Metoxaleno S.A.L.F. (Methoxsalen)

Methoxsalen is a psoralen used in PUVA phototherapy for several dermatologic conditions.

• Psoriasis: reduces hyperproliferative skin plaques when combined with UVA exposure.
• Vitiligo: promotes repigmentation of depigmented areas under UVA treatment.
• Lichen planus: may improve inflammatory lesions when administered with UVA as part of PUVA protocol.

• Methoxsalen intercalates between DNA base pairs and, after activation by UVA light, forms covalent cross‑links with pyrimidine residues. These cross‑links inhibit DNA synthesis and cell division, leading to reduced keratinocyte proliferation and modulation of immune responses in the skin. The photochemical reaction also induces melanocyte activation, contributing to repigmentation in vitiligo. The effect is localized to treated skin areas, minimizing systemic toxicity.

Methoxsalen may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Nausea: mild gastrointestinal upset after oral administration.
• Headache: transient cranial discomfort.
• Erythema: mild skin redness at treated sites.
• Hyperpigmentation: increased skin coloration in exposed areas.
• Pruritus: itching of the skin.
• Phototoxicity: heightened skin sensitivity to light.

Serious or Rare Side Effects

• Severe phototoxic burns: blistering and ulceration after UVA exposure.
• Hepatotoxicity: abnormal liver enzymes indicating liver injury.
• Aplastic anemia: rare bone‑marrow suppression.
• Severe nausea and vomiting: persistent gastrointestinal distress.
• Allergic reactions: rash, angioedema, or anaphylaxis.

When using Methoxsalen, several safety measures should be observed to minimize risks.

• Liver function assessment: evaluate hepatic enzymes before initiating therapy.
• Skin type evaluation: determine phototype to adjust UVA dose.
• Sun exposure avoidance: limit natural sunlight during treatment.
• Blood count monitoring: check complete blood count periodically.
• Pregnancy contraindication: avoid use in pregnant patients due to unknown fetal risk.
• Store at ambient temperature: keep in original container, protect from moisture and light.

Methoxsalen can interact with other medications, requiring careful management.

Major Interactions (Avoid)

• Oral retinoids: combined use markedly increases skin toxicity.
• Tetracycline antibiotics: may enhance phototoxic reactions.
• Warfarin: Methoxsalen can potentiate anticoagulant effect, raising bleeding risk.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: may reduce efficacy of hormonal contraception.
• Azole antifungals: can increase Methoxsalen plasma levels.
• Diuretics (thiazides): may augment photosensitivity.
• NSAIDs: monitor for increased gastrointestinal irritation.