Lack of relationship between glibenclamide metabolism and debrisoquine or mephenytoin hydroxylation phenotypes

The pharmacokinetics of a single oral dose of 1.75 mg glibenclamide were studied in 15 healthy Caucasians including five poor metabolisers of debrisoquine and five poor metabolisers of S-mephenytoin. Plasma glibenclamide concentrations and the urinary concentrations of trans-4- and cis-3-hydroxyglibenclamide were analyzed by h.p.l.c. Thirty-six +/- 6% (mean +/- s.d., n = 15) of the given dose of glibenclamide was excreted in 48 h urine as hydroxylated metabolites, 27 +/- 4% as trans-4-hydroxyglibenclamide and 8 +/- 2% as cis-3-hydroxyglibenclamide. There were no differences in the plasma pharmacokinetics of glibenclamide or in the urinary excretion of the metabolites between poor and extensive metabolisers of debrisoquine, neither between the two mephenytoin hydroxylator phenotypes. The study thus indicates that the disposition of glibenclamide is not influenced by these two independent polymorphisms of drug oxidation.

Metrifonate in healthy volunteers: interrelationship between pharmacokinetic properties, cholinesterase inhibition and side-effects

Metrifonate concentrations in plasma, its inhibition of blood cholinesterase, and side-effects were studied in 16 healthy volunteers who received a single oral dose of 2.5, 5, 7.5 or 15 mg/kg in a randomized double-blind study (4 subjects for each dose). Metrifonate was determined by a gas chromatographic method. Peak plasma levels were reached within 2 hours; the half-life in plasma, oral clearance, and normalized Cmax and AUCs did not differ significantly between the four groups. Plasma cholinesterase (BuchE) was inhibited to low levels in all subjects, while erythrocyte cholinesterase (AchE) was affected in a dose-dependent fashion. The occurrence of side-effects correlated strongly with peak plasma levels but not with maximum AchE inhibition or with increase in salivation. This study shows that the absorption of metrifonate was not significantly different for doses between 2.5 and 15 mg/kg. The plasma levels of this drug correlated with the occurrence of side-effects.

Disposition of perphenazine is related to polymorphic debrisoquin hydroxylation in human beings

The pharmacokinetics of a single oral dose of 6 mg perphenazine was studied in a group of six slow and six rapid hydroxylators of debrisoquin. Peak serum concentrations of perphenazine were significantly higher in slow hydroxylators than they were in rapid hydroxylators (2.4 +/- 0.6 versus 0.7 +/- 0.3 nmol/L, p less than 0.001). The AUC(0-12) was also higher in slow hydroxylators than it was in rapid hydroxylators (18.5 +/- 6.2 versus 4.5 +/- 2.5 nmol.L-1.hr, p less than 0.001). The data suggest that the disposition of the antipsychotic drug perphenazine covaries with polymorphic debrisoquin hydroxylation.

Glucuronidation of amitriptyline in man in vivo

The urinary excretion of amitriptyline (AT) as N-glucuronide was studied in healthy volunteers after single oral doses of AT and in patients on continuous treatment with AT. In the volunteers, 8 +/- 3% of a 25 mg dose of AT was recovered in urine as glucuronide during 108 hr. No difference between slow and rapid debrisoquine hydroxylators with respect to the excretion of AT glucuronide was seen. 0.08 to 1.68% of the given AT dose was recovered in urine in unchanged form. The excretion of unchanged AT correlated with the debrisoquine metabolic ratio (rs = 0.61; p less than 0.01). In 5 patients on continuous treatment with AT (125-150 mg/day), 8 +/- 5% of the daily dose was recovered in 24-hr urine as AT glucuronide. The present study shows that direct glucuronidation is a minor metabolic pathway of AT in man in vivo both after single low doses and during continuous treatment with therapeutic doses.

Stereoselective disposition of racemic E-10-hydroxynortriptyline in human beings

The disposition and elimination kinetics of the enantiomers of E-10-hydroxynortriptyline (E-10-OH-NT) were studied in six rapid and four slow hydroxylators of debrisoquin after a single oral dose of 75 mg racemic E-10-OH-NT hydrogen maleate. The plasma levels and the AUC of unconjugated (-)E-10-OH-NT were two to five times higher than those of (+)E-10-OH-NT. The plasma half-lives of both enantiomers were 8 to 9 hours. A significantly higher proportion of the given dose of (+)E-10-OH-NT (64.4% +/- 12.1%) than of (-)E-10-OH-NT (35.3% +/- 9.7%) was recovered in urine as glucuronide conjugate, but more (-)E-10-OH-NT was recovered unchanged in urine. The total oral plasma clearance and the metabolic clearance by glucuronidation were significantly (p less than 0.0001) higher for (+)E-10-OH-NT than for (-)E-10-OH-NT. The findings indicate that first-pass glucuronidation of E-10-OH-NT is enantioselective in human beings in vivo, with preference for (+)E-10-OH-NT. The renal clearance of unbound (-)E-10-OH-NT (0.57 +/- 0.16 L.kg-1.hr-1), on the other hand, exceeded that of (+)E-10-OH-NT (0.44 +/- 0.14 L.kg-1.hr-1) (p less than 0.005), which suggests enantioselective tubular secretion. The debrisoquin hydroxylation status was not associated with any of the investigated kinetic processes that relate to E-10-OH-NT.

Use of prescription forgeries in a drug abuse surveillance network

Data on forged prescriptions in Sweden in 1982-1986 were studied as an indicator in an epidemiological survey of medication abuse. The annual number of prescription forgeries doubled during the 5-year period. Psychotropic drugs accounted for 62% and analgesics for 25% of all forgeries. Benzodiazepines were the major single drug group, comprising 52% of all forgeries during the period. The major benzodiazepines on the market in Sweden (diazepam, oxazepam, nitrazepam and flunitrazepam) were the subject of largest number of forgeries. When calculated in relation to the utilization (either total sales or the number of prescriptions), the analgesics codeine, pentazocine and ketobemidone were clearly at the head of the list, suggesting greater abuse liability of these drugs. It is suggested that the data on forged prescriptions can be used as a "signalling mechanism" in epidemiological surveillance of medication abuse, aimed at detecting changes in the prevalence as well as in the pattern of abuse.

Effects of repeated oral doses of fenflumizole on platelet aggregation and thromboxane formation in man ex vivo

Anti-platelet effects of fenflumizole, a new cyclo-oxygenase inhibitor, were studied in man ex vivo. Fenflumizole was given to male volunteers at the oral doses of 25, 50 or 100 mg per day, each dose for a period of seven days. The formation of thromboxane B2 (TXB2) during whole blood clotting, platelet aggregation induced by arachidonic acid and ADP, the formation of TXB2 during aggregation as well as serum concentration of fenflumizole were measured repeatedly during drug administration and for a fortnight after drug discontinuation. TXB2 formation during whole blood clotting was decreased dose-dependently by fenflumizole. The degree of inhibition of TXB2 formation was proportional to fenflumizole concentration in serum within each individual. The lag phase of platelet aggregation induced by arachidonic acid was prolonged and the formation of TXB2 during aggregation decreased by fenflumizole. No total inhibition of either TXB2 synthesis or platelet aggregation was caused by the fenflumizole doses used. The results show that the degree of inhibition of platelet thromboxane forming capacity by repeated doses of fenflumizole is closely related to the concentration of the drug in blood. Platelet aggregation however is less sensitive to changes in fenflumizole levels and cannot be assessed solely on the basis of cyclo-oxygenase activity.

Formation of a quaternary N-glucuronide of amitriptyline in human liver microsomes

Amitriptyline N-glucuronide was isolated from urine of a patient treated with therapeutic doses of amitriptyline. The glucuronide was hydrolyzed by hot alkaline treatment and, to a lesser degree, by treatment with beta-glucuronidase. A method for the direct measurement of amitriptyline glucuronide by HPLC was developed. Human liver microsomes were shown to glucuronidate amitriptyline in the presence of UDPGA, and the activity varied 7-fold among microsomes from 13 different human livers. The glucuronidation of amitriptyline was inhibited by p-nitrophenol but not by morphine. E-10-hydroxynortriptyline, a major metabolite of amitriptyline, had only a slight inhibitory effect on the glucuronidation of amitriptyline. No significant correlation was found between the glucuronidation of amitriptyline and that of E-10-hydroxynortriptyline in the microsomes studied.