No development of tolerance to analgesia by repeated administration of H1 antagonists

The effect produced by repeated administration of the H-1-antihistaminics diphenhydramine, promethazine and pyrilamine on their ability to induce antinociception was evaluated in the mouse hot-plate and abdominal constriction tests. Contrary to morphine, baclofen and oxotremorine, the three H-1 antagonists investigated did not promote the development of tolerance to the analgesic effect after 14 days of repeated treatment. H-1 antagonists could, therefore, represent a promising pharmacological approach to the management of chronic pain. (C) 1998 Elsevier Science Inc.