In vitro metabolic products of RWJ-34130, an antiarrythmic agent, in rat liver preparations

The in vitro metabolism of RWJ-34130, an antiarrhythmic agent, was conducted using rat hepatic 9000 x g supernatant (S9) and microsomes in an NADPH-generating system, and the rat liver perfusion. The 100 and 20 microg ml(-1) concentrations of RWJ-34130 aqueous solution were used for microsomal incubation and liver perfusion, respectively. Unchanged RWJ-34130 (approximately 77-78% of the sample in both S9 and microsomes) plus a major metabolite, RWJ-34130 sulfoxide (20% of the sample in both S9 and microsomes) were profiled, isolated and identified from both hepatic S9 and microsomal incubates (60 min) using HPLC and mass spectrometry (MS), and by comparison to a synthetic RWJ-34130 sulfoxide, which was synthesized by reacting RWJ-34130 with MCPBA (meta-chloroperoxy benzoic acid). No unchanged RWJ-34130 was detected in the 3 h liver perfusate, however, 1-phenyl-2-oxo-pyrrolidine was profiled, isolated and identified as a major hydrolyzed metabolite of liver perfusate. RWJ-34130 is not extensively metabolized in vitro in rat hepatic S9 and microsomes. All HPLC metabolic profiles of hepatic S9 and microsomal samples (30 min, 60 min) were qualitatively and nearly quantitatively identical.

Common noncompartmental pharmacokinetic variables: are they normally or log-normally distributed?

We investigated the hypothesis that distributions of continuous pharmacokinetic variables are positively skewed in nature and that logarithmic transformation of these variables restores normality. The distributions of common continuous noncompartmental pharmacokinetic variables were investigated for four different Glaxo Wellcome compounds, administered by three different routes of administration: ranitidine (po), sumatriptan (sc), ondansetron (iv), and bismuth, from ranitidine bismuth citrate (po). The distributions of all the investigated noncompartmental pharmacokinetic variables were adequately described by a log-normal distribution, whereas statistically significant departures from normality occurred in the majority of cases. Thus, unless there is strong and consistent evidence for a departure from log-normality, the parametric statistical analysis of common noncompartmental pharmacokinetic variables should be carried out after a priori log transformation.

The bioavailability of oral GI147211 (GG211), a new topoisomerase I inhibitor

Topoisomerase I inhibitors are new compounds of interest for cancer chemotherapy. We performed a study with GI147211, a new semisynthetic camptothecin analogue, to determine the absolute bioavailability of the drug given orally. Patients with a histologically confirmed diagnosis of a solid tumour refractory to standard forms of therapy were eligible for the study. GI147211 was given orally on day 1 and as a 30-min infusion daily on days 2-5. The treatment course was repeated every 3 weeks. In subsequent patient cohorts, the dose of the oral formulation was escalated from 1.5 mg m(-2) to 6.0 mg m(-2); the dose for i.v. administration was fixed at 1.2 mg m(-2). Plasma pharmacokinetics was performed on day 1 and 2 of the first course and on day 1 of the second course using a validated high-performance liquid chromatographic assay. Nineteen patients were entered into the study; one patient was not evaluable because the treatment course was stopped prematurely. Eighteen patients received a total of 47 treatment courses. The absolute bioavailability of GI147211 averaged 1.3 +/- 5.2%. Drug appeared quickly in plasma with a median Tmax at 0.5 h. Fasting or fed state had no significant influence on the bioavailability of GI147211. The terminal half-life after administration of oral GI147211 was 6.85 +/- 3.13 h, similar to the half-life after intravenous administration. The major toxicities were neutropenia and thrombocytopenia. Nadirs for neutropenia and thrombocytopenia occurred on day 8 and day 15 respectively. Other toxicities predominantly consisted of mild and infrequent nausea and vomiting, and fatigue. The oral administration of the drug is well tolerated. Oral administration of topoisomerase I inhibitor GI147211 results in a low bioavailability with relatively wide interpatient variation. The intravenous route of administration is advised for further development of this promising topoisomerase I inhibitor.

Pharmacokinetics of ondansetron in patients with hepatic insufficiency

Ondansetron is primarily eliminated via hepatic metabolism; thus, liver disease may affect its clearance. The pharmacokinetics of ondansetron in patients with different degrees of hepatic insufficiency (N = 12 with hepatic impairment, as categorized by Pugh's classification method) were assessed and the results compared with results for age- and gender-matched control subjects with normal liver function (n = 12). A secondary objective was to correlate the Pugh method of assessing hepatic impairment and quantitative metabolic markers used to assess hepatic function (antipyrine clearance and indocyanine green clearance) with changes in the pharmacokinetics of ondansetron. This was an open-label study in which 8 mg ondansetron was given orally and intravenously, following a randomized crossover design. Clearance of ondansetron was lower among patients with hepatic impairment that control subjects. After a single, oral dose of ondansetron, mean absolute bioavailability increased markedly with increased hepatic insufficiency (approaching 100% in the group with severe hepatic impairment versus 66% for control subjects). These data suggest that there is a reduced first-pass effect in patients with liver disease resulting in a higher AUC0-infinity. A correlation existed between clearance of ondansetron and decreased antipyrine clearance; a smaller correlation existed between ondansetron clearance and indocyanine green clearance. Mean percent of ondansetron bound to plasma proteins was significantly lower in patients with liver disease than in control subjects. None of the patients experienced any severe adverse reactions attributed to ondansetron. A reduction in the clearance of ondansetron is associated with increasing degrees of hepatic insufficiency; therefore, patients with severe hepatic impairment (Pugh score of > 9) should have their daily dose of ondansetron limited to 8 mg (or 0.15 mg/kg).

Comparison of quantitative methods to assess hepatic function: Pugh's classification, indocyanine green, antipyrine, and dextromethorphan

STUDY OBJECTIVES

To compare three quantitative metabolic markers used to assess hepatic function, indocyanine green (ICG), a high-extraction marker; antipyrine, a low-extraction marker; and dextromethorphan, a P-450IID6 marker, with the clinically used Pugh's classification.

DESIGN

Comparison of 12 healthy controls with 12 age- and sex-matched patients with different degrees of liver disease.

SETTING

Research center in a university-affiliated teaching hospital.

PATIENTS

The 12 patients had different degrees of liver disease: 4 mild (Pugh's score 6 or 7); 4 moderate (Pugh's score 8 or 9); and 4 severe (Pugh's score > or = 10). Each level had an equal number of men and women subjects.

MEASUREMENTS AND MAIN RESULTS

Clearance of ICG detected mild alterations in hepatic function as efficiently as it did for moderate and severe impairment, but it lacked the specificity to distinguish among the classification groups. In contrast, antipyrine was effective in identifying moderate and severe hepatic impairment; however, its clearance was not reduced in mild liver disease. Pugh's classification appears to be a clinically useful method of assessing the global degree of hepatic impairment in patients with chronic disease, and there was a significant correlation between it and antipyrine clearance (r = 0.67, p = 0.0003) and ICG clearance (r = 0.86, p = 0.0001). Four of eight patients with a Pugh's score greater than 8 had a dextromethorphan metabolic ratio expression reflective of a poor metabolizer phenotype based on 0- to 4-hour urine collection, but only two of those eight patients were classified as poor metabolizers based on 4- to 12-hour urine collection. These percentages of poor metabolizers are substantially higher than for historical controls (8.5-10.4%) and most likely reflect a decrease in the P-450IID6 functional ability with progression of liver disease. However, due to small sample size and lack of knowledge of the patients' genotypes, these data are only suggestive.

CONCLUSION

Pugh's classification appears to be a reliable indicator of the degree of chronic liver disease and could be employed as a drug development research classification tool; however, it does not replace quantitative metabolic markers, especially isozyme-specific markers.

Effects of hemodialysis on plasma protein binding of bepridil

The effects of end-stage renal disease (ESRD) and hemodialysis on the in vitro plasma protein binding of bepridil hydrochloride were investigated. The possible influence of bepridil metabolites on bepridil-protein binding in ESRD patients was also examined. Plasma samples were obtained from six patients with ESRD. Bepridil-plasma protein binding was measured by microequilibrium dialysis after addition of freshly prepared bepridil-14C (239 microCi/mg) at a final concentration of 2 micrograms/mL. The percentage of free bepridil in peripheral venous samples drawn on a nondialysis day was lower (i.e., binding was greater) in the patients with ESRD relative to previous observations in healthy subjects (0.15% +/- 0.04% versus 0.31% +/- 0.05% (mean +/- SD). The plasma concentrations of alpha-1-acid glycoprotein (AAG), the principal bepridil binding protein, were also higher in ESRD patients (110 +/- 32 mg/dL) than previously reported in healthy subjects. Although hemodialysis resulted in significant increases in AAG, total protein, and albumin concentrations, no significant difference in bepridil-plasma protein binding was detected between predialysis and postdialysis peripheral venous samples in the presence (0.16 versus 0.18) or absence (0.20 versus 0.17) of bepridil metabolites. The percentage of free bepridil in plasma from both the arterial and venous limbs of the dialyzer during hemodialysis (means of free bepridil ranged from 0.24-0.28%) was higher than in samples drawn from a peripheral vein. This displacement of bepridil from its binding sites as blood passes through the dialyzer may have been owing to the presence of high local concentrations of plasticizers. Confirmation of this hypothesis will require further investigation.

Pharmacokinetics and bioavailability of topiramate in the beagle dog

Male and female beagle dogs showed rapid absorption following oral administration of single oral gavage (40 mg/kg) and single or multiple (15 days) oral capsule (10, 40, and 150 mg/kg) doses of the novel anticonvulsant drug, topiramate, with the peak plasma concentration (Cmax) occurring between 0.6 and 3.8 hr. The absolute bioavailability of an oral dose of topiramate was estimated to be in the range of 27-59%, depending on the formulation. The mean topiramate Cmax values increased in a dose-proportional manner for both single (9.2-137.7 micrograms/ml) and multiple (10.3-145.2 micrograms/ml) oral capsule administrations, whereas the corresponding area under the plasma concentration vs. time curve (AUC) values increased in a dose-related but nonproportional manner for both single (51-1131 micrograms.hr/ml) and multiple (54-858 micrograms.hr/ml) doses. Over the 10-150 mg/kg dosing range, oral plasma clearance and terminal half-life values were found to be 2.4-3.6 ml/min/kg and 2.6-3.7 hr following a single oral administration, and 3.0-4.2 ml/min/kg and 2.0-3.8 hr after multiple doses. There were no significant differences between the pharmacokinetic parameters calculated following the first and fifteenth daily doses of topiramate at the 10 and 40 mg/kg levels, indicating that there was no accumulation and no autoinduction or inhibition of enzymes that metabolize topiramate resulting from multiple dosing at these levels. A slight (24%) decrease in AUC was observed at the 150 mg/kg level after the fifteenth daily dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral ondansetron pharmacokinetics: the effect of chemotherapy

The effect of a typical 5-day chemotherapy treatment with cisplatin (20-40 mg/m2 per day) and 5-fluorouracil (5-FU, 1 gm/m2 per day) on the pharmacokinetics of ondansetron was investigated. Twenty cancer patients received 8 mg of ondansetron in three periods, including an oral tablet on day 1, an intravenous infusion on day 4, and an oral tablet on day 5. Absolute bioavailability after the oral dosing on day 1 was 87.5 +/- 31.3%, and on day 5 was 85.2 +/- 22.1% (P > .05). Mean values of AUC, Cmax, Tmax, and half life on days 1 and 5 were 399 +/- 275 and 381 +/- 222 ng.hour/mL, 53.3 +/- 26.8 and 43.6 +/- 21.7 ng/mL, 1.9 +/- 1.4 and 2 +/- 1.4 hours, and 5.21 +/- 1.78 and 6.19 +/- 1.99 hours, respectively. These values were not significantly different (P > .05). In summary, this study showed that cisplatin and 5-FU did not significantly alter the pharmacokinetics of oral ondansetron in cancer patients during the 5 days of chemotherapy. Oral bioavailability of ondansetron appeared to be greater in cancer patients than in healthy subjects.

Ondansetron absorption in adults: effect of dosage form, food, and antacids

Ondansetron is a competitive serotonin 5-HT3 receptor blocker that has proved useful in the prevention of emesis due to cisplatin and other cancer chemotherapeutic agents. In a randomized, open-label, crossover study in 24 healthy male subjects, the relative bioavailability of a single 8-mg tablet was compared with that of an 8-mg solution using the two one-sided t-tests. The tablet and solution formulations were bioequivalent, as confirmed by similarities in mean Cmax (26.3 vs 27.7 ng/mL), Tmax (1.79 vs 1.70 h), and AUC (166.0 vs 167.3 ng.h/mL) values. In another randomized, open-label, crossover study in 12 healthy male subjects, the bioavailability of an 8-mg ondansetron tablet administered 5 min after a standard meal was slightly but significantly greater than in fasted subjects, as indicated by comparative mean AUC values [201.4 ng.h/mL (fed) vs 172.5 ng.h/mL (fasted)]. Coadministration of a magnesium hydroxide/aluminum hydroxide antacid did not affect the bioavailability of the ondansetron tablet.

Validation of a liquid chromatography post-column derivatization assay for the determination of cisplatin in plasma

Method validation results are described for a cisplatin LC post-column derivatization assay. Cisplatin plasma samples were treated with acetonitrile and a citrate buffer solution to enhance cisplatin stability. Processed samples were analysed on a chemically generated anion exchange column using a customized post-column derivatization platform and refrigerated autosampler. The UV response was monitored at 290 nm. The retention time of cisplatin was 9 min. The assay was linear from 0.06 to 30.0 micrograms ml-1 (r > 0.998) with inter-run precisions (RSD) of 8.2% (n = 8), 5.9% (n = 8) and 4.0% (n = 8) for low (0.18 microgram ml-1), medium (1.5 microgram ml-1) and high (24.0 micrograms ml-1) quality control samples, respectively. The validated assay was used to monitor cisplatin levels in cisplatin drug interaction studies.

Comparison of the pharmacokinetics of an ondansetron solution (8 mg) when administered intravenously, orally, to the colon, and to the rectum

Ondansetron, an antagonist of the serotonin type 3 (5-HT3) receptor, is indicated for the treatment of chemotherapy-induced emesis. This study compares the pharmacokinetics, especially the bioavailability, of an ondansetron 8-mg solution when administered intravenously, orally, to the colon via nasogastric intubation, and to the rectum using a retention enema. Six healthy, male volunteers received ondansetron infused into the colon during the first treatment period. These subjects then received the remaining three treatments in random order, with a minimum 1-week washout period between treatments. Serial plasma samples were obtained for up to 24 hr after dosing in each treatment period. Absolute bioavailability after the oral dosing, colonic infusion, and rectal administration averaged 71 +/- 14, 74 +/- 26, and 58 +/- 18%, respectively. These values were not significantly different (P > 0.05). Values of Tmax and Cmax were also not significantly different among the nonparenteral routes. Mean absorption half-lives were 0.66, 1.1, and 0.75 hr after the oral, colonic, and rectal administrations, respectively. These results indicate that ondansetron is well absorbed in the intestinal segments studied including the upper small intestine, the colon, and the rectum and that sustained-release and suppository formulations of ondansetron are feasible.

Mechanism of intestinal absorption of ranitidine and ondansetron: transport across Caco-2 cell monolayers

We have investigated the transport of ranitidine and ondansetron across the Caco-2 cell monolayers. The apparent permeability co-efficients (Papp) were unchanged throughout the concentration range studied, indicating a passive diffusion pathway across intestinal mucosa. No metabolism was observed for ranitidine and ondansetron during the incubation with Caco-2 cell monolayers. Papp values for ranitidine and ondansetron (bioavailability of 50 and approximately 100% in humans, respectively) were 1.03 +/- 0.17 x 10(-7) and 1.83 +/- 0.055 x 10(-5) cm/sec, respectively. The Papp value for ranitidine was increased by 15- to 20-fold in a calcium-free medium or in the transport medium containing EDTA, whereas no significant change occurred with ondansetron, indicating that paracellular passive diffusion is not rate determining for ondansetron. Uptake of ondansetron by Caco-2 cell monolayers was 20- and 5-fold higher than that of ranitidine when the uptake study was carried out under sink conditions and at steady state. These results suggest that ranitidine and ondansetron are transported across Caco-2 cell monolayers predominantly via paracellular and transcellular pathways, respectively.

Clinical pharmacology of ondansetron in postoperative nausea and vomiting

Ondansetron is a 5-HT3 receptor antagonist which is effective and well tolerated as an antiemetic for emesis induced by cancer chemotherapy and radiation therapy, and in the prevention and treatment of postoperative nausea and vomiting. Ondansetron is rapidly absorbed after oral administration (tmax 1.9 h) with an absolute bioavailability of around 60%. Its terminal elimination half-life is 3.5 h and it is extensively hepatically metabolized. Plasma clearance is 0.38 litre h-1 kg-1 and volume of distribution is 1.8 litre kg-1. Plasma clearance is reduced by age (31% reduction) and hepatic failure (80% reduction in severe failure). In patients undergoing general anaesthesia there is a slight prolongation of terminal half-life, which is not of clinical significance. Ondansetron is very well tolerated in volunteer studies. Headache, mild abdominal pain, and constipation occur infrequently. There is no evidence for effects of ondansetron on cardiac function (electrocardiogram, cardiac output, blood pressure and heart rate), and haemostatic function in volunteers and patients. Respiratory depression induced during general anaesthesia is not potentiated by ondansetron. No drug interactions have been noted with temazepam, atracurium, alfentanil and alcohol in man. There are also no interactions seen in animal studies using pentobarbitone, morphine, neostigmine, prednisolone and diazepam.

Ondansetron metabolism and pharmacokinetics

Hepatic oxidative metabolism accounts for more than 95% of ondansetron clearance from the body. The major excreted metabolites are conjugates of 7-hydroxy or 8-hydroxyondansetron, which appear to contribute little to the activity of the parent drug. Ondansetron plasma clearance averages approximately 0.45 L/h/kg, is similar in young male volunteers and cancer patients undergoing cisplatin-based chemotherapy, and does not change significantly with repeated dosing. Clearance decreases with increasing age, whereas volume of distribution remains unchanged. The result is an increase in mean plasma half-life from 3.5 hours in young volunteers (18-40 years) to 5.5 hours in volunteers over 75 years of age. Clearance and volume of distribution are higher in young (7-12 years) cancer patients, resulting in a mean plasma half-life of 2.5 hours. Plasma clearance is slightly slower in females. Ondansetron clearance decreases and half-life increases in patients with severe hepatic insufficiency. Clearance may be enhanced in patients receiving known hepatic enzyme inducers. Because of large intersubject variability in clearance and the relative safety of ondansetron, adjustments in ondansetron dosing based on age or gender alone are not recommended. Ondansetron is rapidly and completely absorbed when administered as a tablet. A relationship exists between control of emesis and the area under the plasma concentration-time curve for ondansetron. All data collected to date support the thesis that ondansetron is a competitive antagonist of the 5-hydroxytryptamine (5-HT3) receptor in humans.

Disposition of bepridil in laboratory animals and man

1. The disposition and pharmacokinetics of bepridil (Bp) were studied in mouse, rat, rabbit, rhesus monkey, and man. Bp was essentially completely absorbed by all species. 2. Maximum plasma Bp concentrations were achieved within 2 h of drug administration. Linear but non-proportional, dose-related increases in the area under the curve (AUC) for plasma Bp vs. time were noted after increasing oral doses of Bp.HCl to rats (30-300 mg/kg) and monkeys (25-200 mg/kg). 3. Daily administration of Bp.HCl to rats (100 mg/kg per day for 15 days) and monkeys (200 mg/kg per day for 13 days) produced no statistically significant changes in Bp pharmacokinetic parameters. 4. Oral plasma clearance (CLp) of Bp was very low in man (ca. 0.93 l/h per kg) compared to experimental animals (14.8-63.8 l/h per kg). Terminal elimination half-lives were 1.5-2.0 h for mouse and rat, ca. 4.4 h for monkey and ca. 48 h for man. 5. Bp and a total of 12 metabolites were identified and quantified. Metabolite formation in the five species was adequately described by four interrelated pathways, namely, aromatic hydroxylation, followed by N-dealkylation, N-debenzylation, and N-acetylation. Metabolites produced by this pathway included 4-hydroxy-Bp, N-benzyl-4-aminophenol, 4-aminophenol, and N-acetyl-4-aminophenol. Comparison of the proposed pathways revealed qualitative similarity among species.

Age and gender effects on ondansetron pharmacokinetics: evaluation of healthy aged volunteers

Modest differences in the clearance of the 5HT3 antagonist, ondansetron, among different age groups were detected in two groups of healthy elderly volunteers, one group aged 61 to 74 years ("elderly") and the other 75 to 82 ("aged") years, in addition to young healthy subjects. Both a single 0.15 mg/kg intravenous dose and a single 8 mg oral dose were administered according to a randomized crossover design with a minimum 3-day washout period between treatments. Mean plasma clearance decreased (young, 0.349 L/hr/kg; elderly, 0.279 L/hr/kg; aged, 0.214 L/hr/kg; p less than 0.05) with increasing age. Volume of distribution at steady state was unaffected by age (young, 1.81 L/kg; elderly, 1.94 L/kg; aged, 1.71 L/kg), resulting in increases in mean plasma half-life (young, 3.4 hours; elderly, 4.5 hours; aged, 5.4 hours) and mean absolute bioavailability (young, 57%; elderly, 61%; aged, 69%) with increasing age. Female subjects cleared ondansetron more slowly than males (p less than 0.05), resulting in higher absolute bioavailability. Ondansetron was well tolerated by all age groups with no increase in the number of adverse events observed in older volunteers.

Relationships between ondansetron systemic exposure and antiemetic efficacy and safety in cancer patients receiving cisplatin

Single concentration estimators of systemic exposure to the serotonin type 3 receptor antagonist and antiemetic, ondansetron, were established in 55 cancer patients receiving cisplatin-based chemotherapy plus a daily regimen of ondansetron given every 4 h for 3 doses on each day of chemotherapy. Ondansetron plasma concentration measured 4 h after the first daily dose of ondansetron (C[4h]) proved to be a reliable index of AUC and hence of systemic exposure. In patients receiving dosages of cisplatin < 95 mg/m2, the risk of emesis was greatest among those with the lowest systemic exposure to ondansetron. Most patients (64%) experienced emesis if C[4h] was < 20 ng/ml, whereas emesis did not occur in any patient with C[4h] > 80 ng/ml. Among patients receiving very high dosages of cisplatin (> 95 mg/m2), comparable levels of systemic exposure were not totally effective in preventing emesis. For these patients, more ondansetron was required to block the greater emetic stimulus produced by higher doses of cisplatin. This difference reflects a shift in the log exposure versus response relationship, and is consistent with serotonin antagonism at a receptor. In contrast, reported side effects of ondansetron were not related to exposure.

Suppression of rat mammary cancer development by N-(4-hydroxyphenyl)retinamide (4-HPR) following surgical removal of first palpable tumor

A study was conducted to determine whether N-(4-hydroxyphenyl)retinamide (4-HPR) affects the development of new mammary tumors subsequent to the surgical removal of the first palpable tumor. Sprague-Dawley female rats were injected i.v. with 35 mg N-methyl-N-nitrosourea (MNU) per killogram body weight at 50 days of age. The first palpable tumor was removed when 0.3-0.5 cm in diameter, and the animals placed on diets containing either 1, 2 or 3 mmol 4-HPR/kg diet. Placebo diet without 4-HPR served as control. Some animals were killed at the time of surgical removal of the first tumor and whole mounts of the mammary glands were prepared. Moreover, five animals per group were bled at 1, 3 and 6 months after commencing the 4-HPR diet and the levels of 4-HPR and N-(4-methoxyphenyl)retinamide (4-MPR) were determined. 4-HPR decreased tumor multiplicity in a dose-related manner, but cancer formation was only inhibited at the 2 and 3 mmol levels of 4-HPR. Whole mounts of mammary glands of rats treated with MNU demonstrated the presence of nonpalpable microscopic tumors in addition to the palpable tumor which was excised. Plasma levels of 4-HPR and 4-MPR increased with increasing dietary dose levels, but a linear relationship was not evident. However, the increase in plasma 4-HPR was directly correlated with an increased survival of the tumor-bearing animals. The results indicate that 4-HPR effectively inhibits the appearance of subsequent mammary tumors following excision of the first palpable tumor, and thus may be suitable for use as a chemopreventive agent in patients at increased risk for breast disease.

Effect of tolmetin glycine amide (McN-4366), a prodrug of tolmetin sodium, on adjuvant arthritis in the rat

The glycine amide of tolmetin sodium (TGA) functions as a prodrug and was demonstrated to be more potent than the parent compound as an inhibitor of developing and established adjuvant arthritis in the female Lewis rat. In contrast, the glycine amide of indomethacin was less potent than indomethacin. The superiority of TGA relative to tolmetin sodium in alleviating this condition was demonstrated by inhibition of paw swelling and reduction of the degenerative bone changes that are associated with the progression of this chronic animal model of rheumatoid arthritis in humans. These properties were not evident when equimolar mixtures of tolmetin sodium and glycine were administered concurrently. Pharmacokinetic analyses revealed that TGA was absorbed completely and hydrolyzed to tolmetin in the female adjuvant arthritic rat. The combined effects of absorption, distribution and hydrolysis of TGA produced lower peak plasma tolmetin levels than an equivalent dose of tolmetin sodium, but plasma concentrations were sustained for a longer period of time contributing to an apparent increase in potency. Furthermore, TGA displayed a decreased propensity to cause gastrointestinal irritation compared to tolmetin sodium. Several additional amino acid amides of tolmetin were similar to the glycine amide in exhibiting increased potency and reduced gastrointestinal toxicity in comparison to equivalent doses of tolmetin sodium.

Teratogenicity of N-(4-hydroxyphenyl)-all-trans-retinamide in rats and rabbits

N-(4-hydroxyphenyl)-all-trans-retinamide (HPR) has potential efficacy in the treatment of dermatologic, arthritic, and neoplastic disorders. The teratogenicity of such a compound is of special concern in light of the known adverse effects of retinoids, in general, on the developing conceptus. In these studies, Sprague-Dawley rats and New Zealand White rabbits were treated orally from gestation days 6 to 15 and 6 to 18, respectively, with 0, 20, 125, or 800 mg/kg/day of HPR. In rat fetuses, low incidences of hydrocephaly (mid- and high-dosage groups) were observed. Fetal tissue (ng/g) and maternal plasma (ng/ml) concentrations of HPR, its major metabolite (N-[4-methoxyphenyl] retinamide [MPR]) and retinol were determined in separate groups of similarly-treated rats 3 h following the last dose on gestation day 15. Fetal tissue concentrations of HPR and MPR were approximately one-half maternal plasma concentrations. A dose related reduction in maternal plasma and fetal tissue concentrations of retinol were also observed. In mid- and high-dosage rabbit fetuses, a dose-related increase in the incidence of dome-shaped head was observed. Subsequent skeletal evaluation revealed delays in skull bone ossification and a widening of the frontal and frontoparietal sutures. Microphthalmia was also observed in two high-dosage fetuses. A dose-dependent and statistically significant reduction in maternal plasma retinol levels was observed across all dosage groups.

Evaluation of drug absorption and presystemic metabolism using an in situ intestinal preparation

An in situ rat intestinal preparation was modified to include portal and jugular venous blood collection techniques as well as sampling from the intestinal lumen. Viability could be maintained for 3 h. The utility of the preparation was examined by studying the disposition of four model drugs, each with differing characteristics with respect to absorption and presystemic metabolism. Haloperidol (4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4-fluorophenyl)-1- butanone), a reference compound used for model development, disappeared from the intestinal lumen with a half-life of 14 +/- 3 min. When the antiarthritic agent, tolmetin sodium (sodium 1-methyl-5-(4-methylbenzoyl)-1H-pyrrole-2-acetate dihydrate), was studied in the preparation, it was rapidly absorbed (t1/2 for disappearance from the intestinal lumen = 8 min), achieved plasma concentrations comparable to in vivo data, and underwent little presystemic elimination. In contrast, fenoctimine sulfate (4-(diphenylmethyl)-1-[(octylimino)methyl]piperidine sulfate), an antisecretory compound, disappeared more slowly from the intestinal lumen (t1/2 = 60 min), was present in portal plasma, but was not detected in systemic plasma. Extensive hepatic first-pass elimination of fenoctimine was evident. Tolmetin glycine amide (N-([1-methyl-5-(4-methylbenzoyl)-1H-pyrrol-2-yl]acetyl)glycine), a tolmetin prodrug, disappeared from the intestinal lumen very slowly (t1/2 approximately 3 h) compared with the other agents tested. It was determined that this drug was being hydrolyzed presystemically to tolmetin by the intestinal mucosa and the liver. These results establish the utility of this intestinal preparation for studying drug absorption and presystemic elimination.

Plasma protein binding of bepridil

The binding of the calcium-channel blocking agent, bepridil HCl (Vascor), to plasma proteins was investigated using radiolabeled bepridil and equilibrium dialysis. Greater than 99.7% of added bepridil-14C was found to freshly collected human plasma. The binding was characterized by a saturable high-affinity site (KD = 32 ng/mL = 87 nM) on alpha1-acid glycoprotein (AAG) or on an AAG-human serum albumin complex and lower affinity binding sites on albumin and other plasma macromolecules. Bepridil that is not bound to plasma proteins is extensively distributed into erythrocytes as evidenced by a red blood cell to free drug distribution coefficient of 71 +/- 7. Despite this high value, the blood to plasma ratio of bepridil averaged only 0.67 in humans, indicating that most of the circulating drug is bound to plasma proteins. Bepridil protein binding was not affected by additions of nonesterified fatty acids. Free fractions of bepridil were enhanced by addition of verapamil, nifedipine, diltiazem, disopyramide, and warfarin but only at concentrations above those achieved clinically. Bepridil was also displaced by the plasticizer, tris-(2-butoxyethyl)phosphate. Plasma obtained from a small number of angina patients prior to bepridil administration showed no differences in ability to bind bepridil compared with plasma obtained from healthy subjects.

Stability of Aroclor 1254-induced rat liver postmitochondrial supernatant (S-9) following long-term storage (-75 degrees C)

The stability of Aroclor 1254-induced rat liver postmitochondrial supernatant (S-9) over a 5-year period was investigated in a retrospective study. S-9 was uniformly prepared at 6-month intervals, and aliquots were stored at -75 degrees C. The protein and cytochrome P-450 content of these lots of S-9 were very similar, and no differences attributable to duration of storage were observed in the activities of ethoxycoumarin O-deethylase, aniline hydroxylase, cytochrome P-450 reductase or aryl hydrocarbon hydroxylase. There was no decrease following 5 years of storage in the ability of S-9 to activate 2-aminoanthracene, as measured in the Ames test (TA98), but there was a notable reduction following more than 1 year of storage in the ability of the S-9 to generate Ames test activity with benzo(a)pyrene. Based on the results of these studies, S-9 prepared and stored under these conditions appears to be suitable for use in vitro genotoxicity assays for at least 1 year.

Zomepirac--aspirin interactions in man

The pharmacokinetic interaction between zomepirac and aspirin was studied in 12 healthy males who received a single dose of 100 mg zomepirac sodium on days 1 and 5 and 975 mg aspirin every 6 hours on days 2 to 5. The results indicated that in the presence of salicylate, the peak concentration of zomepirac was depressed; peak time, AUC(0-24 hr), and clearance of total drug remained unchanged. Percentage unbound zomepirac was increased twofold. In the presence of zomepirac, the peak concentration and AUC of salicylate were increased and clearance decreased. The data suggest that zomepirac and salicylate compete with each other for the enzymes and/or cofactors involved in glucuronidation. This competition for metabolic clearance offsets the consequences of the zomepirac-salicylate interactions at the plasma protein binding sites. However, in light of increased unbound zomepirac as well as decreased clearance of unbound drug, concomitant therapy of zomepirac and aspirin is not advised.

Alterations of drug-induced toxicity in the mouse lymphoma assay by a rat hepatic microsomal metabolizing system (S-9)

Large differences in induced cellular toxicity were observed in the presence or absence of a rat liver microsomal metabolizing system (S-9) during drug testing in the mouse lymphoma assay. After studying the fate of three drugs in this test system, several mechanisms were demonstrated whereby S-9 reduced cellular toxicity. For N-(4-hydroxyphenyl)retinamide (HPR), fenoctimine sulfate and methyl palmoxirate, the drug concentrations (EC50) in the presence of S-9 were, respectively, 11.5, 14.3 and 4.1 times the concentrations required to achieve comparable levels of toxicity in the absence of S-9. HPR was metabolized by the S-9 and sequestered in the microsomal membranes. This was associated with a marked reduction in the cellular accumulation of the drug. The reduced toxicity of fenoctimine sulfate in the presence of S-9 was associated with extensive biotransformation to polar metabolites. This was accompanied by a reduction of radioactivity associated with the cells from 5.7% to 0.4% of the administered drug. Methyl palmoxirate was rapidly converted to its acid, palmoxirate, by horse serum enzymes present in the treatment medium. This provides an example of metabolism by a test system component other than the S-9 or lymphoma cells. The reduced toxicity of this drug in the presence of S-9 was attributed to further metabolism of palmoxirate and a reduction of the proportion of total radioactivity associated with the cells from 3.1% to 0.4%. These results emphasize the need for pilot toxicity studies, especially when components of the test system are varied, to assess the effect of drug concentration on the toxic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of uremia and hemodialysis on the plasma protein binding of tolmetin

Binding of the nonsteroidal anti-inflammatory drug, tolmetin, to plasma from uremic patients before hemodialysis and from healthy subjects was compared using microequilibrium dialysis techniques. The percent age of free tolmetin was 2-15 times greater in plasma from uremic patients (1.33-3.08%) than in plasma from healthy volunteers (0.37-0.63%) at all three concentrations of the drug studied (0.5, 5 and 50 micrograms/ml). The reduced plasma binding of tolmetin in plasma from uremic patients was associated with significantly higher dissociation constants for the high-affinity tolmetin binding site on plasma albumin. When added at concentrations of 2.0 mM oleic, stearic and palmitic acids, 3 representative nonesterified fatty acids (NEFA) were found to significantly enhance tolmetin binding to plasma proteins. No differences in total plasma NEFA concentrations were observed between uremic patients before hemodialysis and healthy subjects. However, higher total NEFA concentrations in plasma from uremic patients after hemodialysis were accompanied by increased tolmetin binding. Possible NEFA effects on tolmetin binding could not be dissociated from other influences, such as the removal of endogenous binding inhibitors during hemodialysis.

Influence of uremia, hemodialysis, and nonesterified fatty acids on zomepirac plasma protein binding

Zomepirac binding to plasma of uremic patients before hemodialysis and to that of healthy subjects was compared. Unbound zomepirac in plasma of uremic patients averaged 3.7% to 4.0% of the 14C-zomepirac added (0.2, 2, and 20 micrograms/ml). This was more than the percentage of unbound zomepirac observed when the same 14C-zomepirac concentrations were dialyzed against plasma from healthy subjects (mean 1.3% to 1.4%). Plasma albumin from uremic patients appeared to have lower apparent binding affinity for zomepirac. Oleic, stearic, and palmitic acids, when added to plasma at concentrations of 2.0 mM, markedly reduced zomepirac free fraction, but, there were no significant differences between uremic and normal plasma in total nonesterified fatty acid (NEFA) concentrations after equilibrium dialysis. Thus, plasma NEFAs do not contribute to the differences in zomepirac plasma binding between normal and uremic plasma. Hemodialysis increased zomepirac binding to plasma of uremic patients, but NEFA concentrations were also increased in hemodialyzed plasma. Enhanced zomepirac binding by NEFAs could not be differentiated from other effects of hemodialysis, such as the removal of endogenous inhibitors of drug plasma protein binding. The binding of zomepirac was not affected by its three known metabolites: zomepirac glucuronide, hydroxyzomepirac, and 4-chlorobenzoic acid.

The inhibitory effect of propranolol pretreatment on its own metabolism in the rat

Repetitive oral administration of propranolol to rats (100 mg/kg/day for 5 days) resulted in a marked inhibition of hepatic microsomal metabolism of propranolol when incubated at low initial substrate concentrations (less than 2 microM). Associated with the inhibition of propranolol metabolism was a significant reduction in metabolites derived from naphthalene ring oxidation and an increased formation of N-desisopropylpropranolol. In vivo studies after propranolol pretreatment resulted in: an increased hepatic concentration and an increased systemic availability of propranolol; a decreased hepatic and plasma concentration of polar metabolites; and an increased plasma concentration of metabolites derived from propranolol N-dealkylation. Propranolol was converted both in vitro and in vivo by a hepatic microsomal mixed-function oxidase to a reactive metabolite capable of covalently binding with microsomal macromolecules. We propose that selective covalent binding of the reactive intermediate to the molecular form of cytochrome P-450 that ring hydroxylates propranolol would account for the marked inhibition of propranolol metabolism in vitro and for the increased systemic availability of propranolol in vivo after pretreatment.

Effect of dose and uremia on plasma and urine profiles of propranolol metabolites

The relationship between plasma levels of 4 propranolol metabolites--naphthoxylactic acid (NLA), 4-hydroxypropranolol (4-OH), naphthoxyacetic acid (NAA), and propranolol glycol (PG)--and propranolol plasma levels was determined in healthy, adult male subjects after increasing single oral doses of propranolol. NLA was present at plasma levels 6 to 25 times that of propranolol. More than 90% of circulating NLA was in the plasma fraction, where it was 95% protein bound. The ratio of plasma concentrations of the pharmacologically active metabolite 4-OH to propranolol approached unity 0.5 hr after propranolol, 160 mg or 320 mg orally, but fell rapidly. Plasma levels of NAA were in the same range as propranolol, especially as time progressed. PG circulated at plasma levels less than 12% of propranolol. As oral doses of propranolol were increased from 20 to 320 mg, there was a decrease in intrinsic plasma clearance (Cli) from 425 to 200 1/hr. Half-life rose from 3 to 5 hr. Urinary recovery of 4-OH fell as Cli rose. Urinary recovery of propranolol conjugates, NLA, and N-desisopropylpropranolol (NDIPP) rose as Cli fell. Our results suggest that naphthalene ring oxidation of propranolol represents a high-affinity low-capacity enzymatic pathway(s) that plays an important role in the extensive hepatic extraction of propranolol after small doses orally. Plasma NLA and plasma NAA were determined before and after hemodialysis in 14 uremic patients receiving long-term propranolol therapy. Mean plasma NLA was 4.372 ng/ml, and mean plasma NAA level was 238 ng/ml when mean plasma propranolol level was 15 ng/ml.

The inhibition of rat hepatic microsomal propranolol metabolism by a covalently bound reactive metabolite

Repetitive oral propranolol administration to rats (100 mg/kg/day for 5 days) resulted in an 80% inhibition of propranolol Type I spectral binding capacity. This paralleled a similar reduction in the microsomal metabolism of propranolol when incubated at low substrate concentrations (less than 2 microM). Propranolo was converted both in vitro and in vivo by a microsomal mixed function oxidase to a reactive intermediate metabolite capable of covalently binding with microsomal macromolecules. We propose that covalent binding of the intermediate to the catalytic site of a form(s) of cytochrome P-450 that metabolizes propranolol would account for the marked inhibition of propranolol metabolism observed following propranolol pretreatment.

Measurement of propranolol, 4-hydroxypropranolol and propranolol glycol in human plasma

An HPLC method for the quantitative determination of propranolol, 4-hydroxypropranolol, and propranolol glycol in human plasma is described. The limits of sensitivity for the method were: 1 ng/ml propranolol; 5 ng/ml 4-hydroxypropranolol; and 1 ng/ml propranolol glycol. Data obtained from 6 healthy volunteers given a single 160 mg oral dose of propranolol revealed mean (+/- SEM) peak plasma levels of 31 +/- 10 ng/ml for 4-hydroxypropranolol and 9 +/- 2 ng/ml for propranolol glycol. These plasma levels were less than the peak concentrations recorded for propranolol (123 +/- 34 ng/ml. The rates of plasma decay of these two metabolites were greater than that observed for propranolol.

Determination of propranolol and six metabolites in human urine by high-pressure liquid chromatography

A method for the determination of propranolol and six of its metabolites, as well as their glucuronide and/or aryl sulfate conjugates in human urine is described. Propranolol and its basic and neutral metabolites are extracted into ether at pH 9.8, evaporated to dryness, reconstituted, separated on a reversed-phase, high-pressure liquid chromatographic system and quantitated using fluorescence detection. The aqueous urine aliquot is then made acidic and the acid metabolites extracted and measured using similar methods. The presence of 2% sodium metabisulfite in all urines collected is essential to ensure the stability of 4-hydroxy-propranolol during collection and storage. Preliminary data is presented from 24-h urine samples collected from three patients chronically receiving propranolol.

The contribution of propranolol metabolites to the fluorometric assay of propranolol in human plasma

1. Studies were undertaken to determine the fluorescent properties of several propranolol metabolites under the conditions of the fluorometric propranolol assay. Of the metabolites studied, propranolol glycol and N-desisopropylpropranolol had significant molar fluorescent coefficients relative to propranolol (72 and 79% respectively). N-desisopropylpropranolol was extracted with the same efficiency as propranolol (greater than 90%) wheras the glycol metabolite had only 34% extraction efficiency. Addition of each metabolite to samples of human plasma containing propranolol produced the predicted increase in fluorescent intensity. 2. Gas chromatographic analysis of plasma collected from 22 hypertensive patients chronically receiving oral propranolol revealed low concentrations of propranolol glycol and N-desisopropylpropranolol relative to propranolol. The results of these studies indicate that fluorescent metabolites of propranolol are not present in sufficient concentration to significantly interfere with the fluorometric assay of propranolol.

Studies on the uptake and binding of propranolol by rat tissues

The tissue distribution of propranolol after i.v. administration (1.5 and 7.5 mg/kg) was studied in rats. Lung, brain and kidney showed extensive propranolol tissue binding. Propranolol uptake by lung seemed to be a saturable process. In contrast to the above tissues, liver propranolol concentrations remained low over the time period of study. An increase in the propranolol T1/2 was noted at the high dose and seemed to result from reduced systemic clearance and an increase in the apparent volume of distribution. Microsomal and mitochondrial fractions from several tissues contained substantial amounts of propranolol after i.v. administration and in vitro incubation with homogenates. Cytosol proteins did not bind significant amounts of propranolol. Equilibrium dialysis studies with rat liver mitochondrial and microsomal fractions revealed both high affinity, low capacity propranolol binding sites and low affinity, high capacity sites. At low concentrations, propranolol interaction with rat liver microsomes produced a type I difference spectrum with high affinity binding of similar magnitude to that observed with equilibrium dialysis. Higher concentrations of propranolol produced a saturable shift in the difference spectra with reduced binding affinity for propranolol. Results from these studies indicate that particulate fractions from several tissues contribute to the extensive tissue binding of propranolol.