PENVIR 750 750MG TABLET

Indications

• Herpes zoster infection, treatment
• Genital herpes, treatment of first episode
• Genital herpes, suppression
• Genital herpes infection, treatment of recurrent infection
• Post-exposure prophylaxis of varicella zoster infection

Dosage

Adults: For herpes zoster infection: 500 mg three times a day for 7 days. For genital herpes (first episode): 250 mg three times a day for 5 days, or 500 mg twice daily for 10 days. For genital herpes suppression: 250 mg twice

Mechanism of action

Famciclovir is converted to the active antiviral compound penciclovir, which is phosphorylated in infected cells by viral thymidine kinase to a monophosphate form. This is further converted to penciclovir triphosphate by cellular kinases. Penciclovir triphosphate inhibits herpes simplex virus (HSV) DNA polymerase competitively with deoxyguanosine triphosphate, leading to the selective inhibition of viral DNA synthesis and replication.

Pharmacodynamics

As a prodrug, famciclovir's pharmacodynamic effects primarily arise from its active metabolite, penciclovir. Penciclovir has demonstrated significant antiviral activity against HSV-1, HSV-2, and VZV, effectively inhibiting viral replication by targeting the viral DNA synthesis process.

Pharmacokinetics

Famciclovir is rapidly absorbed and converted to penciclovir. The intracellular half-life of penciclovir triphosphate is approximately 10 hours in HSV-1, 20 hours in HSV-2, and 7 hours in VZV-infected cells in culture. The pharmacokinetics can be influenced by the patient's renal function, as famciclovir is excreted primarily via the kidneys.

Adverse effects

• Abdominal pain
• Diarrhoea

Interactions

• Famciclovir + live vaccines: Unknown (decreases efficacy)
• Famciclovir + herpes zoster vaccine: Unknown (decreases efficacy)
• Famciclovir + live: Unknown (decreases efficacy)

Pregnancy

Manufacturers advise avoiding unless potential benefits outweigh risks.

Breast-feeding

Unknown, caution advised.

Storage

Store in a cool, dry place away from light.

Formulations

• 125 mg tablets
• 250 mg tablets
• 500 mg tablets

Mechanism of action

Famciclovir undergoes rapid biotransformation to the active antiviral compound penciclovir, which has inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and varicella zoster virus (VZV). In cells infected with HSV-1, HSV-2 or VZV, viral thymidine kinase phosphorylates penciclovir to a monophosphate form that, in turn, is converted to penciclovir triphosphate by cellular kinases. In vitro studies demonstrate that penciclovir triphosphate inhibits HSV-2 DNA polymerase competitively with deoxyguanosine triphosphate. Consequently, herpes viral DNA synthesis and, therefore, replication are selectively inhibited. Famciclovir is a prodrug of penciclovir, which has demonstrated inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and varicella zoster virus (VZV). In cells infected with HSV-1, HSV-2 or VZV, the viral thymidine kinase phosphorylates penciclovir to a monophosphate form that, in turn, is converted by cellular kinases to the active form penciclovir triphosphate. Biochemical studies demonstrate that penciclovir triphosphate inhibits HSV-2 DNA polymerase competitively with deoxyguanosine triphosphate. Consequently, herpes viral DNA synthesis and, therefore, replication are selectively inhibited. Penciclovir triphosphate has an intracellular half-life of 10 hours in HSV-1-, 20 hours in HSV-2- and 7 hours in VZV-infected cells grown in culture. However, the clinical significance of the intracellular half-life is unknown.

Pharmacodynamics

Famciclovir is a prodrug that undergoes rapid biotransformation to the active antiviral compound penciclovir. Penciclovir is an anti-viral drug which has inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and varicella zoster virus (VZV). Therefore, herpes viral DNA synthesis and replication are selectively inhibited.