Drug Interactions between Famvir and varicella virus vaccine

Ideally, vaccination should occur when an individual is healthy, thus minimizing the risk of an adverse host reaction and/or vaccine failure. However, a current or recent infection does not necessarily preclude the use of vaccines, depending on the severity of the patient's symptoms and their etiology. Superficial infections and minor acute illnesses such as a mild upper respiratory infection with or without low-grade fever do not contraindicate immunization, particularly if prompt administration of a vaccine is deemed necessary or beneficial. In fact, when vaccines are administered during the course of a minor illness, the risk of adverse events is not increased, and serum antibody response is not often diminished. On the other hand, if fever or symptoms suggest a moderate or severe illness, it is usually appropriate to withhold vaccination until the patient has recovered. In addition to the potential risks already mentioned, evolving signs and symptoms of the illness can sometimes confound the diagnosis of a vaccine reaction if it develops. In the presence of any infection, the decision to administer or withhold/defer immunization should take into consideration the benefits versus the risks to an individual patient.

In general, the use of varicella virus vaccine is contraindicated in patients with primary or acquired immunodeficiency or infection with HIV. Since varicella virus vaccine contains live attenuated virus, the absence of immune competence may potentiate the replication of vaccine virus, increase adverse host reactions, and compromise serum antibody response. The vaccine should not be administered to immunosuppressed or immunodeficient individuals and those receiving immunosuppressive therapy, including individuals receiving immunosuppressive doses of corticosteroids as it may cause an extensive vaccine-associated rash or disseminated disease in these individuals.

Ideally, vaccination should occur when an individual is healthy, thus minimizing the risk of an adverse host reaction and/or vaccine failure. However, a current or recent infection does not necessarily preclude the use of vaccines, depending on the severity of the patient's symptoms and their etiology. Superficial infections and minor acute illnesses such as a mild upper respiratory infection with or without low-grade fever do not contraindicate immunization, particularly if prompt administration of a vaccine is deemed necessary or beneficial. In fact, when vaccines are administered during the course of a minor illness, the risk of adverse events is not increased, and serum antibody response is not often diminished. On the other hand, if fever or symptoms suggest a moderate or severe illness, it is usually appropriate to withhold vaccination until the patient has recovered. In addition to the potential risks already mentioned, evolving signs and symptoms of the illness can sometimes confound the diagnosis of a vaccine reaction if it develops. In the presence of any infection, the decision to administer or withhold/defer immunization should take into consideration the benefits versus the risks to an individual patient.

Penciclovir, the active antiviral metabolite of famciclovir, is primarily eliminated by the kidney. Acute renal failure has been reported in patients with underlying renal disease who did not receive an appropriate dosage reduction. Dosage adjustments are recommended for patients with moderate to severe renal impairment (CrCl < 60 mL/min).

Famciclovir is converted by the liver to the active antiviral metabolite, penciclovir. The bioavailability of penciclovir following a dose of famciclovir was not affected in patients with well-compensated chronic liver disease. However, there are no data on the pharmacokinetic disposition of famciclovir in patients with severe uncompensated liver disease. Therapy with famciclovir should be administered cautiously in these patients, since the clinical significance of possible famciclovir accumulation is unknown. Theoretically, famciclovir may also not be effective in these patients.