Preparative ultracentrifugation of small samples of plasma and the protein binding of methaqualone

Sex-related differences in drug disposition in man

Sex-related differences in the disposition of some analgesics, anxiolytics and hypnotics have recently been reported. With certain benzodiazepines, sex has been shown to be a more important determinant of variability in drug disposition than age, while with other benzodiazepines an age-related decline in clearance was more pronounced in men than women. In young healthy adults these sex-related differences in drug disposition were related to the phase of the menstrual cycle, oral contraceptive steroid administration, and variations in plasma concentrations of albumin, alpha 1-acid glycoprotein, free fatty acids and sex hormones. While none of the sex-related differences so far reported necessitates the modification of a therapeutic dosage regimen, it is prudent that future protocols for pharmacokinetic studies should regard age, sex, the menstrual cycle and oral contraceptive steroids as potential sources of variability.

The kinetics of the urinary excretion of the N-oxide and glucuronides of methaqualone in man

The urinary excretion of the N-oxide and the glucuronides of five C-monohydroxy metabolites of methaqualone has been studied following the oral administration of a single dose of the drug. The apparent first order rate constants for the excretion of each metabolite (kme) were shown to be numerically smaller than the overall elimination rate constant for methaqualone (k10). The Kme values tended to be greater than or equal to the corresponding apparent first order rate constants for the formation of the metabolite (km) but corresponding kme and km values were always of the same order magnitude. The kme values for the glucuronides were much smaller than the literature kme value for paracetemol glucuronide. The rate of renal elimination of the metabolites was variably sensitive to urine flow but over a period of time of 8 hours or greater the total amount of metabolite recovered in the urine was was independent of the total urine volume.

Inter- and intra-individual variation in the metabolism of methaqualone in man after a single oral dose

The urinary excretion of five C-monohydroxy metabolites and the N-oxide metabolite of methaqualone in the 24 h period immediately after oral dosing with 250 mg methaqualone (Melsed) has been measured in ninteen healthy adults (13 male, 6 female) to assess interindividual variations and in five adults (3 male, 2 female) on five separate occasions to assess intraindividual variation. The overall importance of the six metabolites was 4'-hydroxy greater than N-oxide greater than 2'-hydroxymethyl greater than 3'-hydroxy greater than 6-hydroxy = 2-hydroxymethyl. Variations in this order both within the 24 h period and within each of the three eight-hour periods constituting the 24 hours were minor and variations in the absolute amount of each metabolie excreted ranged from two to three-fold. Intraindividual variations were generally smaller than interindividual variations and for each individual the pattern of metabolism was similar on the five occasions. There is evidence that the C-oxidation of methaqualone may be more sensitive to cyclical variations in hormone levels than is N-oxidation.