A post-marketing aciclovir pregnancy registry has documented pregnancy outcomes in women exposed to any formulation of Zovirax. The birth defects described amongst Zovirax exposed subjects have not shown any uniqueness or consistent pattern to suggest a common cause.
The use of Zovirax Cream should be considered only when the potential benefits outweigh the possibility of unknown risks.
Systemic administration of aciclovir in internationally accepted standard tests did not produce embryotoxic or teratogenic effects in rabbits, rats or mice.
In a non-standard test in rats, foetal abnormalities were observed but only following such high subcutaneous doses that maternal toxicity was produced. The clinical relevance of these findings is uncertain. Limited human data show that the drug does pass into breast milk following systemic administration.