Letter: Gentamicin resistance

Development of resistance during antibiotic therapy

The frequency of development of resistance during antibiotic therapy was evaluated by reviewing the literature according to prescribed criteria. Mean resistance rates were calculated to be 9.2% for broad spectrum penicillins, 8.6% for second and third generation cephalosporins, 10.0% for latamoxef, 4.7% for imipenem, 11.8% for ciprofloxacin and 13.4% for aminoglycosides. Emergence of resistance of the infecting organism was associated with therapeutic failure in about half of the cases with the exception of patients treated with aminoglycosides in whom development of resistance resulted in treatment failure in 85% of the cases. The possible benefit of combination therapy in terms of resistance development is discussed.

Emergence of multiple antibiotic resistance during the therapy of Klebsiella pneumoniae meningitis

A patient is described in whom multiple antibiotic resistance developed during the course of therapy of Klebsiella pneumoniae meningitis. Sequential resistance developed to chloramphenicol, gentamicin and eventually amikacin. As previously reported, the use of the chloramphenicol alone in the therapy of gram-negative bacillary meningitis can result in rapid emergence of resistance and treatment failure. In this patient, the subsequent emergence of gentamicin and amikacin resistance may have been related to the omission of intrathecal aminoglycoside. A short review of the literature is presented and recommendations are made for the therapy of gram-negative bacillary meningitis.

Pharmacokinetics of amikacin in infants and pre-school children

The pharmacokinetic properties of amikacin sulfate in infants and children aged from three weeks to 6 years were studied during treatment with doses of 7.5 mg/kg every 12 hours using standard assay methods and technique of two compartment open model kinetic analysis. Peak serum concentrations of amikacin were measured 30 or 60 min after the first intramuscular injection. These ranged from 11.8 microgram/ml to 23 microgram/ml in infants and from 9.0 microgram/ml to 29 microgram/ml in children. Five minutes after the first intravenous bolous injection they varied from 16 microgram/ml to 29.8 microgram/ml in infants and from 34 microgram/ml to 42 microgram/ml in children. Twelve hours after injection serum concentrations were less than 0.8 microgram/ml in all patients. Mean serum half-lives of amikacin in infants and children were 2.1 hours and 2.0 hours after intramuscular, and 2.2 and 2.0 hours after intravenous administration respectively. No evidence of accumulation was observed after four days treatment. The amount of antibiotic recovered within 12 hours from the urine in all patients ranged from 34.5 to 65% of an intramuscular dose, and from 45.8 to 63.3% of an intravenous dose. The dosage regime of 7.5 mg/kg body weight given every 12 hours should be safe and effective for the treatment of infections in the age groups studied.

Anaerobic resistance of clinical isolates of Staphylococcus aureus to aminoglycosides

The anaerobic minimum inhibitory concentration of six aminoglycosides (amikacin, gentamicin, kanamycin, netilmicin, sisomicin, and tobramycin) averaged over 10-fold greater than the aerobic minimum inhibitory concentration for 50 clinical isolates of Staphylococcus aureus. Cultures from osteomyelitis and blood generally showed a somewhat greater increase in minimum inhibitory concentration due to anaerobiosis than did cultures from abscesses and wounds, and amikacin activity was most affected by anaerobiosis.

Tobramycin, amikacin, sissomicin, and gentamicin resistant Gram-negative rods

Sensitivities to gentamicin, sissomicin, tobramycin, and amikacin were compared in 196 gentamicin-resistant Gram-negative rods and in 212 similar organisms sensitive to gentamicin, mainly isolated from clinical specimens. Amikacin was the aminoglycoside most active against gentamicin-resistant organisms, Pseudomonas aeruginosa, klebsiella spp, Escherichia coli, Proteus spp, Providencia spp, and Citrobacter spp being particularly susceptible. Most of the gentamicin-resistant organisms were isolated from the urine of patients undergoing surgery. Gentamicin was the most active antibiotic against gentamicin-sensitive E coli, Proteus mirabilis, and Serratia spp. Pseudomonas aeruginosa and other Pseudomonas spp were most susceptible to tobramycin.