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Acyclovir Patient Tips

Written by C. Fookes, BPharm on Sep 27, 2016

How it works

  • Acyclovir is an antiviral drug that has activity against herpes simplex virus types 1 (HSV-1), 2 (HSV-2), and varicella-zoster virus (VZV).
  • Acyclovir works in a number of different ways to prevent these viruses from replicating. Activity against HSV is greater than activity against VZV.


  • Acyclovir is used to treat infections caused by herpes and varicella zoster viruses, such as genital herpes, cold sores, shingles, and chicken pox.
  • Acyclovir does not cure genital herpes or completely rid the body of the herpes or varicella zoster virus.


If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Nausea, vomiting, diarrhea, headache, and a general unwell feeling. Buccal tablets may cause mouth pain. Rarely, may effect kidneys or cause a bleeding disorder.
  • May not be suitable for everybody, including people with kidney problems, taking certain medications, or in those who are dehydrated.
  • Acyclovir treatment is usually dosed five times daily.

Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.

Bottom Line

Acyclovir is an antiviral drug that helps treat herpes and varicella zoster infections. It is most effective when started within 48 hours of symptom onset.


  • Acyclovir treatment is best started within 72 hours of symptom onset (ie, rash, blisters, tingling, burning) and most effective if started within 48 hours.
  • Take acyclovir for the exact time prescribed by your doctor, even if your symptoms improve.
  • Shake acyclovir oral suspension well before using. Use a proper dosing syringe or medicine cup to correctly measure dosage.
  • If you have been prescribed buccal tablets to treat a cold sore, place the flat side of the buccal tablet against your upper gum, behind your lip and in front of your canine tooth on the same side of your mouth as the cold sore. Close your mouth and gently press on the outside of your lip to hold the tablet in place for 30 seconds. Allow the tablet to slowly dissolve; eating and drinking may continue as normal while the buccal tablet is in place.
  • If you are taking acyclovir long-term and your weight changes, let your doctor know as acyclovir dosages are based on weight.
  • Drink plenty of water while taking acyclovir.
  • Although acyclovir treats viruses, it is not effective against the flu or the common cold.
  • If you have a shingles rash or a cold sore, try and keep it as clean and dry as possible; although you must be careful not to transfer the virus to others, so always use disposable tissues or a separate towel that is washed by itself. Wearing loose clothing may help prevent irritation of a shingles rash.
  • Seek urgent medical advice if you have any signs of an allergic reaction (such as hives; difficulty breathing; facial or throat swelling).
  • Herpes infections are highly contagious and you should cover your rash and avoid intimate contact. Also, avoid touching the rash and then your eyes. Wash hands frequently.

Response and Effectiveness

  • May take up to two hours to reach peak plasma concentrations after oral acyclovir administration.
  • May take up to three days for symptom reduction; however, acyclovir should be taken until the course prescribed is completed. Best started within 48 hours of symptom onset.


Acyclovir capsules [Package Insert] Revised 08/2016 DAVA Pharmaceuticals, Inc

  • Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use acyclovir only for the indication prescribed.

  • Disclaimer: Every effort has been made to ensure that this information is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. This drug information does not endorse drugs, diagnose patients or recommend therapy. It is an informational resource designed as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of this information. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2017 Revision Date: 2016-10-05 00:00:00