Effect of ampicillin on bleeding time in very low birth-weight neonates during the first week after birth

On the day of birth, the bleeding time of very low birth-weight (VLBW, <1500 g) neonates is generally prolonged, compared with term neonates. However, their bleeding time generally improves (shortens) over the next 7 to 10 days. Ampicillin can prolong the bleeding times of term and late preterm neonates, but its effect on VLBW neonates, who already have a somewhat prolonged bleeding time initially, is not known.

This was a prospective, single-centered, paired, before vs after test of the effect of ampicillin on template bleeding time and PFA-100 time (platelet function analyzer). Ampicillin was dosed at every 12 h intravenously, but decisions about discontinuation were made by the responsible clinician, independent of this study.

A total of 20 VLBW neonates were studied. They ranged from 23- to 30-weeks gestation at birth and weighed 500 t 1410 g. Initial bleeding times averaged 166 s (95% CI, 138 to 194) and initial PFA-100 times averaged 119 s (95% CI, 90 to 148). In all, 10 had ampicillin dosing stopped after a shorter course (4 to 7 doses) and 10 had it continued for a longer course (10 to 15 doses). Blood cultures were sterile in all 20, and no differences in laboratory or clinical features were found between those treated with a shorter vs longer course. After stopping the ampicillin following a short course the bleeding times and PFA-100 times were similar to the initial values. However, after a longer course the bleeding times were prolonged by an average of 2 min, to 284 s (95% CI, 242 to 326; P=0.001 vs initial). The PFA-100 times also trended longer by an average of 44 s (P=0.07). The number of doses of ampicillin received in the first week correlated with the degree of prolongation in bleeding time (r=0.68).

Over the first week of life, a period when the bleeding time of VLBW neonates normally shortens, the opposite occurred (the bleeding time lengthened) if ≥ 10 doses of ampicillin were administered.