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. |
| Molecular Weight | 354.1 |
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 | Idoxuridine is an antiviral agent with potential teratogenicity based on animal studies; avoid use in first trimester unless benefit outweighs risk. Systemic absorption from topical ophthalmic application is minimal, but risk of fetal harm cannot be excluded. |
| 2nd trimester | Limited human data; use only if clearly needed. Topical ophthalmic use results in negligible systemic exposure, but caution advised. |
| 3rd trimester | Similar to second trimester; systemic absorption is minimal, but use only if benefit outweighs potential risk. Avoid during labor and delivery due to unknown effects. |
Clinical note
Comprehensive clinical and safety monograph for STOXIL (STOXIL).
| Placental transfer | Systemic absorption is minimal after topical ophthalmic use; thus, placental transfer is expected to be negligible. If given systemically (not typical), idoxuridine crosses the placenta in animal studies. |
| Breastfeeding |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to idoxuridine or any component of the formulation
| 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. |
| Food/Dietary | No significant food interactions. STOXIL is applied topically to the eye; systemic absorption is negligible, so dietary restrictions are not required. |
| Clinical Pearls |
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| Systemic absorption following topical ophthalmic administration is negligible. It is unlikely to cause adverse effects in a nursing infant. However, due to lack of data, use with caution. Avoid applying near the breast area to prevent infant contamination. |
| Lactation Rating | L3 (Moderately Safe) |
| 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. |
| 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. |
| STOXIL (idoxuridine) is a topical antiviral for herpetic keratitis. Frequency of application is critical: every 1–2 hours during waking hours, with less frequent dosing at night. Use with caution in patients with corneal epithelial defects or stromal involvement; while effective for epithelial keratitis, stromal keratitis may require adjunctive corticosteroids. Monitor for ocular irritation, photophobia, or punctal stenosis with prolonged use. Do not exceed 21 days of continuous therapy due to risk of corneal toxicity (e.g., punctate keratitis, superficial punctate keratopathy). STOXIL is a DNA analogue antimetabolite; systemic absorption is minimal with topical use. |
| Patient Advice | Wash hands before and after applying the eye drops or ointment. · Tilt head back, pull down lower eyelid, and place one drop or small ribbon of ointment into the conjunctival sac. · Avoid touching the tip of the dropper or tube to the eye or any surface to prevent contamination. · Use STOXIL exactly as prescribed—typically every 1–2 hours during the day and less often at night. · Do not use for longer than 21 days unless directed by your doctor; prolonged use can damage the cornea. · Do not share this medication with others; it is for your eye only. · If you wear contact lenses, remove them before applying the medication and wait at least 15 minutes before reinserting. · Common side effects include temporary stinging, burning, or blurred vision upon application. · Report any severe eye pain, vision changes, or signs of infection (e.g., pus, increasing redness) to your healthcare provider immediately. · Store STOXIL at room temperature away from moisture and heat. Keep the bottle or tube tightly closed when not in use. |