Treatment of gram-negative infections in patients with renal impairment: new alternatives to aminoglycosides

Formation of a toxic metabolite from gentamicin by a hepatic cytosolic fraction

We have demonstrated recently that incubation of the aminoglycoside gentamicin with an hepatic post-mitochondrial fraction produces a compound toxic to sensory cells from the inner ear in short-term culture; in contrast, the parent aminoglycoside was non-toxic in vitro (Huang MY and Schacht J, Biochem Pharmacol 40: R11-R14, 1990). In the present study, we investigated the subcellular distribution of the enzymatic activity and the nature of the metabolite. Isolated outer hair cells from the guinea pig cochlea were used to assay for cytotoxicity. The enzyme(s) responsible for this novel reaction of aminoglycosides was exclusively localized to the cytosolic fraction of guinea pig liver. No activity was detected in nuclear, lysosomal/mitochondrial or microsomal preparations. Furthermore, the toxin-forming enzymatic activity was associated with the high molecular weight fraction of the cytosol and did not require low molecular weight components. Filtration of the toxin through molecular weight cut-off membranes showed a molecular size of approximately 500. This evidence is consistent with the toxin being a gentamicin derivative.

Clinical use of aztreonam in a psychogeriatric population

Aztreonam is a safe, well-tolerated antibiotic with a good response in psychogeriatric patients. The combination of aztreonam with flucloxacillin is an acceptable first-choice treatment for severe infections in psychogeriatric patients.

A comparison of netilmicin and tobramycin therapy in patients with renal impairment

We evaluated the toxicity and efficacy of netilmicin and tobramycin in 89 older adults with serious bacterial infections and pre-existing renal impairment in a prospective, blinded, randomized trial. Complete resolution or improvement of infection occurred at 34/36 (94%) evaluable sites in netilmicin-treated patients and at 26/31 (84%) evaluable sites in tobramycin-treated patients. 10/44 (23%) netilmicin- and 7/45 (16%) tobramycin-treated patients experienced nephrotoxicity during treatment. The mean serum creatinine level improved significantly at the end of therapy compared to pre-treatment in those patients who did not experience nephrotoxicity in both treatment groups. 5/19 (26%) netilmicin-treated patients and 2/18 (11%) tobramycin-treated patients assessable for ototoxicity experienced decrements in auditory thresholds. Ototoxic netilmicin-treated patients had higher serum netilmicin levels than did non-ototoxic patients. Patients who experienced ototoxicity were not more likely to have experienced nephrotoxicity. The rates of toxicity were not statistically different and were similar to those seen in studies of patients with normal pre-treatment renal function.