Effects of varying doses of tramadol on gastric pH

Tramadol is licensed primarily as an analgesic, but has additional properties, one of which is the ability to increase gastric pH. However, it has not been established if this action is dose related, hence we set out to provide further evidence about this action of tramadol.

Fifty-five female adult patients presenting for gynecological surgery were randomized into three groups. After induction, 2.5 ml of gastric juice was aspirated to determine baseline pH, after which groups 1, 2, and 3 received 50 mg, 75 mg, and 100 mg of IV tramadol, respectively. Gastric pH was subsequently assessed every 30 min for as long as the surgery lasted.

There was no significant difference in the pH of the three groups before anesthesia (3.88 ± 0.75, 3.54 ± 0.73, and 3.75 ± 0.70; P = 0.393). Similarly, no significant statistical difference was observed in the pH of the three tramadol groups during the subsequent three readings (pH1: 4.21 ± 0.93, 4.27 ± 0.95, 4.07 ± 0.82; pH2: 4.75 ± 1.00, 4.68 ± 0.94, 4.59 ± 0.78; pH3: 5.33 ± 0.86, 5.13 ± 0.95, 4.97 ± 0.78; P = 0.793, 0.876, and 0.490). There were statistically significant increases in the pH of each group when the baseline pH was compared with the subsequent three readings, with P values of 0.002, 0.0001, 0.001 in the 50 mg group, 0.0001, 0.0001, 0.0001 in the 75 mg group, and 0.008, 0.0001, 0.001 in the 100 mg group.

Our result further confirms that tramadol elevates gastric pH. However, the degree of elevation was not found to be dose dependent.