Pharmacokinetics and safety of multiple doses of daptomycin 6 mg/kg in noninfected adults undergoing hemodialysis or continuous ambulatory peritoneal dialysis

AIMS

The purpose of this study was to characterize the pharmacokinetics and tolerability of daptomycin in subjects undergoing hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD).

METHOD

16 noninfected adults on stable dialysis regimens were enrolled. Daptomycin 6 mg/kg was administered after HD during a 48 h - 48 h - 72 h dialysis week or before a CAPD dwell time over a 48 h - 48 h - 48 h dialysis week. Pharmacokinetic parameters were described, and adverse events were monitored.

RESULTS

Daptomycin had mean half-lives in HD subjects of 28.0 and 35.9 h on Days 1 and 5, with corresponding values of 25.8 and 26.7 h in CAPD subjects. Steady state was reached by Day 5 in both groups. At steady state, HD subjects had a mean peak plasma concentration (Cmax) of 81.6 µg/ml and a mean trough concentration of 15.3 µg/ml (on Day 8). In CAPD subjects, Cmax was 93.9 µg/ml and the trough was 20.7 µg/ml (on Day 7). Adverse events were experienced by 71.4% and 66.7% of HD and CAPD subjects, respectively. Most of these were mild or moderate in intensity; however, 2 subjects experienced muscle spasms and mild creatine phosphokinase elevations although neither event was considered to be related to study drug.

CONCLUSIONS

The pharmacokinetics of daptomycin 6 mg/kg support a dosing regimen of every 48 h in CAPD and thrice-weekly dosing in HD.

A pilot study of high-dose short duration daptomycin for the treatment of patients with complicated skin and skin structure infections caused by gram-positive bacteria

BACKGROUND

Methicillin-susceptible and -resistant (MRSA) Staphylococcus aureus are significant causes of complicated skin and skin structure infections (cSSSI). The bactericidal antibiotic daptomycin is approved for gram-positive cSSSI at 4 mg/kg/day for 7-14 days, but the optimal dose level and duration of therapy have not been firmly established. This pilot study evaluated the efficacy and safety of daptomycin at 10 mg/kg every 24 h for 4 days [high-dose short duration (HDSD) regimen] vs. standard of care therapy with vancomycin or semi-synthetic penicillin for the treatment of cSSSI.

METHODS

This was a semi-single blind, randomised, multicentre, comparative trial. The primary efficacy end-point was the clinical response 7-14 days posttherapy.

RESULTS

One hundred patients were randomised; 48 in each arm were treated. The treatment groups were well balanced with respect to demographics, comorbidities and the type of infection (75% because of MRSA). Overall, clinical success rates were 75.0% (36/48) for daptomycin and 87.5% (42/48) for comparator (95% confidence interval for the difference: -27.9, 2.9). The median duration of comparator therapy was 8 days. Two comparator patients and no daptomycin patients experienced treatment-related serious adverse events requiring hospitalisation.

CONCLUSION

We found that the HDSD regimen had a safety profile similar to that seen in previous studies. Although the differences were not statistically significant, clinical success rates for comparator were higher than for daptomycin. In post hoc analyses HDSD daptomycin performed better in some subgroups (e.g. outpatients) than in others (e.g. certain MRSA infections). These observations require confirmation in larger trials.

The pharmacokinetic and pharmacodynamic characteristics of a long-acting growth hormone (GH) preparation (nutropin depot) in GH-deficient adults

A pharmacokinetic-pharmacodynamic study of a long-acting GH [Nutropin Depot; somatropin (rDNA origin) for injectable suspension] was performed in 25 patients with adult GH deficiency. Single doses of 0.25 mg/kg and 0.5 mg/kg, based on ideal body weight, were administered sc. After either dose, serum GH concentrations rose rapidly in both sexes. In men, the lower dose maintained serum IGF-I levels within 1 SD of the mean for age and sex for 14-17 d; the higher dose raised IGF-I levels 2 SD above the mean. In most women, all of whom were receiving oral estrogen, the lower dose did not normalize IGF-I levels; the higher dose maintained IGF-I near the mean for approximately 14 d. Increases in IGF binding protein-3 and acid-labile subunit levels were observed in both sexes; however, a sex-related difference was not obvious. Fasting glucose and insulin concentrations were transiently elevated in men receiving the higher dose. Patients tolerated the injections well. We concluded that a single injection of Nutropin Depot at these doses in patients with adult GH deficiency increased serum IGF-I to within normal limits for 14-17 d. Estrogen-treated women required approximately twice the dose needed in men to produce comparable IGF-I concentrations.

A pharmacokinetic/pharmacodynamic study of controlled-release oxycodone

A single-dose, analytically blinded, randomized, crossover study was conducted in 22 healthy male volunteers to compare the bioavailability of one 20 mg with two 10 mg controlled-release (CR) oxycodone tablets. In addition, pharmacodynamic effects were assessed using both objective and subjective measures for up to 48 hr after dosing. The two treatments were bioequivalent, with comparable rates (Cmax of one 20 mg tablet was 109% of two 10 mg tablets; 90% confidence limits: 98.4%-120%) and extents (AUC0-infinity: 107%; 100%-114%) of absorption. In addition, no significant differences between tablets were found for mean values of Tmax, T/12abs, or T/12elim. Correlations between plasma oxycodone concentrations and most pharmacodynamic measures were significant. The strongest correlations were observed for pupil size (r = -0.53) and subjects' assessment of drug effect (r = 0.53), with changes in plasma concentration accounting for more than 25% of the observed changes in these variables. This study demonstrated bioequivalence of two 10 mg and one 20 mg CR oxycodone tablet, with significant correlation between plasma oxycodone concentrations and pharmacodynamic effects in normal volunteers.

Differential effects of food on the bioavailability of controlled-release oxycodone tablets and immediate-release oxycodone solution

The effects of a high-fat meal on the bioavailability of oxycodone hydrochloride, administered as a recently developed 40 mg controlled-release (CR) tablet or a 20 mg immediate-release (IR) solution, were evaluated in a randomized crossover study in 22 normal male and female subjects. Serial blood samples were collected for 36 h after dosing and analyzed for oxycodone by a validated method using gas chromatography/mass spectrometry. There was no significant food effect with CR oxycodone as judged by 90% confidence interval (CI) analysis of AUC0-infinity and Cmax values under fed and fasted conditions. For the IR solution, both oxycodone bioavailability and peak plasma oxycodone concentration were significantly altered by consumption of the high-fat meal, with the mean value for AUC0-infinity increasing to 120% (CI = 109-132%) and the mean value for Cmax decreasing to 82% (CI = 47-91%) of values observed in the fasted condition. Adverse events reported for both formulations were mostly mild to moderate in severity and typical of those observed with opioids.

Pharmacokinetic-pharmacodynamic relationships of controlled-release oxycodone

Plasma concentrations of oxycodone, oxymorphone, and noroxycodone were determined after administration of 20 mg oral controlled-release oxycodone tablets to four subject groups: young (aged 21 to 45 years) men, elderly (aged 65 to 79 years) men, young women, and elderly women. Area under the oxycodone and noroxycodone concentration-time curve (AUC) values were comparable among the four groups. Compared with oxycodone, the oxymorphone AUC values were small, with significant differences between subject groups. AUC values were also calculated for the pharmacodynamic variable "drug effect," scored on a 100 mm visual analog scale. The two groups with the highest oxycodone AUC values (young and elderly women) had the lowest oxymorphone AUC values and the greatest drug effect AUC values. The two groups with the lowest oxycodone AUC values (young and elderly men) had the highest oxymorphone AUC values and the lowest drug effect AUC values. These results support oxycodone, and not oxymorphone, as being primarily responsible for pharmacodynamic and analgesic effects.

Nephrotoxicity of pravadoline maleate (WIN 48098-6) in dogs: evidence of maleic acid-induced acute tubular necrosis

Single oral administration of pravadoline maleate (WIN 48098-6), the maleic acid salt of WIN 48098, induced acute tubular necrosis (ATN) in male and female beagle dogs at dosages > or = 40 mg/kg (WIN 48098 base (31 mg/kg) and maleic acid (9 mg/kg)). Subsequent oral studies were conducted with equimolar dosages of maleic acid and WIN 48098-7, the ethanesulfonate salt of WIN 48098, to determine the nephrotoxic moiety of WIN 48098-6. ATN was observed for dogs given only maleic acid at single oral dosages > or = 9 mg/kg. This result provided evidence that maleic acid was responsible for the nephrotoxicity observed in dogs given single oral dosages of WIN 48098-6. The induction of maleic acid-related nephrotoxicity in dogs may confound the interpretation of toxicologic studies of maleic acid salts of basic pharmaceutics, if the dosage of test article results in the delivery of dosages of maleic acid > or = 9 mg/kg. Furthermore, the results of these studies underscore the importance of establishing maximum no-observed-effect dosages and target organ toxicity profiles for acids and bases that are commonly used in the development of salts of pharmaceutics.

Subchronic oral and intravenous (i.v.) safety evaluation and pharmacokinetics in rats and dogs of ipazilide fumarate (Win 54, 177-4), an antiarrhythmic agent

Ipazilide fumarate (Win 54, 177-4) is a chemically novel antiarrhythmic agent that prolongs ventricular refractoriness and possesses antiectopic activity. Subchronic (29 days) nonclinical safety evaluation of ipazilide was conducted following oral and iv administration in Sprague-Dawley rats (20-320 mg/kg oral and 1.25-10 mg/kg iv) and 14 and 28 days in beagle dogs (3-30 mg/kg oral and 2.5-20 mg/kg iv). The pharmacokinetic parameters of ipazilide indicate that ipazilide is absorbed (tmax less than or equal to 1 hr) in fasted rats and dogs following single and repeated oral administrations. The apparent elimination half-life in the two species is approximately 1 hr (except in rats at a dosage of 320 mg/kg), suggesting rapid clearance. Increases in liver weights (rats 320 mg/kg) accompanied by the observation of centrilobular hypertrophy of hepatocytes were considered an expression of an adaptive metabolic response of the liver to ipazilide and may be associated with the induction of microsomal enzymes. Duodenal villous atrophy and epithelial hyperplasia (rats, 80 and 320 mg/kg) were interpreted to represent an irritant response to the drug. Local irritation was also observed at the injection site in rats and dogs. Dogs tolerated the oral and the iv administration of ipazilide at dosages of up to 30 and 20 mg/kg, respectively. Despite emesis (oral dogs), which was reduced in frequency following repeated treatment over several weeks, plasma levels in treated dogs (i.e., Cmax 4-5 micrograms/ml) were approximately twice that required to convert spontaneous arrhythmias in the conscious dog model 24 hr after myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of a novel steroidal androgen receptor antagonist (Win 49596) in human plasma using solid-phase extraction and high-performance liquid chromatography with ultraviolet detection

A rapid, sensitive and selective method was developed for the determination of a novel steroidal androgen receptor antagonist (Win 49596, I) in human plasma. The procedure involved extraction from plasma using a solid-phase phenyl support and elution directly onto a reversed-phase C8 column using a mobile phase consisting of 0.2 mol/l sodium acetate buffer at pH 7-acetonitrile (45:55, v/v). Drug was monitored by ultraviolet detection at a wavelength of 238 nm. Linear responses were observed for standards over the range 0.01-5.0 micrograms/ml. The minimum quantifiable level was 0.02 microgram/ml, using a 0.5-ml plasma sample. The precision was 5.5% and the accuracy ranged from -9.4% to 0.23%. The analytical method has been used to quantify I in plasma from dogs and rats and is projected for use with human plasma from clinical trials.

Effect of the acetylator phenotype on amrinone pharmacokinetics

Ten healthy male subjects were phenotyped with isoniazid for their acetylator status and then received intravenous amrinone at a dose of 75 mg during a period of 10 minutes. Blood samples were drawn at specified times during a 24-hour period after dosing. Plasma concentrations of amrinone were determined by a specific HPLC method. The plasma concentration data were fitted to a biexponential model by nonlinear regression. The mean apparent first-order elimination t1/2 for amrinone in the slow acetylators was 4.4 hours, whereas it was 2.0 hours in the fast acetylators (P less than 0.05). There was little difference in the volume of distribution at steady state. Clearance was lower in the slow acetylators, 16.6 L/hr, than in the fast acetylators, 37.2 L/hr (P less than 0.05). The AUC was higher for the slow acetylators, 4.96 micrograms X hr X ml-1, than for the fast acetylators, 2.20 micrograms X hr X ml-1 (P less than 0.01). Concentrations of amrinone and its N-acetyl metabolite in the urine from each volunteer were determined. The ratio of N-acetylamrinone to amrinone was calculated and, as expected, the fast acetylators had a higher ratio than did the slow acetylators (P less than 0.01).

Use of WIN 51711 to prevent echovirus type 9-induced paralysis in suckling mice

The systemic efficacy of the antipicornavirus agent WIN 51711 was assessed in suckling mice infected with echovirus type 9 (Barty strain). Single, daily intraperitoneal doses of WIN 51711 as low as 10 mg/kg significantly (P less than .01) slowed the rate of onset of echovirus-induced paralysis and reduced the number of paralyzed animals. Intraperitoneal administration beginning 2 hr before infection or 48 hr after infection was equally effective in preventing paralysis. Oral administration of WIN 51711 twice daily beginning 72 hr after infection was the most-effective dosage regimen, with doses as low as 3 mg/kg preventing paralysis in 75% of the animals. Titers of virus in asymptomatic mice on day 6 after infection were reduced by up to 4.75 log pfu in WIN 51711-medicated mice when compared with placebo. Maximal concentrations of WIN 51711 in adult mice after oral medication with a 100 mg/kg dose were 24.3, 21.5, 10.4, 9.8, 6.9, and 4.1 micrograms/g in heart, kidney, brain, liver, serum (micrograms/ml), and muscle, respectively at 0.5-1.0 hr after medication.

Pharmacokinetics of the bipyridines amrinone and milrinone

The pharmacokinetics of milrinone were studied in sequential ascending doses in New York Heart Association Class III and IV patients receiving oral and intravenous medication. The parameters determined after parenteral administration were estimated by fitting the plasma concentration data to an open two-compartment body model. After oral medication, regression-independent parameters were determined. After either oral or parenteral administration of milrinone, plasma levels were dose dependent and the drug had an apparent first-order terminal elimination half-life of approximately 2 hr. The apparent volume of distribution was approximately 400 to 500 ml/kg, and total body clearance was approximately 130 ml/kg/hr. These values obtained in patients receiving milrinone were compared with those obtained for milrinone in volunteers, as well as those noted with the other inotropic bipyridine, amrinone. Milrinone's elimination from the blood stream patients was slower that that in normal healthy subjects and faster than amrinone's elimination in patients with congestive heart failure. Milrinone's pharmacokinetic parameters in these patients were unchanged after approximately 30 days of continuous oral medication.

Analysis of amifloxacin in plasma and urine by high-pressure liquid chromatography and intravenous pharmacokinetics in rhesus monkeys

An analytical method for the quantitation of amifloxacin, 6-fluoro-1,4-dihydro-1-(methylamino)-7-(4-methyl-1-piperazinyl)-4-oxo-3- quinolinecarboxylic acid, in plasma and urine has been developed. The method involves extraction with chloroform, back-extraction into 0.1 M sodium hydroxide, and subsequent analysis by reverse-phase high-pressure liquid chromatography with UV detection. The precision of the assay calculated as the overall standard deviation was +/- 4.9% in plasma and +/- 1.1% in urine. The range of mean percent differences from the nominal values was used as an estimate of accuracy and was 93.6 to 103% of the nominal values in plasma and 95.2 to 107% of the nominal values in urine. The minimum quantifiable levels were 0.032 micrograms/ml in plasma and 2.7 micrograms/ml in urine. The methods were employed in a pharmacokinetic analysis of amifloxacin after intravenous administration to rhesus monkeys. The decline in drug plasma levels was described by a biexponential process with mean rates of 8.4 h-1 and 0.32 h-1 with corresponding half-lives of ca. 5 min and 2.2 h. Amifloxacin was rapidly excreted, with ca. 53% of the dose appearing in the urine within 48 h after medication. The mean renal clearance +/- standard deviation was 4.4 +/- 1.0 ml X kg-1 X min-1 and is compatible with passive glomerular filtration in this species.

Metabolism and disposition of amifloxacin in laboratory animals

Sprague-Dawley rats received [14C]amifloxacin mesylate either orally or intravenously at 20 mg (base equivalent) per kg. Blood radioactivity peaked at 0.5 h after oral administration and was equivalent to 7.54 micrograms/ml for males and 6.73 micrograms/ml for females. After intravenous administration to rats, 52.5% of the dose was recovered in the urine of males and 45.3% in the urine of females within 72 h. The corresponding values after oral administration were 50.8% for males and 37.2% for females. The remainder of the dose was recovered in the feces. After intravenous administration of [14C]amifloxacin mesylate at 10 mg (base equivalent) per kg to female rhesus monkeys, 80.3% of the radioactivity was excreted in the urine at 24 h. The apparent first-order terminal elimination half-life of intact amifloxacin in plasma was 2.3 h; radioactivity in plasma was eliminated more slowly. Male rats excreted 26.2% of the dose in the urine as amifloxacin and 17.8% as the piperazinyl-N-oxide derivative of amifloxacin after intravenous administration. The corresponding amounts for female rats were 29.0% as amifloxacin and 7.8% as the piperazinyl-N-oxide metabolite. Similar excretion profiles were observed after oral administration. After intravenous administration, female monkeys excreted 54.5% of the dose in the urine as amifloxacin, 12.9% as the piperazinyl-N-desmethyl metabolite, and 5.6% as the piperazinyl-N-oxide during the first 12 h. In contrast, there was no evidence of the piperazinyl-N-desmethyl metabolite in rats.

Relative bioavailability and pharmacokinetics: a combination of pentazocine and acetaminophen

The relative bioavailability and pharmacokinetics of a combination product containing pentazocine and acetaminophen were studied in 20 healthy human males. Each subject, in a single-dose three-way crossover design, received two different preparations containing 50 mg of pentazocine (as base) and 1300 mg of acetaminophen either as capsule-shaped tablets or as a solution. Plasma concentrations of pentazocine and acetaminophen were determined from 0.25 to 12 h following oral administration. The plasma data for both compounds in the tablet formulation were described by an open one-compartment body model with first-order absorption. The average (+/- SD) bioavailability of the tablet relative to that of the solution was 85.0 +/- 31.1 and 88.6 +/- 13.1% for pentazocine and acetaminophen, respectively. The apparent first-order regression-dependent elimination rate constants for pentazocine from the tablet and solution preparations were 0.19 +/- 0.08 and 0.20 +/- 0.06 h-1, respectively, while the rate constants for acetaminophen were 0.26 +/- 0.03 and 0.25 +/- 0.03 h-1 for the tablet and solution preparations, respectively. These rate constants correspond to terminal elimination half-lives of approximately 3.6 h for pentazocine and approximately 2.7 h for acetaminophen.

Disposition of arildone, an antiviral agent, after various routes of administration

[14C]arildone was administered both topically and intravaginally to mice 5 times a day for 7 days to simulate conditions of clinical usage. Urinary and fecal excretion of radioactivity indicated that arildone was extensively absorbed by both routes of administration. The levels of radioactivity in the vagina and skin declined from about 12 micrograms equivalents per g to 3 micrograms equivalents per g between 1 and 2 days after the last application. Only small amounts of unchanged arildone were found in urine from the vaginally treated animals; the major urinary metabolites were chloromethoxyphenol, its sulfate ester, and chlorohydroquinone sulfate. After about 1 month of daily oral administration of arildone to rats and monkeys or vaginal administration three times a day for 20 days to dogs, only low levels of intact drug were found in the systemic circulation. The disposition or beta-phase half-life of arildone in monkeys after intravenous administration was about 0.5 h. The disposition of [14C]arildone in mice, rats, dogs, and monkeys after various routes of administration was also investigated.

The disposition of quinfamide in the rat

The disposition of quinfamide 1-(dichloroacetyl)-6-(2-furoyloxy)-1, 2, 3, 4-tetrahydroquinoline, an enteric anti-amoebic agent, was studied in the rat. A peak blood level equivalent to 2.3 micrograms/ml of quinfamide was observed at 7 hr following a 20 mg/kg oral dose. Urinary recovery of radioactivity was much higher (84%) following intravenous than oral (48%) administration. Drug levels, in all of the tissues examined. were low. The major pathways of quinfamide metabolism in the rat involve hydrolysis of one or both ester groups, acetylation of the de-acylated product to 1-acetyl-1, 2, 3, 4-tetrahydro-6-quinolinol, oxidation of this to the 1-glycolyl metabolite, and aromatization to 6-hydroxyquinoline.

Metabolism of amrinone in animals

The biotransformation of 14C-amrinone was studied in rats, dogs, and monkeys by automated gradient high-performance liquid chromatography. The major pathways of metabolism elucidated are: A) glucuronidation at the primary amino nitrogen atom and/or the enolized oxygen atom of the pyridone ring; B) addition of glutathione at the pyridone 2-position and ultimate hydrolysis of this compound to the 2-S-cysteinyl metabolite; C) formation of the primary amino N-acetyl derivative and subsequent oxidation of this to the corresponding N-glycolate. In each species studied, urine was the primary route of elimination and unchanged amrinone was the major urinary excretion product, the other known pathways being: rat, A and C; dog, A and B; monkey, A.

Metabolism and disposition of sulfinalol in laboratory animals

Peak levels of radioactivity in blood occurred 1.0 hr after oral administration of 3H-sulfinalol hydrochloride to rats, dogs, and monkeys. The plasma decay curve for intact sulfinalol in the dog was biphasic, with apparent first-order half-lives of 0.55 and 6.2 hr. Rats excreted 42.5% of the dose in the urine and 31.8% in the feces after 24 hr. Urinary and fecal recovery were 53.8% and 41.2%, respectively, after 10 days for dogs and 57.8% and 38.0%, respectively, after 9 days for monkeys. Free sulfinalol (11.8% of the dose) was the major component in dog feces with lesser amounts of the sulfide and sulfone metabolites, also in the unconjugated form. All metabolites in dog urine were conjugated with glucuronic acid, with sulfinalol (28.5%) and desmethylsulfinalol (8.5%) representing the major constituents, whereas the sulfone and sulfide metabolites were minor ones. Monkey feces contained primarily unconjugated forms of the desmethyl sulfide metabolite (17.0%) and sulfinalol (7.5%); lesser amounts of desmethylsulfinalol and the sulfone metabolite were present. Desmethylsulfinalol (8.7%) and its sulfate (7.0%) and glucuronide (4.0%) conjugates were the major urinary metabolites in the monkey; sulfinalol (1.4%), its glucuronide conjugate (5.1%), the desmethyl sulfide metabolite (and its sulfate conjugate), and the sulfone metabolite were also present.

Metabolism of arildone, an antiviral agent, in laboratory animals

After arildone administration, four compounds were identified in the excreta of laboratory animals: unchanged drug, arildone; the O-desmethyl metabolite, 4-[6-(2-chloro-4-hydroxy)phenoxy]hexyl-3,5-heptanedione; the sulfate ester of 2-chloro-4-methoxyphenol; and a labile conjugate of chlorohydroquinone, tentatively characterized as the sulfate ester. The concentrations of each of these were determined in the urine and/or plasma of rats, dogs, and mice after administration of 14C-arildone.

Disposition of a series of tetrahydrocarbazoles

Cyclindole was extensively metabolized and eliminated primarily via the kidneys from most laboratory animals and man. Only in the dog was cyclindole a major urinary component. Cyclindole was metabolized by N-demethylation and/or hydroxylation. In studies utilizing radiolabeled drug, the primary urinary component was polar material which probably resulted from conjugation of the hydroxylated products. When desmethylcyclindole was administered to rats and dogs, large amounts of unchanged drug were administered to rats and dogs, large amounts of unchanged drug were recovered in the urine; there was no 3-aminotetrahydrocarbazole present. Significant amounts of urinary radioactivity were thought to represent hydroxylated and/or conjugated products. When 7-hydroxycyclindole was administered to dogs, only free parent drug was recovered from the urine; there was no evidence for N-demethylation. Flucindole, the 6,8-difluoro analog of cyclindole was metabolized by dog and man via N-demethylation with the formyl derivative being a probable intermediate in this reaction; both products were found in the urine. No didesmethyl metabolite was detected. In contrast to cyclindole, the N-oxide of flucindole was found in urine from both species. The route of elimination of oxarbazole and its metabolites was species specific: urinary excretion was 96.5, 38.7, 24.5, and 2.0% for the guinea pig, monkey, rat, and dog, respectively. The major urinary metabolite was O-demethyl oxarbazole; this metabolite was conjugated in all species except the guinea pig. The dog and monkey excreted small quantities of conjugated N-debenzoylated oxarbazole in urine. The profound changes in pharmacological activity that result from relatively small chemical modifications of the tetrahydrocarbazole nucleus make it likely that many further investigations of this class of compounds will be undertaken in the future.

Blood levels, tissue distribution and the duration of action in rats of ciprofibrate, a new hypolipidemic agent

The blood levels, distribution and duration of action of ciprofibrate, an orally active hypolipidemic agent, was investigated in rats. Serum concentrations of 30 micrograms of ciprofibrate/ml are associated with significant reductions in both serum cholesterol and triglycerides in rats on a hyperlipidemic diet. Increasing the plasma concentrations of ciprofibrate to 69 micrograms/ml resulted in only a modest incremental reduction in serum lipids. The distribution of radioactivity from [14C]ciprofibrate within rat tissues was not affected by prior treatment for 14 days with ciprofibrate at either 1.5 or 3.0 mg/kg/day. Varying the dosage regimen of ciprofibrate at 30 mg/kg, with medication at intervals of one, 2 or 3 days resulted in similar peak plasma levels of about 300 micrograms/ml, 4 h after medication. The half-life of ciprofibrate, during the terminal disposition phase, was about 82 h. Levels of serum cholesterol remained suppressed up to 3 days after medication with ciprofibrate was discontinued; triglyceride levels returned to control values more slowly.

Absorption and disposition of N-(1, 1-dimethylethyl)-N'-[2-(4-pyridinyl)-4-pyrimidinyl]urea in rats and dogs

N-(1, 1-Dimethylethyl)-N'-[2-(4-pyridinyl)-4-pyrimidinyl]urea, Win 40, 882, was eliminated from the blood stream of dogs by two apparent first-order processes with alpha- and beta-phase half-lives of 0.2 hr and 1.4 hr, respectively. Radioactivity of the administered dose was excreted by rats in the feces and via the kidneys; about 40-45% of the dose was recovered in the feces, with the remainder in the urine, over a six day period. One of the terminal methyl groups of the tert-butyl moiety of Win 40,882 is sequentially oxidized by the rat to the alcohol, aldehyde and carboxylic acid. In addition, some of the aldehyde was further metabolized to generate two different monohydroxylated aldehydic metabolites; these hydroxyaldehydes accounted for less than 10% of the dose administered. An unusual metabolic pattern was noted in the excretion of Win 40,882. Over 30% of the urinary metabolites contained the carboxaldehyde function; only8% of the urinary radioactivity was represented by the further oxidation of the aldehyde group to generate the carboxylic acid.

Absorption, excretion and disposition of cyclindole in laboratory animals and human volunteers

Radioactivity from orally administered single doses of cyclindole-14C was excreted primarily in the urine of the rat (99%/48 hr), monkey (80%/120 hr), and dog (70%/144 hr). Approximately 38-58% of a daily dose of cyclindole was recovered from 24-hr human urine, as determined by gas chromatography. Substantial amounts of unchanged drug were voided by dogs. Cyclindole was metabolized primarily by N-demethylation and/or hydroxylation in the 7-position. Hydroxylation at the 6-carbon atom was of minor importance in humans only; none of the animal species excreted the 6-hydroxy metabolite. Dogs were capable of N-demethylation, but no metabolites oxidized at the 6- or 7-carbon atoms were detected in dog urine.