Drug-induced photosensitivity reactions reactions

Drug Store News, July 20, 1998 by Carol Dickson McKee

The pharmacist is in a unique position to counsel patients on both prescription and non-prescription medications, herbal and other "natural" products and perhaps even cosmetics, shampoos and similar purchases. Many medications and topical products can cause photosensitivity reactions or increase a patient's risk of developing sunburn. This article will describe photosensitivity reactions, Discuss the patient populations most at risk, list the medications, common herbal products and topical agents most likely to cause these reactions and suggest ways to prevent or treat them. Possible long-term effects from chronic exposure to the sun and/or tanning apparatus will also be discussed, particularly as this relates to photosensitivity reactions.

What is a drug-induced photosensitivity reaction?

A drug-induced photosensitivity reaction most commonly appears as an exaggerated sunburn. It occurs when one takes certain medications or applies, either intentionally or unintentionally, offending agents to the skin and is exposed to appropriate wavelengths of ultraviolet radiation sunlight or tanning apparatus. A photosensitivity reaction should be considered in patients experiencing sunburn of greater severity than would normally be expected for them, or who develop rashes in areas exposed to the sun or tanning apparatus.

How common are drug-induced photosensitivity reactions?

Drug-induced photosensitivity reactions are common, and are actually increasing in frequency with the increased emphasis on health that includes outdoor exercise during both the summer and winter. Despite publicity about skin cancer, sunbathing and the use of tanning apparatus are still popular, People are living longer and are likely to retire to warm climates, which usually increases exposure to the sun; older "seasoned citizens" also tend to take more medications, many of which may be implicated in drug-induced photosensitivity reactions. The use of herbal and other "natural" products is also increasing, and people may not be aware that some of these can also cause photosensitivity reactions. Photosensitizing chemicals are wedely used in medications, cosmetics, lotions, shampoos, hair dyes, soaps an(l other topical products.

Who gets drug-induced photosensitivity reactions?

As discussed above, drug-induced photosensitivity reactions are quite common and can occur in virtually anyone, though to widely varying degrees of severity. People with fair complexions; red, blonde or light brown hair; blue or green eyes; and who generally sunburn easily and do not tan are most at risk. A history of severe sunburn(s) may also increase the risk, as may a history of allergies, especially contact hypersensitivities, to cosmetics or other topical agents. The frequency, type and amount of UVR the person is likely to receive should also be considered. For example, a person who receives only casual exposure to sunlight outside its most intense hours of 10 a.m to 3 p.m. would be less likely to have a reaction than would someone who routinely sunbathes or visits a tanning salon.

Are all drug-induced photosensitivity reactions the same?

Drug-induced photosenstivity reactions, which include reactions caused by medications administered[ systemically, herbal products or their metabolites and medications or other agents either intentionally or unintentionally applied to the skin, can be divided into two types, phototoxic and photoallergic reactions (See Table 1). 1 The same medication or agent may produce both phototoxic and photoallergic reactions, and it may at times be difficult to differentiate between the two types of reactions clinically.

By far. the most common type of (1mg-induced photosensitivity reaction is the phototoxic type, where the offending agent is thought to act as a chromophore, absorbing ultraviolet radiation. When the chromophore reaches a sufficient concentration in or on the skin, and when the skin is exposed to the appropriate wavelength of ultraviolet radiation, energy is emitted which damages the adjacent tissue to cause a phototoxic reaction.' The wavelength of radiation necessary to produce such a reaction depends on the absorption spectrum of the offending agent.

Phototoxic photosensitivity reactions are dose-dependent and will occur in almost any one who takes or applies an adequate amount of the offending agent. The dose necessary to produce such a reaction varies from person to person, and will depend upon such factors as complexion, hair and eye color, usual ability to tan and type and amount of ultraviolet radiation exposure. Phototoxic photosensitivity reactions are not immunologically mediated, are not allergic reactions, can occur on first exposure to the agent and generally show no cross-sensitivity to chemically related agents.

A phototoxic reaction usually has a rapid onset (within several hours after exposure to ultraviolet radiation) and presents as an exaggerated or intensified sunburn with erythema (redness), pain and prickling or burning. Blistering, desquamation (peeling) and hyperpigmentation (abnormally increased coloration of the skin) may occur in severe [cases.sup.(1)(6)]. Symptoms usually peak 24 to 48 hours after initial exposure and are usually limited to the areas of the skin exposed to ultraviolet radiation.