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

The American Cancer Society estimatesthat 106,680 new cases of colorectalcancer will be identified in 2006,with an estimated 55,170 deaths thisyear alone.¹ Risk factors for colorectalcancer include advancing age, family orpast medical history of colorectal cancer,inflammatory bowel disease, colorectalpolyps, physical inactivity, smoking,excessive alcohol intake, and obesity.² Itis predicted that 30,000 lives could besaved annually by having patientsscreened for colorectal cancer withtechniques such as colonoscopies.³

In March 2006, the FDA approvedOsmoPrep, a preparation agent used forcolonoscopy procedures in adults overthe age of 18. OsmoPrep is manufacturedby Salix Pharmaceuticals Inc.

Pharmacology

OsmoPrep contains sodium phosphatemonobasic monohydrate USP andsodium phosphate dibasic anhydrousUSP and is microcrystalline cellulose(MCC)-free. Each administration ofOsmoPrep has a purgative effect, whichcleanses the entire colon—a processthat can last 1 to 3 hours. This result maybe due to the osmotic effect of sodium,thus allowing water to be drawn into thecolon, promoting bowel evacuation.⁴

Clinical Studies

A phase 3 study was conducted toevaluate the efficacy and safety ofOsmoPrep and to assess the noninferiorityof OsmoPrep and Visicol. Visicol, alsomanufactured by Salix PharmaceuticalsInc, contains the same primary ingredientsas OsmoPrep but contains 13%MCC.⁵ Patients included in this studywere between 21 and 89 years old andwere undergoing elective colonoscopies.These patients were randomized to 1 of3 treatment groups: OsmoPrep 48 g (32tablets), OsmoPrep 60 g (40 tablets), andVisicol 60 g (40 tablets).⁴

The overall colon-cleansing responserate in the 4-point Colonic Contents Scalewas utilized as the primary end point. Thisscale uses responses defined by ratingssuch as "excellent" or "good" as determinedby a blinded colonoscopist. "Excellent" ratings were 76% for the OsmoPrep48-g group, 73% for the OsmoPrep 60-ggroup, and 51% for the Visicol group.Overall response rates were 95%, 97%,and 94% for the 3 groups, respectively.These responses demonstrated thatOsmoPrep was noninferior, when comparedwith Visicol.⁴

A majority of the patients in all 3 treatmentgroups experienced hyperphosphatemiaon the day of the procedure.Other electrolyte abnormalities werenoted in the participants in this study,although not nearly as high in incidence.⁴

Safety

The most common adverse eventsreported with the use of OsmoPrepincluded abdominal pain, bloating, nausea,and vomiting.⁴ Diarrhea was not consideredto be an adverse event due to thenature of the use of this medication.OsmoPrep should be used with caution inpatients who have severe renal insufficiencybecause of the effects on theserum phosphate levels. There have beenrare reports of cardiac arrhythmias(specifically QT prolongation), seizures,and renal failure in patients taking sodiumphosphate products.⁴

Outlook

Each OsmoPrep tablet contains 1.102 gof sodium phosphate monobasic monohydrateand 0.398 g of sodium phosphatedibasic anhydrous. The recommendeddose for adult patients is 32 tablets (48 gof sodium phosphate), which should betaken orally with 2 quarts of clear liquid.On the evening prior to the procedure,patients should be instructed to take 4tablets with 8 oz of clear fluids every 15minutes, for a total of 20 tablets. The followingmorning, patients should bedirected to take 4 tablets, beginning 3 to5 hours prior to the procedure, the sameway as the previous evening, for a total of12 tablets.⁴

Dr. Soo is a senior research pharmacistwith the Investigational DrugService at Brigham and Women'sHospital, Boston, Mass. Ms. Drew is asixth-year PharmD candidate fromMassachusetts College of Pharmacy,currently on clinical clerkship in theInvestigational Drug Service atBrigham and Women's Hospital.

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