Valaciclovir is one of the two main antivirals used (with aciclovir) in outbreaks of herpes or shingles. How does this medication work? When should it be taken? Is it really effective?
What is valaciclovir?
Valaciclovir is a antiviral drug for systemic use (non-local), with a structure very close to that of aciclovir, antiviral belonging to the class of nucleosides and nucleotides. Valaciclovir is very specific for certain viruses such as that of herpes (HSV types 1 and 2), cytomegalovirus (CMV) or even the varicella zoster virus (VZV). It is a prodrug of aciclovir, that is to say that once absorbed, it quickly releases in the body aciclovir and valine. He acts by preventing the reproduction of viruses in the cells, by blocking the synthesis of their DNA. It is mainly used in certain forms of herpes, in case of shingles or, in some situations, in pprevention of CMV infections. Valaciclovir reduces the intensity and duration of pain associated with shingles (neuralgia) as well as the ocular complications that may result from it. It may also reduce the risk of transmission of genital herpes when taken for prevention. Finally, it helps to avoid rejection of kidney or heart transplants by conferring protection against CMV and by limiting the risk of occurrence of other opportunistic infections such as those caused by VZV or HSV. It is marketed as Zelitrex® or its generics (Valaciclovir Almus, Alter, Arrow, Biogaran, EG, Evolugen, Mylan, Sandoz, Sun, Teva, Zentiva, Zydus). It comes in the form of tablets dosed at 500 mg, in boxes of 10, 42 or 112 tablets depending on the dosage required for the indication concerned.
Indications: why use valaciclovir?
Valaciclovir is used in the treatment of shingles and ophthalmic shingles in immunocompetent and immunocompromised adults, in the treatment and prevention of HSV skin and mucous membrane infections (genital herpes, ocular herpes, orofacial herpes) as well asin the prevention of CMV infections after organ transplantation in adults and adolescents.
How effective on shingles?
Valaciclovir is efficient in the treatment of shingles provided it is taken as soon as possible after the appearance of skin symptoms, either within 72 hours. Valaciclovir decreases the intensity, frequency and duration of pain, in particular acute neuralgia and postherpetic neuralgia. It also prevents eye complications of shingles. It does not eliminate the virus from the body, which is why shingles is always likely to reactivate. Valaciclovir, on the other hand, is intended to prevent viral replication in cells during active outbreaks and to relieve the pain and discomfort caused by this virus.
How long does it take for the effects to appear?
Its peak concentration in the blood is reached on average after 45 min to 2 hours depending on dose administered. Once metabolized to aciclovir and valine, it diffuses into the brain, kidneys, lungs, liver, muscles and in vaginal secretions. It is then mostly eliminated in the urine, still in the form of aciclovir, its half-life (time after which half of its dose is eliminated) being approximately 3 hours. However, the effects on pain and other symptoms are not noticeable immediately, they generally fade over the days following the intake of valaciclovir. Despite treatment, some pain can sometimes persist for a long time. Treatment with valaciclovir does not totally eliminate the pain or discomfort caused by the virus, but allows reduce the duration of symptoms by a few days.
Is it available with or without a prescription?
Valaciclovir (or Zelitrex®) is included in list I of poisonous substances, a prescription is therefore necessary to get it.
What are the side effects of valaciclovir?
The most common side effects with valaciclovir are headaches, nausea, dizziness, vomiting, diarrhea or skin rashes (including sun sensitivity and itching). Other effects may occur but are rarer, such as low white blood cells or plateletsallergic reactions, confusion, hallucinations, tremors, agitation, neurological disturbances which can go as far as a coma, breathing difficulties, abdominal discomfortof the liver disorders (increased bilirubin and liver enzymes), hivesof the angioedema, kidney pain, blood in the urine or kidney failure. In people who are very immunocompromised (example: in the case of advanced HIV), renal failure, microangiopathic haemolytic anemia and thrombocytopenia may also occur. The dosage of valaciclovir should be adjusted in case of renal insufficiency and in the elderly, in order to avoid toxicities and the risks linked to an overdose (neurological disorders, digestive disorders).
What are the contraindications of valaciclovir?
Valaciclovir (or Zelitrex®) is contraindicated in case of hypersensitivity valacicovir, aciclovir or any of the excipients of the medicinal product concerned. It is also contraindicated in the event of a DRESS type skin reaction (manifested by eosinophilia and systemic signs), as this reaction can be serious or even fatal. Sufficient fluid intake is necessary with treatment with valaciclovir and special vigilance is required in the event of dehydration or kidney failure. Certain medicinal products toxic to the kidneys may increase the risk of renal insufficiency, which must be subject to increased monitoring in the event of concomitant administration with valaciclovir. Other drugs may also increase valaciclovir concentrations and thus its toxicity. It is therefore important to inform the doctor of any other medication taken before taking valaciclovir.