Therapeutics, Pharmacology and Photomedicine
Scope
Questions cover topical and systemic drugs, biologic mechanisms, monitoring, phototherapy, and photoprotection.
Core rules
- Topical corticosteroids: class by potency; use lowest effective potency; risks include atrophy, striae, and tachyphylaxis.
- Methotrexate: weekly dosing; monitor CBC, liver enzymes; supplement folate; teratogenic.
- Cyclosporine: nephrotoxicity and hypertension; azathioprine requires TPMT testing.
- Biologics: TNF inhibitors, IL-17 inhibitors, IL-23p19 inhibitors, IL-4Rα blocker (dupilumab), and JAK inhibitors.
- Retinoids: isotretinoin is teratogenic; pregnancy prevention is mandatory; monitor lipids and liver.
- Dapsone requires G6PD testing; hydroxychloroquine requires retinal screening.
- Phototherapy: NB-UVB 311 nm, PUVA, UVA1; contraindicated in xeroderma pigmentosum and lupus; cumulative carcinogenic risk.
Worked example
A patient with psoriasis and psoriatic arthritis needs systemic therapy. Reasoning: methotrexate addresses both skin and joint disease; check liver and renal function, CBC, and pregnancy status. A TNF inhibitor is an alternative if methotrexate fails.
Traps
Methotrexate is weekly, not daily. Isotretinoin requires pregnancy testing and contraception. Cyclosporine is avoided in hypertension and renal disease.