As with any drug, anti-tuberculosis drugs have a therapeutic margin, that is the difference between the minimum drug concentration required to inhibit the growth of M. tuberculosis and the maximum concentration that can be given without provoking drug toxicity.

This therapeutic margin varies for the different drugs.  It is large for isoniazid (INH) and rifampicin (RMP), but rather narrow for the other four drugs.  As a consequence, deviations from the recommended dosages are more serious for some than for other medications.

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