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 an organ transplant such as 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 an organ transplant 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 an organ transplant, in order to help the body kill off any CMV virus.
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.
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.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.
For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
You should tell your doctor or pharmacist what medicines you are using, particularly those listed below, before you start treatment with this medicine. This includes those bought without a prescription and herbal medicines. Likewise, check with your doctor or pharmacist before starting any new medicines while you are taking this medicine, to make sure that the combination is safe.
There may be an increased risk of side effects on the kidneys if valaciclovir is used in combination with the following medicines, and your doctor may want to monitor your kidney function if you are taking valaciclovir with any of these:
The blood level of this medicine may be increased by the following medicines:
This is not normally clinically important. However, where high doses of valaciclovir are being used to prevent CMV infection, eg following an organ transplant, your doctor may consider using alternatives to these medicines, or simply monitor you more closely.
Valaciclovir tablets are also available without a brand name, ie as the generic medicine.