Open-label, dose-ranging pilot study of 4 weeks of low-dose therapy with sodium phosphate tablets in chronically constipated adults.

BACKGROUND

The tablet formulation of sodium phosphate (NaP) is a prescription osmotic purgative that has been marketed since 2001. The use of NaP tablets in patients with constipation has not been studied previously.

OBJECTIVE

This study assessed the tolerability and efficacy of 28 days of therapy with NaP tablets (1.5 g NaP/tablet) in patients with chronic constipation.

METHODS

Adults with functional constipation or constipation-predominant irritable bowel syndrome and Z-3 spontaneous bowel movements (BMs) during the 7-day screening/baseline period were eligible for this open-label, dose-ranging study. Patients were randomized to receive starting doses of 4 NaP tablets (group A) or 8 NaP tablets (group B) each morning for 28 days. After a minimum of 48 hours, the NaP dose could be titrated upward (in the case of no BM or no relief of symptoms) or downward (in the case of a predefined excess laxative response) by 2 tablets/d to a minimum of 2 tablets/d or a maximum of 12 tablets/d. Patients kept a diary of their BMs and gastrointestinal symptoms. A serum chemistry panel was obtained weekly. The primary end points were the constipation response (based on the change from baseline in weekly number of BMs) and the global sense response (based on daily scores for the patient's overall sense of change in their bowel problems).

RESULTS

At randomization, there were 18 patients in group A and 25 in group B. Of these, 40 patients (16 group A, 24 group B) had > or 7 days of diary information while taking study treatment and were evaluable for efficacy. The constipation response rate was 100% in group A and 95.8% in group B, and the respective global sense response rates were 68.8% and 79.2%. Four patients in group B withdrew due to adverse events, none of which were serious. Five patients had occasional hypokalemia that required no treatment. Changes from baseline in serum concentrations of calcium, inorganic phosphorus, and potassium were not clinically significant and did not require treatment.

CONCLUSIONS

In this small study, NaP tablets taken daily were generally well tolerated (particularly in the low-dose group) and produced prompt relief of constipation--generally within the first week of treatment--that was sustained over the 28-day treatment period. A reasonable starting dose appears to be 2 to 4 tablets (3-6 g NaP) daily.