Abstract
In a controlled cross‐over study comprising eight healthy subjects of effervescent acetylsalicylic acid (ASA) and an experimental ASA formulation were compared with unbuffered ASA and placebo concerning effects on the urinary pH within a dosage interval after 2 days' medication with 3 g ASA daily. The effects on the urinary pH were related to the morning plasma salicylate concentrations observed.
Both the buffered formulations significantly increased the median pH of the period studied compared to unbuffered ASA, the effervescent by 1·5 units and the experimental by 0·6 units. Unbuffered ASA significantly decreased the median pH compared to placebo. Those subjects with the most acidic urine during placebo treatment showed the most pronounced pH elevations due to effervescent ASA. The plasma salicylate concentration was significantly lower with the effervescent formulation compared with unbuffered ASA, but there was no statistical difference between the experimental tablet and unbuffered ASA.
The variable effects on the urinary pH and the plasma salicylate concentrations induced by the two buffered preparations are explained by the different absorbabilities of the buffering agents included. The results presented are consistent with recommendations not to use bicarbonate‐containing ASA formulations continuously when high plasma levels are desirable.