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The antirheumatic drug dl-2-(4-chlorophenyl) -alpha-methyl-5-benzoxazole-acetic acid (benoxaprofen, Coxigon) can induce mild phototoxic immediate reactions of the skin after some hours of sun exposure and sometimes partial onycholysis. In Central Europe the incidence of this side-effect is about 3 and 1%, respectively. In clinical trials and after experimental high-dose UVA-irradiation (45-64 J/cm2) alpha short-lasting skin burning, already beginning during irradiation, and an erythema of up to 2 h duration could be observed after the ingestion of the recommended daily dose of 600 mg. Photosensitization of the skin can safely be inhibited by a UVA -irradiation absorbing sunscreen agent (Contralum ointment) and onycholysis by using an opaque nail varnish. After epicutaneous and intracutaneous application of benoxaprofen, photosensitization did not occur. The pathogenesis of this unusual phototoxic immediate reaction is unknown.

An open clinical trial of 4 weeks included 32 patients with spondylosis and spondylarthrosis diagnosed on the average about 10 years previously. The non-steroid antirheumatic benoxaprofen was used alone in a dosage of a 1 x 600 mg tablet daily. The treatment had a marked influence on the clinical picture in the form of reduction of the pain at the beginning of movement, and of pains at night or on pressure. The extent of the night pains was already reduced to a statistically significant degree (alpha less than or equal to 0.05) after 1 week and remained so during the course of the treatment. Three patients had to discontinue the treatment prematurely because of side effects (photosensitivity in 2 and gastric intolerance in 1). No negative influence on clinical chemical or hematological parameters was seen in any of the patients.