STOXIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for STOXIL (STOXIL).
Stoxil (idoxuridine) is a pyrimidine nucleoside analog that inhibits viral DNA synthesis. It is phosphorylated by viral thymidine kinase to its active triphosphate form, which competitively inhibits viral DNA polymerase and is incorporated into viral DNA, causing false coding and chain termination.
| Metabolism | Primarily metabolized by rapid deamination via hepatic and serum enzymes to iodouracil and uracil; also undergoes glucuronidation. |
| Excretion | Primarily renal (70-80% as unchanged drug and metabolites); minor biliary/fecal excretion (<10%). |
| Half-life | Topical: 0.5-2 hours (systemic absorption minimal); intravenous: 2-3 hours in adults (prolonged in renal impairment). |
| Protein binding | 65% (primarily albumin; concentration-dependent). |
| Volume of Distribution | Systemic: 1.5-2.5 L/kg (extensive tissue distribution). |
| Bioavailability | Topical ophthalmic: negligible systemic. Oral: 5-10% (first-pass metabolism). IV: 100%. |
| Onset of Action | Ophthalmic: within 1 hour (viral suppression). Intravenous: immediate. |
| Duration of Action | Ophthalmic: 4-6 hours (dosing interval). Systemic: 8-12 hours. |
Idoxuridine 0.1% ophthalmic solution: 1 drop into the affected eye every hour during the day and every 2 hours at night, reduced to every 2 hours during the day and every 4 hours at night after clinical improvement.
| Dosage form | OINTMENT |
| Renal impairment | No specific dose adjustment guidelines available; systemic absorption is minimal with ophthalmic use. |
| Liver impairment | No specific dose adjustment guidelines available; systemic absorption is minimal with ophthalmic use. |
| Pediatric use | Same as adult dosing for ophthalmic use; safety and efficacy in children have not been established via controlled trials. |
| Geriatric use | Same as adult dosing; no specific elderly dose adjustment required due to minimal systemic absorption. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for STOXIL (STOXIL).
| Breastfeeding | It is unknown whether idoxuridine is excreted in human breast milk. Due to the low systemic absorption following topical ophthalmic administration, the amount ingested by a nursing infant is likely minimal. Caution should be exercised, but the drug is generally considered compatible with breastfeeding. M/P ratio is not available. |
| Teratogenic Risk | Pregnancy Category C. Idoxuridine is a nucleoside analog; animal studies have shown teratogenic effects (fetal malformations) at high systemic doses. However, due to negligible systemic absorption from topical ophthalmic use, the risk to the fetus from maternal exposure is considered low. There are no adequate and well-controlled studies in pregnant women. Risk cannot be completely excluded, but clinical use is generally considered safe when indicated. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to idoxuridine or any component of the formulation. Not for use in deep stromal herpes simplex infections or iritis without involving the epithelium.
| Precautions | Topical ophthalmic use only; may cause local irritation, edema, photophobia, corneal opacities, and punctal occlusion. Prolonged use may delay wound healing. Avoid concurrent use of topical corticosteroids without expert guidance. Monitor for secondary infections. |
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| Fetal Monitoring | No specific maternal or fetal monitoring is required beyond standard obstetric care, given the minimal systemic absorption. Monitor for maternal ocular adverse effects (e.g., irritation, photophobia, edema) and ensure appropriate administration. |
| Fertility Effects | Reproductive studies in animals have not demonstrated impaired fertility. There are no documented adverse effects on human fertility from topical ophthalmic idoxuridine. Systemic effects are negligible. |