Acyclovir

Acyclovir is an antiviral used to treat and manage several infections caused by herpes viruses. The specific approved uses vary by product form:

• Shingles (herpes zoster) — oral tablets, capsules, and suspension
• Chickenpox (varicella) — oral tablets, capsules, and suspension
• Initial and recurrent genital herpes — oral tablets, capsules, and suspension; acyclovir ointment and Zovirax Ointment for initial genital herpes and limited mucocutaneous herpes in immunocompromised patients
• Suppression of recurrent genital herpes — Valacyclovir tablets (long-term use)
• Cold sores (herpes labialis) in immunocompetent adults and adolescents 12+ — Valacyclovir tablets, Sitavig buccal tablet, Zovirax Cream, and acyclovir cream 5%
• Herpes simplex (HSV-1 and HSV-2) infections of the skin and mucous membranes in immunocompromised patients — acyclovir and Acyclovir Sodium injections
• Severe initial genital herpes in immunocompetent patients — acyclovir and Acyclovir Sodium injections
• Herpes simplex encephalitis (herpes infection of the brain) — acyclovir and Acyclovir Sodium injections
• Neonatal herpes simplex infections (in newborns and infants) — acyclovir and Acyclovir Sodium injections
• Shingles (varicella-zoster) in immunocompromised patients — acyclovir and Acyclovir Sodium injections
• Acute herpetic keratitis (herpes ulcer on the cornea) — Avaclyr ophthalmic ointment

Acyclovir is an antiviral drug that specifically targets alpha-herpesviruses — the family that includes herpes simplex virus (HSV-1 and HSV-2) and varicella-zoster virus. It works by blocking a key enzyme the virus needs to copy its DNA. Without that ability, the virus can't multiply and spread as effectively, which helps your body's immune system get the infection under control and reduces the severity and duration of symptoms.

When taken by mouth as valacyclovir, the body converts it into acyclovir, which then goes to work against the virus. When Sitavig buccal tablet is applied to the gum, it releases acyclovir directly into the saliva at high local concentrations, while very little enters the bloodstream.

How acyclovir is taken depends entirely on the form prescribed and the condition being treated. Oral tablets, capsules, and suspension are taken by mouth multiple times per day — often 2 to 5 times daily — with or without food. Valacyclovir tablets specifically can be taken without regard to meals. Topical creams and ointments are applied directly to the affected skin several times a day. Sitavig buccal tablet is applied just once as a single dose to the upper gum at the first sign of a cold sore — it is not swallowed. Avaclyr eye ointment is applied to the affected eye multiple times daily until the ulcer heals, then less frequently for another week. Injectable acyclovir is given by a healthcare professional by slow intravenous infusion over at least one hour.

• Start treatment as early as possible — timing matters for all forms
• For long-term suppressive therapy for genital herpes, your doctor will re-evaluate the need after one year
• Never adjust your dose or stop early without talking to your prescriber

The most commonly reported side effects with oral acyclovir/valacyclovir include:

• Headache
• Nausea
• Abdominal (stomach) pain
• Vomiting
• Dizziness
• Fatigue
• Rash

More serious reactions that require prompt medical attention include signs of kidney problems (decreased urination, swelling), confusion or hallucinations (central nervous system effects), and unusual bruising or bleeding, which may signal a rare but life-threatening blood disorder called TTP/HUS. Stop taking acyclovir and contact your doctor immediately if any of these occur.

• Kidney damage: Acyclovir can cause acute kidney failure, especially in older adults, people with existing kidney problems, those not drinking enough fluids, and those on other kidney-affecting drugs. Staying well hydrated is essential. Doses must be adjusted for impaired kidney function.
• Central nervous system reactions: Confusion, hallucinations, agitation, seizures, and encephalopathy (brain dysfunction) have been reported — more commonly in elderly patients and those with kidney problems. Stop acyclovir and seek medical care if these occur.
• TTP/HUS (thrombotic thrombocytopenic purpura/hemolytic uremic syndrome): A rare, potentially fatal blood disorder has been reported in immunocompromised patients. Stop treatment immediately if signs appear.
• IV injection safety: Injectable acyclovir must be given by slow IV infusion only — never by rapid injection, intramuscular, or subcutaneous injection. Rapid IV injection increases the risk of kidney damage.

Drug interaction information varies by form. For topical acyclovir cream, no significant interactions with other topical or systemic drugs have been identified, and systemic interactions are unlikely due to minimal absorption through the skin.

• Drugs that affect the kidneys: Using acyclovir (especially oral or IV forms) alongside other nephrotoxic drugs (medicines that can harm the kidneys) increases kidney risk — tell your prescriber about all your medications
• Adequate hydration is important to prevent acyclovir from crystallizing in the kidneys, which can happen if you're not drinking enough fluids

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Tell your doctor if you have kidney disease or reduced kidney function — dosing adjustments are required
• Older adults face higher risks of kidney problems and central nervous system side effects — extra monitoring may be needed
• Do not use acyclovir cream if you have a known allergy to acyclovir, valacyclovir, or any ingredient in the formulation
• If you are pregnant: use acyclovir only if your doctor decides the benefit clearly outweighs the risk; registry data on over 700 pregnancies did not show an increased rate of birth defects, but the data are not large enough to rule out all risks
• If you are breastfeeding: acyclovir does pass into breast milk; use with caution and discuss with your doctor
• Sitavig buccal tablet and Zovirax Cream are approved for cold sores in adults and adolescents 12 years and older; not all forms are approved for young children
• Immunocompromised patients (weakened immune system) may have different dosing needs and are at higher risk for serious complications — make sure your doctor knows your full health history

Taking too much acyclovir has been associated with agitation, coma, seizures, and lethargy. Overdose can also cause acyclovir to crystallize in the kidneys, leading to kidney failure with elevated waste products in the blood. If kidney failure occurs, hemodialysis (a kidney-filtering treatment) may be needed until kidney function recovers. If you think you or someone else has taken too much, seek emergency medical help immediately.

When Sitavig buccal tablet is applied to the gum, it releases high concentrations of acyclovir directly into saliva — levels that are well within the range needed for antiviral activity. The tablet adheres for a median of about 14 hours. Very little acyclovir from the buccal tablet reaches the bloodstream, and the low plasma levels that do appear are below what would be needed for systemic antiviral effect. Acyclovir is broken down in the body by oxidation and hydroxylation into metabolites, and is primarily excreted unchanged by the kidneys.

stored at 20 to 25°C (68 to 77°F) ; excursions between 15 and 30°C (59-86°F) permitted at room temperature. Protect from moisture and keep out of reach of children.