Gentamicin and Tobramycin: Comparison of Ototoxicity

One hundred forty-five patients treated with tobramycin and/or gentamicin were prospectively monitored for drug-induced ototoxicity. Patients were tested weekly by audiometry and electronystagmography. Twice weekly determinations of drug serum levels and renal function were also performed. Each patient's medical condition was assessed at various times during and after therapy, and the results were analyzed for possible associations with the development of ototoxicity. Overall, tobramycin appeared to be less toxic than gentamicin, but the drugs differed significantly only in their tendency to cause vestibular toxicity. Antibiotic toxicity was correlated with several parameters, including total dose of drug, fever, decreased hematocrit (tobramycin), or elevated hematocrit (gentamicin). Increased creatinine clearance correlated with the development of cochlear toxicity, and elevated levels of serum creatinine were associated with nephrotoxicity, poor health or critical illness, and the duration of therapy (>10 days). Parameters that did not correlate with the development of drug-induced toxicity included: dose of drug, serum drug levels, patient's age or prior exposure to noise, prior aminoglycoside treatment, treatment with other ototoxic drugs, underlying disease, or the total number of conditions that might predispose the patient to ototoxicity. Drug-induced ototoxicity developed independently of druginduced nephrotoxicity.