8-MOP
Clinical safety rating: caution
8-MOP (methoxsalen) is a psoralen derivative used in combination with UVA light (PUVA therapy) to treat severe, recalcitrant psoriasis, vitiligo, and cutaneous T-cell lymphoma. It acts as a photosensitizer, enhancing DNA crosslinking upon UVA activation.
8-MOP (methoxsalen) is a psoralen compound that intercalates into DNA. Upon UVA irradiation, it forms covalent cross-links between pyrimidine bases, inhibiting DNA synthesis and cell division. It also reduces the proliferation of epidermal cells and suppresses cutaneous immune responses by inhibiting antigen presentation and cytokine release.
| Metabolism | Primarily hepatic via cytochrome P450 enzymes (including CYP1A2 and CYP2A6); extensive first-pass metabolism; undergoes O-demethylation, hydroxylation, and glucuronide conjugation. |
| Excretion | Renal excretion of metabolites (~95%) with <0.5% unchanged; biliary/fecal elimination ~5%. |
| Half-life | Terminal elimination half-life is 1–2 hours; however, clinical effect persists longer due to sustained phototoxic reaction. |
| Protein binding | Highly bound (>90%) primarily to albumin. |
| Volume of Distribution | Vd approximately 0.2–0.3 L/kg, indicating limited extravascular distribution. |
| Bioavailability | Oral: ~90–95% (highly variable with food); topical: minimal systemic absorption. |
| Onset of Action | Oral: 1–2 hours; topical: 30–60 minutes; with subsequent UVA exposure. |
| Duration of Action | Oral: 6–12 hours (phototoxic reaction); topical: 12–24 hours; erythema peaks at 48–72 hours. |
| Molecular Weight | 216.24 |
Psoriasis: 0.4–0.6 mg/kg orally 2 hours before UVA exposure, 2–3 times per week. Vitiligo: 20 mg (0.3–0.4 mg/kg) 2 hours before UVA. Dose adjusted based on skin type and UVA dose.
| Dosage form | CAPSULE |
| Renal impairment | No specific adjustment guidelines; caution in severe renal impairment due to limited data. |
| Liver impairment | Use with caution in hepatic impairment; dose reduction may be needed due to reliance on hepatic metabolism. No specific guidelines. |
| Pediatric use | Not FDA-approved for children <12 years; use only if benefits outweigh risks. Dosing extrapolated from adult data (0.4–0.6 mg/kg) with careful UVA monitoring. |
| Geriatric use | Use with caution due to increased risk of photosensitivity and skin damage. Lower initial doses and slower dose escalation recommended. |
| 1st trimester | Contraindicated due to teratogenicity; avoid use in first trimester. |
| 2nd trimester | Contraindicated; potential fetal harm outweighs benefits. |
| 3rd trimester | Contraindicated; risk of fetal toxicity near term. |
Clinical note
Pregnancy Category C. Methoxsalen is not recommended for use during pregnancy due to potential genotoxicity and carcinogenicity. Limited human data; animal studies suggest fetal harm. Use only if clearly needed and no alternatives.
| Placental transfer | Yes; crosses placenta with potential for fetal accumulation and toxicity. |
| Breastfeeding | Contraindicated during breastfeeding; excreted in milk and may cause neonatal phototoxicity and other adverse effects. Discontinue nursing or drug. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Common Effects | Nausea, Pruritus, Erythema, Headache, Dizziness, Mild edema, Hypertrichosis |
| Serious Effects | Severe burns from UVA overexposure, Cataract formation without eye protection, Premature skin aging, Increased risk of cutaneous squamous cell carcinoma and melanoma, Hepatotoxicity, Severe nausea and vomiting |
PregnancyBreastfeedingPhotosensitivity disordersConcurrent use of photosensitizing drugsMelanoma or other skin cancer predispositionSevere hepatic impairment
| Precautions | Severe burns and blistering from UVA exposure, Risk of skin cancer (including squamous cell carcinoma and melanoma) with long-term PUVA therapy, Photosensitivity reactions due to sunlight or UVA exposure, Ocular toxicity (cataracts, corneal opacities) if not wearing UVA-blocking eyewear during and after treatment, Potential for severe allergic or phototoxic reactions, Monitor liver function due to hepatic metabolism |
Loading safety data…
| L5 (Contraindicated) |
| Teratogenic Risk | 8-MOP (methoxsalen) is contraindicated in pregnancy. First trimester: Known teratogen in animals; no adequate human studies, but potential for fetal harm. Second and third trimesters: Risk remains; avoid use due to phototoxic and potentially mutagenic effects on developing tissues. |
| Fetal Monitoring | Pre-treatment: Confirm pregnancy status. During therapy: Monitor for signs of phototoxicity, skin burns, and ocular toxicity. Fetal monitoring: Ultrasound for fetal growth and development if inadvertent exposure occurs. Avoid concurrent photosensitizing drugs. |
| Fertility Effects | Reproductive impact: Possible impairment of spermatogenesis in males; ovarian toxicity in females based on animal studies. May reduce fertility in both sexes. Use effective contraception during treatment. |
| Food/Dietary |
| Avoid high-fat meals as they delay absorption. Grapefruit and grapefruit juice may increase toxicity. No alcohol during treatment. Limit foods high in natural psoralens (e.g., figs, parsley, celery, limes) as they may enhance photosensitivity. |
| Clinical Pearls | 8-MOP (methoxsalen) is a psoralen used in PUVA therapy for psoriasis, vitiligo, and cutaneous T-cell lymphoma. Administer with low-fat meal to reduce nausea and optimize absorption. Monitor liver function and eye exams; protect eyes from UVA for 24 hours post-dose. Risk of severe burns if combined with other photosensitizers. |
| Patient Advice | Take 8-MOP exactly as prescribed with a low-fat meal or milk. · Avoid sun exposure and tanning beds for 24 hours after taking this medication. · Wear UVA-protective sunglasses and sunscreen (SPF 30+) after dosing. · Do not take other photosensitizing drugs (e.g., tetracyclines, thiazides) unless approved by your doctor. · Report any skin redness, blistering, or vision changes immediately. |