The relationship between nicotinamide adenine dinucleotide concentration and antibacterial activity of isoniazid in Mycobacterium tuberculosis.

The relationship between the antibacterial effect of isoniazid and the intracellular concentration of nicotinamide adenine dinucleotide (NAD) was investigated in Mycobacterium tuberculosis strain H37Rv given continuous and pulsed exposures to the drug. Depletion of NAD to a plateau value occurred rapidly during exposure, and recovery after a pulse of isoniazid was also rapid. It seemed unlikely that NAD depletion was the direct cause of the antibacterial activity because (1) insufficient depletion occurred at low isoniazid concentrations; (2) antibacterial activity, but not NAD depletion, was proportional to the product of isoniazid concentration and the exposure period; and (3) NAD depletion was not related to antibacterial activity in cultures of differing physiologic state.