Acyclovir is a medication used to treat viral infections such as herpes simplex, varicella-zoster, and herpes zoster. While acyclovir is generally well-tolerated, there are some rare side effects that may occur.

According to DrugPatentWatch [1], rare side effects of acyclovir may include confusion, hallucinations, seizures, and tremors. These side effects are more likely to occur in people with kidney problems or in those taking high doses of acyclovir.

Medical News Today [2] reports that other rare side effects of acyclovir may include anemia, low platelet count, and liver problems such as hepatitis and jaundice. These side effects are more likely to occur in people with pre-existing liver or blood disorders.

WebMD [3] notes that while rare, some people may experience an allergic reaction to acyclovir, which can cause symptoms such as rash, itching, swelling, and difficulty breathing.

It is important to note that while rare, these side effects can be serious and require immediate medical attention. If you experience any unusual symptoms while taking acyclovir, it is important to contact your healthcare provider right away.

Sources:
1. https://www.drugpatentwatch.com/p/tradename/ACYCLOVIR
2. https://www.medicalnewstoday.com/articles/acyclovir-side-effects
3. https://www.webmd.com/drugs/2/drug-941/acyclovir-oral/details