The pharmacokinetics of once-daily dosing with gentamicin in women with postpartum endometritis

Once-daily dosing of gentamicin in obstetrics and gynecology

Gentamicin, an aminoglycoside with broad antimicrobial activity, is commonly used in both obstetrics and gynecology. Traditional dosing regimens for gentamicin have called for 3 times daily dosing, but recent insights into the pharmacodynamics of the drug have led to multiple studies of once-daily dosing regimens. Many studies have demonstrated efficacy, safety, and economy of the 24-hour dosing interval, resulting in recommendations that this become the standard for aminoglycoside administration. However, because of the unique considerations for drug administration in pregnant and postpartum women, the once-daily dosing regimens have not been widely adopted. Additional studies in pregnant and postpartum women have demonstrated therapeutic noninferiority, no increase in adverse events, and significant cost savings with once-daily dosing versus 3 times daily dosing of gentamicin. We review the literature and present rationale based on multiple controlled studies supporting single-daily dosing of gentamicin, 5 mg/kg/d actual body weight, for many common obstetrics-gynecology infections.

Single daily dosing of gentamicin: pharmacokinetic comparison of two dosing methodologies for postpartum endometritis

OBJECTIVE

We compared the pharmacokinetics of two methods for dosing gentamicin for the treatment of postpartum endometritis with the goal of achieving adequate peak serum concentrations (>12 mg/L) and prolonged trough levels below 2 mg/L.

METHODS

Group-I subjects (n = 5) received intravenous gentamicin, 5 mg/kg per total body weight over 60 min., with a maximum dose of 500 mg. Group-II subjects (n = 17) were dosed intravenously according to the following formula: Dose = desired peak concentration (fixed at 14 mg/L) * (volume of distribution, i.e., 0.35 L/kg) * adjusted body weight (in kilograms). Serum gentamicin levels were obtained 1 hr. and 8-12 hr. after infusion of the second dose. Pharmacokinetic parameters for the subjects in each group were calculated according to standard formulas.

RESULTS

Subjects in Group I had significantly higher doses and peak drug concentrations (P < 0.01), while in Group II, 76% of patients had peak levels less than desired (<12 mg/L). Both groups maintained trough levels of <2 mg/L in excess of 12 hr.

CONCLUSIONS

Changing to the adjusted body weight formula for Group I, while maintaining a dose between 4 and 5 mg/kg, would reduce excessive peak concentrations. Using a calculated volume of distribution of 0.4 L/kg in Group II would improve peak serum concentrations to the desired levels. Both dosing regimens ensure adequate aminoglycoside pharmacokinetic parameters and avoid the need for monitoring serial serum drug concentrations, provided the expected clinical response is also achieved. While the first dosing formula is simpler to calculate, the second dosing formula allows for more individualized dosing considerations.

The use of once-daily dosing of gentamicin in obstetrics and gynecology

Gentamicin is a widely-used antimicrobial agent for obstetric and gynecologic infections. Renewed excitement in this antibiotic has arisen from recent information supporting less frequent dosing. In this symposium, we will describe the pharmacokinetics of gentamicin and review new information advocating the use of once-daily administration of gentamicin.

The use of once-daily dosing of gentamicin in obstetrics and gynecology

Gentamicin is a widely-used antimicrobial agent for obstetric and gynecologic infections. Renewed excitement in this antibiotic has arisen from recent information supporting less frequent dosing. In this symposium, we will describe the pharmacokinetics of gentamicin and review new information advocating the use of once-daily administration of gentamicin.