Nurses Compass
Drug Guide
Famciclovir
Classification
Therapeutic: Antiviral
Pharmacological: Penciclovir derivative, Guanine analog
FDA Approved Indications
- Herpes zoster (shingles)
- Genital herpes simplex virus (HSV) infections
- Cold sores (herpes labialis)
Mechanism of Action
Famciclovir is converted in the body to penciclovir, which inhibits viral DNA synthesis by terminating DNA chain elongation, thereby inhibiting viral replication.
Dosage and Administration
Adult: 200 mg every 12 hours for herpes zoster; 250 mg three times daily for genital herpes; 125 mg twice daily for cold sores.
Pediatric: Safety and efficacy not established in children.
Geriatric: Use with caution; consider renal function adjustments.
Renal Impairment: Reduce dosage based on degree of renal impairment.
Hepatic Impairment: No specific dosage adjustment documented; use with caution.
Pharmacokinetics
Absorption: Well absorbed orally.
Distribution: Widely distributed in body tissues.
Metabolism: Converted to penciclovir, primarily in the liver.
Excretion: Renally excreted as unchanged drug and metabolites.
Half Life: Approximately 4-6 hours.
Contraindications
- Hypersensitivity to famciclovir or penciclovir.
Precautions
- Use cautiously in pregnant or breastfeeding women; consult healthcare provider.
- Renal impairment may require dose adjustment.
Adverse Reactions - Common
- Headache (Common)
- Nausea (Common)
- Fatigue (Common)
Adverse Reactions - Serious
- Seizures (Rare)
- Hypersensitivity reactions including rash, swelling, and difficulty breathing (Rare)
Drug-Drug Interactions
- Probenecid may increase famciclovir levels.
- Concurrent nephrotoxic drugs may increase risk of renal toxicity.
Drug-Food Interactions
N/ADrug-Herb Interactions
N/ANursing Implications
Assessment: Assess renal function before and during therapy.
Diagnoses:
- Risk for infection related to immunosuppression.
- Impaired skin integrity related to herpes lesions.
Implementation: Administer with or without food; ensure adequate hydration; monitor renal function periodically.
Evaluation: Observe for decrease in herpes lesion severity, lesion healing, and absence of adverse effects.
Patient/Family Teaching
- Take medication exactly as prescribed.
- Report any signs of allergic reaction or unusual side effects.
- Maintain proper hygiene to prevent spread of infection.
- Stay well-hydrated.
- Avoid pregnancy unless approved by healthcare provider.
Special Considerations
Black Box Warnings:
- None currently. See FDA updates for any recent warnings.
Genetic Factors: Genetic variations in drug metabolism are not well characterized.
Lab Test Interference: No known interference.
Overdose Management
Signs/Symptoms: Nausea, vomiting, dizziness, drowsiness.
Treatment: Supportive care; hemodialysis may be considered in severe cases.
Storage and Handling
Storage: Store at room temperature, away from moisture and light.
Stability: Stable for the shelf life indicated in labeling.