Diclofenac systemic exposure is not increased when topical diclofenac is applied to ultraviolet-induced erythema

Diclofenac is a non-steroidal anti-inflammatory drug used for a variety of painful and inflammatory conditions. A new low-dose, topical-gel form of diclofenac sodium (diclofenac-Na) has been developed for pain relief and redness reduction after sunburn. The objective was to compare exposure to oral diclofenac-Na with the systemic exposure to diclofenac after application of the new topical diclofenac-Na 0.1% Emulgel gel (diclofenac-Na gel) to normal skin and to that with ultraviolet-induced erythema relative. This study was an open, single-centre, three-period, non-randomised trial in 18 healthy Caucasian subjects. During the first period, 12.5 g gel (12.5 mg diclofenac-Na) was applied twice on a single day to normal skin. During the second period, a 25-mg diclofenac-Na, enteric-coated tablet was given orally three times in a single day. During the third period, the diclofenac-Na gel was applied, as in the first period, but during the early phase of an erythema induced by three times the ultraviolet minimal erythema dose, i.e. a first-degree sunburn associated with pain. During each period, venous blood samples were collected over 24 h and urine was collected over 72 h after first administration for the determination of diclofenac in plasma and urine and of 4'-OH-diclofenac in urine. The systemic exposure after topical application of 25 mg diclofenac-Na on sunburned skin was less than 3% that of 75 mg oral diclofenac-Na and was not increased to that measured on normal skin. The diclofenac-Na 0.1% Emulgel gel can be applied safely to sunburned skin (superficial sunburn, i.e. first degree) as well as to normal skin.