Dermatologic Therapy: Topical, Systemic, Biologic and Phototherapy
Domain 11 tests drug choice, monitoring and adverse effects, which dominate safe dermatology practice.
Topical and phototherapy
- Corticosteroid potency is class-based; risks are atrophy, striae, telangiectasia and tachyphylaxis. Use the lowest effective potency, especially on the face and flexures.
- Calcineurin inhibitors for face and neck; vitamin D analogues and coal tar for psoriasis.
- NBUVB 311 nm is first-line phototherapy for psoriasis and vitiligo; PUVA increases squamous cell carcinoma risk.
Systemic agents
- Methotrexate is a folate antagonist; monitor blood count, liver and renal function; avoid trimethoprim and NSAIDs in renal impairment.
- Cyclosporine causes hypertension and nephrotoxicity; azathioprine requires TPMT testing; dapsone requires G6PD testing.
- Isotretinoin is teratogenic: pregnancy testing, lipid and liver monitoring; avoid tetracyclines because of pseudotumor cerebri.
Biologics
- Screen for latent tuberculosis and hepatitis before TNF inhibitors.
- IL-17 inhibitors: candidiasis, caution in inflammatory bowel disease. IL-23 inhibitors have favourable safety. Dupilumab: conjunctivitis and injection-site reactions.
Worked example
A 45-year-old with severe psoriasis has a positive interferon-gamma release assay. Before starting adalimumab, treat latent tuberculosis and document it. Reasoning: TNF blockade reactivates granulomatous infection; screening and prophylaxis are mandatory.
Traps
Do not combine methotrexate with trimethoprim. Do not start isotretinoin without pregnancy testing. Do not attribute new pustules on a biologic to infection without considering a paradoxical reaction.