PATRICK JOSEPH RYAN, Fordham University


Isoniazid is a potent agent in the treatment of tuberculosis. In addition to its therapeutic action several side effects have been reported including peripheral neuropathy and hepatitis. The present investigation was undertaken to improve current knowledge of isoniazid metabolism through a study of human urinary metabolites.^ This study comprised several steps. First a series of volunteer subjects were given 75 (mu)Ci of C('14)-labelled isoniazid with the label in the carboxyl carbon along with a therapeutic dose of non-labelled isoniazid (300 mg). After ingestion urine was collected from all subjects for forty-eight hours in five collections at two, four, and six hours, after twenty-four hours and after forty-eight hours. Aliquots from each collection were counted to determine the amount of label excreted in each time period. After neutralization and concentration, paper chromatograms of each of the first four collections were prepared. Development in 2-propanol-1-butanol-H(,2)O (60:25:15 V/V) followed by scintiscanning localized several radioactive bands, the location and quantity of labelled metabolites generated a metabolic profile for each subject.^ Concentrated urine samples from several subjects were used for the isolation of metabolites. Chromatography in several solvent systems, multiple development and differential solubility allowed the separation of sixteen metabolites in varying amounts. During these procedures the various samples were combined and concentrated to allow the isolation of minor metabolites.^ After isolation the metabolites were characterized to determine their identity. Chromatographic behavior, ultraviolet spectra and reaction with several reagents were used as preliminary characteristics. Comparison of this data with results obtained with a series of model compounds indicated that ten metabolites resembled model compounds so closely as to suggest identity. Crystallization to constant specific activity confirmed the occurrence of isonicotinic acid, one isomer of pyruvate-isoniazid hydrazone, free isoniazid, 1-acetyl-2-isonicotinyl hydrazide and isonicotinamide among the metabolites. The presence of N-methyl-isonicotinic acid, N-isonicotinyl glycine amide, a second isomer of pyruvate-isoniazid hydrazone, and a D-glucose-isoniazid hydrazone was supported by FT NMR. One metabolite which did not develop in any solvent system, resembled an (alpha)-ketoglutarate-isoniazid hydrazone. Co-crystallization was inconclusive.^ The remaining six metabolites include five that did not resemble any model compound and one that was present in insufficient amount. Fourier transform NMR data coupled with the preliminary data allowed some conclusions concerning the structures of the remaining five metabolites. One appears to be 1-acetyl-2-isonicotinyl hydrazine substituted on the pyridine nitrogen with a carbohydrate, to yield a pyridinium compound. Incubation of this metabolite with beef liver (beta)-glucuronidase failed to show either the free acetyl isoniazid of isonicotinic acid or an ether glucuronide of 2-hydroxy-isonicotinic acid. This compound was hydrolyzed by beef (beta)-glucuronidase supporting the assignment.^ The remaining three compounds were not characterized by these techniques. Two with Rf values higher than acetyl isoniazid appear to be alicyclic compounds possessing the hydrazine moiety, with an absence of unsaturated bonds. The final metabolite appears to be substituted on the pyridine nucleus. The ultraviolet spectrum of this compound suggests a tautomeric structure similar to 2-hydroxy isonicotinic acid which would exist predominantly in the keto form.^ In the discussion the current concept of isoniazid hepatotoxicity is considered and an alternate hypothesis is proposed. This hypothesis is based primarily on literature data which suggests that a redox shock occurs in individuals unable to cope with the alternation due to an abnormal ascorbate or selenium level. ^

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Recommended Citation

RYAN, PATRICK JOSEPH, "HUMAN URINARY METABOLITES OF ISONIAZID" (1980). ETD Collection for Fordham University. AAI8020082.