Cystagon works by reducing the amount of cystine (an amino acid) in the body.

Cystagon is used to treat nephropathic cystinosis (NEF-roe-PATH-ik SIS-tin-OH-sis), a rare genetic condition that causes a build-up of cystine in the kidneys and other organs. Too much cystine can cause kidney failure or other medical problems.

Cystagon is for use in adults and children, but Procysbi should not be given to a child younger than 1 year old.

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

Follow all directions on your medicine label and package. Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

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

Swallow the capsule whole and do not crush or chew it.

If you cannot swallow a capsule whole, carefully follow the patient instructions for opening the capsule and mixing the medicine with certain foods. Your doctor may recommend that you use Cystagon oral granules.

Do not crush or chew oral granules.

Procysbi works best if you take it without food, at least 30 minutes before or 2 hours after a meal. If you cannot take the medicine without eating, eat only a small amount (1/2 cup) of food within 1 hour before or 1 hour after you take the medicine.

Whether you take the medicine with or without food, take it the same way each time.

To mix the oral granules or medicine from a capsule with food:

• Empty the entire contents of the granule packet or the open capsule into 1/2 cup of applesauce, berry jelly, water, or fruit juice (but not grapefruit juice).

• Swallow the mixture without chewing, and use it within 30 minutes after mixing. Do not save it for later use.

• Avoid eating high-fat foods within 1 hour before or 1 hour after you take Procysbi.

Procysbi also comes with instructions for giving the mixture through a gastronomy tube (14 French or larger).

Cystagon doses are based on weight (especially in children and teenagers). Your dose needs may change if you gain or lose weight.

You will need frequent medical tests.

You should not stop using Cystagon without your doctor's advice. Stopping suddenly may make your condition worse.

Cystinosis is often treated with a combination of drugs, including vitamin and mineral supplements. Use all medications as directed and read all medication guides you receive. Do not change your dose or dosing schedule without your doctor's advice.

Store at room temperature away from moisture, heat, and light.

You should not use Cystagon if you are allergic to Cystagon or penicillamine.

Tell your doctor if you have ever had:

• any type of skin rash;

• bone problems (including fractures);

• epilepsy or other seizure disorder;

• liver disease;

• low white blood cell (WBC) counts;

• depression, drowsiness, or nervous system disorder; or

• stomach ulcer, or bleeding in your stomach or intestines.

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

You should not breastfeed while using this medicine.

Take the missed dose as soon as you remember.

• For Cystagon: Skip the missed dose if your next dose is due in less than 2 hours.

• For Procysbi: If you are less than 8 hours late for the dose, use the medicine as soon as you can. Skip the missed dose if your next dose is due in less than 4 hours.

Do not use two doses at one time.

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

Avoid driving or hazardous activity until you know how Cystagon will affect you. Your reactions could be impaired.

Avoid drinking alcohol while taking Procysbi. Alcohol can make the medicine less effective or cause side effects.

Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Call your doctor at once if you have any of these side effects (some of these may be caused by your cystinosis disorder and not by Cystagon):

• depressed mood, extreme drowsiness;

• a seizure;

• unusual bruising or streaks on the skin;

• bone pain, abnormal joint movement;

• an electrolyte imbalance--increased thirst or urination, confusion, constipation, leg cramps, irregular heartbeats, tingly feeling;

• increased pressure inside the skull--severe headaches, ringing in your ears, dizziness, vision problems, pain behind your eyes; or

• stomach problems--pain, nausea, vomiting, loss of appetite, coughing up blood or vomit that looks like coffee grounds.

Common side effects of Cystagon may include:

• drowsiness, feeling tired;

• stomach pain, nausea, vomiting, loss of appetite, diarrhea;

• unusual breath odor or skin odor;

• rash;

• fever; or

• headache.

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.