Turning to adverse effects of active therapy, the researchers found no differences between acyclovir and placebo groups, and there were no adverse events that led to discontinuation of the study drug.
Previous studies have suggested that acyclovir may be associated with neutropenia. There were no differences in absolute neutrophil counts between acyclovir and placebo groups in either CASG 103 or CASG 104, although there was a nonsignificant trend toward neutropenia with acyclovir. Low-normal absolute neutrophil counts (500 cells/mcL or less) developed in 25% of the subjects receiving acyclovir in CASG 103 and in 20% of those receiving acyclovir in CASG 104, compared with only 5% and 7%, respectively, of babies receiving placebo.
However, "it is possible that there is indeed an association that our studies were underpowered to detect; thus, we believe that neutropenia should continue to be considered as a possible toxic effect of longer-term oral acyclovir therapy," Dr. Kimberlin and his associates said.
These studies were supported by the National Institute of Allergy and Infectious Diseases. Oral acyclovir and matching placebo were provided by GlaxoSmithKline, Alpharma USPD, and Pharm Ops. Dr. Kimberlin’s associates reported ties to numerous drug companies.