Kuvan (Sapropterin) - Oral

What Is Kuvan?

Kuvan (sapropterin) is an orally administered prescription medication used to lower the levels of an amino acid called phenylalanine in the blood of adults and children aged 1 month and older who have a rare, inherited disorder called phenylketonuria (PKU).

PKU is an inherited disorder caused by a defective gene. In people with PKU, the defective gene causes a deficiency of an enzyme called phenylalanine hydroxylase.

Kuvan contains the active ingredient sapropterin. Sapropterin belongs to a drug class called phenylalanine hydroxylase (PAH) activators.

If PKU is not diagnosed right away, a person's phenylalanine (Phe) levels will build up as they consume protein. Within a few months, they will start to have symptoms such as seizures and developmental delays.

To prevent these outcomes, newborns are routinely screened for PKU using a blood test within the first few days of life.

Kuvan is a brand-name drug in the form of a tablet or a powder that is mixed into an oral solution (liquid solution). There is also a generic version of the drug that is marketed under the name sapropterin, and it comes in an oral form.

Drug Facts

Generic Name: Sapropterin

Brand Name(s): Kuvan

Drug Availability: Prescription

Therapeutic Classification: Endocrine-metabolic agent

Available Generically: Yes

Controlled Substance: N/A

Administration Route: Oral

Active Ingredient: Sapropterin dihydrochloride

Dosage Form(s): Tablet, powder for solution

What Is Kuvan Used For?

The Food and Drug Administration (FDA) has approved Kuvan to lower the levels of an amino acid called phenylalanine (Phe) in the blood of adults and children aged 1 month and older who have a condition called phenylketonuria (PKU).

PKU is a genetic disorder. In people with the disorder, the body lacks or only makes a limited supply of an enzyme called phenylalanine hydroxylase (PAH). This enzyme’s job is to break down phenylalanine (Phe).

People with a specific form of PKU have a limited supply of PAH. Sapropterin works by activating PAH and making it work harder. This helps prevent too much Phe from building up in the blood.

Specifically, Kuvan is used in people whose bodies produce at least some PAH. This type of PKU is known as tetrahydrobiopterin (BH4)-responsive PKU.

Sapropterin is a synthetic version of BH4—a cofactor that helps the PAH enzyme break down Phe to make sure it does not build up in the blood.

This medication is used along with a low-phenylalanine diet called the “PKU diet.”

The PKU diet includes foods that are low in protein and Phe. People with PKU must avoid foods that are high in protein and Phe, such as meat, eggs, and certain fruits and vegetables.

Phe is also found in an artificial sweetener called aspartame (e.g., Equal, NutraSweet). Therefore, diet drinks and foods that contain aspartame must be avoided.

How to Take Kuvan

Take Kuvan as directed by your healthcare provider. Kuvan is taken once daily with a meal. You should take it at the same time each day.

You should follow a low-Phe diet while taking Kuvan. Do not make any changes to your diet while you are taking this medication without talking to your healthcare provider first.

Kuvan tablets can be swallowed whole. If you have trouble swallowing, the tablet can be crushed and mixed into a small amount of applesauce or pudding, or dissolved in 120 to 240 milliliters of water or apple juice. You should take the mixture within 15 minutes of making it. Do not prepare it too far in advance.

The tablet may not dissolve completely in water or juice—it may just break apart into small pieces. If there are still pieces in the cup after you drink the solution, refill the cup with a little more water or juice and drink it until there are no visible pieces of the tablet left in the cup.

Kuvan powder for oral solution should be dissolved in 120 to 240 milliliters of water or apple juice. It can also be stirred into a small amount of applesauce or pudding. The powder should dissolve completely. Take the mixture within 30 minutes of making it.

For infants who weigh less than 22 pounds, Kuvan powder can be dissolved in 5 to 10 milliliters of water or apple juice and given with an oral syringe.


Store Kuvan in a sealed container at room temperature away from areas that have high levels of moisture (e.g., the bathroom). Keep this medicine out of reach of children and pets.

How Long Does Kuvan Take to Work?

Kuvan will start to lower the levels of Phe in your blood within 24 hours of taking your first dose. It may take up to a month to see the full effects of the medication. After starting Kuvan, your healthcare provider will check your Phe levels after a week, then periodically during the first month of treatment.

What Are the Side Effects of Kuvan?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects.

If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at fda.gov/medwatch or 1-800-FDA-1088.

Common Side Effects

The most common side effects of Kuvan are:

Severe Side Effects

Call your healthcare provider right away if you develop serious side effects while taking Kuvan. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency.

Rarely, Kuvan may cause serious side effects.

While you are taking Kuvan, watch for the following side effects and their symptoms:

  • Inflammation of the lining of the upper digestive tract, such as esophagitis or gastritis. This can cause discomfort or pain in the upper abdomen, nausea, vomiting, blood in your stool or vomit, black and tarry stools, trouble swallowing, loss of appetite, or throat pain.
  • Hyperphenylalaninemia (a milder form of UKT where there is a decreased amount of phenylalanine in the blood) can occur if blood levels drop too low (which will show up on blood tests). Children under the age of 7 may have a higher risk of this side effect, so their Phe levels should be monitored closely.
  • Hyperactivity, with symptoms like fidgeting, moving around, or talking more than usual.
  • Allergic reaction or anaphylaxis, with symptoms like a rash, flushing, feeling lightheaded, or trouble breathing.

Long-Term Side Effects

Hypophenylalaninemia is a possible side effect of Kuvan. Children younger than age 7 might be more likely to have this side effect than older children. If this side effect occurs and is not treated, it can negatively affect a child’s growth.

To help prevent this side effect, you and your healthcare provider will establish a plan for monitoring your blood Phe levels. If your levels get too high or too low, your provider will advise you on how to get them within a healthy range.

Report Side Effects

Kuvan may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting Program or by phone (1-800-332-1088).

Dosage: How Much Kuvan Should I Take?

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The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage forms (solution or tablets):
    • Adults and children 7 years of age and older—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 10 to 20 milligrams (mg) per kilogram (kg) of body weight per day. Your doctor may adjust your dose if needed.
    • Children 1 month to 6 years of age—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 10 mg per kg of body weight per day. Your doctor may adjust your dose if needed.
    • Children younger than 1 month of age—Use and dose must be determined by your doctor.


Your healthcare provider will recommend a starting dosage of Kuvan for you based on your age and weight.

After you start taking Kuvan, you will have your blood Phe level checked within one week. If your Phe level is still too high, your dose may increase.

Your healthcare provider will continue to check your blood Phe levels periodically. Within one month, you and your provider should be able to tell if Kuvan is working for you. If it does not work within this timeframe, they will have you stop the medication.

If you have certain risk factors or other medical conditions, you may need to have your Phe levels monitored more closely than usual.

Missed Dose

If you miss a dose of Kuvan, take it as soon as you remember that day. Do not take more than one dose of Kuvan per day.

Overdose: What Happens If I Take Too Much Kuvan?

The following symptoms have occurred in people who took higher-than-usual dosages of Kuvan:

What Happens If I Overdose on Kuvan?

If you think you or someone else may have overdosed on Kuvan, call a healthcare provider or the Poison Control Center (1-800-222-1222).

If someone collapses or is not breathing after taking Kuvan, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your or your child's progress at regular visits to make sure this medicine is working properly. Blood tests may be needed to check for unwanted effects.

This medicine may cause serious allergic reactions, including anaphylaxis. Anaphylaxis can be life-threatening and requires immediate medical attention. Call your doctor right away if you have a rash, itching, lightheadedness or fainting, trouble breathing, trouble swallowing, or any swelling of your hands, face, or mouth while you or your child are using this medicine.

This medicine may cause esophagitis (inflammation of the esophagus) and gastritis (inflammation of the stomach). Check with your doctor right away if you or your child have a burning feeling in the chest or stomach, heartburn, indigestion, pain or burning in the throat, stomach upset, tenderness in the stomach area, trouble swallowing.

This medicine may cause hyperactivity (too much or constant activity). Tell your doctor if you or your child have any signs of the following: fidgeting or moving around too much or talking too much.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Kuvan?

Potential users of Kuvan should be aware of the following before starting treatment:

Allergies: You should not take Kuvan if you are allergic to sapropterin or any other of its ingredients.

Fever, infection: Fever and infection may cause Phe levels to increase. People with a fever or an infection may need an adjustment in their Kuvan dose or dietary management to keep Phe levels within an acceptable range.

Gastrointestinal (GI) disease: During clinical trials, severe gastritis has been associated with sapropterin use. If you have GI symptoms or conditions, tell your healthcare provider before beginning Kuvan.

Kidney impairment: People with kidney impairment have not been specifically studied in clinical trials. Therefore, people with a history of symptoms or conditions affecting their kidney health should be monitored when receiving Kuvan.

Liver disease: Kuvn has not been specifically studied in people with liver disease. People with liver disease should be monitored when receiving Kuvan, as liver damage has been associated with impaired Phe metabolism.

Anorexia nervosa, bulimia nervosa: Phe levels should be closely monitored in pepple with anorexia nervosa or bulimia nervosa. Dietary intake of Phe is needed to stop blood Phe levels from falling too low.

Phe levels that become too low lead to catabolism and protein breakdown. Kuvan should be used carefully in people with eating disorders.

Breastfeeding: There is limited data on using Kuvan while breastfeeding. The health benefits of breastfeeding should be considered along with the parent's need for Kuvan and any potential negative effects on the breastfed infant from the drug or from a preexisting parental condition.

Coping With An Eating Disorder

If you or a loved one are coping with an eating disorder, contact the National Eating Disorders Association (NEDA) Helpline for support at 1-800-931-2237. 

For more mental health resources, see our National Helpline Database.

What Other Medications Interact With Kuvan?

Kuvan may interact with certain other medications.

Your healthcare provider may monitor you more closely if you take one of the following prescription drugs:

What Medications Are Similar?

Kuvan is a unique medication. Currently, there are no FDA-approved drugs that work exactly the same way as Kuvan.

However, in 2018, the FDA approved a drug called Palynziq (pegvaliase) to reduce very high levels of Phe in adults with PKU.

Palynziq works differently than Kuvan. It is given as an injection under the skin (subcutaneous) either once daily or once weekly. It can be used by people who tried Kuvan in the past.

Palynziq is not meant to be used together with Kuvan.

Talk to your healthcare provider if you have questions about available treatment options.

Frequently Asked Questions

  • Do I need to continue my PKU diet while taking Kuvan?

    Yes. Kuvan must be used along with a low-Phe diet. However, do not make any changes to your diet without first discussing it with your provider.

  • Is there a lower-cost generic alternative for Kuvan?

    Yes. Kuvan is available as a generic product called sapropterin.

  • Does Kuvan work for everyone with PKU?

    Not everyone with PKU will respond to treatment with Kuvan. It is not possible to predict how you will respond to this medication. Your first month of treatment will be a trial.

    During the first month, you will have your Phe levels checked often to monitor how well Kuvan is working. If your Phe levels are not lowered within a month of starting Kuvan, your healthcare provider will likely stop the treatment.

  • Will Kuvan keep working long term?

    It should. In Kuvan’s clinical trials, the drug continued to work for the duration of the studies, some of which were longer than three years.

How Can I Stay Healthy While Taking Kuvan?

Kuvan treatment can help lower Phe levels in people with PKU. This is important because high Phe levels can negatively affect the brain.

Taking Kuvan as directed by your provider and having your Phe levels checked regularly are essential to living a healthy life with PKU.  

However, just taking Kuvan is not enough—the medication must be used with a low-protein, low-Phe diet.

Having a limited diet can be challenging, but there are still plenty of low-protein food choices that are delicious, nutritious, and will keep you satisfied.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Food and Drug Administration. Kuvan (Sapropterin dihydrochloride) label.

  2. National PKU Alliance. About PKU.

  3. National Library of Medicine, MedlinePlus. Sapropterin.

  4. Mitchell JJ, Trakadis YJ, Scriver CR. Phenylalanine hydroxylase deficiencyGenet Med. 2011;13(8):697-707. doi:10.1097/GIM.0b013e3182141b48

  5. National Library of Medicine, DailyMed. Label: Sapropterin dihydrochloride tablet.

  6. National Library of Medicine, MedlinePlus. Phenylketonuria.

  7. National PKU Alliance. Returning to Diet: Management Tips & Pointers From Adults With PKU.

  8. National PKU Alliance. Chapter 3: Monitoring Blood Phenylalanine Levels.

  9. Prescribers' Digital Reference. Sapropterin dihydrochloride - drug summary.

  10. Qu J, Yang T, Wang E, et al. Efficacy and safety of sapropterin dihydrochloride in patients with phenylketonuria: a meta-analysis of randomized controlled trialsBr J Clin Pharmacol. 2019;85(5):893-899. doi:10.1111/bcp.13886

  11. Food and Drug Administration. Palynziq (Pegvaliase-pqpz) label.

By Patricia Weiser, PharmD
Patricia Weiser, PharmD, is a licensed pharmacist and freelance medical writer. She has more than 14 years of professional experience.