Photochemistry and Photobiology, 2003, 77(4): 356–361 Photomutagenic Properties of Terfenadine as Revealed by a Stepwise Photostability, Phototoxicity and Photomutagenicity Testing Approach { A. Tarozzi* 1 , V. Andrisano 2 , J. Fiori 2 , V. Cavrini 2 , G. Cantelli Forti 1 and P. Hrelia 1 1 Department of Pharmacology, University of Bologna, Bologna, Italy and 2 Department of Pharmaceutical Sciences, University of Bologna, Bologna, Italy Received 4 October 2002; accepted 12 January 2003 ABSTRACT Administration of the second-generation antihistamine, terfe- nadine, is sometimes associated with photosensitivity and other skin reactions. To obtain information on its photo- reactivity, we used a stepwise experimental approach in- volving tests for photostability, phototoxicity (PT) (mouse fibroblast cell line [3T3] neutral red uptake [NRU] test) and photomutagenicity (with standard Ames salmonella tester strains TA98, TA100 and TA102). Terfenadine was not phototoxic to cultured mammalian cells under the conditions used (i.e. 5000/161 mJ cm 22 UVA–UVB). Natural sunlight and UV radiations caused considerable drug decomposition and formation of several photoproducts. Addition of the irradiated terfenadine solution (i.e. a mixture of photoproducts) to the tester did not significantly increase background mutation frequency. Irradiation of terfenadine coplated with the TA102 strain induced a clear-cut photomutagenic response, the magnitude of which was dependent upon the precursor compound concentration and the UV dose (212/7 to 339/11 mJ cm 22 UVA–UVB). These findings demonstrate that in vitro terfenadine is photomutagenic in absence of PT. Further in vitro and in vivo studies are therefore needed to provide an adequate safety assessment of the photochemical genotoxicity– carcinogenicity potential of terfenadine. In the meantime, patients should be advised to avoid excessive exposure to sunlight. INTRODUCTION Many different classes of drugs have been reported to be photosensitizers in the clinical setting, including antimicrobials, nonsteroidal antiinflammatory drugs (NSAIDs), antidepressants, anticonvulsants, diuretics and antihypertensives (1). Acute photo- irritation reactions resembling sunburn can occur. However, immediate subclinical effects with long-term consequences that may not become apparent for many years are thought to be much more common. Skin photoreactions are evoked when a sufficient quantity of a photosensitizing drug is present in the skin, and exposure to light from the sun or artificial sources induces the formation of aggressive molecules that damage the cellular component (2). When DNA is targeted, mutagenic or carcinogenic events (or both) may occur (3). Data from animals and humans suggest that at least some photosensitizers enhance UV-associated skin carcinogenesis. For instance, furocoumarins such as 8-methoxypsoralen (8-MOP), phenothiazines and some porphyrins are photosensitizers that can cause DNA damage (4–6). Humans chronically exposed to psoralen and UVA radiation have an increased risk of skin cancer, particularly of squamous cell cancer (7) and melanoma (8,9). Recently fluoroquinolone antibiotics have also been reported to exert photochemical genotoxicity (10–13), and several are known to enhance UVA-induced skin tumors in hairless mice (14). The duration of use of phototoxic drugs is generally limited, and, in most cases, patients are warned to avoid exposure to sunlight during the treatment period. However, data are lacking for many classes of pharmaceuticals, and the frequency of phototoxic reactions is probably underestimated. The photosensitizing potential of an agent is often only noted during clinical trials or in the postmarketing stage of product development. Withdrawal of the agent at this late stage is extremely costly for the manufacturer. Although various animal skin phototoxicity (PT) models exist, rapid and sensitive methods are being developed to identify photosensitivity effects before widespread human exposure (15). Terfenadine is a second-generation antihistaminic drug currently used for the symptomatic relief of hypersensitivity reactions including rhinitis and skin disorders (16). In clinical practice, its administration can give rise to photosensitivity and other skin reactions, including erythematous rashes, urticaria and peeling skin on the hands and feet (17,18). Photochemically, the terfenadine molecule absorbs the UV light spectrum leading to the formation of photodegradation products (19). Terfenadine distributes widely into various body tissues, including the skin (20). To obtain further information on the photoreactivity of terfenadine, we used a stepwise experimental approach involving photostability, PT and photomutagenicity testing. In particular, we used the mouse fibroblast cell line (3T3) neutral red uptake (NRU) PT test (3T3 NRU PT test) (21), an in vitro method that has been officially accepted by European Commission and the EU {Posted on the website on 1 February 2003. *To whom correspondence should be addressed at: Department of Pharmacology, University of Bologna, Via Irnerio 48, 40126 Bologna, Italy. Fax: 39-051-248862; e-mail: atarozzi@biocfarm.unibo.it Abbreviations: DAD, photodiode array detector; DMSO, dimethyl sulfoxide; HBSS, Hank’s buffered salt solution; HPLC, high-perfor- mance liquid chromatography; LC–MS, liquid chromatography–mass spectroscopy; 8-MOP, 8-methoxypsoralen; NRU, neutral red uptake; NSAID, nonsteroidal antiinflammatory drugs; PIF, photoirritancy factor; PT, phototoxicity; 3T3, mouse fibroblast cell line. 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