Do anticholinergics interact with histamine H2 receptor antagonists on night intragastric acidity in active duodenal...

The effect of administering low doses of famotidine or ranitidine alone or in combination with an M1-receptor-selective antagonist, pirenzepine, on night intragastric acidity was evaluated in 16 active duodenal ulcer patients to verify 1) whether anticholinergics and H2-antagonists have a synergic effect on inhibition of night gastric acidity, and 2) whether patients with vagal hypertone are more sensitive to anticholinergics than the remainder of the duodenal ulcer population. The endogastric pH was continuously recorded for 12 h (8 PM-8 AM) after random, single-blind administration of one of the following drug regimens: 20 mg famotidine, 150 mg ranitidine, 50 mg pirenzepine, 20 mg famotidine plus 50 mg pirenzepine, and 150 mg ranitidine plus 50 mg pirenzepine. Six patients with a basal acid output:peak acid output BAO:PAO greater than 0.3 were considered "vagal hypertone" subjects. Night gastric acidity inhibition was -39.6% with pirenzepine (p less than 0.001) and -73.7% and -71.5% with famotidine or ranitidine (p less than 0.001 vs. pirenzepine). The simultaneous administration of pirenzepine with famotidine or ranitidine provoked only a slight, insignificant increase in percent suppression, 5.1% and 6.3%, respectively, and did not modify either the time lag to onset of anti-H2 action or the duration of action. Patients with a BAO:PAO greater than 0.3 were not more sensitive to anticholinergic treatment than other duodenal ulcer patients. Our study furnishes evidence that combined administration of anti-H2 and anticholinergics is not significantly better than anti-H2 alone, in active duodenal ulcer patients.