The relation between blood levels and urinary excretion of amphetamine under controlled acidic and under fluctuating urinary pH values using [14C]amphetamine

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Abstract
Plasma, blood cell and urine levels of amphetamine were determined after the oral administration of S-(+)-[14C]amphetamine sulphate to two subjects under conditions of controlled acidic and fluctuating urinary pH. The decline in plasma concentration of the drug was more rapid under the controlled acidic conditions than under conditions of fluctuating urinary pH. Under controlled conditions, the concentration time profiles of drug and metabolite in urine or plasma (as opposed to body levels), were suitable for kinetic analysis. The apparent rate of urinary excretion of amphetamine was proportional to its plasma concentration only under the controlled acidic urinary conditions. Amphetamine was cleared from blood more rapidly than could be accounted for by glomerular filtration under acid conditions, but when urinary pH fluctuated, clearance of the drug could be accounted for by this route.