Treatments and drugs

By Mayo Clinic Staff

The main phenylketonuria treatment is a strict diet with very limited intake of phenylalanine, which is mostly found in foods containing protein. Doctors used to believe it was OK for a person with PKU to stop the diet in adolescence, but today, doctors recommend sticking to the diet and PKU formula for life. Without PKU formula, your body can't get enough of essential nutrients called amino acids that are crucial for growth and general health. For example, the amino acid tyrosine is usually a byproduct of phenylalanine metabolism, a process that doesn't occur in people with PKU.

A safe amount of phenylalanine differs for each person. Your doctor will determine a safe amount through regular review of diet records, growth charts and blood levels of phenylalanine. Frequent blood tests will monitor PKU levels as they change over time, especially during childhood growth spurts and pregnancy. In general, the idea is to consume only the amount of phenylalanine that's necessary for normal growth and body processes, but no more.

Another possible addition to the PKU diet may be a supplement called neutral amino acid therapy powder or tablets. 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.

Which foods to avoid

Because the amount of phenylalanine adults can safely eat is so low, it's crucial they avoid all high-protein foods, including:

  • Milk
  • Eggs
  • Cheese
  • Nuts
  • Soybeans
  • Beans
  • Chicken
  • Steak and other beef products
  • Pork
  • Fish
  • Chocolate candy
  • Peas
  • Beer

Children and adults should also avoid foods, including many diet sodas, and medications made with aspartame (NutraSweet, Equal). Aspartame, found in many artificial sweeteners, releases phenylalanine when digested.

Adults and children with PKU also have to limit portions of lower protein foods, such as:

  • Fruit
  • Vegetables
  • Desserts

Low-protein rice, pasta noodles and crackers are often fine to eat without calculating the phenylalanine content.

It's key to remember that too much of a good thing can sometimes be harmful. Even if you're eating approved foods, eating too many at one time can be dangerous. Consider the total amount of phenylalanine in all the foods you eat when planning your diet.

Formula for babies

You might wonder how someone, even a baby, can get all of the necessary nutrition with these dietary limitations. The answer is a formula — a special nutritional drink or supplement for people with PKU. The phenylalanine-free formula provides protein and other essential nutrients in a form that is safe for people with PKU.

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 a protein substitute formula daily, as directed by a doctor or dietitian. Your daily dose of formula should be 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.

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, it's the only way to prevent the serious health problems people with PKU can develop. Families need to commit to this lifestyle change wholeheartedly, realizing that it may be difficult but not impossible.

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

Nov. 17, 2011