What is drug-induced photosensitivity?
Drug-induced photosensitivity occurs when certain photosensitising medications cause unexpected sunburn or dermatitis (a dry, bumpy or blistering rash) on sun-exposed skin (face, neck, arms, backs of hands and often lower legs and feet). The rash may or may not be itchy.
Medications can also cause onycholysis (the nail plate lifting off the nailbed). This is known as photo-onycholysis.
Photo-onycholysis induced by doxycycline
What causes drug-induced photosensitivity?
Drug- and chemical-induced photosensitivity occurs when a drug or chemical agent combines with UV radiation to cause a phototoxic or photoallergic reaction. These agents are called photosensitisers and can be topical agents or medications that are taken orally. The following table lists the most common medications and topical agents causing photosensitivity.
Common photosensitising medications
- Fluoroquinolones (eg, ciprofloxacin)
- Sulfonylureas (eg, glipizide, glyburide)
- Phenothiazines (eg, chlorpromazine, fluphenazine)
- Thioxanthenes (eg, chlorprothixene)
- 5-aminolevulinic acid
- Methyl-5-aminolevulinic acid
- Porfimer sodium
- Methoxsalen (8-methoxypsoralen)
Common photosensitising topical agents
- Para-aminobenzoic acid (PABA)
- 6-methyl coumarin
What are the clinical features of drug-induced photosensitivity?
The clinical features of drug-induced photosensitivity vary according to the photosensitising agent involved and the type of reaction it causes in the skin. The reaction can be phototoxic and/or photoallergic.
Phototoxic reactions result from direct damage to tissue caused by light activation of the photosensitising agent, whilst photoallergic reactions are a cell-mediated immune response in which the antigen is the light-activated photosensitising agent.
Photoallergic reactions occur less commonly than phototoxic reactions and are mostly caused by photosensitising topical agents. Although some oral photosensitising medications can cause photoallergic reactions, most cause phototoxic reactions. A handful of medications can cause both phototoxic and photoallergic reactions.
The clinical features differ between phototoxic and photoallergic reactions.
- Skin reaction occurs minutes to hours after exposure to agent and light
- Appears as an exaggerated sunburn reaction (reddening and swelling)
- Vesicles, blisters and bullae may occur in severe reactions (pseudoporphyria)
- May or may not be itchy
- Less commonly, the skin may change colour, for example, a blue-green pigmentation is associated with amiodarone
- The reaction is limited to sun-exposed skin
- Photo-onycholysis (separation of the distal nail plate from the nail bed) may arise with many oral photosensitising medications and may be the only sign of phototoxicity in dark-skinned individuals
- Eczematous, itchy type reaction occurs 24-72 hours after exposure to agent and light
- May spread to areas that have not been sun-exposed
- Hyperpigmentation does not occur
What is the treatment for drug-induced photosensitivity?
The main goal of treatment is to identify the photosensitising agent and if possible to avoid it. In cases where medication is being taken to treat an existing condition and cannot be discontinued, patients should be advised to follow strict sun protection strategies, including wearing sun protective clothing and using high protection-factor, broad-spectrum sunscreen.