Med of the Month: Acyclovir

Before valacyclovir and famciclovir, there was acyclovir — the OG of targeted antivirals. Discovered by Nobel Prize-winning chemist Gertrude Elion, acyclovir transformed how we treat herpes viruses by targeting only infected cells and sparing the rest. But just because it’s old doesn’t mean it’s obsolete. Dentists still encounter this drug often—whether managing post-op herpes outbreaks or treating patients already taking it. Here's a refresher on what makes acyclovir fascinating, and what makes it risky.

Generic Name: Acyclovir

Brand Name(s): Zovirax, Sitavig

Pronunciation: a SYE klo veer

About this drug:

• Acyclovir is an antiviral medication used to treat infections caused by the herpes virus such as cold sores, shingles, genital herpes, and chicken pox.

• It will not cure a common cold or flu, nor will it cure herpes but it will help reduce the symptoms.

• It is not effective in treating non-viral aphthous stomatitis (canker sores).

Dentistry-related tidbits:

• Acyclovir may increase bleeding and bruising.

• Acyclovir has many drug interactions with medications commonly prescribed in the dental setting. Referencing a resource like the MedAssent DDS Rx Check tool can help prevent potential drug interactions or adverse effects. 

• Here are some of the most important interactions to pay attention to if you’re prescribing:

  • Combining NSAIDs, aspirin, aspirin-containing products, or the lincosamide antibiotic Clindamycin with acyclovir may increase acyclovir levels and the risk of nephrotoxicity.

  • Combining benzodiazepines, anticonvulsants (e.g. gabapentin, pregabalin, carbamazepine), or the narcotic tramadol with acyclovir may decrease the seizure threshold.

  • This medication may increase bleeding and bruising.

  • Combining the muscle relaxant tizanidine with acyclovir may increase the risk of hypotension, orthostasis, syncope, bradycardia, CNS depression, and diminished psychomotor function.

• If prescribing acyclovir, here are some helpful things to keep in mind:

  • The Sitavig buccal tablets are extremely expensive. Prescribe only if there is no other choice. This medication is not commonly carried in the pharmacy and may require a special order in addition to needing preauthorization by the insurance company if the patient has drug coverage insurance.

  • Do not prescribe acyclovir to a patient who is pregnant or breastfeeding.

  • Consider prescribing 2% Viscous Lidocaine to apply to ulcers if the patient complains about pain.

  • Consider prescribing chlorhexidine (Peridex Rinse) if you think the patient will not be able to brush well.

  • Remind the patient to drink large quantities of liquids to keep the kidneys working properly.

  • Speak with the patient's physician before prescribing acyclovir for chronic or immunosuppressed patients requiring long-term therapy.

  • Inform patients that they may still transmit herpes while they are taking this medication. Infected areas are contagious, so do not touch and be sure to wash hands often to prevent spreading infections.

  • Acyclovir may slow thinking or reactions. Advise the patient to be careful when driving, operating machinery, or engaging in other activities that require them to be alert until they know how this medication affects them.

Fun facts:

• Acyclovir was the first true targeted antiviral, discovered in the 1970s by Nobel Prize winner Gertrude Elion, and marked a turning point in the treatment of viral infections.

• It works by mimicking guanosine, a DNA building block, and once inside a virus-infected cell, it halts DNA replication by acting as a chain terminator. Its genius lies in its selectivity: it’s only activated by viral enzymes (thymidine kinase), which means it targets infected cells while sparing healthy ones.

• Due to low oral absorption (~10–30%), the prodrug valacyclovir was later developed to enhance bioavailability and improve dosing convenience.

• Acyclovir may make the skin burn more easily in the sunlight. Advise patients to apply sunscreen SPF 30 or higher when outdoors.

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