The time course and effect on serum electrolytes of oral sodium phosphates solution in healthy male and female volunteers.

Background: Although oral sodium phosphates solution is used extensively for bowel preparation, the pharmacokinetic profile of 2 x 45 mL oral sodium phosphates solution has not been reported.

Objectives: The primary objective of this study was to evaluate the time course and degree of electrolyte shifts in two age groups and two gender groups following administration of oral sodium phosphates solution. Secondary objectives included evaluation of electrocardiograms, postural blood pressure, standard serum chemistry and hematology panels, and adverse experiences.

Methods: Twenty-four healthy adult volunteers were divided equally into groups based on age and gender. Each received 2 x 45 mL oral sodium phosphates solution at 7:00pm (hour 0) and at 7:00am (hour 12). Serum electrolytes were measured at sixteen different time points.

Results: Mean serum phosphate concentrations exceeded the upper normal limit within 1 hour following the first dose, peaking at 3 hours (6.26 mg/dL; p < 0.0001) before decreasing. Following the second dose at 12 hours, mean serum phosphate concentrations peaked at 14 hours (6.86 mg/dL; p < 0.0001), before decreasing to normal limits by hour 24. Mean serum sodium, potassium, and calcium concentrations fluctuated within the normal range. However, serum sodium concentrations peaked at 1 hour following the second dose of phosphate, showing a statistically significant (p < 0.0001) increase of 2.4% from baseline to 144.8 mmol/L. No clinically significant changes in ECG were observed. Mean reductions in supine and standing systolic blood pressure were not associated with postural change. No subject had postural decreases in systolic blood pressure of greater than 20 mmHg.

Conclusions: Administration of 2 x 45 mL oral sodium phosphates solution 12 hours apart with proper hydration caused transient serum electrolyte shifts, which were clinically insignificant and resolved within 24 hours.