DIFFERENCES IN PHOTOTOXIC POTENCY SHOULD BE CONSIDERED WHEN TETRACYCLINES ARE PRESCRIBED DURING SUMMER-TIME - A STUDY ON DOXYCYCLINE AND LYMECYCLINE IN HUMAN VOLUNTEERS, USING AN OBJECTIVE METHOD FOR RECORDINGERYTHEMA

In order to test the phototoxic potency of the two tetracyclines most frequently prescribed in Sweden, a double-blind cross-over study using a double-dummy technique with doxycycline 0.1 g twice daily, lymecycl ine 0.6 g twice daily, and placebo, was performed in 15 healthy volunt eers. Drugs were given for 3 consecutive days, and on the third day vo lunteers were tested with 25, 50, 75 and 100 J/cm(2) of artificial lon g-wave ultraviolet radiation (UVA), and assessed 6 h later for erythem atous photoreactions. Objective readings were made using skin reflecta nce spectrophotometry. All three substances were tested in each indivi dual at weekly intervals. Within 50, 75 and 100 J/cm(2) of UVA, lymecy cline showed a slight increase in erythema compared with placebo, brit this was not significant (50 and 100 J/cm(2)), or was of low signific ance (75 J/cm(2)). However, with the same doses, doxycycline showed a substantial increase in erythema compared with placebo, which was high ly significant. We conclude that doxycycline has a higher phototoxic p otency than lymecycline, and this is in agreement with earlier in vitr o experimental data. We recommend that therapy with doxycycline is avo ided during summer-time, and during holidays in a sunny climate.