Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
Quick facts
- How it is given
- intravenous
- Type
- human prescription drug
- Brand names
- ELCYS
- RxNorm ID
- 1486165
We do not publish dosing. How much of this medicine to take, how often, and for how long depends on your age, weight, kidney and liver function, other conditions and other medicines. That is a decision for the person who prescribes or dispenses it. Follow the directions on your own pack and ask your pharmacist if anything is unclear.
What it is used to treat
® is indicated for use as an additive to amino acid solutions to meet the nutritional requirements of newborn infants requiring total parenteral nutrition (TPN); and of adult and pediatric patients with severe liver disease who may have impaired enzymatic processes and require TPN. It can also be added to amino acid solutions to provide a more complete profile of amino acids for protein synthesis. ELCYS ® is a sulfur-containing amino acid indicated to meet the nutritional requirements of newborn infants requiring total parenteral nutrition (TPN); and of adult and pediatric patients with severe liver disease who may have impaired enzymatic processes and require TPN. It can also be added to amino acid solutions to provide a more complete profile of amino acids for protein synthesis. ( 1 )
About this medicine
® (cysteine hydrochloride injection) is a sterile, nonpyrogenic solution for intravenous use. Each 50 mL of ELCYS ® contains 2500 mg of cysteine hydrochloride, USP (equivalent to 345 mg of cysteine) in water for injection. Sodium hydroxide and/or hydrochloric acid are used as needed to adjust the pH. The pH range is 1.0 to 2.5. The active ingredient is cysteine hydrochloride. Cysteine is a sulfur-containing amino acid. The chemical name of cysteine hydrochloride is L-cysteine hydrochloride monohydrate and is chemically designated as C 3 H 7 NO 2 S • HCI • H 2 O having a molecular weight of 175.63. Cysteine hydrochloride is a white crystalline powder soluble in water. Cysteine aqueous solution is prone to oxidation when exposed to air, and when mixed with amino acids solutions, cysteine may convert to insoluble cystine which leads to precipitation over time. It has the following structural formula: ELCYS ® contains no more than 120 mcg/L of aluminum. Structure
How it works
12.1 Mechanism of Action Endogenous cysteine is synthesized from methionine by the enzyme, cystathionase, via the trans-sulfuration pathway, and serves as a precursor substrate for both glutathione and taurine. ELCYS ® provides cysteine to the systemic circulation of patients who require PN and cannot synthesize adequate quantities of cysteine due to insufficient or deficient cystathionase activity.
Who should not take it
® is contraindicated in: • Patients with known hypersensitivity to one or more amino acids. • Patients with inborn errors of amino acid metabolism due to risk of severe metabolic or neurologic complications. • Patients with pulmonary edema or acidosis due to low cardiac output. • Hypersensitivity to one or more amino acids ( 4 ) • Inborn errors of amino acid metabolism ( 4 ) • Pulmonary edema or acidosis due to low cardiac output ( 4 )
Warnings and cautions
• Pulmonary Embolism due to Pulmonary Vascular Precipitates: If signs of pulmonary distress occur, stop the infusion and initiate a medical evaluation. ( 5.1 ) • Vein Damage and Thrombosis: Solutions with osmolarity of 900 mOsm/L or more must be infused through a central catheter. ( 2.1 , 5.2 ) • Increased blood urea nitrogen (BUN): Monitor laboratory parameters and discontinue if exceeds normal postprandial limits and continues to increase. ( 5.3 ) • Acid-Base Imbalance: Monitor laboratory parameters and supplement with electrolytes as needed. ( 5.4 ) • Hepatobiliary Disorders: Monitor liver function parameters and ammonia levels. ( 5.5 ) • Hyperammonemia: Neurocognitive delay possible in infants; monitor blood ammonia levels. ( 5.6 , 8.4 ) • Aluminium Toxicity: Increased risk in patients with renal impairment, including preterm infants. ( 5.7 , 8.4 ) • Monitoring and Laboratory Tests: Monitor fluid and electrolytes, serum osmolarity, blood glucose, kidney and liver function, blood count and coagulation parameters throughout treatment. ( 5.8 ) 5.1 Pulmonary Embolism due to Pulmonary Vascular Precipitates Pulmonary vascular precipitates causing pulmonary vascular emboli and pulmonary distress have been reported in patients receiving PN. In some fatal cases, pulmonary embolism occurred as a result of calcium phosphate precipitates. Precipitation following passage through an in-line filter and suspected in vivo precipitate formation has also been reported. If signs of pulmonary distress occur, stop the PN infusion and initiate a medical evaluation. In addition to inspection of the solution [see Dosage and Administration ( 2.1 , 2.2 )], the infusion set and catheter should also periodically be checked for precipitates. 5.2 Vein Damage and Thrombosis ELCYS ® must be diluted and used as an admixture in PN solutions. It is not for direct intravenous infusion. Solutions with an osmolarity of 900 mOsm/L or greater must be infused through a central catheter [see Dosage and Administration ( 2.1 )] . The infusion of hypertonic nutrient injections into a peripheral vein may result in vein irritation, vein damage, and/or thrombosis. […]
Reported side effects
The following serious adverse reactions are discussed in greater detail in other sections of the prescribing information: • Pulmonary embolism due to pulmonary vascular precipitates [see Warnings and Precautions ( 5.1 )] • Vein damage and thrombosis [see Warnings and Precautions ( 5.2 )] • Increased BUN [see Warnings and Precautions ( 5.3 )] • Acid-base imbalance [see Warnings and Precautions ( 5.4 )] • Hepatobiliary disorders [see Warnings and Precautions ( 5.5 )] • Hyperammonemia [see Warnings and Precautions ( 5.6 )] • Aluminum toxicity [see Warnings and Precautions ( 5.7 )] Adverse reactions with the use of cysteine hydrochloride injection were identified in clinical studies or postmarketing reports. Because some of these reactions were reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. • Local infusion site reactions, including a warm sensation, erythema, phlebitis and thrombosis at the infusion site • Generalized flushing, fever and nausea Most common adverse reactions are local reactions (warm sensation, erythema, phlebitis and thrombosis at the infusion site), generalized flushing, fever and nausea ( 6 ). To report SUSPECTED ADVERSE REACTIONS, contact Exela Pharma Sciences, LLC or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.
Use in specific groups
8.1 Pregnancy Risk Summary Appropriate administration of ELCYS ® is not expected to cause major birth defects, miscarriage or adverse maternal or fetal outcomes. Animal reproduction studies have not been conducted with cysteine hydrochloride. The estimated background risk for major birth defects and miscarriage for the indicated populations is unknown. All pregnancies have a background risk of birth defect, loss or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defect and miscarriage in the clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. 8.2 Lactation Risk Summary Data available on the effects of cysteine hydrochloride on infants, either directly or through breastmilk, do not suggest a significant risk of adverse events from exposure. Although there are no data on the presence of cysteine hydrochloride in human or animal milk or the effects on milk production, appropriate administration of ELCYS ® is not expected to cause harm to a breastfed infant. The development and health benefits of breastfeeding should be considered along with the mother’s clinical need for ELCYS ® and any potential adverse effects on the breastfed infant from ELCYS ® or from the underlying maternal condition. 8.4 Pediatric Use ELCYS ® is approved for use in pediatric patients, from birth to 17 years of age, for use as an additive to amino acid solutions to meet the nutritional requirements of newborn infants, including preterm infants, requiring total parenteral nutrition (TPN) and pediatric patients with severe liver disease who may have impaired enzymatic processes and require TPN . The safety profile for ELCYS ® use in pediatric patients includes risks of acid-base imbalance and hyperammonemia. Acid-base imbalance, including metabolic acidosis, may occur with ELCYS ® administration in preterm infants. Frequent clinical and laboratory assessments are necessary to monitor and manage fluid balance, electrolyte concentrations, and acid-base balance during parenteral nutrition therapy [see Warnings and Precautions ( 5.4 )] . Hyperammonemia is of special significance in infants (birth to two years of age). […]
If too much is taken
In the event of over hydration or solute overload, re-evaluate the patient and institute appropriate corrective measures [see Warnings and Precautions ( 5.3 , 5.4 , 5.5 , 5.7 , 5.8 )] .
Before you take anything new
Tell your pharmacist or doctor about every medicine you take — including ones bought without a prescription, herbal products and supplements. Interactions are one of the most common avoidable causes of harm from medicines, and a pharmacist can check your full list in a couple of minutes.
This page is built from the openFDA record of the U.S. Food and Drug Administration's approved labelling for this product, effective 9 April 2026. Label text has been shortened and reformatted for readability; safety wording has not been altered in meaning. FDA labelling describes products approved in the United States — brand names, strengths, formulations and approved uses may differ in your country. Always read the leaflet that comes with your own pack. PocketsInfo is not affiliated with, and is not endorsed by, the FDA. Retrieved 2026-07-30.