Cystagon

[sis´tah-gon] trademark for a preparation of cysteamine, used in treatment of nephropathic cystinosis.

cysteamine

(sis-tee-a-meen) cysteamine,

Cystagon

(trade name),

Procysbi

(trade name)

Classification

Therapeutic: cystine depleting agent
Pregnancy Category: C

Indications

Management of nephropathic cystinosis.

Action

Prevents the accumulation of intracellular cystine by favoring conversion to cysteine and cysteine compounds that are able to leave the intracellular space.

Therapeutic effects

Prevention of damage to organs and tissues (especially kidneys) in patients with nephropathic cystinosis.

Pharmacokinetics

Absorption: Well absorbed after oral administration.Distribution: Distributes into the intracellular compartment.Metabolism and Excretion: Unknown.Half-life: Unknown.

Time/action profile (effect on leukocyte cystine levels)

ROUTE	ONSET	PEAK	DURATION
PO	rapid	1.4 hr†	5–6 hr

†Blood levels

Contraindications/Precautions

Contraindicated in: Hypersensitivity to cysteamine or penicillamine; Lactation: Lactation.Use Cautiously in: Obstetric: Use only if potential benefit justifies potential risk.

Adverse Reactions/Side Effects

Central nervous system

seizures (life-threatening)
lethargy (most frequent)
ataxia
confusion
depression
dizziness
encephalopathy
headache
hallucinations
intracranial hypertension
nightmares
somnolence

Cardiovascular

hypertension

Ear, Eye, Nose, Throat

hearing loss
papilledema

Gastrointestinal

anorexia (most frequent)
diarrhea (most frequent)
vomiting (most frequent)
abdominal pain
abnormal liver function studies
bad breath
constipation
dyspepsia
GI bleeding
GI ulcers
nausea

Dermatologic

erythema multiforme (life-threatening)
toxic epidermal necrolysis (life-threatening)
rash
striae
urticaria

Fluid and Electrolyte

dehydration

Hematologic

anemia
leukopenia

Musculoskeletal

fractures
leg pain
osteopenia
tremor

Miscellaneous

fever (most frequent)

Interactions

Drug-Drug interaction

None significant.

Route/Dosage

CystagonOral (Adults and Children >12 yr and >110 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—500 mg 4 times daily.Oral (Children <12 yr) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—1.3 g/m²/day or 60 mg/kg/day in 4 divided doses.ProcysbiOral (Adults and Children ≥6 yr and >110 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—1000 mg every 12 hr.Oral (Adults and Children ≥6 yr and 91–110 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—900 mg every 12 hr.Oral (Adults and Children ≥6 yr and 71–90 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—800 mg every 12 hr.Oral (Adults and Children ≥6 yr and 51–70 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—700 mg every 12 hr.Oral (Adults and Children ≥6 yr and 41–50 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—600 mg every 12 hr.Oral (Adults and Children ≥6 yr and 31–40 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—500 mg every 12 hr.Oral (Adults and Children ≥6 yr and 21–30 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—400 mg every 12 hr.Oral (Adults and Children ≥6 yr and 11–20 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—300 mg every 12 hr.Oral (Adults and Children ≥6 yr and 0–10 lb) Initial dose— 1/4–1/6 of the maintenance dose in divided doses increased gradually over 4–6 wk to maintenance dose. Maintenance dose—200 mg every 12 hr.

Availability

Capsules (Cystagon): 50 mg, 150 mg Capsules (Procysbi): 25 mg, 75 mg

Nursing implications

Nursing assessment

Assess patient for rash throughout therapy. If rash occurs, withhold cysteamine until rash clears; then resume at a lower dose and monitor closely for recurrence. Titrate slowly to maintenance dose. If severe rash (erythema multiforme bullosa, toxic epidermal necrolysis) occurs, do not readminister cysteamine.
Monitor neurologic status throughout therapy. If CNS symptoms develop (seizures, lethargy, somnolence, depression, encephalopathy), hold dose until symptoms resolve. Resume at a lower dose and titrate slowly to maintenance dose.
Assess patient for anorexia, nausea, vomiting, and abdominal pain. If these symptoms are severe, hold dose until symptoms resolve, then resume at a lower dose. Titrate slowly to maintenance dose.
Lab Test Considerations: Monitor leukocyte cystine levels monthly for 3 mo, then quarterly, then twice yearly. Patients transferred from cysteamine HCl or phosphocysteamine solutions to capsules should have white cell cystine levels measured in 2 wk and every 3 mo thereafter. Obtain leukocyte cystine measurements 12.5 hr after evening cysteamine administration and 30 min after following morning dose. Leukocyte cystine levels of <1 nmol/ 1/2 cystine/mg protein are the goal of therapy.
- Monitor CBC and liver function tests periodically during therapy. May occasionally cause reversible leukopenia and abnormal liver function studies.

Potential Nursing Diagnoses

Impaired urinary elimination (Indications)
Imbalanced nutrition: less than body requirements (Side Effects)

Implementation

Therapy should be started as soon as the diagnosis of nephropathic cystinosis is confirmed. Increase dose gradually over 4–6 wk to avoid intolerance.
Oral: Administer on empty stomach at least 30 min before or 2 hrs after meals. If unable to swallow capsule, may sprinkle capsule contents over 1/2 cup of applesauce or berry jelly or mix in 1/2 cup of apple or orange juice and shake gently for 5 min. Administer within 30 min of mixing. May also mix with 1/2 cup of applesauce and administer via feeding tube within 30 min. Flush with 8 oz of apple or orange juice. If unable to take without mixing with food, take only 1/2 cup of food mixture between 1 hr before and 1 hr after administration. Must be taken consistently with relation to food.

Patient/Family Teaching

Instruct patient or parents to take cysteamine exactly as directed. If a dose is missed, take as soon as possible unless less than 4 hrs before next dose. Do not double doses.
Instruct patient to remain well-hydrated (2–3 L/day).
May cause drowsiness. Caution patient to avoid driving or other activities requiring alertness until response to medication is known.
Advise patient to notify health care professional immediately if signs and symptoms of benign intracranial hypertension (headache, tinnitus, dizziness, nausea, double vision, blurry vision, loss of vision, eye pain), drowsiness, fever, increased thirst, nausea or vomiting, rash, sore throat, trembling, or seizures occur.
Advise female patient to notify health care professional if pregnancy is planned or suspected, or if breastfeeding.
Emphasize the importance of routine lab tests to monitor progress and side effects.

Evaluation/Desired Outcomes

Leukocyte cystine levels <1 nmol/1/2 cystine/mg protein. Patients who have difficulty tolerating cysteamine may still receive benefit if leukocyte cystine levels are <2 nmol/1/2 cystine/mg protein.