Isonicotinyl hydrazone

Synonyms. o-Hydroxybenzal Isonicotinyl Hydrazone INSH SAH Salizid. 

After oral administration, isoniazid reaches a peak plasma concentration of 3-5 micrograms/ml within 1-2 hours. It equihbrates into all body fluids and tissues and 75-95% is excreted in the urine within 24 hours. The most important urinary metabolites are products of acetylation (acetyliso-niazid) and hydrolysis (isonicotinic acid). Isonicotinyl glycine, isonicotinyl hydrazones, and A-methylisoniazid appear in only small amounts. The rate of acetylation of isoniazid significantly alters its plasma concentrations and half-life. The mean half-Ufe of isoniazid in rapid acetyla-tors is about 70 minutes and in slow acetylators 3 hours. 

The USP states that rifampin raw material contains not less than 95.0% and not more than 103.0% of C43H5gN40i2, calculated on the dried basis.When formulated into capsules and suspensions, it must contain not less than 90.0% and not more than 110.0% of the labeled amount, injections between 90.0% and 115%, FDC products containing isoniazid between 90% and 130%, and 3FDC and 4FDC products between 90.0% and 110.0%. The higher maximum concentration allowed when combined with isoniazid is because when present together rifampin and isoniazid (H) interact with each other, especially when moisture is present, to form isonicotinyl hydrazone. This reduces the bioavailability of rifampin in an FDC... 

Mariappan, T.T. Jindal, K.C. Singh, S. Overestimation of rifampicin during colorimetric analysis of antituberculosis products containing isoniazid due to formation of isonicotinyl hydrazone. J. Pharm. Biomed. Anal. 2004, 36 (4), 905-908. 

It has already been said above that, in addition to minima, there are also maxima on the polarograms for many phenylhydrazones, semi- and thiosemicarbazones, isohydrazones, and isonicotinyl-hydrazones. It has been shown that the appearance of maxima on the waves for the hydrazones is due to tangential movements of the electrode surface. Investigation of the electrocapillary curves has shown that the maxima appear in the region of potentials where desorption of the larger part of the depolarizer occurs. 

Isonicotinyl hydrazide (INH), one of the most effective drugs against tuberculosis, is inhibitory to pyridoxal kinase, the enzyme that converts pyridoxal to PLP.C Apparently, the drug reacts with pyridoxal to form a hydrazone which blocks the enzyme. Pyridoxal kinase is not the primary target of INH in mycobacteria. However, patients on long-term isonicotinyl hydrazide therapy sometimes suffer symptoms of vitamin B6 deficiency. ... 

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