Patients with Renal Impairment and in Elderly Patients: Aciclovir is eliminated by renal clearance; therefore the dose must be reduced in patients with renal impairment (see Dosage & Administration). Elderly patients are likely to have reduced renal function and therefore the need for dose reduction must be considered in this group of patients. Both elderly patients and patients with renal impairment are at increased risk of developing neurological side effects and should be closely monitored for evidence of these effects. In the reported cases, these reactions were generally reversible on discontinuation of treatment (see Adverse Reactions).
Hydration Status: Care should be taken to maintain adequate hydration in patients receiving high oral doses of aciclovir.
Effects on the Ability to Drive or Operate Machinery: The clinical status of the patient and the adverse event profile of Zovirax should be borne in mind when considering the patient's ability to drive or operate machinery. There have been no studies to investigate the effect of aciclovir on driving performance or the ability to operate machinery. Further, a detrimental effect on such activities cannot be predicted from the pharmacology of the active substance.
Use in pregnancy: 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 aciclovir should be considered only when the potential benefits outweigh the possibility of unknown risks.
Use in lactation: Following oral administration of aciclovir 200 mg 5 times a day, aciclovir has been detected in breast milk at concentrations ranging from 0.6-4.1 times the corresponding plasma levels. These levels would potentially expose nursing infants to aciclovir dosages of up to 0.3 mg/kg/day. Caution is therefore advised if Zovirax is to be administered to a nursing woman.