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PKU Basics

Understanding PKU

Phenylketonuria (PKU) is a genetic condition requiring lifelong management. Although PKU is a serious condition, there are steps you or your loved one can take to help maintain a healthy, productive life.

In someone with PKU, the phenylalanine hydroxylase (PAH) enzyme is either missing or not working properly, which can cause a buildup of phenylalanine (Phe) in the blood. High and/or unstable blood Phe levels can cause problems in the way you think, feel, and act.

Learn more about PKU

Symptoms of PKU

Symptoms of PKU can range from mild to severe and are the result of high or unstable blood Phe levels.

In children, symptoms may include:

  • Being cranky or fretful
  • Inability to focus
  • Anxiety
  • Severe intellectual disability (if left untreated)

In adults, symptoms may include:

  • Headache
  • Forgetfulness
  • Fatigue
  • Trouble focusing
  • Depression
  • Anxiety
  • Irritability
  • Isolation
  • Feeling “foggy”

Learn more about PKU signs and symptoms

Maintaining a Healthy, Productive Life With PKU

You can effectively manage PKU by1:

  • Starting treatment at birth and continuing for life
  • Controlling blood Phe levels every day

KUVAN®(sapropterin dihydrochloride) Tablets or Powder for Oral Solution is the first and only prescription medication for PKU. Experts recommend that everyone with PKU be offered a trial of KUVAN to determine if it can help lower blood Phe levels.*1

Sign up for the FREE trial of KUVAN for up to 30 days

Your clinic team is dedicated to helping you manage your PKU. Find a PKU clinic near you.
Talk with your clinic team to find out if KUVAN is right for you.

*Except those with two null mutations in trans.

Connect With the PKU Community

Discover an online community offering educational information, recipes, and other resources to people living with PKU.

Feeling Forgetful? Easily Confused?

It could be the PKU. According to the experts, those who have stopped PKU therapy (including diet and medication) can see improvement in their symptoms if they restart therapy.1 Get the facts and find support to help you get back on track.


  1. Vockley J, Andersson HC, Antshel KM, et al; for the American College of Medical Genetics and Genomics Therapeutic Committee. Phenylalanine hydroxylase deficiency: diagnosis and management guideline. Genet Med. 2014;16(2):188-200.


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, nausea, and nose irritation. 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 RareConnections™ at 1-877-MY-KUVAN (1-877-695-8826).

Please read the full Patient Information by clicking here.