Increased serum phosphate levels and calcium fluxes are seen in smaller individuals after a single dose of sodium phosphate colon cleansing solution: a pharmacokinetic analysis

Sodium phosphate containing colonoscopy preparations may cause electrolyte disturbances and calcium-phosphate nephropathy. Decreased body weight is an unexplored risk factor for complications with sodium phosphate ingestion. To perform a pharmacokinetic analysis of a single dose of Fleet Phospho-Soda in smaller and larger individuals. Seven subjects weighing < 55 kg (Group I) and six weighing > 100 kg (Group II) consumed 45 mL Fleet Phospho-Soda. Serum electrolytes were measured. Hydration was closely maintained by monitoring weight, fluid intake and total body water. Marked increases in serum phosphate were seen in Group I compared to Group II. For example, mean serum phosphate at 120 min was 7.8 +/- 0.5 mg/dL in Group I and 5.1 +/- 0.8 mg/dL in Group II (P < 0.001). Normalized area under the phosphate vs. time curve for Group I was 1120 +/- 190 mg/dL*min and 685 +/- 136 mg/dL*min for Group II (P < 0.001). Twelve-hour urine calcium was lower in Group I (16.4 +/- 7.6 mg) than in Group II (39.2 +/- 7.8 mg, P < 0.001). Increased serum phosphate occurs in smaller individuals after ingestion of sodium phosphate preparations, even with strict attention to fluid intake. Smaller body weight poses a potential risk for calcium-phosphate nephropathy.