The metabolism and urinary excretion in man of phentermine, and the influence of N-methyl and p-chloro-substitution

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Abstract
The urinary excretion of phentermine, mephentermine and chlorphentermine was examined after oral administration of phentermine and chlorphentermine hydrochlorides and mephentermine sulphate to man under normal and acidic conditions of urinary pH. The rate of excretion of both phentermine and mephentermine fluctuated with changes in urine pH, a more acidic pH causing a faster rate of excretion; changes in urine flow rate had only a slight effect. The rate of excretion of chlorphentermine was affected by changes in pH and urinary flow rates. Phentermine and mephentermine were recovered almost quantitatively within 24 h from subjects under acidic urine control; only about 35% chlorphentermine was recovered under similar conditions.