Photosensitizing drug reactions
Photosensitizing drug reactions are drug-induced skin eruptions confined to sun-exposed areas, occurring as phototoxic reactions (common, dose-dependent, an exaggerated sunburn from UVA-absorbing drugs) or photoallergic reactions (uncommon, a delayed eczematous type IV response). Diagnosis is clinical from the photodistribution and drug history, and management is stopping the culprit, photoprotection, and topical corticosteroids.
- Topic reviewThe full article, organized the way the exam asks it.
- ABIM-format MCQsVignettes with an explanation for every wrong answer.
- Key factsThe numbers and thresholds worth memorizing, up front.
- AI tutorMedBrain answers the question you're stuck on.
What this article covers
- Overview
Definition: photosensitizing drug reactions are cutaneous eruptions triggered when a drug plus ultraviolet (UV) light damages the skin, presenting in a photodistributed pattern.
- Epidemiology
Phototoxic reactions are common: the most frequent drug-induced photoeruption.
- Risk factors
Phototoxic drugs: tetracyclines (doxycycline), fluoroquinolones, NSAIDs, amiodarone, thiazide diuretics, phenothiazines, voriconazole, and targeted agents (vemurafenib).
- Pathophysiology
Phototoxic mechanism: the drug absorbs UV (mainly UVA) energy and releases it into the skin, directly damaging cells; it is non-immune, dose-dependent, and can occur on first exposure.
- Clinical features
Photodistribution: eruption on the face, V of the neck, dorsal hands, and extensor forearms, sparing shaded sites (under the chin, behind the ears).
- Differential diagnosis
Ordinary sunburn: photodistributed erythema without a photosensitizing drug.
- Diagnosis
Diagnose clinically from the photodistribution plus drug history, distinguishing the two mechanisms: a drug photosensitivity reaction is established by an eruption confined to sun-exposed skin in a…
- Management
First-line, stop or substitute the culprit drug when feasible, which is the definitive step.
- Complications
Severe blistering phototoxic reactions: resembling burns, with pain and secondary infection.
- Prognosis
Resolves with drug withdrawal: phototoxic reactions settle over days to weeks once the drug and sun exposure are removed.
- Prevention
Counsel photoprotection when prescribing known photosensitizers: broad-spectrum UVA sunscreen (SPF 30 or higher), protective clothing, and sun avoidance.
Read the whole article
Subscribing to Internal Medicine opens every article, the full question bank and MedBrain, on the web, iPhone and Android.