Drug-induced photosensitivity is one of the most under-recognised adverse effects in community pharmacy. An estimated 8% of cutaneous drug reactions are photosensitivity-related, according to dermatology literature, yet patients are frequently unaware that their medication increases vulnerability to UV radiation. With UK summers producing increasingly strong UV indices, pharmacists have a practical role in identifying at-risk patients and delivering targeted sun-safety advice.
How Photosensitivity Works
Drug-induced photosensitivity falls into two broad categories:
Phototoxic reactions account for approximately 90% of cases. The drug absorbs UV radiation (usually UVA) and releases energy that directly damages skin cells. This produces an exaggerated sunburn response — redness, blistering and peeling — confined to sun-exposed areas. It can occur on first exposure and is dose-dependent.
Photoallergic reactions are immune-mediated. UV radiation alters the drug's chemical structure in the skin, creating a hapten that triggers a delayed hypersensitivity response. The rash may spread beyond sun-exposed areas, takes 24–72 hours to appear, and requires prior sensitisation.
Common Photosensitising Medicines
The following table lists frequently dispensed medicines with documented photosensitivity risk, based on BNF side-effect profiles:
| Drug class | Common examples | Photosensitivity type |
|---|---|---|
| Tetracyclines | Doxycycline, lymecycline | Phototoxic (dose-related) |
| Fluoroquinolones | Ciprofloxacin, levofloxacin | Phototoxic |
| NSAIDs | Naproxen, piroxicam, ketoprofen | Both |
| Thiazide diuretics | Bendroflumethiazide, hydrochlorothiazide | Phototoxic |
| Retinoids | Isotretinoin, acitretin | Phototoxic |
| Amiodarone | Amiodarone | Phototoxic (can be severe) |
| Phenothiazines | Chlorpromazine | Both |
| Sulphonamides | Co-trimoxazole, sulfasalazine | Both |
| Antifungals | Voriconazole | Phototoxic (severe — skin cancer risk) |
| Statins | Simvastatin, atorvastatin (rare) | Phototoxic (uncommon) |
| St John's Wort | Hypericum perforatum (OTC) | Phototoxic |
Doxycycline is the most commonly implicated drug in UK community pharmacy, given its widespread use for acne, rosacea, respiratory infections and malaria prophylaxis. Photosensitivity risk is dose-dependent and highest at 200 mg daily.
St John's Wort deserves particular attention as an OTC product. Patients purchasing it for mild depression may not associate a herbal supplement with sun sensitivity — proactive counselling at point of sale is valuable.
Counselling Points for Pharmacists
When dispensing known photosensitisers, particularly during spring and summer:
- Inform the patient that their medication may make their skin burn more easily in sunlight
- Recommend SPF 30+ broad-spectrum sunscreen (must protect against UVA, which drives most phototoxic reactions — look for the UVA circle logo)
- Advise reapplication every 2 hours during prolonged outdoor exposure and after swimming
- Suggest protective clothing — wide-brimmed hat, long sleeves, UV-rated sunglasses
- Warn about indirect UV exposure — reflection from water, sand and snow; UV penetration through cloud cover and car windows
- Note timing — for newly started drugs, photosensitivity risk often peaks in the first 1–2 weeks as tissue drug levels build
For patients on amiodarone, counsel that photosensitivity may persist for months after discontinuation due to the drug's extremely long half-life (40–55 days). Blue-grey skin discolouration is a known long-term complication of amiodarone photosensitivity.
For patients on voriconazole, the BNF specifically warns of increased skin malignancy risk with prolonged sun exposure — this requires active counselling and dermatological monitoring.
Identifying Photosensitivity at the Counter
Patients presenting with sunburn-like symptoms that seem disproportionate to their sun exposure should be asked about their medication. Key clues:
- Rash strictly confined to sun-exposed areas (face, neck, forearms, dorsa of hands) with sharp clothing-line demarcation
- Reaction after modest sun exposure that would not normally cause burning
- Recent start of a new medication
- Use of topical products containing ketoprofen or other photosensitising agents
What to Recommend
- Mild phototoxic reaction: emollient, hydrocortisone 1% cream for inflammation, cool compresses, oral antihistamine for itch
- Moderate reaction: as above, plus advise GP review if blistering occurs or the causative drug needs to be continued
- Severe or widespread reaction: refer to GP — may need oral corticosteroids or drug substitution
Prevention Is Better Than Treatment
The most effective pharmacy intervention is anticipatory counselling. Flagging photosensitising drugs at the point of dispensing — particularly at the start of treatment in spring or summer — takes 30 seconds and can prevent a week of painful skin damage.
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Sources: British National Formulary, NICE CKS Sunburn and Sun Protection, British Association of Dermatologists, Drug Safety (photosensitivity review literature).