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Carbenicillin-gentamicin interaction in acute renal failure
American Journal of Hospital Pharmacy
|October 1, 1977
Summary
High doses of carbenicillin can inactivate gentamicin, leading to subtherapeutic levels in patients with renal failure. Reducing carbenicillin dosage and monitoring drug levels are crucial for effective gentamicin therapy.
Area of Science:
- Pharmacology
- Nephrology
- Infectious Diseases
Background:
- Gentamicin is a critical antibiotic for severe infections, often used in patients with renal impairment.
- Carbenicillin, a penicillinase-resistant penicillin, is sometimes co-administered with gentamicin.
- In vitro studies suggest potential inactivation of gentamicin by carbenicillin.
Observation:
- A case study involving a 77-year-old male with acute renal failure receiving both carbenicillin and gentamicin.
- Despite separate administration, subtherapeutic gentamicin serum levels (<2 microgram/ml) were observed.
- High carbenicillin dosage (15 g/day) correlated with elevated carbenicillin levels (>500 microgram/ml) and rapid gentamicin inactivation.
Findings:
- Carbenicillin significantly inactivated gentamicin, resulting in ineffective therapeutic levels even with high gentamicin doses (1.8 mg/kg/day).
- Discontinuation of carbenicillin allowed for achievement of therapeutic gentamicin levels with standard dosing (0.9-1.8 mg/kg/day).
- The rate of gentamicin inactivation was directly influenced by the carbenicillin dose and resulting serum concentrations.
Implications:
- In patients with severe renal failure, high-dose carbenicillin therapy may necessitate a reduced carbenicillin dose to prevent gentamicin inactivation.
- Frequent therapeutic drug monitoring of both gentamicin and carbenicillin serum levels is recommended when co-administered in renal impairment.
- This case highlights the importance of considering drug-drug interactions and pharmacokinetic changes in patients with compromised renal function.