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Acyclovir (Buccal mucosa)

Generic name: acyclovir [ ay-SYE-kloe-vir ]
Drug class: Purine nucleosides

Medically reviewed by Last updated on Feb 7, 2023.

Uses for acyclovir

Acyclovir buccal tablet is used to treat the symptoms of herpes simplex virus infection on the lips and around the mouth (cold sores) in adults with normal immune systems. Although this medicine will not cure herpes simplex, it may help the sores to heal faster and relieve some of the pain and discomfort. Acyclovir is an antiviral agent (treats a virus).

This medicine is available only with your doctor's prescription.

Before using acyclovir

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of acyclovir buccal tablets in the pediatric population. Safety and efficacy have not been established. Use in younger children is not recommended due to the potential risk of choking.


Although appropriate studies on the relationship of age to the effects of acyclovir buccal tablets have not been performed in the geriatric population, no geriatric-specific problems have been documented to date.

Breast Feeding

Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Bupropion
  • Dichlorphenamide
  • Emtricitabine
  • Fexinidazole
  • Foscarnet
  • Leflunomide
  • Nitisinone
  • Tenofovir Alafenamide
  • Teriflunomide

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Fosphenytoin
  • Phenytoin
  • Valproic Acid

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Allergy to milk protein concentrate—Should not be used in patients with this condition.
  • Weak immune system—This medicine may not be safe to use in patients with this condition.

Proper use of acyclovir

Use this medicine exactly as directed by your doctor to benefit your condition as much as possible. Do not use more of it, do not use it more often, and do not use it for a longer time than your doctor ordered.

This medicine should come with a patient information leaflet. Read and follow these instructions carefully. Ask your doctor or pharmacist if you have any questions.

This medicine is only for cold sores on the lips and around the mouth.

To use:

  • Peel the blister back to remove the tablet. Do not push the tablet through the blister as this may damage the tablet.
  • Use this medicine within 1 hour after you have the first symptom of a cold sore, such as itching, redness, burning, or tingling, and before a cold sore begins.
  • Place the tablet in the mouth, on the upper gum above the incisor tooth, with a clean, dry finger. Press on the upper lip lightly for 30 seconds to ensure adhesion.
  • For comfort, place the rounded side of the tablet facing the upper gum
  • The tablet will dissolve slowly during the day. Do not crush, chew, suck, or swallow the tablet.
  • Apply the tablet on the same side of the mouth with the cold sores symptoms.
  • You may eat and drink while the tablet is in placed on your upper gums.
  • Drink more liquids if your mouth becomes dry while using this medicine.
  • Avoid chewing gums, touching or pressing the tablet after it is placed, wearing upper dentures, or brushing your teeth while using this medicine.
  • Do not remove the tablet if it sticks to your upper gum. If the tablet does not stick or falls off of your upper gum within the first 6 hours that you have applied, use the same tablet and place it back onto your upper gum. If it still does not stick, replace it with a new tablet.
  • If you swallow the tablet within the first 6 hours of applying it, drink a glass of water and place a new tablet on your upper gum.
  • Do not reapply a new tablet if it falls out or if you swallow it after it has been placed 6 hours or longer.


The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For buccal dosage form (tablets):
    • For cold sores:
      • Adults—50 milligrams (mg) as a single dose.
      • Children—Use and dose must be determined by your doctor. Use in younger children is not recommended due to the potential risk of choking.


Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Precautions while using acyclovir

It is very important that your doctor check your progress after you use this medicine to see if it is working properly.

If your symptoms do not improve within a few days, or if they become worse, check with your doctor.

Side Effects of acyclovir

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

Less common

  • Canker sores
  • pain in the gums
  • sores, ulcers, or white spots on the tongue or inside the mouth

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

  • Flushing or redness of the skin
  • rash
  • unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
  • unusually warm skin

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Frequently asked questions

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.