Relationship between cimetidine plasma levels and gastric acidity in acutely ill patients.

The relationship between cimetidine plasma levels and gastric acidity was studied in acutely ill patients. Patients in surgical intensive care for stress ulcer who were being managed with nasogastric suction were studied. Nine patients (Group 1) received 300 mg of intravenous cimetidine over 30 minutes every six hours. Titratable acidity and pH of gastric aspirates and plasma cimetidine levels were measured at peak (1.5--2.5 hours) and trough (5--6 hours) times following cimetidine administration, in Group 1. Titratable acidity and pH were measured for nine Group 2 patients (control) who did not receive cimetidine. In Group 1, mean gastric acid output was significantly lower (p less than 0.05) and mean pH was significantly higher (p less than 0.005) than in Group 2. In Group 1, plasma cimetidine concentration correlated poorly with gastric pH and gastric acid output (r = 0.21). The study indicates that the correlation between plasma cimetidine levels and gastric acid secretion is poor, but that the cimetidine dosage used suppressed acid output during the entire dosing interval.