Interactions of ceftazidime and tobramycin in patients with normal and impaired renal function.

We studied the in vivo interaction of ceftazidime and tobramycin in normal volunteers and anuric patients given each drug separately or both drugs in combination. Kinetic analysis of plasma concentration data showed minor changes in the disposition of these agents when they were given concurrently. However, the resulting clearance of both tobramycin and ceftazidime was unchanged when these drugs were given concurrently. The volume of distribution of tobramycin at steady state was increased by 20% in normal volunteers when given with ceftazidime. The increase in distribution was accompanied by a slight decrease in ceftazidime elimination rate. No additional alteration in dosing over those necessary to adjust for a decrease in renal function is necessary when giving this combination.