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In a double-blind trial, 21 patients with severe plaque psoriasis were randomly assigned to receive oral cyclosporine, 14 mg/kg/d, or its vehicle. After four weeks of therapy the 11 cyclosporine recipients had the following response to treatment: two had total clearing and six improved markedly, two moderately, and one minimally; whereas ten vehicle-treated patients showed no change or minimal improvement. Vehicle-treated patients, after a switch to cyclosporine for four weeks, demonstrated impressive improvement similar to that seen in patients who initially received only cyclosporine. Moderate or marked improvement or total clearing was noted in 17 (81%) of 21 and 20 (95%) of 21 after one and four weeks of therapy, respectively. Mitotic figures and leukotriene B4 levels in lesions decreased 86% and 64%, respectively, after seven days of cyclosporine therapy. Mononuclear (including activated T cells) and polymorphonuclear leukocyte infiltrates were markedly reduced in lesions of all patients after seven days of cyclosporine therapy. These results suggest that (1) psoriasis may have an immunologic basis mediated by activated T cells and/or other immune cells; (2) if a long-term regimen with a favorable efficacy—side effect ratio can be determined, cyclosporine would be a significant advance in the treatment of psoriasis.(JAMA 1986;256:3110-3116)

In a 16-week randomized, double-blind, vehicle-controlled study of topical tretinoin in the treatment of photoaging, all patients applied topical tretinoin to one forearm and vehicle cream to the other. Half of the patients received tretinoin to the face, and half received vehicle cream. All 30 patients who completed the study showed statistically significant improvement in photoaging on the tretinoin-treated forearms, but not on the vehicle-treated forearms. Fourteen of the 15 patients who received tretinoin to the face had improvement in photoaging, whereas none of the vehicle-treated patients' faces improved, a statistically significant difference in response between the two groups. Statistically significant histologic changes were seen in forearm skin treated with tretinoin, but not with vehicle cream. Side effects were limited to irritation of tretinoin-exposed skin.(JAMA 1988;259:527-532)

In Reply.—In answer to Dr Pazmiño, laboratory and drug absorption studies were not done in our study because of the known safety of topical tretinoin.Plasma levels of tretinoin were undetectable after applications of 0.025% tretinoin cream to the arms, legs, and back twice daily for 28 days or 1.0% tretinoin cream once to the entire body.1Any minimal absorption of tretinoin through intact skin and any prostaglandins in the skin (which are metabolized locally) would be unlikely to affect the kidney directly. Based on our experience with retinoids2,3 and on 17 years of safe use of tretinoin without reported vasculitis or effects on kidney function (E. G. Thorne, MD, Ortho Pharmaceutical Company, oral communication, March 1988), we conclude that it is unnecessary to perform kidney function measurements in patients using tretinoin topically.Day-to-day variation and laboratory or collection errors could account for some of the findings