Gentamicin dosage intervals in neonates: longer dosage interval--less toxicity.

OBJECTIVES The aim of this study was to determine the incidence of toxic trough serum gentamicin levels in neonates in the first week of life, with different dosage intervals. METHODS This was a retrospective study of neonates born between 01.07.95 and 31.12.95, who received gentamicin. Data were collected on birth weight, gestation, gentamicin dose, the trough level of gentamicin, serum creatinine and urine output. A trough serum gentamicin level of > or =1.5 mg/L was considered toxic. RESULTS One hundred and seventy infants met the study criteria. All 21 infants in group one (24-29 weeks) received gentamicin with a dosage interval of 24 h. Sixteen (76%) infants had toxic trough serum gentamicin levels. In group two (30-34 weeks) 8 infants had gentamicin q12hly and all (100%) had toxic trough serum gentamicin levels. Fourteen infants had gentamicin every 18 h and 13 (93%) had toxic trough serum gentamicin levels. Sixty-one infants had gentamicin q24hly and 25 (41%) had toxic trough serum gentamicin levels. The differences in proportions with toxic levels were statistically significant. In group three (> or =35 weeks) 29 infants had gentamicin q12hly and 25 (86%) had toxic trough serum gentamicin levels. Six infants had gentamicin every 18 h and 2 (33%) had toxic trough serum gentamicin levels. Thirty-one infants had gentamicin q24hly and 4 (13%) had toxic trough serum gentamicin levels. The differences in proportions comparing infants having gentamicin q12hly with those having it q24hly were statistically significant. CONCLUSIONS A starting gentamicin dosage interval of 12 h in infants of any gestational age, or a starting dosage interval of 24 h for infants of less than 30 weeks gestational age, leads to most having toxic trough serum gentamicin levels. In infants of 30 weeks gestational age or greater, most have safe non-toxic trough serum gentamicin levels if started on a dosage interval of 24 h.