Regional variations in analgesic efficacy of EMLA cream. Quantitatively evaluated by argon laser stimulation.

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Abstract
The effect of EMLA cream (a eutectic mixture of local analgesics) applied for 30, 60, 90 and 120 min on the forehead, cheek, back, cubital fossa, and dorsum of the hand was studied. Analgesic onset, efficacy and duration were evaluated by sensory and pain thresholds to laser stimulation measured before, and 5, 60, 120, and 180 min after the cream was removed from the skin. Cutaneous blood flow was measured and found to be 4-5 times as high on the face as on the other locations. On the forehead the analgesic efficacy decreased with increased application time. For all other locations, efficacy increased with increasing application time. On the back, onset was rapid and sufficient analgesia could be obtained, but analgesias began to wane immediately after removal of the cream. In the cubital fossa and on the hand, onset was tardy, and efficacy continued to increase for 60 min after cream removal, followed by a slow decline. Blood flow, epidermal and dermal thickness are important factors affecting onset, efficacy and duration of EMLA analgesia.