Famvir Vs. Valtrex
Both Famvir (Famciclovir) and Valtrex (Valacyclovir) are antiviral medicines used primarily in the treatment of certain viral diseases like Genital Herpes, Herpes Labialis (Cold Sores), Herpez Zoster (Shingles) and Chicken Pox. Both of them are closely related to Aciclovir (Zovirax), which was the first antiviral drug to be successfully used in these viral diseases. Both Famvir and Valtrex are prodrugs, which get converted to another more active ingredient within the body cells. They are both taken orally, and used primarily for alleviation of symptoms and severity of the episode. However, in spite of their similar profile, there are certain important differences in their drug formulation, activity, efficacy and adverse effects which can decide as to which of them might be preferable in a particular patient.
Famvir is the trade name under which Famciclovir compound is currently marketed by its manufacturer, Novartis Pharmaceuticals. Earlier, it was developed and brought to market by Smithkline Beachem, and first approved by the Food and Drug Administration of United States in 1994 for the treatment of Herpes Zoster (Shingles). Later, the FDA approved its use in Herpes Simplex in 1998. By the end of 2000, Smithkline Beachem sold Famvir to Novartis. In 2002, Famvir was approved for treatment of Genital Herpes. As on date, it is one of the more important antiviral drugs used across the globe to treat viral infections caused by Herpes group of viruses.
Valtrex is the trade name under which the compound Valacyclovir is currently marketed by Glaxo Smithkline. It got approval from the Food and Drug Administration of United States for use in Genital Herpes in 1995. In 1998, it was also approved for use in Herpes Labialis (Cold Sores). It is more effective in children than Famvir and hence also used in Chicken Pox. It is one of the popular antiviral drugs useful in diseases resulting from Herpes Simplex and Varicella Zoster virus.
Famvir Vs Valtrex : A comparison of the two drugs
Active ingredient & Mode of action
The active compound in Famvir is Famciclovir which is a prodrug that gets converted to Penciclovir, which has antiviral properties. The active compound in Valtrex is Valacyclovir, which gets converted to Aciclovir, an antiviral compound, during digestion or in liver. Both Aciclovir and Penciclovir inhibit the multiplication of the Herpes Simplex and Herpes Zoster virus, and thereby provide relief to the patients. The earlier the treatment is initiated, the more effective it will be, as the number of viruses in the body will be reduced to minimum.
Both Famvir and Valtrex are available as tablets. Famvir tablets are available in strength of 125 mg, 250 mg and 500 mg, usually in bottles of 30. Famvir tablets contain lactose, something that may make them less preferable for those with lactose intolerance, severe lactase deficiency or glucose-galactose malabsorption.
Valtrex tablets are shaped like capsules and available in strength of 500 mg and 1 gram, usually in bottles of 30 or 90. For use in children, Valtrex oral suspension with strength of 25 mg/mL or 50 mg/mL can be prepared at the time of dispensation using the tablets of Valtrex.
Use in Herpes Labialis (Cold Sores) and Genital Herpes
Both Famvir and Valtrex are antiviral drugs. They do not cure the disease for which they are used, but reduce the severity of symptoms and the duration of the episode. Both Famvir and Valtrex can be used to treat adult patients with Herpes Labialis (Cold Sores), Genital Herpes and Herpes Zoster (Shingles). The beneficial role of both Famvir and Valtrex is clearly established in Herpes Labialis (Cold Sores). Both Famivir and Valtrex are equally effective in treating the recurrent episodes of Genital Herpes, provided the treatment is initiated six hours within the onset of symptoms or lesion. If taken beyond six hours of onset, the impact of both Famivir and Valtrex is somewhat unpredictable. Both Famvir and Valtrex are also used, with comparable efficacy as suppressive therapy to suppress the onset of outbreaks in Genital Herpes. Both Famvir and Valtrex are equally effective in treating Herpes Zoster (Shingles), but here again the treatment must be initiated within 72 hours. Unlike Famvir, Valtrex is also useful in the treatment of initial episode of Genital Herpes, if treatment is given within 72 hours.
Use in Children
For children, Valtrex is preferred over Famvir. The efficacy and safety of Famvir in children is not well established. Valtrex is effective in treatment of Herpes Simplex (Cold Sores) in children aged twelve years and above. It shows best results if the treatment is initiated at the earliest with the first symptoms like tingling, itching or burning. Its efficacy is limited when the treatment in started after the sore has fully developed. Valtrex can also be used in Chicken Pox to treat children aged two years or older. In Chicken Pox too, the best results are seen if treatment is initiated within 24 hours of onset of rash.
In recent years, some limitations have been observed with Famvir and added to its prescribing information. It has not been found very effective for treatment of Recurrent Genital Herpes in Black and African American patients. Its efficacy in Ophthalmic Zoster, i.e. Herpes Zoster (Shingles) involving the eyes is also not established.
Use in Pregnancy and other vulnerable groups
Both Famvir and Valtrex can be used in pregnancy, with neither offering any established benefit over the other, but in view of the limited experience of their use in pregnant mothers, they should be used only if specifically needed. Caution needs to be exercised in the use of either Famvir or Valtrex in lactating mothers, where they should be used only when it is considered essential. Based on current experience and literature, Famvir can be considered safer than Valtrex for treating HIV infected adult patients with Herpes Labialis (Cold Sores) or Genital Herpes.
Both Famvir and Valtrex are reasonably well tolerated by patients and serious adverse reactions are not very common. Those known to be allergic to Denavir (Penciclovir cream) should not take Famvir.
With both Famvir and Valtrex, the most common adverse effects in adults are headache, nausea and abdominal pain. Other less common adverse reactions with them include vomiting, diarrhea and fatigue. The most common adverse reaction of Valtrex in children is headache.
Both Famvir and Valtrex can occasionally lead to serious adverse reaction. These include Platelet deficiency, acute renal failure, liver function abnormalities, allergic reactions and behavioral problems like aggression, agitation, confusion and hallucinations. Acute Renal Failure usually results from higher dose given in people with already compromised kidney function. Platelet deficiency is of greater concern with Valtrex, and can manifest as Thrombotic Thrombocytopenic Purpura (TTP)/ Hemolytic Uremic Syndrome (HUS). Hence treatment with Valtrex must be immediately stopped if any symptom suggesting TTP/HUS are seen. The behavioral problems are more common in people with high age and may need further adjustment of dosage.
Viral resistance can develop with both Famvir and Valtrex. It is usually a result of a mutation in the viral Thymidine Kinase (TK) or DNA Polymerase genes of the virus, as a result of which the drug does not become sufficiently active. In cases of poor response to treatment, viral resistance should always be considered a possible cause. Since resistance is usually drug specific, changing from one drug to another may be helpful when viral resistance is suspected. However, it may be remembered that cross-resistance has been observed among DNA Polymerase inhibitors, where those resistant to Aciclovir, the active compound in Valtrex are often observed to be resistant to Penciclovir, the active ingredient of Famvir.
Both Famvir and Valtrex are reasonably effective in bringing relief to the patients affected by Shingles or Herpes Labialis (Cold Sores). In case of Genital Herpes too they are more or less equally effective for controlling outbreaks or suppressing recurrence. However, in case of initial episode of Genital Herpes, only Valtrex is effective. In children, Valtrex is preferred. Thus, only Valtrex is used for treatment of Chicken Pox. Valtrex is also preferable for those who have lactose intolerance of any kind, or those known to be allergic to Denavir (Penciclovir cream). Famvir may be preferable in patients with immunocompromized functions, including those infected with HIV.
Both Famvir and Valtrex can lead to adverse reactions, and those unable to tolerate one of them may find it useful to shift to the other. Valtrex can lead to some severe reactions like Thrombotic Thrombocytopenic Purpura / Hemolytic Uremic Syndrome, and those taking Valtrex should always report any unusual symptoms immediately to their physician. Reviews by patients using the two drugs indicate that if one of the drugs do not give satisfactory results in a patient, shifting to other may be helpful.