Metoxsalene G.L. Pharma (Methoxsalen)

Methoxsalen is used in dermatologic conditions that respond to psoralen‑UVA (PUVA) therapy.

• Psoriasis: reduces plaque formation and scaling by inhibiting keratinocyte proliferation.
• Vitiligo: promotes repigmentation of depigmented patches through melanocyte stimulation.
• Cutaneous T‑cell lymphoma: controls skin lesions by suppressing malignant T‑cell growth.

• Methoxsalen acts as a photosensitizer that intercalates between DNA base pairs. Upon exposure to UVA radiation, it forms covalent cross‑links with DNA, thereby blocking DNA synthesis and cell division. This photochemical interaction selectively reduces hyperproliferative skin cells and modulates immune responses in affected skin regions.

Methoxsalen may cause a range of adverse reactions, most of which are related to its photosensitizing properties.

Common Side Effects

• Nausea: mild to moderate gastrointestinal upset after oral administration.
• Headache: transient cranial discomfort.
• Erythema: mild skin reddening after UVA exposure.
• Pruritus: itching of treated skin areas.
• Hyperpigmentation: darkening of skin in exposed zones.

Serious or Rare Side Effects

• Severe phototoxic reactions: blistering or ulceration of skin.
• Cutaneous malignancies: increased risk of skin cancer with prolonged use.
• Hepatic toxicity: abnormal liver function tests.
• Anaphylaxis: rare systemic allergic response.
• Persistent photodermatitis: chronic skin sensitivity to light.

Methoxsalen requires careful patient assessment and monitoring before and during therapy.

• Pregnancy: contraindicated (Category X) due to teratogenic risk; avoid use in pregnant patients.
• Breastfeeding: not recommended as drug may be excreted in milk.
• UV exposure: limit UVA exposure to prescribed intervals to reduce phototoxicity.
• Liver function: assess hepatic status before initiation and periodically thereafter.
• Eye protection: use protective eyewear during UVA treatment to prevent cataract formation.
• Store below 25°C: keep in original packaging, protect from moisture and light.

Methoxsalen can alter the activity of several concomitant medications, necessitating vigilance.

Major Interactions (Avoid)

• Warfarin: increased anticoagulant effect, risk of bleeding.
• Azathioprine: enhanced immunosuppression, potential bone marrow toxicity.
• Other photosensitizers (e.g., tetracyclines, retinoids): additive phototoxic risk.

Moderate Interactions (Monitor Closely)

• Oral contraceptives: reduced efficacy, consider alternative contraception.
• Antihistamines: possible increased sedation.
• Diuretics: monitor electrolyte balance.
• Antidepressants (SSRIs): watch for serotonin syndrome signs when combined with other serotonergic agents.