PENCICLOVIR
Clinical safety rating: safe
Animal studies have demonstrated safety
Penciclovir is a nucleoside analog that inhibits viral DNA polymerase. It is phosphorylated by viral thymidine kinase to penciclovir triphosphate, which competitively inhibits viral DNA polymerase and terminates DNA chain elongation.
| Metabolism | Penciclovir is not significantly metabolized; it is primarily excreted unchanged in the urine. |
| Excretion | Renal excretion: >70% as unchanged penciclovir via glomerular filtration and tubular secretion. |
| Half-life | Terminal half-life: 2.0–2.5 hours (healthy adults); prolonged to ~9–10 hours in renal impairment (CrCl <30 mL/min); clinical context: dosing interval adjusted based on renal function. |
| Protein binding | <20% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | 1.5 L/kg (indicating extensive distribution into total body water and tissues). |
| Bioavailability | Topical: Negligible systemic absorption (<1%) after repeated application; oral: not available (only as prodrug famciclovir with ~77% oral bioavailability converted to penciclovir). |
| Onset of Action | Topical (1% cream): Onset of symptom relief (pain, itching) within 1–2 hours of application for herpes labialis; intravenous: not applicable for clinical effect in typical outpatient use. |
| Duration of Action | Topical: Duration of action corresponds to dosing interval (every 2 hours while awake); clinical note: maximal effect if initiated early in prodrome. Systemic: T1/2 determines dosing interval for IV; prolonged effect in renal impairment. |
Topical: Apply 1% cream every 2 hours while awake (approximately 9 times/day) for 4 days. Oral: 500 mg twice daily for 5 days.
| Dosage form | CREAM |
| Renal impairment | No dose adjustment required for topical use. For oral: CrCl 30-49 mL/min: 250 mg twice daily; CrCl 10-29 mL/min: 250 mg once daily; CrCl <10 mL/min or hemodialysis: 250 mg after each dialysis. |
| Liver impairment | No dose adjustment required. |
| Pediatric use | Topical: Approved for ≥12 years, apply same as adult. Oral: Not approved for <18 years. |
| Geriatric use | No specific adjustment; monitor renal function as clearance may be reduced. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
No significant drug interactions For topical use only not for ophthalmic or oral use.
| Breastfeeding | Unknown if penciclovir is excreted in human milk. Systemic absorption after topical application is negligible (<1%), making significant infant exposure unlikely. Caution is advised; manufacturer recommends caution during breastfeeding. No M/P ratio available. |
| Teratogenic Risk | Penciclovir is a nucleoside analog antiviral with limited human data. In animal studies (rats, rabbits), no evidence of teratogenicity or fetal harm was observed at systemic exposures up to 80 times the human therapeutic dose. Based on FDA pregnancy category B, no adequate and well-controlled studies in pregnant women exist, but potential benefits may warrant use. Risk cannot be ruled out; use only if clearly needed. |
■ FDA Black Box Warning
None
| Common Effects | Application site reaction |
| Serious Effects |
["Hypersensitivity to penciclovir or any component of the formulation."]
| Precautions | ["Use with caution in patients with renal impairment; dose adjustment may be necessary.","Apply only to intact skin; avoid contact with eyes or mucous membranes.","The safety and efficacy in immunocompromised patients have not been established."] |
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| Fetal Monitoring | No specific maternal or fetal monitoring required beyond routine prenatal care. For intravenous or oral use (if applicable), monitor for renal function due to excretion, but penciclovir is primarily topical. For severe infections, standard fetal surveillance may be considered. |
| Fertility Effects | No human data on fertility impairment. In animal studies, no adverse effects on fertility or reproductive performance at systemic doses up to 80 mg/kg/day in rats. No known clinical impact on fertility. |