Hydrochlorothiazide-Induced Photosensitivity
The patient's flushed red rash exacerbated by sun exposure is most likely caused by hydrochlorothiazide (HCTZ), and the drug should be discontinued immediately and replaced with a non-photosensitizing antihypertensive agent. 1, 2
Most Likely Culprit Medication
Among the four medications this patient recently started, HCTZ is the most consistently implicated photosensitizing drug and warrants the highest level of suspicion. 1, 2, 3
- HCTZ causes photosensitivity reactions in 1-2% of patients, manifesting as exaggerated sunburn reactions, dermatitis, and lichenoid eruptions in sun-exposed areas. 1
- The photosensitivity typically occurs with UVA exposure (315-400 nm), though UVB reactions (308 nm) have been documented. 4, 5
- Metformin, amoxicillin-clavulanate (Augmentin), and benzonatate (Tesslon Perles) are NOT photosensitizing agents and are unlikely culprits. 1
Diagnostic Confirmation
Review the medication timeline carefully: 28-64% of HCTZ-associated photosensitivity cases begin within one year of starting the medication. 6
Key diagnostic features to document:
- Distribution limited to sun-exposed areas (face, neck, dorsal hands, forearms) 7, 8
- Flat erythematous rash with flushing pattern 5
- Temporal relationship between sun exposure and symptom onset 8
- Recent initiation of HCTZ 2, 3
Phototesting is not immediately necessary for clinical diagnosis when history and presentation are classic, though it can confirm abnormal responses to UVA alone or both UVA and UVB if diagnosis is uncertain. 5
Immediate Management Algorithm
Step 1: Discontinue HCTZ Immediately
- Stop HCTZ and do not rechallenge, as 28.8% of patients experience complete or partial remission after discontinuation. 6
- Substitute with a non-photosensitizing antihypertensive (ACE inhibitors, ARBs, and calcium channel blockers carry only theoretical photosensitivity risk, not consistent clinical evidence). 1
Step 2: Treat Active Photosensitivity Reaction
- Apply high-potency topical corticosteroids to affected sun-exposed areas for symptomatic relief. 7, 3
- For mild reactions (Grade 1: <10% body surface area): topical emollients and mild-to-moderate potency topical corticosteroids. 7, 1
- For moderate reactions (Grade 2: 10-30% BSA or limiting activities): consider oral prednisone 0.5-1 mg/kg tapered over 4 weeks. 7, 1
Step 3: Implement Strict Photoprotection
- Apply broad-spectrum sunscreen (SPF ≥30) daily to all exposed skin, with emphasis on high UVA protection. 7, 8, 1
- Avoid sun exposure during peak hours (10 AM to 4 PM) and seek shade when outdoors. 8, 1
- Wear protective clothing including broad-brimmed hats, long-sleeved shirts, and long pants. 8
- For 24 hours after any phototherapy exposure, no sunlight exposure should occur; if driving, apply commercially available UVA-blocking window films. 7
Critical Precautions and Pitfalls
Common pitfall: Assuming all four medications are equally likely culprits. HCTZ has the strongest evidence base for photosensitivity among this patient's medications. 1, 2, 3
Important caveat: If the patient had been taking HCTZ for years without issue, sudden onset photosensitivity can still occur, as 36% of cases in one series started HCTZ prior to developing lesions but experienced delayed reactions. 6
Long-term surveillance consideration: Patients with HCTZ-induced photosensitivity may have higher risk of developing skin malignancies at sites of earlier reactions, warranting annual dermatology skin examinations. 8, 2
Expected Timeline for Resolution
- Improvement should begin within days to weeks after HCTZ discontinuation with strict photoprotection. 6
- If no improvement occurs after 2-4 weeks despite HCTZ discontinuation, consider dermatology referral for phototesting to evaluate for alternative photodermatoses (polymorphic light eruption, chronic actinic dermatitis, solar urticaria). 8