Antibiotic blood concentrations in patients successfully treated with tobramycin

Thirty-nine patients with severe Gram-negative infections were treated with parenteral tobramycin. Thirty-one (79%) were cured of their infection. Tobramycin was most effective in the therapy of patients with urinary tract infections, arthritis and skin and soft tissue infections and relatively less effective in patients with septicaemia, pneumonia, and osteomyelitis. The infection was cured more frequently in patients who achieved a high ratio between the peak serum concentration of tobramycin and the minimal inhibitory concentration of tobramycin against the pathogenic organism (so-called therapeutic ratio). The ratio was greater than 4.0 in 11 of 13 (85%) assays performed in 12 cured patients, whereas this ratio was achieved in only 3 of 10 (30%) instances in 5 patients in whom the therapy failed (P less than 0.05). The latter group also included a greater proportion of patients with an ultimately fatal illness, such as lung cancer and uraemia, compared to the former successfully treated group. Adverse effects of tobramycin on renal function were transitory. No significant effect of tobramycin on the hearing was observed.