ABSTRACT
The aims of the early phase evaluation of a novel analgesic are to examine kinetics and limits to dosage by side-effects, and to establish the therapeutic dose. This chapter aims to concentrate upon methods to establish efficacy, and then touch upon other pharmacodynamic properties of analgesics. Few models fulfil these criteria. None have been sufficiently tested to exclude non-analgesics causing artefactual pain relief, and in many models known analgesics do not cause detectable analgesia. Visual analogue scales are lines, usually horizontal, anchored at both ends by terms such as ‘no pain’ and ‘worst possible pain’. Pain intensity can be indicated by placing a mark on the line or by moving a cursor along a computer-generated scale. Most research into category judgements of pain intensity has focused upon the pain threshold and upon delineating accurately the stimulus intensity at that boundary.
