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Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets, taken in two doses of 30 grams (the complete regimen contains a total of 60 grams of sodium phosphate) approximately twelve hours apart, induces diarrhea, which effectively cleanses the entire colon. Each administration has a purgative effect for approximately 1 to 3 hours. The primary mode of action is thought to be through osmotic action of sodium, causing large amounts of water to be drawn into the colon, promoting colon evacuation.

Pharmacokinetics

An open-label pharmacokinetic study of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) in healthy volunteers was performed to determine the concentration-time profile of serum inorganic phosphorus levels after Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) administration. All subjects received a total of 60 grams of sodium phosphate with a total liquid volume of 3.6 quarts. Subjects received a 30 gram dose (20 tablets given as 3 tablets every 15 minutes with 8 ounces of clear liquids) beginning at 6 PM and then received a second 30 gram dose (20 tablets given as 3 tablets every 15 minutes with 8 ounces of clear liquids) the following morning beginning at 6 AM.

Twenty-three healthy subjects (mean age 57 years old; 57% male and 43% female; and 65% Hispanic, 30% Caucasian, and 4% African-American) participated in this pharmacokinetic study. The serum phosphorus level rose from a mean (± standard deviation) baseline of 4.0 (± 0.7) mg/dL to 7.7 (± 1.6 mg/dL), at a median of 3 hours after the administration of the first 30 gram dose of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets (see Figure 1).

Figure 1. Mean (± standard deviation) serum phosphorus concentrations

The serum phosphorus level rose to a mean of 8.4 (± 1.9) mg/dL, at a median of 4 hours after the administration of the second 30 gram dose of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets. The serum phosphorus level remained above baseline for a median of 24 hours after the administration of the initial dose of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets (range 16 to 48 hours).

The upper (4.5 mg/dL) and lower (2.6 mg/dL) reference limits for serum phosphate are represented by solid bars.

Special Populations

Renal insufficiency: The effect of renal dysfunction on Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets pharmacokinetics has not been studied. Since the inorganic form of phosphate in the circulating plasma is excreted almost entirely by the kidneys, patients with renal disease may have difficulty excreting a large phosphate load. Thus, Visicol® Tablets should be used with caution in patients with impaired renal function (see WARNINGS).

Hepatic insufficiency: Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets have not been investigated in patients with hepatic failure. Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) is not expected to be metabolized in the liver.

Geriatric: In a single pharmacokinetic study of sodium phosphate tablets, which included 6 elderly volunteers, plasma half-life increased two-fold in subjects > 70 years of age compared to subjects < 50 years of age (3 subjects and 5 subjects, respectively).

Gender: No difference in serum phosphate AUC values were observed in the single pharmacokinetic study conducted with Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) in 13 male and 10 female healthy volunteers.

Clinical Studies

A total of 957 adult patients were enrolled and treated in the controlled clinical trials of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets. Males and females were about equally represented. Approximately 87% of the study population was Caucasian. Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets were found to be comparable in cleansing efficacy to the comparison drug, a commercially available polyethylene glycol-salt (PEG-salt solution) solution (Cherry Flavor NuLYTELY®). Two identical, single (investigator) blind, randomized, multicenter trials were conducted comparing the efficacy and safety of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets and the PEG-salt solution comparator as a colon cleansing agent in patients undergoing routine diagnostic colonoscopy. In each study, over 200 patients were randomized to self-administer the Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets and over 200 were randomized to self-administer the PEG-salt solution comparator. Colonoscopy was generally performed within 5 hours of the second dose. Physicians used a four-point, validated Physician Questionnaire to assess efficacy. The distribution of "excellent", "good", "fair" and "inadequate", as evaluated by the physician performing the colonoscopy, was comparable in both groups. Cleansing efficacy observed in these studies is described in Table 1.

Table 1: Observed overall colon cleansing efficacy of Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets versus PEG-salt solution comparator in the all assessed patient population

The efficacy of overall colonic cleansing with the Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets was comparable to the PEG-salt solution. In addition, the incidence of "Inadequate" colon cleansing ratings due to poor purgative preparation was similar between Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets and the PEG-salt solution comparator. Also, cleansing efficacy in the ascending colon with Visicol® (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) Tablets was comparable to the PEG-salt solution.

Last reviewed on RxList: 4/17/2009
This monograph has been modified to include the generic and brand name in many instances.