Sodium phosphate dibasic/sodium phosphate monobasic (By mouth)

Sodium Phosphate, Dibasic (SOE-dee-um FOS-fate, dye-BAY-sik), Sodium Phosphate, Monobasic (SOE-dee-um FOS-fate, mono-BAY-sik)

Helps empty your bowels before surgery or a medical procedure (including colonoscopy). Also treats constipation.

Brand Name(s):

Leader Saline Laxative, OsmoPrep, Phospha-Lax, Saline Laxative

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. Do not use it if you had an allergic reaction to sodium phosphate dibasic or sodium phosphate monobasic. Do not use it if you have stomach or bowel problems (including blockage, perforation, toxic colitis, toxic megacolon), if you had acute phosphate nephropathy, or if you have had stomach surgery (including gastric bypass or stapling surgery).

How to Use This Medicine:

Liquid, Tablet

  • Follow the instructions on the medicine label if you are using this medicine without a prescription. If you are using the over-the-counter preparation for constipation, do not use more than 1 dose in 24 hours.
  • Follow the schedule given to you by your doctor if you are using this medicine to empty your bowels before a surgery or medical test.
  • Tablets:
    • You will take several tablets at the same time. Your doctor will tell you how many tablets to take.
    • Drink 8 ounces of clear liquids each time you take a group of tablets. Examples of clear liquids include water, flavored water, clear broth, herbal tea, black tea, coffee, clear soda, gelatin, popsicles, lemonade (no pulp), ginger ale, white grape juice, or apple juice.
    • Do not eat or drink alcohol, milk, anything purple or red, or any foods that have pulp while you use this medicine.
    • OsmoPrep®: Eat or drink only clear liquids after 12:00 PM (noon) on the day before and until after your colonoscopy. Do not eat solid food.
  • Oral liquid: Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup. Mix the oral liquid with at least 4 ounces of water before you drink it. After taking the liquid medicine, drink another full glass (8 ounces) of water.
  • Drink as much extra liquid as you can before, during, and after taking this medicine. This will help replace the fluids you are losing with your bowel movements. This will also keep your kidneys working well.
  • This medicine should come with a Medication Guide. Ask your pharmacist for a copy if you do not have one.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. The oral liquid can be chilled to improve the taste. Do not freeze the oral liquid.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • There are many other drugs that can interact with sodium phosphate. Tell your doctor about all other medicines you are taking, especially the following:
    • Diuretic (water pill)
    • Blood pressure medicine (including ACE inhibitors, ARBs)
    • NSAID pain or arthritis medicine (including aspirin, ibuprofen, naproxen)
    • Sodium phosphate-based laxative or enema to treat constipation
    • Tricyclic antidepressant (including amitriptyline, nortriptyline)
  • Do not take any oral medicines within 1 hour before or after each dose of OsmoPrep®. Do not take OsmoPrep® if you have already used it in the last 7 days.

Warnings While Using This Medicine:

  • Tell your doctor if you are pregnant or breastfeeding, or if you have kidney disease, heart failure, heart rhythm problems (including arrhythmia, QT prolongation), angina (chest pain), inflammatory bowel disease, ulcerative colitis, trouble with swallowing or gastric reflux, or a history of seizures or electrolyte imbalance. Tell your doctor if you had a recent heart attack or heart surgery. Tell your doctor if you are also on a low-salt diet.
  • This medicine may cause the following:
    • Kidney problems
    • Heart rhythm problems
    • Seizures
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Bloody urine, lower back or side pain, sharp back pain just below your ribs
  • Decrease in how much or how often you urinate
  • Dizziness, lightheadedness, or fainting
  • Dry mouth, increased thirst, muscle cramps or twitching, confusion, weakness
  • Fast, pounding, or uneven heartbeat
  • Seizures
  • Severe stomach pain, nausea, vomiting, or bloating

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 11/6/2020

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