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Acyclovir (Between cheek and gum)

Acyclovir (ay-SYE-kloe-vir)

Treats cold sores (herpes labialis). This medicine is an antiviral.

Brand Name(s):

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

Do not use this medicine if you have had an allergic reaction to acyclovir or milk protein concentrate.

How to Use This Medicine:


  • Take your medicine as directed.
  • Use this medicine within 1 hour after you have the first symptom of a cold sore and before a cold sore begins.
  • You may eat and drink while the tablet is in place. Drink more liquids if your mouth becomes dry while using this medicine.
  • Avoid chewing gum, touching or pressing the tablet, wearing upper dentures, or brushing your teeth after the tablet has been placed.
  • If the tablet does not stick or falls off within the first 6 hours, use the same tablet and place it back onto your 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 gum.
  • Do not apply a new tablet if the tablet falls out or if you swallow it after it has been in place 6 hours or longer.
  • To use:
    • Peel back the cover of the blister pack to remove the tablet.
    • Apply the tablet on the same side of your mouth with the cold sores symptoms. For comfort, place the rounded side of the tablet against your gum.
    • Place the tablet on your upper gum above the tooth that is next to your front tooth with a clean, dry finger. Press on your upper lip lightly for 30 seconds to make sure it sticks.
    • The tablet will dissolve gradually throughout the day. Do not crush, chew, suck, or swallow the tablet.
  • Read and follow the patient instructions that come with this medicine. Talk to your doctor or pharmacist if you have any questions.

How to Store and Dispose of This Medicine:

  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.
  • Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any outdated medicine or medicine no longer needed.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

Warnings While Using This Medicine:

  • Make sure your doctor knows if you are pregnant or breastfeeding, or if you have a weak immune system.
  • Call your doctor if your symptoms do not improve or if they get worse.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing

If you notice these less serious side effects, talk with your doctor:

  • Pain or irritation of the gums

If you notice other side effects that you think are caused by this medicine, tell your doctor

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

Last Updated: 4/4/2014

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