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Generic name: fosdenopterin [ FOS-den-OP-ter-in ]
Brand name: Nulibry
Dosage form: intravenous powder for injection (9.5 mg)
Drug class: Miscellaneous metabolic agents

Medically reviewed by on Mar 6, 2023. Written by Cerner Multum.

What is fosdenopterin?

Fosdenopterin is used to reduce the risk of death in children with molybdenum cofactor deficiency (MoCD) Type A.

Molybdenum (moe-LIB-den-um) cofactor deficiency is a rare condition in newborn babies that affects brain function and gets worse over time. Babies with MoCD begin to show symptoms within a week after birth, and this condition can lead to severe developmental delays and life-threatening health problems.

Fosdenopterin may also be used for purposes not listed in this medication guide.

Fosdenopterin side effects

Get emergency medical help if your child has signs of an allergic reaction: hives; difficult breathing; swelling of the face, lips, tongue, or throat.

Call your doctor at once if your child has:

  • a fever;

  • severe or ongoing vomiting or diarrhea;

  • bruising, swelling, discomfort, or skin changes around the catheter;

  • cough with mucus, trouble breathing;

  • a seizure; or

  • signs of an ear infection--fever, ear pain, drainage from the ear, fussiness.

Seek emergency medical attention if your child has a skin rash or symptoms of serious sunburn such as skin redness, burning, or blisters.

Common side effects of fosdenopterin may include:

  • problems with the catheter or IV line;

  • fever;

  • vomiting, diarrhea; or

  • cold symptoms such as stuffy nose, sneezing, cough.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Follow all directions on your medicine label and package. Tell each of your child's healthcare providers about all the child's medical conditions, allergies, and medicines.

Before taking this medicine

Your doctor will perform a genetic test to make sure your baby has MoCD.

Fosdenopterin is sometimes given before genetic testing results are available. Treatment will be stopped if the test shows that your baby does not have MoCD.

How should I use fosdenopterin?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your child's dose. Use the medicine exactly as directed.

Fosdenopterin is given using an infusion pump attached to a catheter placed into a vein. A healthcare provider can teach you how to properly use the infusion pump by yourself.

You may need to keep a diary of the dates and times for each dose you give to your child. You may also need to record information about the specific vials and amounts of fosdenopterin you use each time. Take this information with you every time you take your child t the doctor.

Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you don't understand all instructions.

Fosdenopterin must be mixed with a liquid (diluent) before using it. When using injections by yourself, be sure you understand how to properly mix and store the medicine.

Do not shake the mixed medicine.

Prepare an injection only when you are ready to give it. Each infusion should be finished within 4 hours after you mixed the medicine with the diluent.

Do not use if the medicine looks cloudy, has changed colors, or has particles in it. Call your pharmacist for new medicine.

Fosdenopterin doses are based on weight. Your child's dose needs may change if the child gains or loses weight.

Store unmixed fosdenopterin in a freezer. Keep each vial in its original carton and protect from light.

Take the medicine out of the freezer and let it reach room temperature for 30 minutes before mixing with the diluent. You may also warm the medicine in your hands for 3 to 5 minutes. Do not heat the medicine.

You may store mixed medicine in the refrigerator or at room temperature. If stored in a refrigerator, allow the mixture to reach room temperature before giving the injection. Complete the injection within 4 hours after mixing the medicine.

Fosdenopterin dosing information

Usual Adult Dose for Combined Molybdoflavoprotein Enzyme Deficiency:

0.9 mg/kg IV once a day

-Dosing is based on actual body weight; infuse at a rate of 1.5 mL/min with non-DEHP tubing and a 0.2-micron filter.
-Safety and effectiveness for use of this drug in adults with of molybedenum cofactor deficiency (MoCD) Type A have been established based on adequate and well-controlled clinical investigation in pediatric patients.

Use: To reduce the risk of mortality in patients with MoCD Type A.

Usual Pediatric Dose for Combined Molybdoflavoprotein Enzyme Deficiency:

Patients less than 1 year: Dosing is based on gestational age

Gestational age less than 37 weeks (preterm neonates):
-Initial Dosage: 0.4 mg/kg IV once a day
-Dose at one month: 0.7 mg/kg IV once a day
-Dose at three months: 0.9 mg/kg IV once a day

Gestational age 37 weeks and above (term neonates):
-Initial Dosage: 0.55 mg/kg IV once a day
-Dose at one month: 0.75 mg/kg IV once a day
-Dose at three months: 0.9 mg/kg IV once a day

Patients 1 year or older: 0.9 mg/kg IV once a day

-Dosing is based on actual body weight; infuse at a rate of 1.5 mL/min with non-DEHP tubing and a 0.2-micron filter (volumes below 2 mL may require syringe administration through slow intravenous push).
-Therapy may be started upon diagnosis or presumptive diagnosis of molybedenum cofactor deficiency (MoCD) Type A; for a presumptive diagnosis, confirm with genetic testing and discontinue this drug if diagnosis is not confirmed.

Use: To reduce the risk of mortality in patients with MoCD Type A.

What happens if I miss a dose?

Give the medicine as soon as you can, then give the next injection at least 6 hours later and return to the regular daily injection schedule. Do not give two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while using fosdenopterin?

Fosdenopterin could make your child sunburn more easily. Avoid sunlight or tanning beds. Be sure the child wears protective clothing, a hat, and sunglasses while outdoors. Also apply sunscreen (SPF 30 or higher) if your child is at least 6 months old.

What other drugs will affect fosdenopterin?

Other drugs may affect fosdenopterin, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your child's current medicines and any medicines the child starts or stops using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.