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Xenobiotica
the fate of foreign compounds in biological systems
Volume 8, 1978 - Issue 1
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Research Article

The Disposition of Phentermine and its N-Oxidized Metabolic Products in the Rabbit

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Pages 55-60 | Received 03 Feb 1977, Published online: 22 Sep 2008
 

Abstract

1. When phentermine was injected intraperitoneally to rabbits, 77% of the dose was excreted in the urine within 2 days; N-oxidized metabolic products accounted for 62% dose. Major excretion products were N-hydroxyphentermine (28% dose), conjugated N-hydroxyphentermine (32% dose) and unchanged phentermine (16% dose).

2. Similarly injected N-hydroxyphentermine was excreted (62% dose) in the urine in 2 days; only 4% dose was recovered unchanged. Major routes of metabolism of N-hydroxyphentermine were conjugation (36% dose) and reduction to the parent amine (15% dose). Conditions for hydrolysis of urine to liberate N-hydroxyphentermine from its conjugates were studied; N-hydroxyphentermine decomposes in strong acid.

3. Only 10% of injected α,α-dimethyl-α-nitroso-β-phenylethane was excreted in the urine in 2 days.

4. N-Oxidation is the major pathway of metabolism of phentermine in rabbits; the present results suggest that some biological activity may be mediated by the pharmacologically active N-hydroxyphentermine.

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