Long-term urinary excretion of methaqualone in a human subject
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The urinary excretion rates of methaqualone and of one of its metabolites, 6-hydroxymethaqualone (free and conjugated), were determined in a normal male subject over a 30-day period by stable isotope dilution analysis using field ionization mass spectrometry. The excretion rates for methaqualone were fitted by computer to three-and four-exponential functions. The estimated terminal halflife for the drug was approximately 74 hr. 6-Hydroxymethaqualone excretion in the elimination phase was fitted to a single exponential decay curve. Estimated halflives obtained for the free and total (primarily conjugated) metabolite were 78 and 70 hr, respectively. The apparent difference between the latter two values was not statistically significant. The close similarity between the halflives of methaqualone and 6-hydroxymethaqualone indicates that elimination of these compounds is ratelimited by the same pharmacokinetic process. A similarly long halflife, 50 hr, was estimated in a previous study (5) of another subject in which excretion of the compounds was followed over an 11-day period. These results demonstrate that the half-life of methaqualone can be much longer than has been indicated by relatively short-term investigations.
Key wordsdrug metabolism long-term pharmacokinetics mass spectrometry MLAB methaqualone 6-hydroxymethaqualone stable isotopes urinary excretion
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