Sapropterin (Oral)

As a cofactor medication, Sapropterin helps the body break down phenylalanine, an amino acid found in protein.


Sapropterin can be used in combination with a restricted diet to lower the levels of phenylalanine in patients with phenylketonuria (PKU). PKU is condition one is born with and can cause the buildup of phenylalanine in the blood that the body cannot break down on its own. Higher levels of phenylalanine in the blood cause severe mental retardation, seizures, tremors, decreased learning ability, and decreased ability to focus. Unfortunately, sapropterin does not work in all PKU patients, and administering the drug to PKU patients in a test period of time is the only route to discover if it will work for any given patient.

Sapropterin is known as a medication known as a cofactor. Cofactors assist the body's natural functions and make them more efficient. Sapropterin helps the body break down phenylalanine in the blood so it will not build up and cause the unwanted side effects of high levels of phenylalanine.

Conditions Treated

Type of Medicine

  • Cofactor

Side Effects

While using sapropterin, phenylalanine levels in the blood should be monitored closely to ensure the efficacy of the medication and to check for unwanted side effects. The most severe side effect includes anaphylaxis, a life-threatening allergic reaction that requires immediate emergency medical attention. The symptoms of anaphylaxis include

  • Rash
  • Itching
  • Lightheadedness
  • Fainting
  • Trouble breathing
  • Trouble swallowing
  • Swelling of the hands, face, and mouth

Sapropterin can also cause gastritis or inflammation of the stomach. If the patient feels a burning in the chest or stomach area, indigestion, upset stomach or tenderness of the abdomen, a physician should be contacted immediately.

In addition to these more severe side effects, other more minor side effects might exist. It is worth noting that not all patients experience any or all side effects.

A physician should be consulted if any of these side effects are experienced during the administration of sapropterin. Some side effects occur as the body is adjusting to the medication and will cease with time. A physician can help with the prevention or reduction of common side effects. Other side effects experienced by some patients may not be listed, but if any questions arise about the persistence of a condition or if a condition becomes bothersome, the patient should contact a physician.


Only the prescribed dosage from the physician should be administered, and the directions on the label should be followed. The physician will prescribe different dosages to each patient, as each patient has different medical conditions. This makes taking only the instructed dosage critical. When the medication is changed by a physician, the patient should discontinue taking any other medications, regardless of any medication remaining, and dispose of the unused medication properly.

If a physician has prescribed sapropterin, the patient should read the instructions accompanying the medication and follow the instructions as closely as possible. The manufacturer recommends generic dosages as basic guidelines, but the manufacturer recommendations may differ from the prescribed dosage. If there are any doubts, follow the instructions from the physician prescribing the medication. The physician can cater a treatment plan to a specific patient.

Sapropterin is most effective with a specific diet, and this diet should be observed during the duration of the time sapropterin is taken. This specific diet, which is advised by the patient's physician, will maintain a set level of consumed phenylalanine. To maximize the efficacy, dosages should also not be missed. If a dosage is missed, do not take two dosages on the same day. Skip the missed dosage and continue to take the next dosage the next day. If the patient has any questions about missed dosages, consult a physician.
Sapropterin is usually taken once per day and the medication should be taken at the same time each day with a meal. The tablet can be swallowed whole or can be crushed and mixed with water, apple juice, or soft foods like applesauce or pudding. The tablet may not melt entirely in liquid and small pieces may be visible floating on the top of the liquid. These pieces are safe to swallow. If pieces of the tablet are left in the cup after the liquid has been drank, add more liquid, and ensure the entire dosage has been taken. The mixture should be consumed within 15 minutes of preparation. The medication can also be prescribed as an oral powder to help dissolve in liquid.

Dosages are generally prescribed based on body weight. A starting dosage for adults and children 7 years of age and older is typically between 10 to 20 milligrams per kilogram of body weight per day. For children less than 6 years of age to 1 month of age, a starting dose is typically 10 milligrams per kilogram of body weight per day. For children less than 1 month of age, the dose will be determined by the physician as there have been no clinical studies to prove the safety and efficacy of taking sapropterin at this age.

In order to decide on the dosage strength, the physician will first check the level of phenylalanine regularly in the blood. A dosage will be prescribed and the physician will continue to monitor the level of phenylalanine in the blood during the period the drug is being taken. If the level does not decrease, the physician may increase the dosage. If the levels of phenylalanine persist after the dosage has been increased, the physician may investigate different medications and ask the patient to discontinue the sapropterin, as it is not effective in all patients.

Overdosing on sapropterin can produce side effects that are not included in the list above. The side effects from overdosing can include but are not limited to headache and dizziness. If a possible overdose has occurred, or the symptoms associated with an overdose are recognized, the patient needs immediate medical attention. Immediate medical care can be found by dialing 911 or the Poison Control Center (1-800-222-1222).


Some combinations of medications are known to have negative interactions, which can render them useless or harmful to a patient. Because of this, a current list of medications being taken should be kept by all patients in order to inform any physician that is prescribing medications. The list of medications to be given to the physician should include the name on the label, the type of medicine, the frequency the medicine is taken, and the dosage on the label. Both prescribed medications, as well as any non-prescribed medications, like over-the-counter medications or vitamins, should also be on the list as over-the-counter medications could also interfere with the desired results of the prescribed treatment plan. By knowing what the patient is currently taking, the physician can take the necessary precautions and make an appropriate treatment plan for the medical condition.

A total of 26 drugs are known to have a moderate interaction with sapropterin and the generic drug names are listed below.

  • Alprostadil
  • Atovaquone
  • Progunanil
  • Carbidopa
  • Entacapone
  • Levodopa
  • Hydraliazine
  • Hydochlorothiazide
  • Reserpine
  • Isosorbide dinitrate
  • Isosorbide mononitrate
  • Methotrexate
  • Minoxidil
  • Nesiritide
  • Nitroprusside
  • Nitroglycerin
  • Permetrexed
  • Pralatexate
  • Pyrimethamine
  • Sulfadoxine
  • Sildenafil
  • Sulfamethoxazole
  • Trimethoprim
  • Tadalafil
  • Trimetrexate
  • Vardenafil

As a restricted diet must be observed and followed when taking sapropterin, the use of alcohol or tobacco should be discussed with a physician.

In addition to drug interactions, the presence of other medical problems may affect the efficacy of sapropterin. The patient should inform their physician if they have one of the following medical problems.

  • Eating disorder
  • Malnutrition
  • Fever or illness
  • Hypotension (low blood pressure)
  • Liver disease
  • Kidney disease


The patient should advise the physician of any allergies to any medications, medical history, and current health problems prior to using sapropterin. The patient should also inform their physician if they are aware that they are allergic to sapropterin or similar drugs. The physician can then use this knowledge to decide if sapropterin is the best medication to be prescribed.

Sapropterin has not been formally tested in all demographics and caution should be taken if the patient lies in any of these demographics. The demographics without clinical studies include pregnant or breastfeeding women, children, and the elderly. Due to the lack of formal information, sapropterin should only be taken if prescribed.

Other than animal studies, which are not conclusive, the effects to pregnant women or the fetuses using sapropterin are not known. Medical research has also not established whether sapropterin is excreted in breast milk. contact a knowledgeable physician can be contacted with questions regarding the administration of sapropterin to breastfeeding or pregnant women and they can weigh any potential benefits of taking the drug against the negative risks.

No clinical studies have been completed in the case of administering sapropterin to children younger than 1 month of age. No conclusions can be drawn on the age effects or safety in children this young.

Lastly, no relationship has been found between the effects of sapropterin and age to determine its safety and efficacy in the elderly. For geriatric patients with PKU, consult a physician prior to ingesting sapropterin.


All medication should be kept out of reach of children and pets. The medication should only be stored as recommended by the physician or the pharmacist. In addition, those who have not been prescribed this medication should refrain from taking it. More information on storing the drug should be accompanying the drug when it is dispensed. Expired medication should be disposed of and a physician should be contacted for disposal instructions. Take-back programs exist in certain areas and this is the safest way to dispose of any medication.

Sapropterin should be stored in a closed container at room temperature, away from heat, cold, moisture, and direct light. Usually, a desiccant comes with the medication and it should not be removed. It is normal for the tablets to have slightly yellowed over time and they are still safe to take when yellow. If the patient has any questions regarding the color change or storage, ask a pharmacist or doctor for more information.


Patients with PKU have trouble breaking down phenylalanine and the effects of too much of the amino acid phenylalanine in the blood cause severe brain damage. As a cofactor medication, the purpose of sapropterin is to help the body break down phenylalanine in the blood to lower, safer levels. Sapropterin, while it helps treat the effects of PKU is not a cure for PKU and is not effective in all patients with PKU. Blood tests will help to establish a starting dose of sapropterin and to monitor the levels of phenylalanine during the course of administration. Although sapropterin helps treat PKU, which causes severe brain damage on its own, the side effects of sapropterin can also be severe and deadly and must be monitored closely in patients. These severe side effects include anaphylaxis and gastritis, as well as other more moderate side effects, including hyperactivity, nausea, and dizziness. A specific diet should be adhered to while taking sapropterin that will maintain the levels of phenylalanine, and the medication should always be taken with a meal.

Last Reviewed:
January 31, 2018
Last Updated:
April 05, 2018