Effects of triprolidine and dipipanone in the cold induced pain test, and the central nervous system of healthy volunteers.

1 Twelve healthy volunteers took part in a study of the interaction between the antihistamine triprolidine and the opioid dipipanone in the cold induced pain (CP) test and tests of sedation. They received placebo, triprolidine 2.5 mg, dipipanone 8 mg or the combination of the two active treatments according to a double-blind, randomised, balanced, crossover design. 2 Antihistamine activity was demonstrated by triprolidine reducing the size of wheals and flares produced by intradermal histamine 1.6 micrograms. However, triprolidine produced no analgesia in the CP test, nor did it enhance the analgesia produced by dipipanone alone. 3 Neither treatment alone produced statistically significant sedation, assessed by visual analogue scales (VAS), side effect check list, body sway and reaction times. However, the combination did cause significant sedation. 4 Dipipanone reduced pupil size, depressed respiration, and decreased salivation. Triprolidine had no effects on pupil size and respiration, but reduced salivation slightly. It was concluded that histaminergic (H1) mechanisms are unlikely to be involved in pain produced by cold.