, 19.1 micrograms/g in the endometrium, 19.0 micrograms/g in the myometrium, 22.1 micrograms/g in the cervix uteri and 16.4 micrograms/g in the portio vaginalis. These results suggest that the penetration of MK-0787/MK-0791 into female genital tissues is good, and sufficient concentrations are obtained enough to inhibit organisms which are frequently isolated from patients with pelvic inflammatory disease.

[Penetration of imipenem/cilastatin sodium into the tissues of the female reproductive organs]

A new combined preparation, imipenem/cilastatin (MK-0787/MK-0791), was evaluated its penetration into the plasma and tissues with the following results: After an intravenous drip infusion of 500 mg/500 mg of MK-0787/MK-0791, the plasma concentration of drug achieved in the uterine artery was almost equal to that in the antecubital vein, showing good penetration of the drug. After an intravenous drip infusion of 500 mg/500 mg of MK-0787/MK-0791, favorable concentrations were achieved in all of the adnexal and uterine tissues studied. From the results obtained, it is expected that MK-0787/MK-0791 will be highly effective in the field of obstetrics and gynecology.

Imipenem coadministered with cilastatin compared with moxalactam: integration of serum pharmacokinetics and microbiologic activity following single-dose administration to normal volunteers

We administered 1 g of imipenem along with equal amounts of cilastatin (a dehydropeptidase I inhibitor) or 2 g of moxalactam intravenously over a period of 30 min to six volunteers in a crossover manner 1 week apart. The antibiotic concentrations and pharmacokinetics for each drug were determined and integrated with the microbiologic activity by measuring the duration of time that the free drug concentrations remained above the MICs for 90% of 581 clinical isolates and by measuring serum bactericidal activities against organisms which commonly infect granulocytopenic cancer patients. Moxalactam produced serum levels at 1 h after infusion of 99.9 micrograms/ml; these levels were four times greater than the plasma levels of imipenem (22.8 micrograms/ml). The trough (5.5-h) moxalactam serum levels were 10 times greater than those of imipenem (18.5 and 1.7 micrograms/ml, respectively). Essentially all of the imipenem was unbound to protein, whereas 36 to 42% of the moxalactam was unbound. Moxalactam produced free antibiotic concentrations that were above the MIC for 90% of the strains tested for more than 6 h against all of the species tested except Staphylococcus aureus (5.3 h), Enterobacter hafnia (1.6 h), and Pseudomonas aeruginosa (0 h). The imipenem concentrations were above the MIC for 90% of the strains tested for 5.6 h or more against all of the bacteria tested except Proteus spp. and Pseudomonas aeruginosa (4.5 h). The geometric mean peak bactericidal titers from volunteers receiving imipenem were more than 1:8 against all bacteria and were significantly higher than the titers from volunteers receiving moxalactam against S. aureus (1:7.3) and Pseudomonas aeruginosa (1:4.5). These data, in addition to information obtained from animal models, indicate that imipenem is a promising new candidate for carefully controlled clinical trials as a single agent for therapy of serious infections, including empiric therapy for fever in granulocytopenic cancer patients.

[Bone concentrations of imipenem after a dose of imipenem/cilastatin]

The concentration of imipenem in organic bone, determined in 16 patients by bioassay after short infusion (15 min) of 1 g imipenem/cilastatin was 4.3 +/- 2.06 mg/kg (geometric mean +/- standard deviation, n = 13) after 45 minutes, and 2.8 +/- 1.86 mg/kg (n = 26) after 88 minutes. Imipenem penetrates into inorganic hydroxylapatite (imbution), however, its antimicrobial activity is lost. The mean serum concentration in 12 patients (mean age 77 years) with normal renal and hepatic function 15 minutes after the beginning of the infusion was 93.1 mg/l imipenem. The mean serum half life t (1/2 beta) was 1.32 hours, the total body clearance 108.6 1/h, and the volume of distribution during the beta phase V(beta) 12.4 1.

[Hemostatic parameters influenced by imipenem/cilastatin]

Seven patients were treated for bacterial infections with imipenem/cilastatin. Imipenem is a new broad-spectrum beta-lactam antibiotic with antimicrobial activity against gram-positive and gram-negative bacilli. Before and during treatment parameters of blood coagulation and platelet function were studied. Blood coagulation was not influenced by the antibiotic. But there was a temporary inhibition of collagen-induced platelet aggregation during the first days of treatment. No clinical signs of enhanced spontaneous bleeding tendency were observed.

[Imipenem/cilastatin: in vitro activity, concentrations in plasma and prostatic adenoma and therapeutic results in patients with complicated urinary tract infections]

Minimal inhibitory concentrations (MICs) of imipenem, ceftazidime, piperacillin, tobramycin, azthreonam and carumonam were assessed for 400 urinary isolates from hospitalized patients with complicated and/or nosocomial urinary tract infections yielding greater than or equal to 10(5) colony forming units (cfu). More than 90% of the gram-negative pathogens were sensitive to all the antibiotics tested. However, only imipenem and piperacillin exhibited MIC90 values in the therapeutic range for gram-positive pathogens (approximately half of which were staphylococci and enterococci). Perioperative prophylaxis with 0.5 g imipenem/cilastatin administered at different time intervals before the operation (up to six hours) was performed in patients undergoing resection (n = 31), respectively enucleation (n = 1) of a prostatic adenoma or lithotriptic treatment (n = 4). Imipenem yielded peak plasma concentrations of 12.2 to 134.8 mg/l (mean 49.4 mg/l). The estimated half life time in these patients was approximately three hours. Considerable intra as well as interindividual variations were found for imipenem concentrations in prostatic adenoma. However, they were sufficiently high to reach sensitive pathogens (MICs up to 1 mg/l) for up to two-and-a-half hours. Up to six hours after dosing the concentrations in prostatic secretions ranged between 1 and 2 mg/l. A total of 20 urological patients suffering from complicated urinary tract infections (15 men, five women) received a short-term i.v. infusion of 0.5 mg imipenem/cilastatin t.i.d. for seven to 16 days (median seven days). In all these patients urines were sterile during therapy as well as one to two days after therapy. Follow-up examinations performed seven to ten days after the end of treatment in 19 of these patients showed ten patients to be free of infection (55%); these patients were classified as success. Seven patients (37%) presented a relapse (same pathogen) and two patients (10%) a re-infection (different pathogen). Imipenem/cilastatin was well tolerated locally and systemically.

In vitro and in vivo studies of imipenem-cilastatin alone and in combination with gentamicin against Listeria monocytogenes

Imipenem was evaluated for its in vitro and in vivo activities alone and in combination with gentamicin against a clinical isolate of Listeria monocytogenes, and the results were compared with the activities of ampicillin with and without gentamicin. In vitro, the MBC of imipenem was fourfold less than that of ampicillin. Checkerboard determinations of the MBCs exhibited a synergistic response for imipenem-gentamicin but an indifferent response for ampicillin-gentamicin. In vivo studies with experimental bacteremia and meningitis due to L. monocytogenes in newborn rats revealed that both imipenem-cilastatin and ampicillin at a dose of 50 mg/kg produced excellent bactericidal titers in serum. Overall mortality rates were not significantly different among four groups of animals receiving imipenem-cilastatin, imipenem-cilastatin-gentamicin, ampicillin or ampicillin-gentamicin. However, imipenem-cilastatin alone or in combination with gentamicin was significantly less effective than ampicillin-gentamicin, as judged by the rapidity of clearance of bacteria from blood, liver, and spleen. These findings suggest that imipenem-cilastatin and imipenem-cilastatin-gentamicin may not be suitable alternatives for the treatment of listeriosis.

Imipenem/cilastatin therapy for serious bacterial infections

Imipenem was administered intravenously with cilastatin to patients with suspected or documented significant infections. The mean peak serum level of imipenem 30 min after infusion of a 500 mg dose was 18.4 micrograms/ml, and the mean trough level (30 min before infusion) was 2.4 micrograms/ml. The organisms isolated before therapy included Enterobacteriaceae, Staphylococcus aureus, streptococci, Pseudomonas aeruginosa, and anaerobes. The response rate in 25 assessable patients was 96%, with 40% experiencing a complete cure and 56% improvement. Therapy failed in only one instance because an isolate of P. aeruginosa was mistakenly reported to be susceptible on disk testing. Toxicity in the 33 patients treated was generally minimal and included phlebitis, mild liver function abnormalities, eosinophilia, and thrombocytosis. The emergence of resistant organisms during therapy was very uncommon. Imipenem/cilastatin is a promising agent for the treatment of complicated infections.

Disposition of radiolabeled imipenem and cilastatin in normal human volunteers

In the first of two successive studies, four healthy male subjects received 500 mg of 14C-labeled imipenem alone and together with 500 mg of unlabeled cilastatin sodium. In the second study, the same subjects were given 250 mg of 14C-labeled cilastatin sodium alone and together with 250 and 1,000 mg of cold imipenem. Concentrations of imipenem and cilastatin in plasma, urine, and feces were assayed by high-pressure liquid chromatography and radiometry. Plasma concentrations of imipenem assayed radiometrically were higher than those measured by high-pressure liquid chromatography. In one subject studied at the end of drug administration, the open lactam metabolite of imipenem represented 9% of the radioactivity. Plasma levels of cilastatin determined by high-pressure liquid chromatography and radiometry were virtually identical. Urinary recovery of imipenem varied between 12 and 42% of the dose when that drug was given alone but increased to between 64 and 75% when administered with cilastatin sodium at a 1:1 ratio. Almost all radioactivity of imipenem was recovered in the urine within 96 h after drug administration. The open lactam metabolite, resulting from the metabolism of imipenem in the kidneys by a dipeptidase, dehydropeptidase-I, represented 80 to 90% of the effluent radioactivity when imipenem was given alone and about 20% when cilastatin sodium was coadministered. Renal excretion of cilastatin followed closely that of imipenem. Almost all of the administered radioactivity was recovered in 24 h, and about 75% of the dose was recovered as unchanged cilastatin within 6 h. The N-acetyl metabolite of cilastatin was found to represent about 12% of the total radioactivity.

Renal clearance of imipenem in children

Imipenem renal clearance was studied in six children (three males, three females; 2.9-11.2 years of age) following a single intravenous dose (21.7 +/- 5.1 mg/kg) of imipenem/cilastatin (1:1). In an approximately six-hour period following drug administration, 65.3 +/- 9.7% of the imipenem dose was excreted in the urine unchanged. The renal clearance (280.03 +/- 24.34 ml/min/1.73 m2) of imipenem was found to account for 69.2% of the corresponding plasma imipenem clearance (404.89 +/- 24.83 ml/min/1.73 m2). Contrary to existing adult data, the imipenem renal clearance in our subjects was 1.95-fold greater than the estimated creatinine clearance, suggesting significant tubular secretion of imipenem in children. Examination of urinary imipenem excretion rate versus plasma concentration relationships in three of the children revealed a potential renal tubular reabsorption component for imipenem in children. Comparison of renal imipenem clearance data in these children to similar data from adults suggests that quantitatively important developmental differences may exist for the renal handling of imipenem.

The pharmacokinetics of imipenem (thienamycin-formamidine) and the renal dehydropeptidase inhibitor cilastatin sodium in normal subjects and patients with renal failure

The antibiotic imipenum (thienamycin-formamidine) is partially hydrolyzed during excretion by a renal brush border dehydropeptidase. The co-administration of imipenum with the renal dehydropeptidase inhibitor cilastatin results in an increase of the urinary recovery of the antibiotic, both in animals and humans. To study the pharmacokinetics of imipenem and cilastatin, subjects with normal renal function and patients with different degrees of renal insufficiency received intravenously 250 mg imipenum alone and 250 mg imipenem with 250 mg cilastatin. The mean plasma half-life of imipenem varied from 52 min in subjects with normal renal function to 173 min in subjects with end-stage renal failure studied while off-dialysis. The plasma half-life of imipenem was not affected by the co-administration of cilastatin. The mean plasma half-life of cilastatin varied from 54 min in normals to 798 min in patients with end-stage renal failure. The co-administration of cilastatin resulted in an increase of the urinary concentration and in the urinary recovery of imipenem, the effect being more pronounced in the subjects with normal or only mildly impaired renal function. The plasma clearance of imipenem was decreased when cilastatin was co-administered, possibly due to inhibition of tubular secretion of imipenem. Elimination studies performed during haemodialysis indicated efficient removal of both imipenem and cilastatin during a 4 h session. In view of the important increase in half-life of cilastatin as a function of increasing renal failure, a dosage reduction is proposed in patients with severe renal failure. It is recommended that the maximum dose of imipenem/cilastatin would be limited to either 1000/1000 mg twice daily or 500/500 mg four times daily in patients with a creatinine clearance of less than 15 ml/min. Also, a supplementary dose of imipenem and cilastatin after dialysis is recommended.