Long-Term Side Effects of Valtrex

Valtrex, generic name valacyclovir, is an antiviral prescription medication used to treat some herpes infections, including cold sores, shingles and chicken pox. It is also used to treat genital herpes, initially and as a preventative in recurrent infections, with some taking Valtrex long term. According to PubMed Health, Valtrex does not cure the infection but acts to decrease pain and itching. It prevents new sores from forming and heals existing sores more quickly, but there are some side effects associated with its long-term use.

Kidney and Liver Abnormalities

Valtrex can affect kidney function, resulting in kidney failure. Valtrex, taken orally or intravenously, can lead to renal toxicity and renal failure in some who take the drug long term. According to the American Social Health Association, Valtrex converts to acyclovir as it is metabolized, and may crystallize out within the renal tubules, leading to renal toxicity and failure. Inadequate hydration can increase the chances for kidney failure, so drink plenty of water to keep your kidneys hydrated while taking Valtrex. Symptoms of impending kidney problems include decreased urination and renal pain.

Valtrex can also cause liver inflammation in some patients. Signs of liver inflammation include yellowing of the skin and eyes. The elderly and those who have pre-existing kidney disease or liver disease, as well as those with compromised immune systems, as with HIV, may not be able to tolerate Valtrex long-term.


Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome, or TTP-HUS, a life threatening clotting disorder, can occur in those taking Valtrex. According to HealthCommunities.com, TTP-HUS occurs when tiny clots form within the small blood vessels, the capillaries and arterioles of many organs. This condition causes hemolysis, or destruction of red blood cells, and a low platelet count. The symptoms include bleeding into the skin in spots, called purpura, and extreme tiredness and fatigue due to anemia. In some cases, TTP-HUS can result in death.

Nausea, Vomiting and Diarrhea

According to eHealthMe, long-term use of Valtrex can cause gastrointestinal side effects, such as upset stomach, diarrhea and nausea. Taking Valtrex with a meal may help prevent these side effects; Valtrex should always be taken with a full glass of water. Those affected with any side effects should consult their physicians at once.

Allergic Reaction

According to Drugs.com, to clear the signs of the infection for which Valtrex was prescribed, this medication should be taken for as long as prescribed, even if the sores clear up within a few days. Those with genital herpes may be prescribed Valtrex for extended periods of time in an effort to reduce outbreaks. According to the American Social Health Association, suppressive therapy with Valtrex can reduce outbreaks by 75 percent. Taking any drug long-term can increase the potential for an allergic reaction to occur. Signs of a severe allergic reaction include an itchy skin rash, hives, swelling of the mouth and throat and having difficulty breathing. A severe allergic reaction is a medical emergency that requires immediate treatment.

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