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In a retrospective study we have compared the toxic side effects related to the use of two antibiotic regimens in the treatment of febrile episodes in neutropenic, leukaemic patients undergoing first remission-induction. Nephrotoxicity was more severe in the gentamicin-mezlocillin (G/M) group: four patients developed oliguric renal failure and two others showed rises in the serum creatinine of more than 0.03 mmol/l. One of the two patients in the gentamicin-ticarcillin (G/T) group who showed nephrotoxicity developed renal failure. Ototoxicity and skin rashes were more commonly observed with G/M than with G/T, and the differences were statistically significant for both ototoxicity (P = 0.0004) and drug rashes (P = 0.02). The cause of the observed differences in toxicity has not been identified.

The nephrotoxicity of the aminoglycoside gentamicin was evaluated in an open, controlled study of newborn infants randomly allocated to receive either combination drug therapy with gentamicin and ampicillin or single drug therapy with mezlocillin for treatment of presumed neonatal sepsis. There were no significant differences in initial clinical characteristics between the groups. Neonates receiving gentamicin, in contrast to those receiving mezlocillin, had significant nephrotoxicity manifested by a smaller postnatal fall in mean serum creatinine concentration (-9%, P NS vs -21%, P less than 0.005, respectively) and a diminished postnatal rise in mean creatinine clearance (+ 21%, P NS vs + 51%, P less than 0.01, respectively). In neonates with a fall in creatinine clearance, the mean decline was significantly greater in those receiving gentamicin (44% vs 20%, P less than 0.01). There was no relationship between the incidence of gentamicin nephrotoxicity and either peak or trough gentamicin levels. For treatment of presumed neonatal sepsis, gentamicin proved more nephrotoxic than mezlocillin.

Forty-six patients with cholangitis were randomized to receive therapy with mezlocillin sodium (24 patients) or a combination of ampicillin sodium--gentamicin sulfate (22 patients). The biliary concentration of mezlocillin was 112 times higher than that of ampicillin and 778 times higher than that of gentamicin. The ratio of the concentration in serum or bile over the minimum inhibitory concentration against aerobic gram-negative bacilli (therapeutic index) was higher for mezlocillin than for either ampicillin or gentamicin. Twenty (83%) of 24 patients were cured following mezlocillin therapy compared with 9 (41%) of 22 patients after ampicillin-gentamicin therapy. The 3 patients with superinfection were in the ampicillin-gentamicin arm of the study. Fewer toxic or adverse effects occurred in association with mezlocillin treatment than with ampicillin-gentamicin treatment. Mezlocillin therapy was more effective, less toxic, and less expensive than treatment with ampicillin and gentamicin for patients with cholangitis.

In 54 patients suffering from a variety of severe systemic infections the combination of mezlocillin (4 g iv 6-hourly) plus cefotaxime (2 g iv 8-hourly) was compared to that of gentamicin (1.5 mg/kg im or iv 8-hourly) plus cefoxitin (2 g iv 6-hourly). In the gentamicin/cefoxitin group metronidazole (500 mg iv 8-hourly) was added for anaerobic infections. Treatment assignment was randomized. The patients' diagnoses were: pyelonephritis (24), pneumonia (14), infected burns (9), osteomyelitis (2), and abdominal infections (5). Pathogens included: Escherichia coli (31), other Enterobacteriaceae (21), Pseudomonas aeruginosa (13), anaerobes (4), and others (2). Treatment with mezlocillin/cefotaxime cured 20 (74%) of 27 patients and caused improvement in 5, while in 19 (70%) patients the pathogens were eradicated. In the gentamicin/cefoxitin group 17 (63%) of 27 patients were cured and 6 improved, while in 15 (56%) pathogens were eradicated. One patient in the first group developed a rash, while in the second group two patients developed thrombophlebitis and another two transient nephrotoxicity. The combination of mezlocillin and cefotaxime can be recommended for the rational and empirical treatment of serious systemic infections.

Two patients developed acute interstitial nephritis (AIN) following treatment with mezlocillin sodium. Diagnosis was made by renal biopsy. Gallium 67 citrate scanning was abnormal in both. All patients were receiving multiple-drug therapy, but AIN has either not been described with the other drugs, or the temporal relationship between the AIN and termination of other drug therapy makes a causative relationship unlikely. All were infected with Pseudomonas aeruginosa. A role for the infecting organism or drug synergism in contributing to the renal disease cannot be excluded.