The pharmacokinetics and tolerability of the oral neuraminidase inhibitor oseltamivir (Ro 64-0796/GS4104) in healthy adult and elderly volunteers.

The tolerability and pharmacokinetics of Ro 64-0802, a potent, selective inhibitor of influenza neuraminidase, and its oral prodrug oseltamivir were investigated in three double-blind, placebo-controlled studies. Two studies involved healthy adult volunteers (18-55 years) (n = 48) who received single (20-1000 mg) or bid doses (50-500 mg) (n = 32) of oseltamivir or placebo for 7 days. Healthy elderly volunteers (> or = 65 years) (n = 24) received oseltamivir 100 to 200 mg bid or placebo for 7 days in a third study. Measurable plasma concentrations of the active metabolite appeared rapidly in plasma and were significantly higher and longer lasting than those of oseltamivir. Pharmacokinetics of both compounds were linear. Multiple-dose exposure was predictable from single-dose data, and steady-state plasma concentrations were achieved within 3 days of bid drug administration. Oseltamivir was well tolerated at single doses of up to 1000 mg and twice-daily doses of up to 500 mg. Adverse events were mild in intensity. Exposure to both prodrug and active metabolite was increased in elderly patients by approximately 25%. However, due to the wide safety margin of both compounds, no dose adjustment is necessary for elderly patients.

The effect of probenecid on the pharmacokinetics of zalcitabine in HIV-positive patients.

PURPOSE: The purpose of this study was to determine the potential effect of probenecid on the pharmacokinetics of zalcitabine in HIV-positive patients. METHODS: Twelve patients received single oral 1.5 mg doses of zalcitabine alone and during probenecid treatment (500 mg at 8 and 2 hours before and 4 hours after zalcitabine dosing) in an open-label, randomized two-way crossover study with a one-week washout period between treatments. Serial blood and urine samples were collected over a 24 hour period and assayed for zalcitabine by a modified GC/MS method. RESULTS: Coadministration of probenecid with zalcitabine resulted in a decrease in mean (%CV) renal clearance of zalcitabine from 310 (28%) ml/min when zalcitabine was given alone to 180 (22%) ml/min with probenecid and a prolonged half-life from 1.7 hours to 2.5 hours. Mean AUCs increased from 59 ng.h/ml when zalcitabine was given alone to 91 ng.h/ml when given with probenecid. Considering the short half-life of zalcitabine (1-3 hours) relative to its dosing schedule, the pharmacokinetic changes observed in this study are not expected to result in significant accumulation during chronic dosing. CONCLUSIONS: The results of this study show that co-administration of probenecid with zalcitabine results in a moderate decrease in renal clearance of zalcitabine due to inhibition of renal tubular secretion and a 50% increase in drug exposure. Although well tolerated in this single-dose study, patients taking this combination should be monitored closely for signs of toxicity and dosage reduction should be considered if warranted.

Phase I evaluation of zalcitabine administered to human immunodeficiency virus-infected children.

The safety, tolerability, and pharmacokinetics of zalcitabine (ddC) in a single oral dose (0.02 mg/kg) was evaluated in 23 mildly symptomatic human immunodeficiency virus-infected children (mean age, 4.2 years). After administration of ddC, blood samples were obtained at 0.5, 1, 1.5, 2, 4, 6, and 8 h for analysis. The drug was well tolerated and no side effects were noted. Plasma ddC levels were determined by ion spray liquid chromatography/tandem mass spectrometry. ddC was rapidly absorbed, with a mean maximum plasma concentration of 9.3 ng/mL (range, 3.2-14.1) attained within a mean of 1 h (range, 0.5-2.0). Mean elimination half-life was 1.4 h (range, 1.0-3.5), mean area under the plasma concentration-time curve was 25 ng.h/mL (range, 11-37), and mean total body clearance was 14.6 mL/min/kg (range, 8.9-30.6). Plasma concentrations were lower and the half-life shorter in these children than in adults given comparable doses, suggesting that ddC may be cleared more rapidly in children than adults.

The effect of food on pharmacokinetics of zalcitabine in HIV-positive patients.

PURPOSE: The purpose of this study was to determine the effect of food on the pharmacokinetics of zalcitabine in HIV-positive patients. METHODS: Twenty patients received single oral 1.5 mg doses of zalcitabine with and without a standard breakfast in an open-label, randomized crossover study with at least a one week washout period between treatments. Serial blood and urine samples were collected over 24 hours and assayed for zalcitabine by a modified GC/MS method. RESULTS: Administration with food delayed and prolonged absorption resulting in a decrease of approximately 39% in maximal plasma concentrations compared to dosing under fasting conditions. Comparison of plasma AUC values indicated a small (14%) reduction in bioavailability when given with food. Approximately 59% and 45% of the dose were excreted unchanged in the urine under fasting and fed conditions, respectively. CONCLUSIONS: The results of this study show that the administration of zalcitabine with food results in a mild reduction in bioavailability. Although these changes are not expected to be of clinical importance, further studies must be conducted for confirmation.

The pharmacokinetic-pharmacodynamic (Digit Symbol Substitution Test) relationship of flumazenil in a midazolam steady-state model in healthy volunteers.

To characterize the plasma concentration-effect relationship of flumazenil in the presence of a predefined midazolam level, a double-blind, placebo-controlled, randomized two-way crossover study was conducted in nine healthy male subjects. After reaching a criterion level of midazolam-induced depression of the Digit Symbol Substitution Test (DSST), volunteers received a dose of flumazenil (1.0 mg) or placebo over 1 minute, with the infusion of midazolam continued. Blood samples were collected, simultaneously with the DSST assessment, at predetermined intervals and were assayed for flumazenil and/or midazolam plasma concentrations. Pharmacokinetic-pharmacodynamic modeling techniques were used to estimate the equilibration rate constant (keo) between plasma concentration and effect for flumazenil; a sigmoidal maximum-effect model was used to relate the DSST score to the flumazenil plasma concentration. Flumazenil exhibited a rapid onset (the half-life of equilibration between drug concentration in the blood and drug effect was 3.3 minutes) and short duration of action (the flumazenil plasma concentration causing half-maximal effect was 7.4 ng/ml, which was reached about 1 hour after dosing). The results of this study also show the competitive nature of flumazenil as a midazolam antagonist.

The effects of cimetidine and ranitidine on the pharmacokinetics of cifenline.

Twelve healthy subjects completed an open single dose study to evaluate the effect of co-administration of cimetidine and ranitidine on the pharmacokinetics of cifenline. Each subject received a single 160 mg dose of cifenline alone, in combination with cimetidine (300 mg four times daily), and with ranitidine (150 mg twice daily). The H2-receptor antagonists were given with breakfast 1 h prior to cifenline dosing and continuing for 48 h. Co-administration of cimetidine significantly increased Cmax (27%) and AUC (44%) and prolonged the half-life (30%) of cifenline. There were no differences in these parameters when ranitidine was co-administered with cifenline. The results of this study suggest that cimetidine, but not ranitidine, lowers the clearance of cifenline by inhibition of hepatic oxidative metabolism.

The pharmacokinetics of etretinate and its metabolites in the dog.

The pharmacokinetics and disposition of etretinate (ET) and its metabolites, etretin (ETA) and isoetretin (c-ETA), were studied in the dog. Administration of ET, ETA, and c-ETA by several routes of administration allowed the use of a physiologically based model to assess the relative contributions of absorption and presystemic metabolism to the oral bioavailability of these compounds. The large Vdss (214 +/- 228 liters/kg) of ET and terminal half-life of greater than 300 hr indicated the wide distribution and prolonged storage of ET in the tissues. After a dose of ET, its two metabolites, ETA and c-ETA, were also detectable in the plasma. The oral bioavailability of ET in the dog was 52.5% with 95.4% of the dose available for absorption from the gut lumen. Of the ET that was absorbed from the gut lumen, 26.4% and 25.5% was removed by the gut wall and liver, respectively. ETA was found to be a formation rate-limited metabolite of ET. Although the oral bioavailability of ETA could not be determined because its administration was not possible by the iv route, it appeared that only 16% of an orally administered dose entered the portal circulation from the gut. c-ETA was detected after administration of either ET or ETA. ETA and c-ETA were shown to be interconvertible metabolites, but the equilibrium of the conversion between c-ETA and ETA favored the formation of ETA. The oral bioavailability of c-ETA was 42.4%, but the liver showed little metabolic activity toward c-ETA.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of food on the pharmacokinetics and ACE inhibition of cilazapril.

1. The influence of food on the pharmacokinetics and angiotensin-converting enzyme (ACE) inhibitory effects of oral 5 mg doses of cilazapril was investigated in a two-way crossover study in 16 volunteers. 2. Plasma and urine concentrations of cilazaprilat, the active diacid metabolite of cilazapril, and plasma ACE activity were determined by a radio-enzymatic method. 3. Cmax decreased by 30% (P less than 0.05) with a delay in (t)max of 1 h (P less than 0.05) and area under curve (AUC) was decreased by 14% (P less than 0.05). The elimination rate was unaltered. 4. Onset of ACE inhibition was delayed by approximately 30 min but degree and duration were unaffected. 5. The effect of food on the bioavailability of cilazapril at this dose would not be expected to be clinically significant.

Effect of renal impairment on the pharmacokinetics of cibenzoline.

Sixteen subjects completed an open-label study designed to assess the effect of renal impairment on the disposition of cibenzoline. The study included 10 patients with mild or moderate renal impairment creatinine clearance less than 60 ml/min/70 kg) and six healthy subjects in the same age range, each of whom received a single 130 mg oral dose of cibenzoline. The pharmacokinetic parameters observed in the healthy volunteers were similar to those reported previously. Maximum plasma concentration, time of maximum concentration, and apparent volume of distribution after single doses in patients with renal impairment were in the same range as those observed in healthy volunteers. The elimination half-life increased with decreasing renal function from a mean value of approximately 8 hours in healthy volunteers to more than 20 hours in patients with moderate renal impairment. Renal clearance and the fraction of the dose excreted unchanged in the urine decreased with decreasing creatinine clearance. The results of this study suggest that the dosage of cibenzoline should be reduced or the dosage interval increased in patients with reduced renal function to avoid excessive drug accumulation.

Effect of oral cibenzoline on steady-state digoxin concentrations in healthy volunteers.

The effect of oral cibenzoline on steady-state digoxin concentrations was studied in 12 healthy subjects ranging from 41 to 55 years of age. Each subject received an oral dose of 0.25 mg or 0.375 mg digoxin once daily for 27 days. On days 14 to 21, 160 mg of oral cibenzoline were administered concomitantly every 12 hours for a total of 15 doses. Plasma digoxin concentration-time profiles obtained before, during, and after cibenzoline coadministration were compared to determine the effect of oral cibenzoline on steady-state digoxin concentrations. The maximum plasma concentration, time of maximum concentration, area under the curve during a dosing interval and steady-state trough plasma concentration for digoxin, during and after concomitant doses of cibenzoline were similar to those before administration, indicating that cibenzoline did not affect the pharmacokinetics of digoxin. In addition, plasma cibenzoline concentration-time profiles after the first and last dose of cibenzoline were similar to those observed in previous studies in which multiple doses of cibenzoline alone were administered. The results of this study indicate that there is no pharmacokinetic interaction between digoxin and cibenzoline when the two drugs are coadministered to healthy subjects in multiple doses.

Gold disposition in the rat: studies of its plasma half-life and its urinary, biliary and fecal elimination pathways.

The biologic half-life of gold, a subject of controversy for many years, was found to be much longer in the rat than that reported for other species in the bulk of the literature. The longer observed half-life supports recent findings in man and is more consistent with the monthly maintenance dosing normally used in patients with rheumatoid arthritis. Excretion studies revealed that, after administration of gold sodium thiomalate, gold was eliminated via urinary and fecal pathways by approximately a 2:1 ratio. The relative importance of these pathways was not altered after multiple dosing. Biliary and intestinal excretion studies were performed to identify the means by which gold is eliminated via the feces. Only a small percentage of the dose was recovered from the bile after 2 hr, and biliary excretion was shown to be dose dependent. Results suggest that passive diffusion may be responsible for plasma-to-bile transfer and stand in contrast to the results of similar studies on other metals. Administration of gold as gold chloride [Au(III)] instead of gold sodium thiomalate [Au(I)] did not alter the excretion into bile, nor did stimulation of metallothionein, a metal-binding protein in the liver and kidney, by Cd pretreatment. Intestinal excretion was shown to be an insignificant pathway of gold elimination. The results of these studies suggest that, at high doses, gold-binding sites on plasma proteins may be saturated, resulting in an increase in excretion into the urine and bile, as well as an increase in distribution to peripheral tissues where tissue binding results in an overall increase in half-life.

Effect of congestive heart failure on the pharmacokinetics of cibenzoline.

Six patients with chronic congestive heart failure (CHF) (New York Heart Association functional class II or III) and five healthy subjects completed this study designed to determine if CHF alters the pharmacokinetics and absolute bioavailability of cibenzoline when compared with healthy subjects. Each subject or patient was administered a one-hour intravenous infusion of 80 mg of 15N2-cibenzoline and simultaneously received an 80-mg oral dose of cibenzoline that allowed for analytic separation of each route of administration. Resulting plasma concentration-time profiles and urinary excretion rate data were used to determine pharmacokinetic parameters for cibenzoline. There were no statistically significant differences in any pharmacokinetic parameter between patients with CHF and healthy subjects. The absolute bioavailability ranged from 74% to 97% in those with CHF. The volume of distribution following the intravenous dose ranged from 3.4 to 6.1 L/kg, and plasma clearance ranged from 245 to 642 mL/min, with an apparent elimination half-life of approximately ten hours. Approximately 60% of the dose was recovered in the urine. Overall, the pharmacokinetics of cibenzoline in patients with chronic CHF do not differ from those observed in healthy subjects.

Pharmacokinetics of single and multiple ascending doses of the antiallergic agent tiacrilast in man.

Five groups of six healthy subjects received single oral doses of 150, 300, 450, 600 or 750 mg tiacrilast 150 mg capsules, followed 24 h later by the same dose given every 6 h for 7 days, in a study designed to assess the pharmacokinetics of single and multiple doses of tiacrilast. Plasma samples were obtained at specified times after the initial dose, after 4 days of multiple dosing and after the last dose of tiacrilast. Samples were assayed for unchanged drug by a specific HPLC method. Wide variability was seen in the plasma concentration-time data. Plasma concentrations and pharmacokinetic parameters were nearly proportional to dose over the 150 to 750 mg dose range studied. Moreover, there was no evidence of unexpected accumulation of the drug in the plasma during multiple dosing and food did not appear to alter the bioavailability of tiacrilast to any clinically significant extent. The apparent elimination half-life was similar after single and multiple doses and ranged from 1 to 3 h.

Pharmacokinetics of cibenzoline after single and repetitive dosing in healthy volunteers.

Twenty-five healthy, adult male volunteers entered two open-label parallel studies, each designed to define the pharmacokinetics of single and multiple oral doses of cibenzoline. Each volunteer received a single 160-mg oral dose of cibenzoline followed two or three days later by 160 mg of cibenzoline q12h for seven days. Plasma concentration-time profiles and urinary excretion rate data were used to determine pharmacokinetic parameters for unchanged drug. The apparent half-life following administration of the last dose (9.7 hours) was slightly longer than that observed after the first dose (8.4 hours). Total body clearance and nonrenal clearance were decreased after the last dose compared with the first dose, whereas renal clearance was not significantly altered. After both the first and last dose, the renal clearance greatly exceeded the glomerular filtration rate, suggesting that tubular secretion participates in the renal excretion of cibenzoline. Plasma concentrations from samples collected during the multiple-dose regimen suggest that a slight but statistically significant diurnal variation in the absorption and/or clearance of drug occurred during the course of the study. Overall, the pharmacokinetics of cibenzoline are characterized by a slightly longer half-life during multiple dosing than that observed following a single dose, due to a decrease in the nonrenal clearance. The multiple-dose pharmacokinetics reported herein are consistent with bid dosing for the maintenance of therapeutic plasma concentrations in patients taking chronic therapy.

Effect of food on cibenzoline bioavailability.

Eighteen healthy adult volunteers received 160 mg oral capsule doses of cibenzoline in an open-label, four-way randomized crossover study designed to determine the influence of food on cibenzoline pharmacokinetics. Cibenzoline was administered 1 h prior to, with, and 1 h following a standard breakfast as well as under fasting conditions. There was no change in any bioavailability parameter when the data following drug ingestion 1 h prior to food were compared to the fasted state. Bioavailability parameters obtained when drug was taken during the meal or 1 h after the meal suggested that the rate of absorption was slightly decreased in the presence of food, while the extent of absorption was unaltered. The decreased absorption rate in the presence of food is not expected to be of clinical significance. The presence of food is not expected to affect the bioavailability of cibenzoline to the extent of clinical significance.

The disposition and metabolic fate of 14C-cibenzoline in man.

The disposition and metabolic fate of cibenzoline (CBZ) following single oral 153-mg doses of 14C-CBZ succinate were studied in five healthy adult males. The mean maximum plasma radioactivity of 386 ng eq/ml occurred at 2.4 hr after administration. The mean half-life, determined from the 14C plasma concentration and urinary excretion rate data, was 13.1 and 14.8 hr, respectively. The mean maximum CBZ concentration was 196 ng/ml at 1.2 hr post-dose. The mean half-life, determined from the plasma concentration and urinary excretion rate data, was 7.2 and 7.3 hr, respectively. The mean total clearance of radioactivity and CBZ was 300 ml/min and 1224 ml/min, respectively, due to elimination via both renal and nonrenal pathways. The only unconjugated metabolite in the plasma was 4,5-dehydrocibenzoline which, together with other unidentified metabolites, is presumed responsible for the longer observed half-life for total radioactivity. Approximately 75% of the dose was recovered in the urine in the first 24 hr after dosing, 80% of which was present at CBZ and known metabolites. After 6 days, a mean of 85.7% of the dose was excreted in urine and 13.2% in feces. The predominant excreted compound was CBZ (55.7% of the dose) in the 0-72 hr urine. Although several metabolites were identified in urine samples, none were found in substantial amounts relative to the parent drug. Two of these substances showed slight antiarrhythmic activity, whereas the 4,5-dehydro metabolite, representing approximately 4% of radioactivity in urine, was inactive.

Pharmacokinetics of furosemide after three different single oral doses.

Furosemide solution was orally administered to 21 healthy adult males to determine dose proportionality over the dose range used and the reproducibility of disposition following a repeated dose. Furosemide solution was given in doses of 20, 40, and 80 mg, with the 40 mg dose repeated once. Blood was collected for 12 hours post-dose and urine for 24 hours. The maximum plasma concentrations resulting from 20, 40, and 80 mg doses were significantly different (p less than 0.05). Dose normalized maximum concentrations for the 20 and 80 mg doses were significantly different (p less than 0.05). Mean time to Cpmax was 50 minutes, with no differences observed among doses. Plasma AUCs were significantly different (p less than 0.05) for 20, 40, and 80 mg. Dose normalized AUCs were not significantly different. Mean amounts of furosemide in urine (Xu) were 9.62, 16.7, and 32.0 mg for the 20, 40, and 80 mg doses, respectively. These amounts were significantly different (p less than 0.05); dose normalized amounts were not significantly different. Renal clearances of furosemide following the three doses were not significantly different. Regressions of Cpmax, AUC and Xu on dose were significant. There were no significant differences in Cpmax, tmax, AUC or Xu for 40 mg given on two separate days. Renal clearance of furosemide was statistically different for 40 mg given on two separate days, but the difference was not clinically significant. The pharmacokinetics of furosemide are linear over the dosage range studied. Furosemide 40 mg given on two separate days results in similar disposition parameters.

The pharmacokinetics of intramuscular gold sodium thiomalate in normal volunteers.

Four normal male volunteers participated in a study designed to examine the disposition of gold given intramuscularly as gold sodium thiomalate. Blood samples were collected for 32 days following the administration of 10 mg of gold sodium thiomalate. Plasma gold concentrations were determined by atomic absorption spectrometry. A triphasic decay pattern in plasma gold concentrations was observed. Terminal log-linear phases corresponded to a mean disposition half-life of 25 days. Apparent total body clearance of gold was 7.0 +/- 0.6 ml kg-1 day-1 and the apparent volume of distribution was 0.26 +/- 0.051 kg-1. These pharmacokinetic data are in contrast to previous data from other investigators who have reported half-lives of approximately 5 days. Data from the current study provide a sound rationale for the currently used empiric dosing regimens.

Disposition and absolute bioavailability of furosemide in healthy males.

Furosemide (40 mg) was administered to 18 healthy adult males as an intravenous dose, an oral solution, and in tablet form. The pharmacokinetics of intravenous furosemide were studied, determining a total body clearance rate of 117.6 +/- 41.3 ml/min and a harmonic mean half-life of 78 min. The mean absolute bioavailability determined by ratio of areas under the plasma-time curves was 64 and 71% for the solution and tablet, respectively. The mean absolute bioavailability determined by the ratio of urinary cumulative excretion data was 61 and 66% for the solution and tablet, respectively. The absolute bioavailability of furosemide determined with plasma and urine data were not significantly different. Thus, urine data alone may be used to establish bioavailability of furosemide. Inspection of plasma-time curves revealed secondary maxima in several subjects, suggesting enterohepatic cycling.

Pharmacokinetics of gold sodium thiomalate.

Two normal males participated in a study designed to examine the disposition of gold given intravenously and intramuscularly as gold sodium thiomalate. Blood samples were collected for 30 days, urine and feces for ten. A triphasic decay pattern in plasma gold concentrations was observed. Terminal log-linear phases corresponded to a mean disposition half-life of 12.5 days. Absolute bioavailability of IM gold sodium thiomalate appears to be variable with one subject having complete absorption and the other absorbing 64% of the administered IM dose. The major route of elimination of an IV dose of gold sodium thiomalate is urinary excretion, with a mean of 35% of the dose found in the urine in ten days. Fecal elimination accounts for an additional 9.4% of the IV dose excreted in ten days, probably as a result of biliary secretion.