The disposition of antituberculous drugs in plasma of elderly patients. II. Isoniazid, rifampicin and pyrazinamide.

The pharmacokinetics of isoniazid (INH), rifampicin (RIF) and pyrazinamide (PZA) were studied in 18 elderly patients (67-89 years of age) and 19 young adult patients (19-59 years of age) on the first day and at one month of treatment for pulmonary tuberculosis. Elderly patients exhibited more side effects but there were no age-related changes in the pharmacokinetics of any of the three drugs when used in this combination. The clearance for INH and RIF at steady-state were significantly lower than after first-dose, while that of PZA remained unchanged. At steady-state the clearances for INH and RIF were not characteristic of polymorphic metabolism and auto-enzyme induction, respectively. Elderly patients are more sensitive to antituberculous (anti-TB) drugs; therefore, a modification in the dosage for this patient group should be considered.