Penciclovir is a synthetic acyclic guanine nucleoside analogue with antiviral activity. It is an active pharmaceutical ingredient used primarily in topical antiviral formulations for the management of herpes simplex virus infections. Penciclovir inhibits viral DNA replication after conversion inside infected cells to its active triphosphate metabolite.
Penciclovir has CAS Number 39809-25-1, molecular formula C10H15N5O3, and molecular weight 253.26 g/mol. Its chemical name is 2-amino-9-[4-hydroxy-3-(hydroxymethyl)butyl]-1H-purin-6-one, and it is also known by the development code BRL-39123.
Penciclovir is a member of the 2-aminopurine and acyclic guanine derivative classes. It is structurally related to guanine and contains a hydroxy-hydroxymethylbutyl side chain attached to the purine system. The compound is supplied as a white to pale-yellow powder according to the current USP-NF proposed monograph information.
Penciclovir has relatively limited aqueous solubility. The current USP description states that it is slightly soluble in pH 2 aqueous buffer, very slightly soluble in water, and practically insoluble in methanol and propylene glycol.
Identity testing for Penciclovir can be performed using validated spectroscopic and chromatographic methods. The current USP-NF proposal describes a liquid chromatographic assay method using an L11 phenyl stationary phase, with a typical Penciclovir retention time of approximately 11 minutes. The proposed organic-impurities method uses an L96 stationary phase, with a typical retention time of approximately 10 minutes.
These methods are particularly useful for API quality control because they allow Penciclovir to be differentiated from structurally related substances and process-related impurities.
The current USP-NF material identifies validated LC procedures for both assay and organic impurities, but the publicly accessible preview does not display the complete numerical acceptance criteria. USP specifically states that the new Penciclovir monograph is proposed because there was no existing USP monograph for the drug substance.
Therefore, a CMS page should not incorrectly state an assay such as 98.0–102.0% unless it is supported by the actual applicable approved specification.
Commercial research-grade materials may be offered at values such as 98.0% or higher, but those are supplier-specific material specifications and should not be represented as a universal pharmaceutical pharmacopoeial limit.
Penciclovir is a selective antiherpesvirus agent with activity against HSV-1 and HSV-2 and activity against varicella-zoster virus. Following uptake by infected cells, viral thymidine kinase converts Penciclovir into penciclovir monophosphate, which is subsequently converted into the active triphosphate form by cellular kinases. Penciclovir triphosphate inhibits viral DNA polymerase and thereby interferes with viral DNA synthesis.
The active ingredient is particularly associated with topical pharmaceutical products for herpes labialis and other herpesvirus-related conditions.
Penciclovir API manufacturing requires controlled chemical synthesis, purification and crystallization to achieve appropriate chemical purity and control structurally related impurities.
The API should be evaluated using validated chromatographic methods capable of controlling assay and organic impurities. Where the applicable pharmaceutical specification includes water, residual solvents or elemental impurities, these should be tested using appropriate validated analytical procedures.
Penciclovir quality control should include identity, assay, organic impurities, water content, residual solvents and elemental impurities where applicable.
Because the current USP-NF public preview does not provide all numerical acceptance limits, those limits should not be fabricated. The exact release specification should be based on the applicable approved drug-substance specification or validated manufacturer specification.
Penciclovir should be stored under controlled conditions established by stability studies and the applicable API specification. Appropriate protection from moisture, excessive heat and unsuitable environmental conditions should be maintained.
For research-grade Penciclovir, some suppliers recommend refrigerated or frozen storage, but commercial pharmaceutical storage should follow the validated drug-substance stability program rather than automatically applying a research-product storage recommendation.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.2% |
| Heavy Metals | NMT 20 ppm |
| Individual Impurity | NMT 0.5% |
| Melting Point | 272.2–275°C |