Frequently Asked Questions
About Treating PKU

Get answers to some of the most common questions about how to treat PKU.

Facts and information

Q: Is PKU curable?

A: There is no cure for PKU, but if managed early and treated throughout life with a special treatment program, people with PKU can lead healthier and more productive lives.

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Q: How is PKU managed?

A: The key to managing PKU is keeping blood Phe low and stable. There are two ways to manage PKU:

  • Low-Phe diet + medical food and formula
  • Low-Phe diet + medical food and formula + KUVAN


The foundation of lifelong treatment for PKU is a low-Phe diet and formula. For many people, KUVAN Tablets or Powder along with a low-Phe diet and formula can work for better Phe control


The foundation of lifelong treatment for PKU is a low-Phe diet and formula. For many people, KUVAN Tablets or Powder along with a low-Phe diet and formula can work for better Phe control

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Q: What are the symptoms of PKU?

A: Symptoms of PKU can vary from mild to severe. The symptoms of PKU are caused by high or unstable blood Phe levels. If untreated in childhood, high or unstable blood Phe levels can cause severe intellectual disability. Even in babies and children who are treated early and continuously, high blood Phe levels may cause symptoms such as being cranky or fretful, inability to focus, and anxiety.

In adults, when blood Phe levels are too high, problems can include:

  • Not being able to focus or pay attention
  • Feeling anxious
  • Depression
  • Slower thinking and responding
  • Feeling “foggy”
  • Bad moods, being cranky or irritable
  • Lower IQ

When PKU is managed well and blood Phe levels stay low, people can expect to lead healthy and fulfilling lives. With low blood Phe levels, excess Phe will not accumulate in the brain to cause problems. Maintaining blood Phe levels within the recommended ranges is the ultimate goal for someone living with PKU.

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Q: How do I learn to properly manage PKU?

A: There are many resources to help you connect with other PKU patients for tips and support. Always work closely with your metabolic clinic and follow their advice. There are also support groups and online communities to help you learn to properly manage PKU–check out the PKU.com community for one!
Work with your metabolic clinic to develop a treatment plan that works best for you.

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Q: What if I can’t follow the diet closely?

A: Children with uncontrolled blood Phe levels are at risk of developing mental and physical problems, which may include mood problems, social problems, or problems focusing.

Teens and adults with uncontrolled blood Phe levels will most likely notice symptoms of uncontrolled PKU including feeling moody, foggy, or anxious. It may also be hard to focus or think clearly and quickly because high blood Phe levels are toxic to the brain.

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Q: Why do I need Phe-free formula?

A: Because the low-Phe diet restricts the amount of protein you eat, the Phe-free formula is prescribed by your doctor or dietitian to provide you with the protein and nutrients you need for a well-balanced diet.

Most of your daily protein will come from a Phe-free formula. All of the Phe that a person with PKU needs will come mostly from low-Phe foods such as grains, fruits, and vegetables. Since most food contains some Phe, people with PKU must be careful about what–and how much–they eat.

Talk to your metabolic clinic team and dietitian if you have any questions. Remember to always consult your dietitian before making changes to your diet.

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Q: How long do I have to stay on treatment?

A: Today the recommendation from the medical community is for individuals with PKU to follow a low-Phe diet for life and maintain Phe levels between 120-360 µmol/L (2-6 mg/dL).1 It is important to stay on the low-Phe diet for life to avoid negative impacts on mood, IQ/thinking, and behavior.

Talk to your metabolic clinic team and dietitian if you have any questions. Remember to always consult your dietitian before making changes to your diet.

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Q: What can happen if I go off the diet?

A: If a child goes off the diet very early in life (from birth to the elementary school years), he or she may suffer physical or mental impairments that may or may not be reversible. These may include mood problems, social problems, or problems focusing.

For a person who goes off the diet later in life, some of the symptoms may include:

  • Lower intelligence (IQ)
  • Bad moods, being cranky or irritable
  • Feeling “foggy”
  • Thinking and responding slower
  • Depression
  • Feeling anxious
  • Not being able to focus or pay attention

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Q: What is a metabolic clinic?

A: A metabolic clinic specializes in diseases like PKU. It is where you will go for regular blood testing, formula, prescriptions, and dietary consultations.

When a newborn first tests positive for PKU, the results are sent to a local metabolic clinic to confirm the diagnosis and begin care. The dietitian and the rest of the staff at the metabolic clinic will help you manage PKU continuously throughout life.

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Q: How often does a person with PKU need blood Phe tests?

A: Your metabolic clinic will tell you how often you should check your blood Phe levels. Testing should continue throughout life.

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Q. What are KUVAN® (sapropterin dihydrochloride) Tablets for Oral Use and Powder for Oral Solution?

A. KUVAN is the first and only medication for the treatment of PKU. KUVAN is a form of BH4, a cofactor (or helper) that already exists in your body.

KUVAN is available in tablet or powder dosage form, so you can choose the option that works best for you or your child

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Q. What is the function of BH4 in the body?

A. Normally, BH4 helps the enzyme known as PAH (short for phenylalanine hydroxylase) work. The PAH enzyme breaks down the amino acid Phe, found in many foods, into other needed chemicals in the body. In PKU, the PAH enzyme is either missing or not working properly, which allows too much Phe to build up in the blood. This can eventually affect the brain if left untreated.

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Q. How does KUVAN work?

A. KUVAN is a form of the cofactor (or helper) BH4 that already naturally exists in your body. In people who respond to treatment with KUVAN, it works in the body just like BH4 does to help stimulate residual PAH enzyme activity to convert Phe to tyrosine and lower blood Phe levels. KUVAN has been prescribed along with a low-Phe diet to lower blood Phe levels in many people with PKU of all ages and types—even those with classic PKU.

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Q. Why should I consider KUVAN?

A. Consistently keeping your blood Phe levels low can be challenging. A low-Phe diet still allows a certain amount of Phe to pass from the food you eat into your bloodstream. KUVAN, together with a low-Phe diet, may help you lower your blood Phe level and keep it low day after day. KUVAN addresses the problem from a different angle than diet alone does. KUVAN works by stimulating the PAH enzyme to break down the Phe in your body, thereby lowering your blood Phe levels.

Treatment guidelines recommend that all people with PKU, except those with two null mutations in trans, be offered a trial of KUVAN in addition to their low-Phe diet to determine if it can help lower blood Phe levels. Even people who have classic PKU could benefit from treatment with KUVAN.1

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Q. Does KUVAN work for everyone?

A. The only way to know if you will respond to KUVAN Tablets for Oral Use or Powder for Oral Solution is to conduct a test for response trial. KUVAN does not work for everyone. Treatment guidelines recommend that all people with PKU, except those with two null mutations in trans, be offered a trial of KUVAN in addition to their low-Phe diet to determine if it can help lower blood Phe levels. Even people who have classic PKU could benefit from treatment with KUVAN.1 Talk to your healthcare provider to see if KUVAN is an option for you or your child.

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Q. Will KUVAN continue to work over time?

A: Yes. In people who respond to KUVAN therapy, KUVAN should continue to work the same way in the body over time. Your PKU may also be impacted by other factors such as compliance with a low-Phe diet. It is important to work with your metabolic clinic to develop and follow a treatment plan that works for you.

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Q. What if I don’t initially respond to KUVAN?

A: Not everyone responds to treatment with KUVAN. If you do not initially respond to KUVAN, your doctor may consider another trial of KUVAN if there is reason to believe that diet, change in use of medical food, or other factors affecting blood Phe level (such as fever or illness) may have affected your results.

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Q. What are the possible side effects of KUVAN?

A. The most common side effects reported when using KUVAN are headache, runny nose and nasal congestion, sore throat, diarrhea, vomiting, and cough. Additional adverse reactions reported in connection with worldwide marketing include sore throat, heartburn or pain in the esophagus, inflammation of the lining of the stomach, indigestion, stomach pain, and nausea.

KUVAN can also cause serious side effects, including:

  • Severe allergic reactions. Stop taking KUVAN and get medical help right away if you develop wheezing or trouble breathing, coughing, lightheadedness or fainting, flushing, nausea, rash
  • Inflammation of the lining of the stomach (gastritis). Gastritis can happen with KUVAN and may be severe. Call your doctor right away if you have any: severe upper stomach-area (abdominal) discomfort or pain, nausea and vomiting; blood in your vomit or stool; or black, tarry stools
  • Too much or constant activity (hyperactivity) can happen with KUVAN. Tell your doctor if you have any signs of hyperactivity, including fidgeting, moving around too much, or talking too much
  • KUVAN may cause low blood Phe levels in children younger than 7 years. Talk to your doctor or dietitian if you have any questions about adjusting your child’s diet

The side effects listed are not all the side effects seen with KUVAN. You should talk to your doctor or pharmacist if you have concerns about these or other side effects. You should also inform your doctor if you have any side effects when taking KUVAN.

Please see the KUVAN Patient Information to learn more.

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Q. What should I tell my doctor before taking KUVAN?

A. Before you take KUVAN, tell your doctor if you:

  • Have a fever
  • Have liver or kidney problems
  • Are allergic to sapropterin dihydrochloride or any of the ingredients in KUVAN
  • Have poor nutrition or have loss of appetite
  • Are pregnant or plan to become pregnant

You should also tell your doctor about any other medicines you are taking, including prescription and nonprescription medicines, vitamins, and herbal supplements. KUVAN and many other medicines may interact with each other. Your doctor needs to know what medicines you take so he or she can decide if KUVAN is right for you.

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Q. What is the difference between KUVAN Tablets and Powder?

A. KUVAN Tablets and Powder contain the same blood Phe-lowering medication. Both dosage forms are taken once a day (at the same time each day) with food—preferably your largest meal of the day. KUVAN can be dissolved in 4 to 8 oz of water or apple juice, or mixed with a small amount of soft food, such as apple sauce or pudding.

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Q. How do you take KUVAN Tablets?

A. KUVAN is taken once a day (at the same time each day) with food—preferably your largest meal of the day. Take KUVAN exactly as your doctor tells you

  • You can take KUVAN Tablets whole, or you can crush and dissolve the tablets in 4 to 8 oz (½ to 1 cup) of water or apple juice. You can crush the tablets before mixing and stir them up to make them dissolve faster, or put the mixture in a sealed container and shake it up. It may take a few minutes of stirring for the tablets to completely dissolve. Tablets can also be crushed and mixed with a small amount of soft food, such as apple sauce or pudding
  • Don’t be concerned if you see small, undissolved pieces floating on top—this is normal and safe for you to swallow
  • Eat or drink the mixture within 15 minutes and make sure you consume all of the food or liquid. If taking with liquid and any powder or tiny pieces remain in the glass, add a little more liquid and drink immediately

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Q. How do you take KUVAN Powder?

A. KUVAN is taken once a day (at the same time each day) with food—preferably your largest meal of the day. Take KUVAN exactly as your doctor tells you.

  • Open the powder packet by tearing along the top from the notch in the upper right-hand corner. You may also cut the packet open with scissors or the packet opener provided
  • Dissolve the powder by emptying the contents of the packet(s) in 4 to 8 oz (½ to 1 cup) of water or apple juice, or mixing it with a small amount of soft food, such as apple sauce or pudding. The powder should dissolve completely in liquid within 15 seconds. Be sure to open and dissolve or mix all the packets needed for your dose of KUVAN
  • Eat or drink the mixture within 30 minutes of preparation and make sure you consume all of the food or liquid. If taking with liquid and any medicine remains in the glass, add 1 to 2 oz (½ cup or less) of liquid and drink immediately
  • Don’t be concerned if the powder changes the color of the liquid you mix it with. This is normal and expected

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Q. How should I store KUVAN?

A.

  • Store in a cool, dry place between 68°F-77°F (20°C-25°C)
  • Do not leave KUVAN in hot or humid places, such as your car or bathroom cabinet
  • Keep KUVAN tablets in the original bottle with the cap closed tightly
  • Protect from moisture. Do not remove the desiccant (the small packet included with your tablets). The desiccant absorbs moisture
  • The packet of KUVAN Powder for Oral Solution should not be opened until ready to use. After opening, use the entire packet
  • The color of the tablets or powder will vary between off-white to yellow and may change over time. This is normal
  • Liquids mixed with KUVAN Powder for Oral Solution may change color; this is normal and safe, and should be fully consumed within 30 minutes of preparation
  • Do not keep KUVAN that is out of date, or that you no longer need. Be sure that if you throw any medicine away, it is out of the reach of children
  • Keep KUVAN and all medicines out of the reach of children

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Indication

KUVAN® (sapropterin dihydrochloride) Tablets for Oral Use and Powder for Oral Solution are approved to reduce blood Phe levels in people with a certain type of Phenylketonuria (PKU). KUVAN is to be used with a Phe-restricted diet.

Important Safety Information

It is not possible to know if KUVAN will work for you without a trial of the medicine.

Your doctor will check your blood Phe levels when you start taking KUVAN to see if the medicine is working.

Starting KUVAN does not eliminate the need for ongoing dietary management. Any change to your diet may impact your blood Phe level. Follow your doctor’s instructions carefully. Your doctor and dietitian will continue to monitor your diet and blood Phe levels throughout your treatment with KUVAN to make sure your blood Phe levels are not too high or too low. If you have a fever, or if you are sick, your Phe level may go up. Tell your doctor and dietitian as soon as possible so they can make any necessary changes to your treatment.

Children younger than 7 years old treated with KUVAN doses of 20 mg/kg per day are at an increased risk for low levels of blood Phe compared with children 7 years and older. Frequent blood monitoring is recommended in this population to ensure that blood Phe levels do not fall too low.

Tell your doctor if you have ever had liver or kidney problems, have poor nutrition or have a loss of appetite, are pregnant or plan to become pregnant, or are breastfeeding or plan to breastfeed.

KUVAN is a prescription medicine and should not be taken by people who are allergic to any of its ingredients. KUVAN and other medicines may interact with each other. Tell your doctor about all the medicines you take, including prescription and over-the-counter medicines, vitamins, herbal and dietary supplements.

If you forget to take your dose of KUVAN, take it as soon as you remember that day. Do not take 2 doses in a day. If you take too much KUVAN, call your doctor for advice.

The most common side effects reported when using KUVAN are headache, runny nose and nasal congestion, sore throat, diarrhea, vomiting, and cough. Additional adverse reactions reported in connection with worldwide marketing include sore throat, heartburn or pain in the esophagus, inflammation of the lining of the stomach, indigestion, stomach pain, and nausea. These are not all the possible side effects seen with KUVAN. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

KUVAN can cause serious side effects, including:

  • Severe allergic reactions. Stop taking KUVAN and get medical help right away if you develop any of these symptoms of a severe allergic reaction:
    • Wheezing or trouble breathing
    • Nausea
    • Flushing
    • Lightheadedness or fainting
    • Coughing
    • Rash
  • Inflammation of the lining of the stomach (gastritis). Gastritis can happen with KUVAN and may be severe. Call your doctor right away if you have any:
    • Severe upper stomach-area discomfort or pain
    • Blood in your vomit or stool
    • Nausea and vomiting
    • Black, tarry stools
  • Too much or constant activity (hyperactivity) can happen with KUVAN. Tell your doctor if you have any signs of hyperactivity, including fidgeting, moving around or talking too much.

For more information, call BioMarin RareConnectionsTM at 1-877-MY-KUVAN (1-877-695-8826). Please read the full Patient Information by clicking here.