Comparison of the effects of oral nizatidine and ranitidine on gastric volume and pH in patients undergoing gynaecological laparoscopy

Ninety patients who presented for elective gynaecological laparoscopy as day cases were allocated at random to three groups and studied on a double blind basis to compare the effects of nizatidine, ranitidine or placebo on gastric secretion. All the patients received the active drugs or placebo orally at least 45 minutes before the induction of anaesthesia. After tracheal intubation gastric fluid was aspirated via an orogastric tube and the volume and pH of the aspirate were measured. Venous blood samples were obtained at the times of gastric sampling to determine the plasma levels of the drugs. The proportion of patients with both pH greater than 2.5 and volume less than 25 ml were 100%, 90%, and 92.9% in the nizatidine, ranitidine and placebo groups respectively. There was no difference in volume between groups. Two patients in the nizatidine group without a measurable aspirate had blood levels less than the therapeutic range. The median pH values in both treated groups were significantly greater than in the placebo group, but there were no differences between the two treated groups. There were 19 (67.8%) patients in the placebo group with pH less than 2.5. This was significantly higher than the 2 (7.4%) and 6 (20%) in the nizatidine and ranitidine groups respectively. When the time interval between drug administration and induction of anaesthesia was divided arbitrarily into 45-90 minutes and greater than 90 minutes, all the patients in the nizatidine and ranitidine groups with pH less than 2.5 were given the drugs in the 45-90 minute interval; this suggests a latent period is required before the gastric pH increases. Nizatidine may be an effective protective agent against acid aspiration syndrome.