The pharmacokinetics of the antidepressant tianeptine and its main metabolite in healthy humans – influence of alcohol co-administration

A balanced 3 way cross-over study involving 12 young healthy volunteers (6 men and 6 women) was used to determine the pharmacokinetic parameters of the antidepressant tianeptine following a single dose administered by oral and intravenous route. The influence of alcohol on the pharmacokinetics of tianeptine when given per os was also investigated. Kinetic parameters of metabolite MC5, the C5 side chain beta-oxidation product of tianeptine, were simultaneously determined. Following intravenous administration total clearance and volume of distribution of tianeptine were 230 +/- 59 ml.min-1 and 0.47 +/- 0.14 l.kg-1 respectively. When given orally, tianeptine was absorbed rapidly (tmax = 0.94 +/- 0.47 h). The mean systemic availability was estimated to be 99 +/- 29%. Tianeptine was eliminated from plasma with a half-life of 2.5 +/- 1.1 h, mainly via extrarenal route since its renal clearance averaged 0.38 +/- 0.47 ml.min-1. Plasma levels of metabolite MC5 were lower than those of the parent drug but decreased with a longer half-life (7.2 +/- 5.7 h). Alcohol co-administration decreased tianeptine absorption rate and lowered tianeptine plasma levels by about 30% but did not affect those of the MC5 metabolite.     

Effects of age and sex on piroxicam disposition

Piroxicam kinetics were studied after a single, oral, 20-mg capsule was taken by 12 young (six women, six men) and 13 elderly (seven women, six men) healthy subjects. Plasma samples were drawn for 216 hr after dosing. Plasma protein binding was studied in vitro by equilibrium dialysis and piroxicam concentrations were measured by HPLC with ultraviolet detection. The apparent volume of distribution was smaller in elderly women (7.8 +/- 0.4 l) than in young men (11.3 +/- 0.3 l) and elderly men (10.8 +/- 0.8 l). There were no such differences when the apparent volume of distribution was normalized for total body weight. There was a strong correlation between total body weight and apparent volume of distribution in all subjects (r = 0.83). Plasma protein binding of piroxicam ranged from 98.90% to 99.54% bound and was not affected by age or sex. Piroxicam body clearance in elderly women (0.026 +/- 0.002 ml/min/kg) was approximately 33% lower than in young women (0.039 +/- 0.003 ml/min/kg). This difference was reflected in different t1/2s of 61.7 and 44.9 hr. Predicted steady-state plasma piroxicam concentrations were 5.7 micrograms/ml in young women, 5.4 micrograms/ml in young men, 5.7 micrograms/ml in elderly men, and 9.3 micrograms/ml in elderly women. The high value in elderly women results from the lower piroxicam body clearance and total body weight. Our data suggest that healthy elderly women eliminate piroxicam at a slower rate than healthy young women. The clinical significance of these data needs to be assessed in patients.     

Determination of bone Gla protein (osteocalcin) by enzyme-linked immunosorbent assay

Bone Gla protein (BGP, osteocalcin) is a marker of bone formation. We present a novel enzyme-linked immunosorbent assay for measuring BGP in plasma and serum. The antibody used was raised in rabbits following immunisation with highly purified bovine BGP conjugated with keyhole limpet hemocyanin. The binding of the antibody to BGP was calcium-dependent. The sensitivity, inaccuracy, and imprecision of the assay equal or exceed existing radioimmunoassays, and the present assay is less tedious. Plasma BGP in 249 healthy adults, aged from 20 to 93 yr, was 8.3 +/- 6.6 micrograms/l (mean +/- 2 SD). A significant decrease was seen in both sexes from the third to the forth decade of life. A subsequent significant increase was seen with age in women. but not in men. Plasma BGP was significantly higher in young men than in young women, and significantly higher in elderly women than in elderly men. Values were in the same range as those found with existing radioimmunoassays.     

Pharmacokinetics of flunitrazepam following single dose oral administration in liver disease patients compared with healthy volunteers

The pharmacokinetic behaviour of flunitrazepam and its main active metabolite, N-desmethyl flunitrazepam, was investigated in 12 patients with liver disease (cirrhosis or hepatitis) compared to 6 healthy volunteers. A gas-liquid chromatographic method allowing for simultaneous determination of flunitrazepam and N-desmethyl flunitrazepam in plasma samples was developed. The accuracy and the precision near the quantification limit of ca. 1 ng/ml were better than 5%. Plasma levels of flunitrazepam were not significantly altered by hepatic failure, whereas plasma levels of N-desmethyl flunitrazepam were lower in patients than in healthy subjects. Pharmacokinetic parameters did not differ significantly between healthy subjects and liver disease patients: the oral clearance was 3.5 +/- 0.8, 3.5 +/- 1.9 and 4.0 +/- 1.2 ml/min/kg, respectively in healthy subjects, patients with hepatitis and patients with cirrhosis. The apparent elimination half-life was 22 +/- 5 h in healthy subjects, 25 +/- 10 h in patients with hepatitis and 20 +/- 6 h in patients with cirrhosis. However, the expected increase of the drug free fraction during liver disease could decrease the therapeutic and toxic ranges of flunitrazepam in these patients.     

Pharmacokinetics of ertapenem in healthy young volunteers

Ertapenem (INVANZ) is a new once-a-day parenteral beta-lactam antimicrobial shown to be effective as a single agent for treatment of various community-acquired and mixed infections. The single- and multiple-dose pharmacokinetics of ertapenem at doses up to 3 g were examined in healthy young men and women volunteers. Plasma and urine samples collected were analyzed using reversed-phase high-performance liquid chromatography with UV detection. Ertapenem is highly bound to plasma protein. The protein binding changes from approximately 95% bound at concentrations of <50 micro g/ml to approximately 92% bound at concentrations of 150 micro g/ml (concentration at the end of a 30-min infusion following the 1-g dose). The nonlinear protein binding of ertapenem resulted in a slightly less than dose proportional increase in the area under the curve from 0 h to infinity (AUC(0- infinity )) of total ertapenem. The single-dose AUC(0- infinity ) of unbound ertapenem was nearly dose proportional over the dose range of 0.5 to 2 g. The mean concentration of ertapenem in plasma ranged from approximately 145 to 175 micro g/ml at the end of a 30-min infusion, from approximately 30 to 34 micro g/ml at 6 h, and from approximately 9 to 11 micro g/ml at 12 h. The mean plasma t(1/2) ranged from 3.8 to 4.4 h. About 45% of the plasma clearance (CL(P)) was via renal clearance. The remainder of the CL(P) was primarily via the formation of the beta-lactam ring-opened metabolite that was excreted in urine. There were no clinically significant differences between the pharmacokinetics of ertapenem in men and women. Ertapenem does not accumulate after multiple once-daily dosing.     

Pharmacokinetics and tolerability of single oral doses of 882C87, a potent, new anti-varicella-zoster virus agent, in healthy volunteers.

882C87 is a nucleoside analog with potent, specific activity against varicella-zoster virus. It is approximately seven times as potent as acyclovir with an in vitro 50% inhibitory concentration of 1 to 2 microM. The tolerability and pharmacokinetics of single doses of 882C87 have been investigated in a series of studies with healthy young and elderly adult volunteers. The young received 50 to 1,600 mg, and the elderly received 50 and 100 mg. Concentrations of 882C87 and its main metabolite, the pyrimidine base 5-(1-propynyl)uracil (5PU), in plasma and urine were assayed by an automated sequential trace enrichment of dialysate-high-performance liquid chromatography procedure, and noncompartmental pharmacokinetic parameters were derived from the data. Concentrations of 882C87 in plasma increased proportionally for doses of up to 400 mg, but after higher doses the increase was less than dose proportional. In young adults, after 200, 400, and 1,600 mg, the maximum concentrations of the drug in plasma were 9.0, 16.3, and 34.7 microM, respectively, and the areas under the concentration-time curve (AUC) from 0 h to infinity were 166.6, 333.7, and 822.9 microM.h, respectively. Elimination half-life was 11.3 to 13.0 h after 50 to 400 mg, increasing to 15.3 h after 1,600 mg, associated with a small decrease in renal clearance. In healthy elderly volunteers concentrations of 882C87 in plasma after 50 and 100 mg were similar to those in young adults after twice the dose; apparent clearance and renal clearance were significantly reduced, and half-life was significantly longer at 15 h. Administration of 882C87 with food produced a small, nonsignificant reduction in mean AUC from 0 h to infinity, but in subjects with a low fasting AUC there was an increase after food and in subjects with a high fasting AUC there was a decrease. Concentrations of 5PU in plasma were one-third to one-half those of 882C87 and, in most subjects, were not dose proportional. There was a lag of at least 5 h after dosing with 882C87 before 5PU was detectable in plasma.     

Oral contraceptive steroids impair the elimination of theophylline

The influence of OCS and sex differences on the disposition of theophylline has been studied in 12 healthy young men (29 +/- 4 years old), 13 healthy young women (29 +/- 12), and 10 healthy young women (24 +/- 3) receiving OCS for a period greater than 6 months. The elimination t1/2 was longer in women taking oral contraceptives (523 +/- 110 min) than in women not on oral contraceptives (386 +/- 157). Weight-normalized plasma clearance of theophylline was less in women taking oral contraceptive steroids (0.70 +/- 0.15 ml X min-1 X kg-1) than in women not on oral contraceptive steroids (0.98 +/- 0.32). Plasma binding and volume of distribution were not different between the two groups of women. Weight-normalized clearance, weight-normalized volume of distribution, plasma t1/2, and plasma binding were not different between men and women not taking OCS.     

Evaluation of the potential for pharmacokinetic interaction between fenofibrate and ezetimibe: A phase I, open-label, multiple-dose, three-period crossover study in healthy subjects

OBJECTIVE: This study was conducted to evaluate the potential for pharmacokinetic interaction between fenofibrate and ezetimibe in healthy subjects. METHODS: This was a Phase I, open-label, multiple-dose,3-period crossover study conducted in healthy adult men and women. Subjects received fenofibrate 145 mg alone, fenofibrate 145 mg with ezetimibe 10 mg, and ezetimibe 10 mg alone for 10 consecutive days, in an order determined by computerized randomization schedule. Blood samples were collected for up to 24 hours after dosing on study day 1 and up to 120 hours after dosing on study day 10 for determination of plasma concentrations of fenofibric acid, unconjugated (free) ezetimibe, and total (conjugated and unconjugated) ezetimibe using validated high-performance liquid chromatography methods with mass-spectrometric detection. Ezetimibe glucuronide concentrations were estimated by subtracting free ezetimibe concentrations from total ezetimibe concentrations. RESULTS: Eighteen healthy adults (12 men, 6 women; 17 white, 1 black) were enrolled in the study. Their mean age was 43.4 years (range, 27-55 years), their mean weight 78.7 kg (range, 60-98 kg), and their mean height 174.9 cm (range, 156-194 cm). Coadministration of multiple doses of fenofibrate and ezetimibe produced no statistically significant effect on the pharmacokinetics of fenofibric acid but significantly increased exposures to total ezetimibe and ezetimibe glucuronide (P < 0.05). Using point estimates, co-administration of fenofibrate and ezetimibe increased AUC central values for total ezetimibe and ezetimibe glucuronide by 43% (90% CI, 29-59) and 49% (90% CI, 34-65), respectively. CONCLUSION: In these healthy volunteers, coadministration of multiple doses of fenofibrate and ezetimibe had no statistically significant effect on the pharmacokinetics of fenofibric acid but was associated with a significant increase in exposure to total ezetimibe and its metabolite ezetimibe glucuronide.     

Pharmacokinetics of chlorproguanil in man after a single oral dose of Lapudrine

The pharmacokinetic parameters of chlorproguanil (Lapudrine) and its active metabolite, chlorcycloguanil, were determined in 6 healthy male volunteers after a single oral dose of 4 Lapudrine tables (80 mg). The mean maximum plasma chlorproguanil concentration was 36.7 +/- (SD) 7.9 ng/ml and was reached at 3.8 +/- 1.3 h. The chlorproguanil elimination half-life was 17.5 +/- 6.7 h and its plasma clearance was 1.28 +/- 0.12 l/h/kg. The mean whole blood to plasma ratio was 3.1 at 4 h after dosing. Chlorcycloguanil could not be quantified in plasma and whole blood at the detection limit of 10 ng/ml using a high-performance liquid chromatographic method. An excretion rate-time plot from urine data shows a rapid (t1/2 = 20 h) and a slow phase (t1/2 = 51 h) in the elimination of chlorcycloguanil. Our findings suggest that the current prophylactic regimen of chlorproguanil hydrochloride (20 mg weekly) may not be optimal in preventing infections with chloroquine-resistant falciparum malaria.     

Pharmacokinetics and electrocardiographic effect of ebastine in young versus elderly healthy subjects

The objective of this study was to compare the single- and multiple-dose pharmacokinetics and electrocardiographic effect of a 10-mg oral dose of ebastine in elderly (ages, 65-85 years) and young (ages, 18-35 years) healthy volunteers. Thirty-seven subjects completed this randomized, double-blind, multiple-dose, placebo-controlled, parallel group study. The elderly group consisted of 18 subjects, with 13 subjects receiving 10 mg ebastine and 5 receiving matching placebo. The young group consisted of 19 subjects, with 13 subjects receiving 10 mg ebastine and 6 receiving matching placebo. On study days 1 and 3 through 10, each subject received a single 10-mg dose of ebastine or matching placebo in the morning with a standard breakfast. No drug was administered on study day 2 because of pharmacokinetic sampling. Blood samples were collected at selected times postdose on study days 1, 2, and 10. Plasma samples were analyzed for ebastine and its active metabolite, carebastine, using a validated high-performance liquid chromatography method. No plasma ebastine concentrations were detected, suggesting essentially complete metabolic conversion of ebastine to its metabolites. Analysis of variance showed no statistically significant differences between young and elderly single- and multiple-dose carebastine pharmacokinetics with respect to area under the plasma concentration-time curve, maximum concentration (Cmax ), terminal elimination rate constant, apparent oral clearance, or apparent volume of distribution. The mean time of maximum concentration value for young subjects was 1 hour longer than that for elderly subjects after single-dose administration but was comparable after multiple-dose administration. Within-group comparisons of both the young and elderly showed that pharmacokinetics between single dose and steady state were not statistically different. However, the mean steady-state carebastine Cmax values were approximately twofold greater than the mean Cmax values obtained after single-dose administration. A twofold increase in Cmax values between single-dose and steady-state administration is predicted for drugs such as carebastine, because its input interval is approximately equal to its elimination half-life. Twelve-lead electrocardiography was performed before dosing on day 1 and repeated 4 hours postdose on days 1, 5, and 10. Twenty-four hour Holter monitoring was also performed before and at the end of the study. No clinically relevant findings were found by electrocardiography or Holter monitoring between ebastine and placebo in the elderly and young subjects.     

Plasma bone Gla protein concentrations in healthy adults. Dependence on sex, age, and glomerular filtration

Plasma bone Gla protein (BGP) was determined by radio-immunoassay in 266 healthy adults, men (n = 132) and women (n = 134), aged 20-79 years. In the women aged 30-69 years, plasma BGP increased significantly with age (r = 0.44, p less than 0.001), and a particularly steep increase was seen from 1.1 +/- 0.5 (mean +/- 1 SD) in the fifth decade to 2.0 +/- 1.4 nmol/l in the seventh decade. In men, aged 30-69 years, no correlation was found between plasma BGP and age (r = -0.07, NS). Plasma bone Gla protein is removed from the circulation mainly by the kidneys and the increased plasma BGP in the women could be caused by decreased renal clearance. The interrelationship was analysed by means of partial correlation. When creatinine clearance was held constant in women, BGP still correlated positively with age (r = 0.40, p less than 0.001), but not with creatinine clearance (r = 0.003, NS) when age was fixed. Plasma BGP was significantly increased above normal in 35 patients with chronic renal failure (10.2 +/- 14.6 nmol/l). Non-linear regression analysis showed that plasma BGP was within the normal range when 24-h creatinine clearance was greater than 30 ml/min, and large increases in plasma BGP did not occur until the 24-h creatinine clearance was below 20 ml/min. We conclude that, in normal subjects and patients with mild to moderate renal failure, plasma elevations of BGP reflect increased bone turnover rather than decreased renal clearance.     

Plasma carnitine and body composition.

Plasma carnitine has been determined in 16 men and 45 women without known muscular disorders. Mean values were 57.3 mumoles/l +/- 12.8 (S.D.) for men and 46.5 mumoles/l +/- 12.4 (S.D.) for women. The difference was statistically significant. Of the variables tested, a positive significant relationship was found between plasma carnitine and age, but not for different variables of body composition, e.g. body cell mass or plasma cholesterol and triglycerides. The daily urinary excretion of carnitine has been compared in a healthy individual during two periods, one on an ordinary diet and one on a gruel diet, giving a constant carnitine intake. The mean value of carnitine excretion (241 mumoles per 24 h) of the two periods did not differ and although the variance was less on the gruel diet, no statistical difference was found.     

Pharmacokinetics and Tolerability of Tenofovir Disoproxil Fumarate 300 mg Once Daily: An Open-Label,Single- and Multiple-Dose Study in Healthy Chinese Subjects

Background

Tenofovir disoproxil fumarate (TDF) has been approved worldwide for the treatment of adults with chronic hepatitis B and, in combination with other antiretroviral agents, HIV-1 infection. Although its use for the treatment of HIV has been approved by the Chinese State Food and Drug Administration, there are no data on the pharmacokinetic profile of TDF in Chinese individuals.

Objectives

This study aimed to investigate the pharmacokinetic properties and tolerability of TDF in healthy Chinese subjects.

Methods

This open-label, single- and multiple-dose study was conducted in healthy Chinese volunteers. Subjects received TDF 300 mg once daily, administered as a single dose (day 1) and multiple doses (days 4–10). Multiple plasma samples were collected over time, and the concentrations of TDF were determined using LC-MS/MS. Pharmacokinetic parameters were estimated using a noncompartmental model. Tolerability was determined using clinical evaluation and monitoring of adverse events (AEs).

Results

Fourteen volunteers were enrolled (7 men, 7 women; mean age, 24.6 years). TDF was rapidly absorbed; median T_max was 0.75 hour, and t_½ was ~21 hours with single dosing. The mean ratio of AUC_0–τ steady state/AUC_0–24 single dose was 1.55. The pharmacokinetic properties of TDF were consistent between the single dose and multiple doses, and between men and women. No serious AEs were reported, and there were no discontinuations due to AEs.

Conclusions

There was an accumulation of approximately 55% in tenofovir exposure in healthy Chinese between multiple dose and single dose. TDF exhibited a pharmacokinetic profile similar to that of healthy Western subjects in a historical comparison. TDF was generally well tolerated in these healthy Chinese subjects. ClinicalTrials.gov identifier: NCT01480622.     

An evaluation of the potential for pharmacokinetic interaction between escitalopram and the cytochrome P450 3A4 inhibitor ritonavir

BACKGROUND: Depression often coexists with a number of disease states, and patients with a diagnosis of depression often receive multiple medications. Thus, it is desirable to avoid coadministration of agents that have a potential for drug interactions in these patients. Although escitalopram and its metabolites are weak to negligible inhibitors of the cytochrome P450 (CYP) 3A4 isozyme and are therefore unlikely to affect plasma concentrations of ritonavir (a CYP3A4 substrate and prototype CYP3A4 inhibitor), ritonavir may potentially affect plasma concentrations of escitalopram, as CYP3A4 is partially responsible for conversion of escitalopram to its major metabolite, S-demethylcitalopram (S-DCT). OBJECTIVES: The aim of this study was to investigate the potential for pharmacokinetic interaction between escitalopram and ritonavir after concomitant administration of a single dose of each in healthy young subjects. METHODS: In this single-center, randomized, open-label, 3-way crossover study, subjects received each of the following: a single dose of escitalopram 20 mg, a single dose of ritonavir 600 mg, and single doses of both escitalopram 20 mg and ritonavir 600 mg. Blood was collected and plasma was analyzed for the pharmacokinetic parameters (maximum plasma concentration [C(max)], time to C(max) [T(max)], area under the plasma concentration-time curve, plasma elimination half-life, oral clearance, and apparent volume of distribution) of escitalopram, S-DCT, and ritonavir. RESULTS: Of 21 subjects (11 men, 10 women; mean [SD] age, 28.4 [4.4] years) who were enrolled, 18 completed the study. After concomitant administration of escitalopram and ritonavir, no statistically significant differences were noted in the pharmacokinetics of escitalopram, with the exception of apparent volume of distribution, which was reduced by approximately 10% (P < 0.001). The pharmacokinetics of S-DCT were unaffected by coadministration of ritonavir, with the exception of T(max), which was increased in the presence of ritonavir. The pharmacokinetic parameters of ritonavir were also unaffected by coadministration of escitalopram. CONCLUSION: In general, no pharmacokinetic interaction was observed between escitalopram and ritonavir in the present study.     

Pharmacokinetics of meropenem and its metabolite ICI 213,689 in healthy subjects with known renal metabolism of imipenem

Six healthy male subjects who had received imipenem without cilastatin in previous studies, were given 500 mg meropenem as single 30 min intravenous infusions. Plasma and urine samples were collected for 12 h and meropenem and its metabolite were assayed by HPLC and RIA, respectively. The mean plasma half-life of meropenem was 0.8 h, mean plasma clearance 277 ml/min and the mean volume of distribution 20.4 l. The metabolite reached mean peak plasma concentrations of 1.5 mg/l. Renal clearance of meropenem averaged 200 ml/min. The mean urinary recovery of the metabolite was 20% and of unchanged drug 72% of the dose given. The recovery of meropenem ranged from 62.2% to 78.2% and was correlated to the urinary recovery of imipenem when given without cilastatin to the same subjects in previous studies (range 15.2-32.2%, rank correlation coefficient = 0.934). The results indicate that meropenem is much less susceptible to renal metabolism than imipenem. The inter-subject variability observed with meropenem correlates with the extent of urinary recovery of imipenem observed in previous studies with imipenem alone, indicating some susceptibility of meropenem to renal dehydropeptidase-I.     

Pharmacokinetic drug interactions in children taking oxcarbazepine

OBJECTIVE: Our objective was to evaluate the drug-drug interactions of oxcarbazepine with coadministered antiepileptic drugs in children. METHODS: In a clinical trial, pediatric patients receiving an oxcarbazepine dose titrated to 30 to 46 mg. kg(-1). d(-1) given twice daily had 1 to 4 blood samples collected per patient for population pharmacokinetic analysis of oxcarbazepine's major bioactive 10-monohydroxy metabolite. With the use of NONMEM, 7 concomitant antiepileptic drugs and 12 additional covariates were examined for their effects on the pharmacokinetics of 10-monohydroxy metabolite. In addition, for each concomitant antiepileptic drug, the ratio of its mean concentration with coadministration of oxcarbazepine to that without coadministration at baseline was calculated to evaluate the effect of oxcarbazepine on the coadministered antiepileptic drugs. RESULTS: The population pharmacokinetic data for 10-monohydroxy metabolite consisted of a total of 376 observations from 109 patients, aged 3 to 17 years. Body surface area and 3 antiepileptic drugs (carbamazepine, phenobarbital, and phenytoin) were significant predictors of the apparent clearance of 10-monohydroxy metabolite, whereas height was a significant predictor of apparent volume. Weight-normalized clearance of 10-monohydroxy metabolite was higher in young children than in older children and adults. Carbamazepine, phenobarbital, or phenytoin administered with oxcarbazepine increased the apparent clearance of 10-monohydroxy metabolite by 31% to 35%, whereas carbamazepine levels decreased by 15% and phenobarbital levels increased by 14%. CONCLUSIONS: Oxcarbazepine has a low propensity to inhibit or induce oxidative enzymes. Young children could be given higher milligrams-per-kilogram oxcarbazepine doses than older children and adults to achieve the same mean steady-state concentration of 10-monohydroxy metabolite. The adjustment is based simply on body size.     

Steady-state kinetics of proguanil and its active metabolite, cycloguanil, in man

The pharmacokinetics of proguanil and its active metabolite, cycloguanil, were determined at steady-state in 6 healthy male volunteers after daily administration of 2 Paludrine tablets (200 mg proguanil hydrochloride). A maximum plasma proguanil concentration of 130.3 +/- 16.0 ng/ml (mean +/- SD) was reached at 3.8 +/- 1.3 h while a maximum cycloguanil concentration of 52.0 +/- 15.2 ng/ml was obtained at 5.3 +/- 1.0 h after dosing. The elimination half-lives of proguanil and cycloguanil were 14.5 +/- 3.0 h and 11.7 +/- 3.1 h, respectively. The plasma clearance of proguanil was 1.43 +/- 0.33 l/h/kg and the apparent volume of distribution was 30.7 +/- 12.3 l/kg. Renal clearance of proguanil (0.33 +/- 0.19 l/h/kg) was about 23% of the plasma clearance and 35.6 +/- 9.6% of the oral dose was recovered as proguanil and cycloguanil.     

Effect of Gender and Menopausal Status on the Pharmacokinetics of Tirilazad Mesylate in Healthy Subjects

The pharmacokinetics of tirilazad were assessed in men ages 40--60 years, women <40 years of age, premenopausal women ages 40--60, and postmenopausal ages 40--60. Eight subjects in each group received single 3.0 mg kg(minus sign1) intravenous infusions of tirilazad mesylate over 10 min. Plasma concentrations of tirilazad and U-89678, an active metabolite, were measured by high-performance liquid chromatography. Tirilazad administration was well tolerated in all groups. Mean tirilazad clearance was 59.6% higher in young women compared to the middle-aged men (35.6 plus minus 8.04 L h(minus sign1) vs. 22.3 plus minus 8.40 L h(minus sign1)). Mean tirilazad clearance in middle-aged women was 30.7% higher than in middle-aged men. Mean clearance in postmenopausal women (26.1 plus minus 4.21 L h(minus sign1)) was not significantly different than that in middle-aged men, but clearance corrected for body weight was significantly different between the men and postmenopausal women. Clearance in premenopausal middle-aged women (32.2 plus minus 7.60 L h(minus sign1)) was not significantly different from that in young women and was 44% greater than that in middle-aged men. Mean AUC(0minus signinfty infinity) and C(max) values for U-89678 were significantly higher in men than in all of the female groups. Among the women, values for U-89678 AUC(0minus signinfty infinity) were lowest in young women (467 plus minus 345 ng h ml(minus sign1), 8.8% of male value) and highest in postmenopausal women (1565 plus minus 1382 ng h ml(minus sign1), 29.4% of male value). The absolute values for U-89678 AUC(0minus signinfty infinity) must be interpreted with caution, as limited assay sensitivity and low plasma concentrations in the latter portion of the concentration-time profile in women precluded accurate determination of the terminal half-life and AUC(0minus signinfty infinity). Regardless, these results show that women, particularly premenopausal women, have lower concentrations of U-89678, an active metabolite of tirilazad, than are achieved in men. The gender differences in tirilazad and U-89678 pharmacokinetics are of sufficient magnitude that they may impact the clinical response of male and female patients to tirilazad treatment.     

Effects of age and sex on the disposition of retigabine

BACKGROUND: The novel antiepileptic drug retigabine is the first selective M-current potassium channel opener for KCNQ2/3 and KCNQ3/5 channels. Retigabine undergoes phase II metabolism (N-glucuronidation, acetylation) exclusively and renal excretion. OBJECTIVE: Our objective was to evaluate the effects of age and sex on the pharmacokinetics of retigabine. METHODS: Healthy young (age range, 18-40 years) and elderly (age range, 66-81 years) white subjects (12 men and 12 women in each group) received a single 200-mg oral dose of retigabine. After dosing, blood was collected over a 72-hour period to determine plasma concentrations of retigabine and its acetylated metabolite, AWD21-360. Pharmacokinetics was compared for age group and sex by ANOVA. RESULTS: In young men, retigabine was rapidly absorbed, with the maximum concentration occurring within 2 hours, and was eliminated with an apparent clearance of 0.67 L x h(-1) x kg(-1) and a mean terminal half-life of 8.5 hours. Subjects were similarly exposed to AWD21-360. Compared with young men, young women had higher retigabine maximum concentration (56%) and exposure (20%) but similar clearance (0.68 L x h(-1) x kg(-1)); these differences were related to differences in body weight. Although maximum concentration was similar in elderly subjects, retigabine elimination was slower (30% lower apparent clearance normalized for weight), resulting in higher exposure (42%) and a longer half-life (30%). Because phase II metabolism is scarcely affected by age, these differences may be related to the known decline of renal function with age. CONCLUSIONS: Although there are no substantial sex-related differences in the disposition of retigabine, a relevant decrease in clearance resulting in higher exposure occurs in elderly patients. The results suggest that decline of renal function with age may account for some of the observed changes.     

Quantitative Determination of Putrescine,Cadaverine, Spermine and Spermidixe

Plasma bone Gla protein (BGP) was determined by radio-immunoassay in 266 healthy adults, men (n=132) and women (n = 134), aged 20–79 years. In the women aged 30–69 years, plasma BGP increased significantly with age (r = 0.44. p<0.001). and a particularly steep increase was seen from 1.1 ± 0.5 (mean±1 SD) in the fifth decade to 2.0 ± 1.4 nmol/l in the seventh decade. In men, aged 30–69 years, no correlation was found between plasma BGP and age (r= ?0.07, NS). Plasma bone Gla protein is removed from the circulation mainly by the kidneys and the increased plasma BGP in the women could be caused by decreased renal clearance. The interrelationship was analysed by means of partial correlation. When creatinine clearance was held constant in women, BGP still correlated positively with age (r = 0.40. p<0.001). but not with creatinine clearance (r=0.003, NS) when age was fixed. Plasma BGP was significantly increased above normal in 35 patients with chronic renal failure (10.2±14.6 nmol/l). Non-linear regression analysis showed that plasma BGP was within the normal range when 24-h creatinine clearance was greater than 30 ml/min, and large increases in plasma BGP did not occur until the 24-h creatinine clearance was below 20 ml/min. We conclude that, in normal subjects and patients with mild to moderate renal failure, plasma elevations of BGP reflect increased bone turnover rather than decreased renal clearance.