Sample size
Sampling was based on the joint primary outcomes, urine pH, and sUA. In a separate pilot study conducted in our center, 60 participants were included under the same inclusion/exclusion criteria, the mean change of pH mean ± standard derivation (S.D) was 0.40 ± 0.517, 0.38 ± 0.371, and 0.64 ± 0.478 in the sodium bicarbonate group, citrate mixture group and TaCCi mixture group, respectively. To detect a 0.232 difference in urine pH between sodium bicarbonate and TaCCi mixture, 75 patients in each group provided > 80% power at a significance level of 0.05. In the pilot study, the mean change of sUA (mean ± S.D) was 134 ± 93.5 μmol/L, 137 ± 80.6 μmol/L, and 175 ± 76.1 μmol/L in the sodium bicarbonate group, citrate mixture group, and TaCCi mixture group, respectively. To detect the 38.4 μmol/L difference in sUA between the citrate mixture group and TaCCi mixture group, 69 patients in each group were required. Based on the urine pH and sUA data, 75 participants in each group would provide > 80% power at a significance level of 0.05. Considering a drop-out rate of 20%, at least 281 participants were needed.