Enantioselective disposition of fexofenadine with the P-glycoprotein inhibitor verapamil

AIMS

The aim was to compare possible effects of verapamil, as a P-glycoprotein (P-gp) inhibitor, on the pharmacokinetics of each fexofenadine enantiomer, as a P-gp substrate.

METHODS

Thirteen healthy Japanese volunteers (10 male and three female) were enrolled. In a randomized, two-phase, crossover design, verapamil was dosed 80 mg three times daily (with total daily doses of 240 mg) for 6 days, and on day 6, a single 120-mg dose of fexofenadine was administered along with an 80-mg dose of verapamil. Subsequently, fexofenadine was administered alone after a 2-week wash-out period. The plasma concentrations of fexofenadine enantiomers were measured up to 24 h after dosing.

RESULTS

During the control phase, the mean AUC_0–∞ of S(−)- and R(+)-fexofenadine was 700 ng h^–1 ml^–1[95% confidence interval (CI) 577, 823] and 1202 ng h^–1 ml^–1 (95% CI 1007, 1396), respectively, with a significant difference (P < 0.001). Verapamil had a greater effect on the pharmacokinetic parameters of S(−)-fexofenadine compared with those of the R(+)-enantiomer, and increased AUC_0–∞ of S(−)-fexofenadine and R(+)-fexofenadine by 3.5-fold (95% CI of differences 1.9, 5.1; P < 0.001) and by 2.2-fold (95% CI of differences 1.7, 3.0; P < 0.001), respectively. The R/S ratio for the AUC_0–∞ was reduced from 1.76 to 1.32 (P < 0.001) by verapamil treatments.

CONCLUSION

This study indicates that P-gp plays a key role in the stereoselectivity of fexofenadine pharmacokinetics, since the pharmacokinetics of fexofenadine enantiomers were altered by the P-gp inhibitor verapamil, and this effect was greater for S-fexofenadine compared with R-fexofenadine.     

Mechanistic study on the intestinal absorption and disposition of baicalein.

The present study aims to investigate the mechanisms of intestinal absorption and disposition of flavonoid baicalein (B) in Caco-2 cell monolayer model, transporter overexpressing membrane, and cellular models. The bidirectional transport studies of B and its metabolite baicalein-7-glucuronide (BG) were conducted at various concentrations and in the absence or presence of the selected transporter inhibitors. To identify specific interactions of BG with ABC transporters, ABC transporter-ATPase assays were carried out on membrane vesicles prepared from Sf9 cells overexpressing human MDR1, MRP1, MRP2, MRP3 and MXR. To further confirm the interactions between BG and specific ABC transporters, inhibition of BG on the transport of substrates of specific transporters were evaluated using membrane vesicles overexpressing MRP1-3 and MXR, or K562MDR cells with overexpressing MDR1. The results showed that B could readily pass through Caco-2 cell monolayer, but with significant glucuronidation and sulfation. The extent of phase II metabolism of B during its transport was in dose-dependent manner. The intracellularly formed glucuronide and sulfate of B were efficiently extruded to both apical and basolateral sides of the Caco-2 monolayer, which were reduced in the presence of MRP inhibitors. Although BG was not permeable from apical to basolateral side, it exhibited significant efflux transport that was inhibited in the presence of MRPs inhibitors. Moreover, BG seemed to activate the ATPase activity of both MRP3 and MXR at a pharmacologically relevant concentration range.     

The disposition and intestinal absorption of zinc in rats

The variety of physiologic and biologic functions of zinc is expected to enable the development of zinc-related medicines. In this study, the distribution of endogenous zinc, the disposition after intravenous injection, and the intestinal absorption of zinc were investigated in vivo using rats from the viewpoints of pharmaceutical science and pharmacokinetics. High levels of endogenous zinc were observed in bone, testis, and liver. RT-PCR analysis on the mRNA of metallothionein in tissues clarified that it is significantly correlated with the distribution of zinc, suggesting that zinc is accumulated in tissues as a complex with MT. Following intravenous injection, uptake of zinc was high in liver, spleen, pancreas, kidney, and intestine. Fractional absorptions of zinc after oral administration to fasted rats were greater than those to fed rats, suggesting that some factors in diet inhibit the absorption of zinc. In fasted rats, fractional absorption was slightly decreased in high-dose group, suggesting the involvement of carrier-mediated transport. Study utilizing an in situ closed-loop method also indicated saturable intestinal absorption of zinc. These findings will further the research and development of zinc-related medicines by providing basic and important information on zinc.     

Long-lasting inhibition of the intestinal absorption of fexofenadine by cyclosporin A in rats

The purpose of the present study is to examine the long-lasting inhibition of intestinal organic anion transporting polypeptides (Oatps) by cyclosporin A (CsA) in rats using fexofenadine (FEX) as a probe drug. We examined the pharmacokinetics of FEX after its intravenous or oral administration to rats at 3 or 24 h after the oral administration of CsA. When FEX was administered at 3 h after the administration of CsA, its plasma concentration increased regardless of whether it was administered intravenously or orally. When FEX was intravenously administered at 24 h after the oral administration of CsA, its plasma concentration was increased; however, that observed after its oral administration was not significantly different from the vehicle-treated control. When FEX was administered at 3 h after the administration of CsA, the hepatic availability (F(h)) and the fraction absorbed in the intestine as an unchanged form (F(a)·F(g)) of FEX were increased, resulting in increased bioavailability (=F(a)·F(g)·F(h)). At 24 h after the administration of CsA, the F(h) of FEX was increased, whereas its bioavailability was decreased, suggesting that its F(a)·F(g) was decreased because of the long-lasting inhibition. In conclusion, CsA has long-lasting inhibitory effects on Oatps in the rat intestine as well as in the liver.     

Vasopressin treatment of verapamil toxicity in the porcine model

Introduction

Vasopressin is a novel vasopressor agent used for intractable hypotension. There is little published data available on its use in the poisoned patient. We performed a randomized, controlled, blinded trial in a porcine model to study the effects of vasopressin infusion on mean arterial pressure after verapamil poisoning.

Methods

Eighteen anesthetized monitored swine received a verapamil infusion of 1 mg/kg/hr until the mean arterial pressure (MAP) had decreased to 70% of baseline. At this time, a continuous infusion of either vasopressin (0.01 U/kg/min) or an equal volume of normal saline was initiated. The swine were monitored for 60 minutes after initiation of the study infusion. The primary outcome was MAP.

Results

There was no statistically significant difference between the two groups in MAP, cardiac output or systemic vascular resistance. One half (four of eight) of the animals in the vasopressin group died, compared with 20% (two of ten) of those in the saline group.

Conclusions

Vasopressin infusion decreased the survival of verapamil-poisoned swine when compared to those treated with saline alone in this experimental model.     

Characteristics of intestinal absorption and disposition of glycyrrhizin in mice

As basic studies to apply an intestinal pressure-controlled colon delivery capsule (PCDC) for glycyrrhizin (GZ), the characteristics of intestinal absorption and disposition of GZ were investigated in mice. In the in vivo study, after intravenous (iv) administration of GZ, 10 mg/kg dose, plasma GZ disappeared from the systemic circulation with t(1/2(alpha)) of 0.0063 h, thereafter, it slowly declined with t(1/2(beta)) of 15.23 h. The area under the plasma drug concentration versus time curve (AUC) values of iv (10 mg/kg), intracolonic (50 mg/kg) and intraduodenum (50 mg/kg) administrations were 115.1, 16.7 and 2.7 microgh/mL, respectively. The AUC values of plasma glycyrrhetic acid (GA), a degradation product after intracolonic and intraduodenum administrations were 2.8 and 8.4 microgh/mL, respectively. In the in situ closed loop study, the concentrations of GZ in plasma and liver after intracolonic administration were significantly increased (p<0.05) in comparison with those after intrajejunum or intraileum administration, while the concentration of GA in plasma and liver after intracolonic administration had trends to increase. These observations clearly suggest that the intracolonic administration is a useful way to improve the oral bioavailability of GZ and to enhance its pharmacological efficacy. These pharmacokinetic results of GZ suggest that GZ is a subject drug to be applied for the PCDC system we previously developed. The PCDCs formulation of GZ will enable us to carry GZ to the colon and enhance the oral bioavailability of GZ.     

First-pass disposition of (-)-6-aminocarbovir in rats: II. Inhibition of intestinal first-pass metabolism.

A CBV [(-)-carbovir, (-)-carbocyclic 2',3'-didehydro-2', 3'-dideoxyguanosine] prodrug, 6AC [(-)-6-aminocarbovir, (-)-carbocyclic 2',3'-didehydro-2', 3'-dideoxy-6-deoxy-6-aminoguanosine], was previously evaluated in rats, and it exhibited superiority to the parent drug in increasing systemic and central nervous system exposure to CBV. The gut wall was determined to be the dominant site of the first-pass activation of 6AC after lumenal administration. If subsequent delivery to the brain is desired, then such a first-pass effect might not be viewed favorably. Because the first-pass conversion of 6AC primarily takes place in the intestine by adenosine deaminase (ADA), quenching of the intestinal activation of 6AC by oral administration of ADA inhibitors may result in an increased 6AC bioavailability, and thus an improved brain exposure to CBV. The objectives of the study were to determine whether the ADA inhibitors 2'-deoxycoformycin and erythro-9-(2-hydroxy-3-nonyl)adenine were capable of achieving a substantial and selective inhibition of gut wall activation of 6AC, and to determine whether the systemic concentrations of 6AC would be thus increased. Thirty-nine male Sprague-Dawley rats were divided into two groups. One group received 6AC by either the portal vein or intralumenally with the coadministration of intralumenal 2'-deoxycoformycin. Similarly, the other group received 6AC with coadministration of erythro-9-(2-hydroxy-3-nonyl)adenine. Substantial suppression of the first-pass conversion of 6AC was achieved with both inhibitors. This inhibition appeared to be relatively selective, allowing the choice of dose of inhibitor that would sufficiently inhibit the first-pass metabolism while leaving the activation capacity in the systemic circulation unaltered. The systemic level of 6AC increased with the escalating dose of inhibitors, thus increasing the driving force for passive uptake into the brain.     

药物的肠吸收与处置研究进展

对近几年药物肠吸收与处置方面的研究进展进行了综述。包括:特定部位吸收、代谢的认识和利用,与药物首过效应有关的肠壁外泌及代谢作用的介绍,促进药物肠道吸收的方法及常用研究模型的比较。     

Relative contribution of absorptive and secretory transporters to the intestinal absorption of fexofenadine in rats

It has been shown that fexofenadine, a selective non-sedating histamine H(1)-receptor antagonist, is a substrate for P-glycoprotein (P-gp) and an organic anion transporting peptide (OATP). This study was undertaken to investigate the relative contribution of these absorptive and secretory transporters to the intestinal absorption of fexofenadine in rats. When 0.1mM fexofenadine was introduced into duodenal, jejunal, and ileal loops, its disappearance was around 10% over 30min. Cyclosporine A, but not ketoconazole, probenecid or mitoxantron, significantly increased fexofenadine disappearance in the ileal loops. The serosal-to-mucosal permeation of fexofenadine across the rat ileal segments was approximately 18-fold greater than its mucosal-to-serosal permeation. The secretory orientation of the ileal permeation of fexofenadine was weakened significantly in the presence of cyclosporine A, moderately in the presence of ketoconazole, but was unchanged in the presence of probenecid. When fexofenadine (0.1 or 0.5mM) was administered to rats intraluminally, plasma concentrations increased linearly up to 120min. The magnitude of the increase in plasma fexofenadine concentrations in the presence of cyclosporine A was more remarkable at 0.5mM than at 0.1mM. The results obtained in this study suggest that the intestinal absorption of fexofenadine is relatively small in rats even if OATP functions as an absorptive transporter for fexofenadine. Low absorption of fexofenadine in rats is attributed to potent secretory transport mediated by P-gp.     

Alteration of fexofenadine disposition in the rat isolated perfused liver following injection of bacterial lipopolysaccharide

1. The aim of the present study was to examine the effect of bacterial lipopolysaccharide (LPS) on the disposition of an organic anion transporting polypeptide and P-glycoprotein substrate in the rat isolated perfused liver. 2. Male Sprague-Dawley rats were divided into four groups. Three of the groups received 1, 2.5 or 5 mg/kg, i.p., Escherichia coli LPS in sterile saline. The fourth group received an equivalent volume of sterile saline i.p. Twenty-four hours after treatment, rats were anaesthetized and the liver isolated and perfused with fexofenadine at an initial concentration of 2000 ng/mL in a recirculating system. Perfusate and bile samples were collected for 60 min and the liver was collected at the end of the perfusion. Fexofenadine concentrations were determined by HPLC. Fexofenadine pharmacokinetic parameters, the final liver : perfusate (L : P) and bile : liver (B : L) concentration ratios were determined. 3. Injection of LPS changed the hepatic disposition of fexofenadine. The changes were most marked in the 5 mg/kg LPS group. Notably, clearance from the perfusate (CL) and into the bile (CLB; 5.9 +/- 0.6 and 1.24 +/- 0.20 mL/min, respectively), L : P (44 +/- 11) and B : L (17 +/- 2) were all reduced (P < 0.05) in this group compared with control (CL 10.0 +/- 1.1 mL/min; CLB 2.7 +/- 0.5 mL/min; L : P 87 +/- 14; and B : L 30 +/- 4). 4. In conclusion CL and CLB were reduced following treatment with LPS in a manner consistent with downregulation of both canalicular and sinusoidal transport.     

The effects of erythromycin on the absorption and disposition kinetics of theophylline

Summary The effects of erythromycin on the kinetics of theophylline were investigated in eight female patients with documented asthma in a crossover study. Theophylline pharmacokinetics were determined at steady state before and after one-week treatment with erythromycin stearate 250 mg given four times a day. Multiple serum samples were collected for 12 h after an aminophylline dose in the two drug treatment phases and assayed by high performance liquid chromatography. The resultant serum theophylline concentration-time data were analyzed by weighted, nonlinear regression analysis to obtain various pharmacokinetic parameters. In this study, the elimination half-live increased from 7.8±1.7 h on the control day to 9.5±1.4 h following treatment with the antibiotic (p<0.02). The estimated apparent volume of distribution for theophylline (V/F) was also observed to increase from 0.42±0.09 l/kg before treatment with erythromycin to 0.53±0.15 l/kg after antibiotic treatment (0.05<p<0.10). In this study, no difference was demonstrated in the apparent clearance rate (Cl_app), apparent first-order absorption rate constant (k_a), maximum serum drug concentration (C_max), time of maximum drug concentration (T_max) or absorption lag time (t_lag) for theophylline before and after treatment with erythromycin. With no apparent alteration in theophylline clearance following erythromycin coadministration, the decrease in the first-order elimination rate constant suggested that the apparent volume of distribution of theophylline is increased in the presence of erythromycin. It is concluded that patients maintained on theophylline derivatives should be closely monitored when erythromycin is coadministered.     

Investigation of mezlocillin disposition with a porcine model

The suitability of the pig as an animal model for mezlocillin disposition was assessed. Serum, urine, and bile were collected after the administration of 50, 100 and 200 mg kg-1 mezlocillin to pigs and drug pharmacokinetics were characterized. Mezlocillin concentrations in biological fluids were determined by HPLC and free mezlocillin was determined by ultrafiltration. The pharmacokinetics of mezlocillin appeared to be independent of dose over the dosage range studied. Total clearance, renal clearance, and biliary clearance were 0.18 (0.05) 1 h-1 kg-1, 0.13 (0.03) 1 h-1 kg-1, and 0.07 (0.02) 1 h-1 kg-1, respectively. The steady-state volume of distribution was 0.29 (0.08) 1 kg-1. The pharmacokinetic parameters determined in the porcine model are similar to those reported for health human volunteers. Therefore, this model appears suitable for the study of mezlocillin disposition, and may be applied to the study of other agents that are appreciably biliary excreted.     

MDR1 gene polymorphisms and disposition of the P-glycoprotein substrate fexofenadine

AIMS: The C3435T polymorphism in the human MDR1 gene is associated with lower intestinal P-glycoprotein expression, reduced protein function in peripheral blood cells and higher plasma concentrations of the P-glycoprotein substrate digoxin. Using fexofenadine, a known P-glycoprotein substrate, the hypothesis was tested whether this polymorphism also affects the disposition of other drugs in humans. METHODS: Ten Caucasian subjects homozygous for the wild-type allele at position 3435 (CC) and 10 individuals homozygous for T at position 3435 participated in this study. A single oral dose of 180 mg fexofenadine HCl was administered. Plasma and urine concentrations of fexofenadine were measured up to 72 h using a sensitive LC/MS method. In addition, P-glycoprotein function was assessed using efflux of the P-glycoprotein substrate rhodamine 123 from CD56+ cells. Results Fexofenadine plasma concentrations varied considerably among the study population. However, fexofenadine disposition was not significantly different between the CC and TT groups (e.g. AUC(0,infinity) CC vs TT: 3567.1+/-1535.5 vs 3910.1+/-1894.8 ng ml-1 h, NS; 95% CI on the difference -1364.9, 2050.9). In contrast, P-glycoprotein function was significantly decreased in CD56+ cells of the TT compared with the CC group (rhodamine fluorescence CC vs TT: 45.6+/-7.2% vs 61.1+/-12.3%, P<0.05; 95% CI on the difference 5.6, 25.5). Conclusions In spite of MDR1 genotype-dependent differences in P-glycoprotein function in peripheral blood cells, there was no association of the C3435T polymorphism with the disposition of the P-glycoprotein substrate fexofenadine in this German Caucasian study population. These data indicate that other mechanisms including uptake transporter function are likely to play a role in fexofenadine disposition.     

The effects of PLGA microparticles on intestinal absorption of p-glycoprotein substrate using the everted rat intestinal sac model

In addition to the effects of physical processes (solubility, tissue permeability, and formulation factors), p-glycoprotein (P-gp) efflux across the apical membrane of enterocytes can affect the rate and amount of compound diffusing across the basolateral membrane of the intestine and entering the blood stream. The first objective was the evaluation of a possible role of intestinal P-gp in the kinetic absorption of a model drug: furosemide. To achieve this goal, two series of transport experiments, apical to basolateral (A → B) and basolateral to apical (B → A) with and without verapamil -a known P-gp inhibitor- were performed. The second objective was to evaluate whether encapsulation into polymeric microparticles might improve the oral absorption of a poorly permeable drug. Thus, spherical poly lactic-glycolic acid (PLGA) microparticles of furosemide were designed, and the concentration of transported drug was evaluated using an in situ everted rat gut sac model. The results indicated that verapamil at various drug concentrations (5–100 μg/mL) significantly decreased the B → A (2–3 fold) and increased the A → B (1.5–2 fold) permeability of furosemide, which showed that this drug could be a P-gp substrate. We found that encapsulation of furosemide in PLGA microparticles can markedly increase (2–4 fold) intestinal absorption of drug even higher than verapamil does. We conclude that biodegradable microparticles are a promising strategy to increase the bioavailability of drugs and have advantages compared to P-gp inhibitors with pharmacological and severe side effects at doses required for efflux pump inhibition.     

Involvement of multiple efflux transporters in hepatic disposition of fexofenadine

Fexofenadine (FEX) is mainly eliminated from the liver into bile in unchanged form. We demonstrated previously that organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are involved in the hepatic uptake of FEX. However, little is known about the mechanisms controlling the hepatic efflux of FEX from the liver to bile and blood. In the present study, the involvement of hepatic efflux transporters in the pharmacokinetics of FEX was investigated in both in vitro and in vivo studies. Vectorial transport of FEX was observed in OATP1B3/human bile salt export pump (hBSEP) double transfectants but not in OATP1B3/human breast cancer resistance protein double transfectants, which indicates the possible contribution of hBSEP to the biliary excretion of FEX in humans. In multidrug resistance-associated protein 2 (Mrp2)(-/-) mice, the biliary excretion clearance based on the plasma concentration and the liver-to-plasma concentration ratio significantly decreased, whereas the biliary excretion clearance based on the liver concentration decreased only with 20%, suggesting the minimum contribution of Mrp2 to its biliary excretion. ATP-dependent transport of FEX was observed in hMRP3-enriched membrane vesicles but not hMRP4. In Mrp3(-/-) mice, the biliary excretion clearance based on both the plasma and liver concentration and the liver-to-plasma concentration ratio increased, suggesting the significant contribution of Mrp3 to its sinusoidal efflux and the up-regulation of its biliary excretion in Mrp3(-/-) mice. On the other hand, pharmacokinetics of FEX remained unchanged in Mrp4(-/-) mice. This information provides a novel insight into the transporters important for FEX disposition.     

Aflatoxin M1 absorption and cytotoxicity on human intestinal in vitro model.

Aflatoxin M1 (AFM1) is the principal hydroxylated Aflatoxin B1 (AFB1) metabolite and is detected in milk of mammals, after consumption of feed contaminated with AFB1. As it is classified as probable human carcinogen (group 2B of the IARC), most countries have regulated its maximum allowed levels in milk in order to reduce AFM1 risk (50 ng/kg the EU and 500 ng/kg in the USA). It was demonstrated that if AFB1 must be converted into its reactive epoxide to exert its effects, and the protein binding may play an important role in its cytotoxicity. Conversely, the AFM1 epoxidation in human liver microsomes is very limited and studies with human cell line (MCL5), expressing or not expressing cytochrome P450 enzymes, demonstrated a direct toxic potential of AFM1 in absence of metabolic activation. For this reason, while AFM1 is generally considered a detoxification product of AFB1 relatively to carcinogenicity and mutagenicity property, this is not always true for cytotoxicity activity. Aim of this work is to evaluate the intestinal absorption of AFM1 using a human in vitro model, the Caco-2 cell line. Either the parental Caco-2 cell line or its derived clone TC7, with higher metabolic competence, have been used. They were treated with different concentrations of AFM1, that mirror the milk contamination level (0.3-32 nM corresponding to 10-10,000 ng/kg), either in undifferentiated or in differentiated phase of growth. After 48 h of treatment in serum free medium, a dose dependent absorption of AFM1 has been detected in both cell lines, especially in differentiated cells, while, no appreciable effects on cell viability were observed, except for a general cellular suffering, revealed by LDH release, particularly evident in the undifferentiated cells. As well, no metabolites or AFM1 conjugates have been detected. The present results may be crucial for the evaluation of human risk to AFM1 exposure, in particular for children's population, due to their large use of milk and derivatives.     

Theoretical model studies of intestinal drug absorption V. Non-steady-state fluid flow and absorption

A reasonably realistic physical model has been described for the simultaneous longitudinal spreading, fluid flow and absorption of drugs in solution under non-steady-state conditions m the small intestinal tract. Various input cases included first-order and zero-order stomach emptying and input from an infinite drug reservoir at constant infusion rate. The mathematical solutions were unique and rigorous. Theoretical simulations using reasonable physical parameter values illustrated the interrelationships of the longitudinal spreading diffusion coefficient, flow rate, apparent permeability coefficient and intestinal length on the change in concentration—distance profiles with time and the kinetics of appearance of unabsorbed drug at the end of the intestinal segment. The model is accessible to the design of intestinal absorption experiments and data interpretation on a quantitative mechanistic basis and also provides the way for studying intestinal absorption under more realistic situations.     

Genetic polymorphisms of OATP transporters and their impact on intestinal absorption and hepatic disposition of drugs

There is convincing evidence that many organic anion transporting polypeptide (OATP) transporters influence the pharmacokinetics and pharmacological efficacy of their substrate drugs. Each OATP family member has a unique combination of tissue distribution, substrate specificity and mechanisms of gene expression. Among them, OATP1B1, OATP1B3 and OATP2B1 have been considered as critical molecular determinants of the pharmacokinetics of a variety of clinically important drugs. Liver-specific expression of OATP1B1 and OATP1B3 contributes to the hepatic uptake of drugs from the portal vein, and OATP2B1 may alter their intestinal absorption as well as hepatic extraction. Accordingly, changes in function and expression of these three OATPs owing to genetic polymorphisms may lead to altered pharmacological effects, including decreased drug efficacy and increased risk of adverse effects. Association of genetic polymorphisms in OATP genes with alterations in the pharmacokinetic properties of their substrate drugs has been reported; however, there still exists a degree of discordance between the reported outcomes in different clinical settings. For better understanding of the clinical relevance of genetic polymorphisms of OATP1B1, OATP1B3 and OATP2B1, the present review focuses on the association of the genotypes of these OATPs with in vitro activity changes and in vivo clinical outcomes of substrate drugs.     

Antipyrine absorption and disposition in the elderly

Twelve young (24-41 years) and 11 elderly (62-77 years) volunteer subjects received a single 1.0-gram dose of antipyrine on three occasions: intravenously, orally in the fasting state and orally following a standard breakfast. Plasma antipyrine concentrations were determined for 24 h after each dose. Compared to young males, elderly men had significantly prolonged elimination half-life (17 vs. 11 h, p less than 0.025) and reduced clearance (32 vs. 54 ml/min, p less than 0.06). However, elderly and young women did not differ in half-life (12 vs. 11 h) or clearance (37 vs. 44 ml/min). After oral dosage in the fasting state, young and elderly groups (regardless of gender) did not differ in peak plasma antipyrine concentration (Cmax) or time of peak concentration (Tmax). Absolute bioavailability was not significantly less than 100% and was not related to age. Postprandial oral dosage of antipyrine caused reduced Cmax and prolonged Tmax in all groups, but absolute bioavailability was not significantly less than 100%. Again, there were no age-related differences. Although aging may lead to reduced clearance of antipyrine among men, there is no evidence that old age is associated with impairment of the rate or extent of antipyrine absorption from the gastrointestinal tract.