Methotrexate in Dermatology: Dosing and Safety Monitoring

Overview / Definition Methotrexate is an antimetabolite and antifolate agent that inhibits the enzyme dihydrofolate reductase, leading to decreased DNA synthesis and cellular proliferation. In dermatology, it is primarily utilized in the management of chronic inflammatory skin conditions, notably psoriasis, psoriatic arthritis, and atopic dermatitis. Epidemiology Methotrexate is one of the most frequently prescribed systemic agents in dermatology. Its use is prevalent among patients with moderate to severe forms of psoriasis, with studies indicating that approximately 20-30% of patients may require systemic therapy at some point in their treatment journey. Commonly used in adult populations, but increasingly prescribed for pediatric cases. Higher prevalence in individuals with obesity and smoking history, which can impact treatment efficacy and safety. Pathophysiology / Mechanism The primary mechanism of action of methotrexate in dermatology involves its ability to inhibit rapid cellular proliferation, particularly in the skin. By interfering with the action of folate, it decreases the production of nucleic acids, thereby affecting mitotic cells such as keratinocytes in psoriatic lesions. Modulates the immune response by reducing the activity of lymphocytes. Exhibits anti-inflammatory effects by decreasing cytokine production. Clinical Presentation Patients receiving methotrexate may present with varying degrees of efficacy and side effects. Clinical responses can typically be observed within 4-12 weeks of initiating therapy, although some patients may experience side effects sooner. Common indications for methotrexate include: Psoriasis vulgaris Psoriatic arthritis Severe atopic dermatitis resistant to topical therapies Potential side effects include: Nausea and vomiting Fatigue Hepatotoxicity Pulmonary toxicity Diagnosis / Workup Diagnosis of the conditions treated with methotrexate typically involves clinical examination and history-taking. Prior to initiating th