Treatments and drugs

By Mayo Clinic Staff

The main treatment for phenylketonuria includes:

  • A lifetime diet with very limited intake of protein, because foods with protein contain phenylalanine
  • Taking a PKU formula — a special nutritional supplement — for life to make sure you get enough essential protein (without phenylalanine) and nutrients that are crucial for growth and general health

A safe amount of phenylalanine differs for each person with PKU and can vary over time. In general, the idea is to consume only the amount of phenylalanine that's necessary for normal growth and body processes, but no more. Your doctor can determine a safe amount through:

  • Regular review of diet records, growth charts and blood levels of phenylalanine
  • Frequent blood tests that monitor PKU levels as they change over time, especially during childhood growth spurts and pregnancy
  • Other tests that may be done to assess growth, development and health

Your doctor may refer you to a registered dietitian who can help you learn about the PKU diet.

Which foods to avoid

Because the amount of phenylalanine that a person with PKU can safely eat is so low, it's crucial to avoid all high-protein foods, such as:

  • Milk
  • Eggs
  • Cheese
  • Nuts
  • Soybeans
  • Beans
  • Chicken
  • Beef
  • Pork
  • Fish

Potatoes, grains and other vegetables that have protein will likely be limited.

Children and adults also need to avoid certain other foods and beverages, including many diet sodas and other drinks that contain aspartame (NutraSweet, Equal). Aspartame, found in many artificial sweeteners, releases phenylalanine when digested.

Some medications may contain aspartame and some vitamins or other supplements may contain amino acids or skim milk powder. Check with your pharmacist about the contents of over-the-counter or prescription medications.

Talk with your doctor or dietitian to learn more about your specific dietary needs.

Formula for people with PKU

Because of the restricted diet, someone with PKU needs to get essential nutrition through a formula that's a special nutritional supplement for people with PKU. The phenylalanine-free formula provides protein and other essential nutrients in a form that's safe for people with PKU. Your doctor and dietitian can help you find the right type of formula.

  • Formula for babies and toddlers. Because regular infant formula and breast milk contain phenylalanine, babies with PKU instead need to consume a phenylalanine-free infant formula. A dietitian can carefully calculate a sparing amount of breast milk or regular formula to be mixed with the phenylalanine-free formula. Parents introduce solid foods with low levels of phenylalanine to children with PKU on the same schedule used for other infants. These foods replace the phenylalanine a baby has been receiving from breast milk or formula and need to be precisely figured into the daily phenylalanine intake.
  • Formula for older children and adults. Older children and adults continue to drink or eat a protein substitute formula daily, as directed by a doctor or dietitian. Your daily dose of formula is divided between your meals and snacks, instead of consumed all at once. The formula for older children and adults is not the same as the one used for infants, but it works on the same principle. It acts as an essential nutritional substitute and is continued for life.

Another possible addition to the PKU diet is a supplement called neutral amino acid therapy in powder or tablet form. This supplement may block some absorption of phenylalanine. However, this is an emerging treatment that hasn't yet been well-studied. Ask your doctor or dietitian if this supplement is appropriate for your diet.

The need for a nutritional supplement, especially if your child doesn't find it palatable, and the limited food choices can make the PKU diet challenging. But families need to commit to this lifestyle change wholeheartedly because it's the only way to prevent the serious health problems that people with PKU can develop.

PKU medication

The Food and Drug Administration (FDA) has approved the drug sapropterin (Kuvan) for the treatment of PKU. It works by increasing your tolerance to phenylalanine. The drug is for use in combination with a PKU diet. But it doesn't work for everyone with PKU.

In approving sapropterin, the FDA directed that studies continue because there are no long-term studies on the drug's efficacy and long-term safety.

Oct. 17, 2017