The bowel purgative Visicol contains microcrystalline cellulose (MCC) residue, which may impair full visibility during a colonoscopy. An MCC residue-free sodium phosphate (RF-NaP; OsmoPrep) tablet was developed.

To investigate appropriate RF-NaP dosing.

Phase 2, randomized, investigator-blinded study.

Six research centers in the United States.

Patients undergoing a colonoscopy received Visicol (n = 34) or 1 of 6 RF-NaP regimens administered as either split (S) dosing (the evening before and the day of colonoscopy) or evening-only (E) dosing. Dosing regimens for RF-NaP were 40 tablets S, 3 every 15 minutes (n = 33); 40 tablets S, 4 every 15 minutes (n = 34); 32 tablets E, 4 every 15 minutes (n = 34); 32 tablets S, 4 every 15 minutes (n = 36); 28 tablets E, 4 every 15 minutes (n = 34); 28 tablets S, 4 every 15 minutes (n = 34). Visicol was administered as 40 tablets S, 3 every 15 minutes.

Overall colon cleansing (OCC) was assessed by a physician questionnaire (4-point scale, based on colonic contents). An OCC rating of “excellent” or “good” was considered a response. Safety measures were also monitored.

Split dosing with RF-NaP was associated with high OCC and achieved response rates of 90%, 97%, and 100% for 28, 32, and 40 tablets, respectively, compared with 86% for Visicol. In addition, RF-NaP evening-only regimen response rates were 90% (32 tablets) and 72% (28 tablets). Transient shifts in electrolyte levels were reduced, and GI adverse events were less common with lower RF-NaP dose regimens.

Administration of RF-NaP retains the benefits of a tablet purgative but eliminates MCC issues. Split dosing and 32-tablet evening-only dosing of RF-NaP tablets were efficacious and well tolerated, and split dosing of RF-NaP tablets is recommended.