/publications/issue/2006/2006-07/2006-07-5679

Salix Pharmaceuticals Inc's OsmoPrep (sodium phosphate monobasic monohydrate USP, and sodium phosphate dibasic anhydrous USP)

Author: Carolyn Soo, PharmD, and Amanda Drew, PharmD candidate

The American Cancer Society estimates that 106,680 new cases of colorectal cancer will be identified in 2006, with an estimated 55,170 deaths this year alone.1 Risk factors for colorectal cancer include advancing age, family or past medical history of colorectal cancer, inflammatory bowel disease, colorectal polyps, physical inactivity, smoking, excessive alcohol intake, and obesity.2 It is predicted that 30,000 lives could be saved annually by having patients screened for colorectal cancer with techniques such as colonoscopies.3

In March 2006, the FDA approved OsmoPrep, a preparation agent used for colonoscopy procedures in adults over the age of 18. OsmoPrep is manufactured by Salix Pharmaceuticals Inc.

Pharmacology

OsmoPrep contains sodium phosphate monobasic monohydrate USP and sodium phosphate dibasic anhydrous USP and is microcrystalline cellulose (MCC)-free. Each administration of OsmoPrep has a purgative effect, which cleanses the entire colon—a process that can last 1 to 3 hours. This result may be due to the osmotic effect of sodium, thus allowing water to be drawn into the colon, promoting bowel evacuation.4

Clinical Studies

A phase 3 study was conducted to evaluate the efficacy and safety of OsmoPrep and to assess the noninferiority of OsmoPrep and Visicol. Visicol, also manufactured by Salix Pharmaceuticals Inc, contains the same primary ingredients as OsmoPrep but contains 13% MCC.5 Patients included in this study were between 21 and 89 years old and were undergoing elective colonoscopies. These patients were randomized to 1 of 3 treatment groups: OsmoPrep 48 g (32 tablets), OsmoPrep 60 g (40 tablets), and Visicol 60 g (40 tablets).4

The overall colon-cleansing response rate in the 4-point Colonic Contents Scale was utilized as the primary end point. This scale uses responses defined by ratings such as "excellent" or "good" as determined by a blinded colonoscopist. "Excellent" ratings were 76% for the OsmoPrep 48-g group, 73% for the OsmoPrep 60-g group, and 51% for the Visicol group. Overall response rates were 95%, 97%, and 94% for the 3 groups, respectively. These responses demonstrated that OsmoPrep was noninferior, when compared with Visicol.4

A majority of the patients in all 3 treatment groups experienced hyperphosphatemia on the day of the procedure. Other electrolyte abnormalities were noted in the participants in this study, although not nearly as high in incidence.4

Safety

The most common adverse events reported with the use of OsmoPrep included abdominal pain, bloating, nausea, and vomiting.4 Diarrhea was not considered to be an adverse event due to the nature of the use of this medication. OsmoPrep should be used with caution in patients who have severe renal insufficiency because of the effects on the serum phosphate levels. There have been rare reports of cardiac arrhythmias (specifically QT prolongation), seizures, and renal failure in patients taking sodium phosphate products.4

Outlook

Each OsmoPrep tablet contains 1.102 g of sodium phosphate monobasic monohydrate and 0.398 g of sodium phosphate dibasic anhydrous. The recommended dose for adult patients is 32 tablets (48 g of sodium phosphate), which should be taken orally with 2 quarts of clear liquid. On the evening prior to the procedure, patients should be instructed to take 4 tablets with 8 oz of clear fluids every 15 minutes, for a total of 20 tablets. The following morning, patients should be directed to take 4 tablets, beginning 3 to 5 hours prior to the procedure, the same way as the previous evening, for a total of 12 tablets.4

Dr. Soo is a senior research pharmacist with the Investigational Drug Service at Brigham and Women's Hospital, Boston, Mass. Ms. Drew is a sixth-year PharmD candidate from Massachusetts College of Pharmacy, currently on clinical clerkship in the Investigational Drug Service at Brigham and Women's Hospital.

For a list of references, send a stamped, self-addressed envelope to: References Department, Attn. A. Stahl, Pharmacy Times, 241 Forsgate Drive, Jamesburg, NJ 08831; or send an e-mail request to: astahl@ascendmedia.com.