Optimal tobramycin dosage in patients with cystic fibrosis - Evidence for predictability based on previous drug monitoring

A retrospective analysis of files of patients with cystic fibrosis and pulm onary exacerbations was performed to investigate whether an individual dosa ge of tobramycin once established by serum level determination allows a rel iable prediction of the adequate dosage in a consecutive exacerbation. All patients hospitalized greater than or equal to 2 times between May 1997 and September 1998 with pulmonary exacerbation due to Pseudomonas aeruginosa i nfection susceptible to tobramycin were included. The initial dosage to tob ramycin was 5 mg/kg body weight every 12 h followed by drug level determina tions to establish the optimal dose. In a consecutive exacerbation the same dosage per kg body weight was used again and drug level determinations wer e repeated. Sixteen patients (six female = 38%) with a mean age of 24 years (median: 26 years, range: 9-33) were hospitalized for 49 pulmonary exacerb ations (2-6 per patient, mean: 3, median: 2 5) During the first episode of tobramycin treatment in the study period all trough levels were < 2 mu g/ml (median: 0.6) and the peak levels were 7.1-16.9 mu g/ml (median: 11.9). In four patients the peak level was > 12 mu g/ml. In 28 consecutive episodes the dosage of tobramycin was chosen based on optimal results of previous dr ug level monitoring and in 27 instances (96%) the previously established op timal dose was confirmed. In five consecutive episodes the tobramycin dosag e had been increased erroneously and this resulted in abnormally high peak levels in three cases. These findings suggest that a safe and therapeutic t obramycin dosage in an individual patient with cystic fibrosis is predictab le based on a previously established optimal dosage.