title: [Analgesic effects of H1 receptor antagonists in the rat model of formalin-induced pain].
abstract: OBJECTIVE
  Histamine receptors mediate nociceptive pathways, especially in the central nervous system. Some studies have demonstrated the analgesic effects of histamine receptor antagonists in the peripheral nervous system. It is not clear whether the local analgesic effect is class-specific or drug-specific.
  
  
  METHODS
  To answer this question, we used three different H1 receptor antagonists (pyrilamine, promethazine, and cetirizine) administered directly in the paw of the rat, intraperitoneally, or in peripheral nerve blockade in the formalin-induced pain model. The effects of the drugs on the number of paw elevations were observed.
  
  
  RESULTS
  In phase I, the local administration of pyrilamine caused a dose-dependent reduction on the number of paw elevations; in the highest dose, the number of paw elevations was reduced by 97.8%. Promethazine decreased it by 92%, while cetirizine decreased by 23.9%. In phase II, pyrilamine decreased the number of paw elevations by 93.5%, promethazine by 78.2%, and cetirizine by 80.1%. Intraperitoneal administration of drugs did not change painful behavior. When used in peripheral nerve block, in phase I pyrilamine reduced the number of paw elevations by 96.7%, promethazine by 73.3%, and cetirizine by 23.9%. In phase II, pyrilamine reduced the number of paw elevations by 86.6%, promethazine by 64.4%, and cetirizine by 19.9%.
  
  
  CONCLUSIONS
  The results demonstrate that H1 receptor antagonists have local analgesic effects, different from the systemic effects, one of them an anti-inflammatory and class-specific effect and the other similarly to the local anesthetic effect, specific for promethazine and pyrilamine.
authors: Departamento de Medicina, Universidade Federal de São Carlos. hazem@hcnet.usp.br
authors: Hazem Adel
authors: HA
authors: Ashmawi
authors: Leandro Mamede
authors: LM
authors: Braun
authors: Angela Maria
authors: AM
authors: Sousa
authors: Irimar de Paula
authors: Ide P
authors: Posso
mesh_terms: D000698:Analgesia; D000818:Animals; D004195:Disease Models, Animal; D005557:Formaldehyde / Q000008:administration & dosage; D006634:Histamine H1 Antagonists / Q000627:therapeutic use*; D008297:Male; D010146:Pain / Q000139:chemically induced / Q000517:prevention & control*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D006634:Histamine H1 Antagonists; D005557:Formaldehyde