Valtrex

How does it work?

Valtrex tablets contain the active ingredient valaciclovir. Valaciclovir is known as a pro-drug. Once inside the body it is broken down into the active ingredient aciclovir, which is an antiviral medicine used to treat infections with herpes viruses. These include the viruses that cause cold sores and genital herpes (herpes simplex 1 and 2) and the virus that causes chickenpox and shingles (varicella zoster or herpes varicellae). Aciclovir works by stopping these herpes viruses from reproducing and infecting more cells in the body.

Aciclovir is converted to a more active form inside cells of the body that are infected with herpes viruses. The activated aciclovir then works by blocking the action of a viral enzyme called DNA polymerase.

The herpes viruses need the DNA polymerase enzyme to copy their genetic material from RNA to DNA. This process is necessary for the viruses to multiply and continue to survive. By blocking the action of DNA polymerase, aciclovir prevents the herpes viruses from multiplying. This controls the infection and helps the immune system to deal with it.

Valaciclovir is taken by mouth to treat herpes infections that cause shingles (herpes zoster). It is also taken to treat herpes simplex infections of the skin and mucous membranes, including genital herpes. Valaciclovir can be used to treat recurrent flare-ups of herpes simplex infection. It is most effective at preventing the sores from developing if treatment is started as soon as the warning signs appear.

If you suffer from frequent herpes simplex flare-ups your doctor may prescribe valaciclovir for you to take regularly, to suppress the virus and prevent recurrences. Valaciclovir taken regularly can also reduce the risk of passing the genital herpes to a sexual partner, provided safe sex practices such as condoms are used as well. However, you should still avoid sexual contact when the sores are present to avoid passing on the virus.

Valaciclovir has a further use in preventing infection with cytomegalovirus (CMV) in people who have had a kidney transplant. CMV is another member of the herpes group of viruses. In healthy people this common virus normally produces symptoms milder than the common cold, but in people whose immune systems are compromised it can cause serious infection because the immune system cannot fight it.

People who have had kidney transplants are given powerful medicines that suppress the immune system in order to stop it attacking the transplanted organ. However, because they suppress the immune system, these medicines also suppress the ability of the body to fight infection. Valaciclovir is therefore given to people who have received a kidney transplant, in order to help the body kill off any CMV virus.

What is it used for?

Genital herpes

Herpes simplex infections of the skin, eg cold sores

Preventing recurrence of herpes simplex infections, eg recurrent cold sores or genital herpes

Reducing the risk of spreading genital herpes to a sexual partner (when used with safe sex practices such as using condoms)

Prevention of cytomegalovirus (CMV) infection in people who have had a kidney transplant

Shingles

Warning!

If you are at risk of becoming dehydrated it is important to drink plenty of fluids while taking this medicine.

When this medicine is used for genital herpes it does not provide a cure, or completely eliminate the risk of passing the virus to a sexual partner. You should continue to practice safe sex, particularly the use of condoms, in addition to taking this medicine. You should also avoid sexual contact while the sores are present.

Use with caution in

Decreased kidney function

Decreased liver function

Not to be used in

Allergy to aciclovir or valaciclovir

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

This medicine should be used with caution during pregnancy, and only if the expected benefit to the mother is greater than any possible risk to the foetus. Seek medical advice from your doctor.

This medicine passes into breast milk. It should be used with caution by breastfeeding mothers and only if the expected benefit to the mother is greater than any possible risk to the nursing infant. Seek medical advice from your doctor.

Label warnings

Take at regular intervals. Complete the prescribed course unless otherwise directed.

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