Large theophylline requirements due to high theophylline clearance: verification by the antipyrine test

Two- and four-day rifampin chemoprophylaxis regimens induce oxidative metabolism

The effects of two short-term chemoprophylaxis regimens of rifampin (2 or 4 days) on oxidative metabolism were investigated in 14 healthy subjects. Seven subjects received 600 mg of rifampin twice daily on study days 6 and 7 (group A), and seven subjects received 600 mg of rifampin once daily on days 4, 5, 6, and 7 (group B). Antipyrine (18 mg/kg of body weight) was administered orally on days 1, 8, and 15. Short-term rifampin regimens increased oral clearance of antipyrine in both groups compared with the baseline value (P less than 0.05), and group B displayed a larger percent increase over the baseline value than group A did (70.5 +/- 14.3 versus 33.1 +/- 18.1; P less than 0.05). The partial metabolic clearance (CLM) of antipyrine to 3-hydroxymethylantipyrine (HMA) on day 8 increased 71 and 108% for regimens A and B, respectively (P less than 0.05 for both). The corresponding increases in CLM to norantipyrine (NORA) were 57 and 98% (P less than 0.05 for both). CLM to 4-hydroxyantipyrine (OHA) on day 8 increased 64% for regimen A (P = 0.08) and 97% for regimen B (P less than 0.05) compared with the baseline. Although CLM to HMA and OHA on day 15 remained greater than 50% over the baseline with both regimens, CLM to NORA on day 15 was less than 25% over the baseline with both regimens. Thus, both short-term rifampin chemoprophylaxis regimens increased antipyrine clearance for at least 1 week. The increase tended to be higher with the 4-day regimen. The pattern observed for the CLMS suggests that more than one P-450 enzyme is affected.

Influence of subject age on the inhibition of oxidative metabolism by ciprofloxacin

Case reports suggest that the magnitude of inhibition of oxidative metabolism produced by ciprofloxacin may be greater in elderly subjects. We examined the effect of oral ciprofloxacin on antipyrine disposition in 13 young (ages, 23 to 34 years) and 9 elderly (ages, 65 to 82 years) healthy volunteers. Ciprofloxacin decreased antipyrine oral clearance in young and elderly subjects (P less than 0.05), with the average decreases being similar in both groups (23.3% for the young subjects and 27.9% for the elderly subjects). Ciprofloxacin concentrations in serum were significantly higher (mean, 57%) in the elderly. The formation clearance of 4-hydroxyantipyrine and 3-hydroxymethylantipyrine was also significantly decreased in both groups of subjects; however, norantipyrine formation, accounting for 15 to 20% of antipyrine clearance, was reduced only in the elderly. These results suggest that elderly subjects are not more sensitive to the inhibitory effect of ciprofloxacin on antipyrine metabolism. However, careful clinical monitoring is necessary with all patients, irrespective of age, taking ciprofloxacin concomitantly with drugs primarily eliminated by the cytochrome P-450 system.

Quinidine does not alter antipyrine metabolism

Quinidine has been reported to be a potent inhibitor of a specific isozyme of cytochrome P-450 (P-450db 1) that is responsible for the metabolism of a select group of drugs. In order to investigate the potential for quinidine to inhibit other isozymes of cytochrome P-450 and to assess whether or not P-450db 1 plays any role in antipyrine metabolism, we studied the effects of quinidine pretreatment on the pharmacokinetics and metabolism of antipyrine in six healthy, male volunteers. Using a randomized, crossover study design with a 2-week washout period between treatments, subjects received a single 1 gram antipyrine dose alone or with quinidine sulfate 200 mg orally every 8 hours for 24 hours prior to the dose of antipyrine and over the 48 hours following antipyrine administration. Mean serum concentrations, apparent oral clearance (1.93 +/- 0.86 vs 2.06 +/- 1.06 L/hr with quinidine) and half-life (13.5 +/- 3.3 vs 12.4 +/- 3.6 hr with quinidine) were not significantly different between the two treatments. The fraction of the administered dose recovered as antipyrine and measured metabolites (56.7% vs 59% with quinidine) as well as the recovery of each individual metabolite was not altered with quinidine pretreatment. In addition, the mean formation clearances for norantipyrine, 4-hydroxyantipyrine and 3-hydroxymethylantipyrine exhibited no change between treatment phases.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of antipyrine coadministration on the kinetics of acetaminophen and lidocaine

Pharmacokinetic interactions between antipyrine and acetaminophen were evaluated in 7 healthy volunteers. On 3 occasions subjects received: 1, antipyrine 1.0 g intravenously (i.v.); 2, acetaminophen 650 mg i.v.; 3, antipyrine 1.0 g and acetaminophen 650 mg i.v. simultaneously. Between Trials 1 and 3, antipyrine elimination t1/2 (17.2 vs 17.4 h), clearance (0.44 vs 0.43 ml.min-1.kg-1) and 24-h recovery of antipyrine and metabolites (313 vs 293 mg) did not differ significantly. Between Trials 2 and 3, acetaminophen VZ was reduced (1.14 vs 1.00 l.kg-1), t1/2 prolonged (2.7 vs 3.3 h), clearance reduced (4.8 vs 3.6 ml.min-1.kg-1), and fractional urinary recovery of acetaminophen glucuronide reduced. Eight additional subjects received 50 mg of lidocaine hydrochloride i.v. in the control state, and on a second occasion immediately after antipyrine 1.0 g given i.v. The two trials did not differ significantly in lidocaine VZ (2.6 vs 2.7 l.kg-1), t1/2 (2.0 vs 2.4 h) or clearance (15.0 vs 13.5 ml.min-1.kg-1). Although acetaminophen does not alter antipyrine kinetics, acute administration of antipyrine appears to impair acetaminophen clearance, possibly via inhibition of glucuronide formation. However, antipyrine has no significant effect on the kinetics of a single i.v. dose of lidocaine.

Induction of cytochrome P-450 and related drug-oxidizing activities in muscone (3-methylcyclopentadecanone)-treated rats

In the present study, we investigated the effects of muscone on both in vitro and in vivo parameters of the hepatic microsomal drug-metabolizing enzyme system and other enzyme activities in rats. In the in vivo study, the serum dimethadione (DMO)/trimethadione (TMO) ratios at 2 hr after oral administration of TMO (100 mg/kg) were significantly increased in both male and female rats treated with 75 and 150 but not 40 mg muscone/kg. Antipyrine metabolite profile in 24 hr urine of rats pretreated with muscone (150 mg/kg) was examined. The results showed that the excretion of norantipyrine was significantly increased as compared to the control group. In the in vitro study, we found that the content of cytochrome P-450, and activities of aminopyrine, N-demethylase, aniline hydroxylase and delta-aminolevulinic acid (ALA) synthetase were significantly increased as compared to the controls in both male and female rats treated with muscone (75 and 150 mg/kg). This type of induction of the hepatic metabolizing enzymes was similar to that seen after treatment with a prototype drug, phenobarbital.