Isoniazid adverse drug response

Serum chemistry markers play an important role in hepatotoxicity evaluation in human and animal safety studies. The classic markers of hepatotoxicity are alanine aminotransferase (ALT), aspartate aminotrasnferase (AST) and alkaline phosphatase (ALP) [124—127]. Drug-induced hepatotoxicity can be difficult to assess in some circumstances. Hepatotoxic responses can be intrinsic (predictable, dose-related) or idiosyncratic (unpredictable, non-dose-related). ALT, AST and ALP are generally not useful for predicting idiosyncratic responses. The administration of some drugs, such as isoniazid, can lead to a high incidence of ALT elevation, but are tolerated by most patients without severe hepatotoxicity. Adverse drug reactions can be masked... 

For example, it has been suggested that the adverse reactions caused by a number of drugs such as isoniazid, procainamide, hydralazine could be due to metabolic activation by myeloperoxidase in neutrophils. Thus neutrophils will metabolize procainamide (Fig. 4.38) to a hydroxylamine metabolite. In the presence of chloride ion, myeloperoxidase will produce hypochlorous acid, a strong oxidizing agent, which may be responsible for metabolic activation and toxicity. One of the products is N-chloroprocainamide (see also sect. "Hydralazine," chap. 7). 

Not understood. One idea is that some kind of synergy occurs between the two drugs because both can produce similar adverse effects if given in high doses. The authors of one report speculate that isoniazid and disulfiram together inhibit two of three biochemical pathways concerned with the metabolism of dopamine. This leaves a third pathway open, catalysed by COMT (catechol-O-methyl transferase), which produces a number of methylated products of dopamine. These methylated products may possibly have been responsible for the mental and physical reactions... 

Other such enzyme deficiencies have been revealed through an individual s adverse reaction to drugs. More than 90% of Orientals are genetically rapid N-acetylators of isoniazid (6.12), whereas only 40% of black or white citizens of the United States showed this trait (Kalow, 1962). Rapid acetylators produce acetylhydrazine, which can cause liver damage. The same inheritance controls the acetylation (deactivation) of the sulphonamide antibacterials. The rise of intraocular pressure when glucocorticoids are placed in the eye is another pharmacogenetic effect. Low and high responses are shown by 66% and 5%, respectively, of a sample white population. 

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