Microsomal Dealkylation of Drugs

Reduction of levopropoxyphene N-oxide to propoxyphene by dogs in vivo and rat liver microsomal fraction in vitro

1. When l-propoxyphene-N-oxide was given orally to dogs, reduction occurred in vivo resulting in substantial plasma levels of l-propoxyphene. 2. When l-propoxyphene-N-oxide was given intravenously, near peak plasma levels of propoxyphene occurred in 10 minutes. This suggests that reduction is occurring at least in part in mammalian tissue rather than in gut flora. 3. Levopropoxyphene oxide was also readily reduced anaerobically in a rat liver microsomal fraction. 4. Results from this study explain our early observation that while l-propoxyphene-N-oxide is demethylated in vivo, demethylation does not occur in vitro when the oxide is incubated in air with liver homogenate. Thus demethylation of the oxide can occur only after reduction of the oxide to the tertiary amine. While reduction occurs readily in vivo it is completely inhibited by oxygen present in the usual microsomal incubation. 5. These studies further confirm that the N-oxide is not an intermediate in the demethylation of propoxyphene.

The formation of an N-hydroxymethyl intermediate in the N-demethylation of N-methylcarbazole in vivo and in vitro

1. The metabolism of N-methylcarbazole has been studied in several mammalian species, both in vivo and in vitro. 2. An important metabolite after incubation of N-methylcarbazole with liver microsomes in vitro was identified as N-hydroxymethylcarbazole. 3. This metabolite was also found as a conjugate (probably the O-glucuronide) in the urine of some species. 4. N-Hydroxymethylcarbazole decomposed spontaneously in solution at pH 7-4 to formaldehyde and carbazole; this breakdown was enhanced by incubation with liver microsomes from several species, especially the guinea-pig. 5. The role of N-methyl hydroxylation, compared with N-oxidation, in the mechanism of N-dealkylation of non-basic N-methyl compounds is discussed.

The metabolism of N-ethyl-N-methylaniline by rabbit liver microsomes: the measurement of metabolites by gas-liquid chromatography

1. A method for the determination of N-ethyl-N-methylaniline and its metabolites by g.l.c. is described. 2. Following incubation in N-ethyl-N-methylaniline with rabbit liver microsomes for 60 min, over 95% of the substrate was accounted for as unchanged compound or metabolites. 3. N-Ethyl-N-methylaniline is metabolized in vitro by rabbit tissues mainly by N-oxidation and N-demethylation and to a lesser extent by N-deethylation and di-dealkylation. 4. Both major routes of metabolism were observed in homogenates prepared from rabbit liver and lung; in addition N-oxidation occurred in kidney and bladder tissue homogenates.

The influence of methyl substitution on the N-demethylation and N-oxidation of normethadone in animal species

N-Monodemethylation and N-oxidation were shown to be the major routes of metabolism of normethadone, (—)-methadone and (—)-isomethadone in vitro by hepatic microsomal preparations from rat, rabbit, guinea-pig, mouse and hamster. The rate of N-oxidation was decreased and the rate of N-demethylation was increased by the introduction of the methyl substituent into normethadone; the configuration of the methyl substituent influenced these processes. Km and Vmax values were determined for liver microsomal N-demethylation of normethadone, (—)-methadone and (—)-isomethadone by rat and guinea-pig and for the N-oxidation of normethadone by guinea-pig. The use of selective inhibitors showed that N-demethylation was not preceeded by N-oxidation in these compounds.

Oxidative N-dealkylation: a mannich intermediate in the formation of a new metabolite of lidocaine in man

Evidence is presented for a new metabolite of lidocaine. Its structure, N(1)-ethyl-2-methyl-N(3)-(2,6-dimethylphenyl)-4-imidazolidinone, suggests reactive electrophilic intermediates for the oxidative removal of N-alkyl groups in general.

A note on the effects of 2,4-diamino-5-phenylthiazole and 1, 2, 3, 4-tetrahydro-9-aminoacridine on morphine metabolism

Chromatographs of extracts of urine from patients receiving mixtures of morphine plus amiphenazole or morphine plus 1, 2, 3, 4-tetrahydro-9-aminoacridine (tha) have a spot which is due to a substance with properties similar to morphine-N-oxide. This spot was not present in urine of patients given morphine, amiphenazole or tha alone. Morphine-N-oxide may be a metabolite of morphine, and amiphenazole and tha may inhibit the further metabolism of morphine-N-oxide.