In this episode, I’ll discuss whether to use actual, ideal, or adjusted body weight when dosing gentamicin in pregnant patients.
Aminoglycosides such as gentamicin are very rarely used in pregnancy to treat infections. Gentamicin crosses the placenta, and is pregnancy category D. Case reports of congenital deafness following maternal use of streptomycin are responsible for the pregnancy category of D that gentamicin receives.
One indication that gentamicin is used for in pregnant patients is intrapartum chorioamnionitis. In one study of 126 women with this condition, gentamicin was dosed by actual body weight. A review article published in 2008 also found that the most common dose used in studies of gentamicin in pregnant patients was 5 mg/kg of actual body weight.
Therefore if gentamicin use in pregnancy cannot be avoided, actual body weight appears to be the dosing weight that has the most published evidence behind it.
Shout out to “Pharmacy Mari-Len” for the idea for this episode!
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This is a surprisingly controversial topic where I work. We had pharmacists from who trained at different hospitals that dose gent in obstetrics on adjusted body weight, while the pharmacist who works most in our OB population utilized actual body weight. We might all be wrong though as Martingano D, et al published 2 studies in 2018 using 5mg/kg of ideal body weight for postpartum endometritis compared to traditional q8h dosing. Between the 2 studies they enrolled 660 patient of which 335 was the 5mg/kg. There was not a significant difference between the 2 groups. This is the largest patient population I have found in any dosing strategy (IBW vs AdjBW vs ActBW).
Another thing to consider in these patients will be if they are pre or post partum. Most all the studies for once daily dosing of gent is in post-partum, so we will typically use traditional dosing while pre-partum.