Absence of antinociceptive tolerance to improgan, a cimetidine analog, in rats

Improgan, an analog of the histamine receptor antagonist cimetidine, produc es highly effective analgesia following intraventricular injection. The pre sent study examined changes in the antinociceptive effects of improgan foll owing once daily intraventricular injections. Improgan (100-150 mu g) produ ced near maximal antinociception 10 and 30 min after daily administration o n all 4 test days, whereas comparable morphine treatments (50 mu g) induced considerable tolerance. Thus, improgan produced highly effective analgesia without the development of tolerance. (C) 1998 Elsevier Science B.V. All r ights reserved.