Sapropterin is used along with a restricted diet to control blood phenylalanine levels in adults and children 1 month of age and older who have phenylketonuria (PKU; an inborn condition in which phenylalanine may build up in the blood and causes decreased intelligence and a decreased ability to focus, remember, and organize information).

Sapropterin will only work for some people who have PKU, and the only way to tell if sapropterin will help a particular patient is to give the medication for a period of time and see whether his or her phenylalanine level decreases. Sapropterin is in a class of medications called cofactors. It works by helping the body to break down phenylalanine so it will not build up in the blood.

Side Effects Of Sapropterin

Sapropterin may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • diarrhea
  • nausea
  • vomiting
  • stomach pain
  • headache
  • cough, throat pain, or cold symptoms
  • fidgeting, moving around, or talking too much

Some side effects can be serious. If you experience any of these symptoms call your doctor immediately:

  • wheezing, shortness of breath, cough, flushing, nausea, rash
  • pain in the upper abdominal area, nausea, vomiting, black, tarry or bloody stool, vomiting blood

Sapropterin may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking sapropterin:

  • tell your doctor and pharmacist if you are allergic to sapropterin or any other medications.
  • tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: levodopa (in Sinemet, in Stalevo); methotrexate (Otrexup, Rasuvo, Trexall, others); PDE5 inhibitors such as sildenafil (Revatio, Viagra), tadalafil (Cialis), and vardenafil (Levitra); proguanil (in Malarone), pyrimethamine (Daraprim), and trimethoprim (Primsol, in Bactrim, Septra). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
  • tell your doctor if you have or have ever had anorexia (an eating disorder in which a person eats too little and/or exercises too much to maintain even the minimum body weight considered normal for his/her age and height) or any other condition that causes you to be poorly nourished, or liver or kidney disease.
  • tell your doctor if you have a fever or if you get sick at any time during your treatment. Fever and illness may affect your phenylalanine level, so your doctor may need to adjust your dose of sapropterin.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking sapropterin, call your doctor.

Dosage Of Sapropterin

Sapropterin comes as a tablet and as a powder to be mixed with liquid or soft foods and take by mouth. It is usually taken once a day with food. Take sapropterin at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take sapropterin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

If you cannot swallow the tablets, place the number of sapropterin tablets you were told to take in a cup that contains 4 to 8 ounces (1/2 to 1 cup or 120 to 240 milliliters) of water or apple juice. Stir the mixture or crush the tablets with a spoon to dissolve the tablets. The tablets may not dissolve completely; there may still be small pieces of tablets floating at the top of the liquid. When the tablets are mostly dissolved, drink the entire mixture. If pieces of tablets remain in the cup after you drink the mixture, pour more water or apple juice into the cup and drink it to be sure you swallow all the medication. Be sure to drink the entire mixture within 15 minutes after you prepare it. Sapropterin tablets can also be crushed and mixed with soft foods such as applesauce and pudding.

To prepare sapropterin powder, add the contents of the powder packet(s) with 4 to 8 ounces (1/2 to 1 cup or 120 to 240 milliliters) of water or apple juice, or a small amount of soft food such as applesauce or pudding. Mix the powder in the liquid or soft food very well until the powder is completely dissolved. Be sure to drink or eat the entire mixture so you will get the complete dose. Eat or drink the mixture within 30 minutes of preparing.

If you are a parent or caregiver giving the powder to a child who weighs 22 pounds (10 kg) or less, you will need to get specific instructions from the doctor about how much water or apple juice to use, and how much of the prepared mixture to give to your child. Measure the amount of water or apple juice you are using with a medicine cup and use an oral dosing syringe to measure and give the dose to the child. Throw away any mixture remaining after the dose is given.

Your doctor will start you on a dose of sapropterin and will check your blood phenylalanine level regularly. If your phenylalanine level does not decrease, your doctor may increase your dose of sapropterin. If your phenylalanine level does not decrease after 1 month of treatment with a high dose of sapropterin, you and your doctor will know that your condition does not respond to sapropterin. Your doctor will tell you to stop taking the medication.

Sapropterin may help to control blood phenylalanine levels, but it will not cure PKU. Continue to take sapropterin even if you feel well. Do not stop taking sapropterin without talking to your doctor.

Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.


Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body’s response to sapropterin.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.