MORPHINE DOES NOT AFFECT LASER-INDUCED WARMTH AND PIN PRICK PAIN THRESHOLDS

The aim of this double-blind, placebo-controlled study was to evaluate the effect of intravenously administered morphine in humans using an argon laser to induce experimental pain. Thirty volunteers were random ised to receive a total of 0.15 mg.kg(-1) morphine intravenously or sa line. The argon laser was used to determine the possible change in war mth thresholds and pin prick pain thresholds. Measurements were perfor med before and at 10, 20, 30 and 40 min after the injection. During th e observation period the warmth thresholds increased 20.7% (P less tha n or equal to 0.05) from baseline (0.82 W +/- 0.42 W) in the morphine group while an increase of 14.3% (P greater than or equal to 0.05) was seen in the placebo group (Baseline: 0.91 +/- 0.37). The pinprick pai n thresholds of the morphine group increased 9.4% (P less than or equa l to 0.05) from baseline (1.39 W +/- 0.7 W) while the corresponding th resholds of the placebo group was 4.6% (P greater than or equal to 0.0 5) (baseline: 1.73 W +/- 0.44 W). The differences seen between the mor phine group and the placebo group were not statistically significant a nd thus it was demonstrated that morphine had no effect of either the feeling of warmth or the pain elicited by the argon laser. The present study supports other investigations and clinical experience suggestin g that intermittent pain is not relieved try morphine unlike continuou s pain, which can be relieved by morphine.