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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Brand Name
Cysteine Hydrochloride
Generic Name
Cysteine Hydrochloride
Active Ingredient
CysteineCategory
Vitamin C [EPC]
Variants
1
Different strengths and dosage forms
| Strength | Form | Route | NDC |
|---|---|---|---|
| 34.5 mg/mL | INJECTION | INTRAVENOUS | 0338-9645 |
Detailed information about Cysteine Hydrochloride
References used for this content
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Cysteine Hydrochloride, you must consult a qualified healthcare professional.
Cysteine is a sulfur-containing amino acid primarily used as an additive to parenteral nutrition for neonates and pediatric patients. It serves as a precursor to glutathione and is essential for protein synthesis and metabolic detoxification.
While Cysteine is primarily used in pediatric populations, its use in adults requiring Total Parenteral Nutrition (TPN) is occasionally indicated when methionine-to-cysteine conversion is impaired (e.g., severe liver disease).
Cysteine dosing in pediatrics is highly specific and based on weight and developmental stage. According to the American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines:
Cysteine and its nitrogenous metabolites are excreted by the kidneys. In patients with impaired renal function, there is an increased risk of nitrogen accumulation (azotemia). Healthcare providers should monitor Blood Urea Nitrogen (BUN) closely and may need to reduce the overall amino acid load, including Cysteine.
Since the liver is the primary site of amino acid metabolism, patients with hepatic insufficiency or liver failure may develop hyperammonemia (high ammonia levels). Dosage should be adjusted based on the patient's ability to tolerate nitrogen, and liver function tests (LFTs) must be monitored frequently.
Clinical studies for L-cysteine injection generally do not include sufficient numbers of patients aged 65 and over. Dosing should be cautious, starting at the lower end of the range, reflecting the higher frequency of decreased hepatic, renal, or cardiac function.
Cysteine hydrochloride injection is a concentrate and must never be administered by direct intravenous injection. It is strictly for addition to amino acid solutions used in TPN.
In the context of TPN, Cysteine is administered continuously or in cycles. If a TPN bag is delayed or missed, healthcare providers will typically restart the infusion at the prescribed rate. Do not "double up" the concentration in the next bag to compensate for a missed dose, as this can lead to metabolic imbalances or precipitation of the IV solution.
An overdose of Cysteine in TPN can lead to amino acid toxicity and metabolic derangements.
> Important: Follow your healthcare provider's dosing instructions precisely. The stability of Cysteine in TPN is highly sensitive to pH and temperature; do not adjust your dose or administration method without medical guidance.
Because Cysteine is an amino acid naturally found in the body, "side effects" are often related to the metabolic consequences of administration via TPN rather than the molecule itself. In neonatal populations, common observations include:
> Warning: Stop taking Cysteine and call your doctor immediately if you experience any of these serious symptoms:
Patients on long-term Cysteine-supplemented TPN are at risk for:
There are currently no FDA black box warnings specifically for Cysteine hydrochloride injection. However, the FDA requires a prominent warning regarding Aluminum Toxicity in the "Warnings and Precautions" section of the label. This warning highlights that the product contains aluminum that may be toxic, particularly to premature neonates with impaired renal function. Exposure to more than 4 to 5 mcg/kg/day of parenteral aluminum is associated with central nervous system and bone toxicity.
Report any unusual symptoms or changes in your child's behavior to your healthcare provider immediately. Regular blood monitoring is the best way to prevent and detect these side effects early.
Cysteine must only be used by healthcare professionals trained in the management of parenteral nutrition. It is a highly concentrated solution that requires careful dilution. The most critical safety concern is the maintenance of the correct acid-base balance and the prevention of mineral precipitation in the IV bag, which can be fatal if infused.
No FDA black box warnings for Cysteine. However, as noted in the side effects section, the Aluminum Toxicity Warning is the most significant clinical precaution mandated by the FDA for this drug class.
Patients receiving Cysteine in TPN require frequent laboratory monitoring, often daily in the initial stages:
Cysteine is typically used in hospitalized neonates or pediatric patients who do not drive. For adults receiving home TPN, Cysteine itself does not cause sedation; however, the underlying condition requiring TPN may affect the ability to drive safely.
There is no direct interaction between Cysteine and alcohol. However, alcohol consumption is generally contraindicated in patients with the severe liver or gastrointestinal diseases that necessitate parenteral nutrition.
Cysteine is discontinued when the patient transitions to enteral (oral or tube) feeding. There is no "withdrawal syndrome," but the transition must be managed carefully to ensure the patient maintains adequate protein and caloric intake. Tapering the TPN rate is standard practice to prevent rebound hypoglycemia, though this is related to the dextrose content, not the Cysteine.
> Important: Discuss all your medical conditions, especially kidney or liver problems, with your healthcare provider before starting Cysteine-supplemented nutrition.
Cysteine hydrochloride injection is relatively inert regarding direct drug-drug interactions, but it is highly reactive in terms of chemical compatibility.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, even if they seem unrelated to your nutritional therapy.
Cysteine must NEVER be used in the following circumstances:
Conditions requiring a careful risk-benefit analysis include:
There is little evidence of cross-sensitivity between L-cysteine and other drugs. However, patients who have had severe reactions to N-acetylcysteine (NAC) should be monitored closely, as the molecules are chemically related. Additionally, patients with sensitivities to sulfites (often used as preservatives in other medications) generally do not have a sensitivity to Cysteine, as Cysteine is a natural amino acid, not a sulfite preservative.
> Important: Your healthcare provider will evaluate your complete medical history, including any genetic metabolic screenings, before prescribing Cysteine.
FDA Pregnancy Category C. There are no adequate and well-controlled studies of L-cysteine hydrochloride injection in pregnant women. Animal reproduction studies have not been conducted. It is unknown whether Cysteine can cause fetal harm when administered to a pregnant woman. However, Cysteine is a normal component of the human diet and is essential for fetal growth. In clinical practice, Cysteine is used in pregnant women requiring TPN only if the potential benefit justifies the potential risk to the fetus. Monitoring for maternal hyperammonemia is essential to prevent fetal distress.
L-cysteine is a natural component of breast milk. When administered intravenously as part of TPN, it is unlikely to achieve concentrations in breast milk that would be harmful to a nursing infant, provided the mother's plasma levels are within the physiological range. However, caution should be exercised, and the infant should be monitored for any signs of protein intolerance if the mother is receiving high-dose parenteral nutrition.
This is the primary population for Cysteine hydrochloride injection. It is specifically approved for neonates (including preterm) and pediatric patients.
Elderly patients are more likely to have decreased renal and hepatic function. While Cysteine is not commonly used as a standalone supplement in the elderly, when used in TPN, the dose must be individualized. There is an increased risk of azotemia and fluid overload in this population. Frequent monitoring of BUN and cardiac status is recommended.
In patients with renal impairment (GFR < 60 mL/min/1.73m²), Cysteine metabolites can accumulate. Dosage reductions of the total amino acid solution are often necessary. For patients on dialysis, Cysteine is cleared during the procedure, and supplemental doses may be required on dialysis days, though this is managed by the renal nutrition team.
Patients with liver disease (Child-Pugh Class B or C) are at high risk for hyperammonemia when receiving amino acid infusions. Cysteine should be used cautiously, and the patient should be monitored for signs of encephalopathy (confusion, tremors). If ammonia levels rise significantly, the amino acid infusion rate must be reduced.
> Important: Special populations, especially premature infants, require individualized medical assessment and precise nutritional calculations by a multidisciplinary team.
Cysteine is a sulfur-containing amino acid. Its primary molecular mechanism involves its role as a precursor for Glutathione (L-gamma-glutamyl-L-cysteinyl-glycine). Cysteine provides the rate-limiting sulfhydryl (-SH) group for glutathione synthesis via the enzymes glutamate-cysteine ligase and glutathione synthetase.
Additionally, Cysteine is essential for the synthesis of Taurine, which is critical for bile acid conjugation and brain development in infants. It also acts as a structural component in proteins, where its thiol groups oxidize to form disulfide bridges, stabilizing the tertiary and quaternary structures of enzymes and hormones.
The pharmacodynamic effect of Cysteine is primarily nutritional and metabolic. The "onset of action" in the context of TPN is the improvement of nitrogen balance and steady weight gain, which is typically observed over several days of therapy. There is no "tolerance" development to Cysteine, as it is a fundamental nutrient. However, the body's ability to handle the acid load (chloride) and nitrogen load determines the maximum tolerable dose.
| Parameter | Value |
|---|---|
| Bioavailability | 100% (Intravenous) |
| Protein Binding | 10-15% (to albumin) |
| Half-life | Approximately 1.5 - 2 hours (plasma) |
| Tmax | Immediate (IV infusion) |
| Metabolism | Hepatic (Conversion to sulfate, taurine, glutathione) |
| Excretion | Renal (>90% as metabolites) |
Cysteine is classified as an Amino Acid [EPC]. Within the therapeutic area of parenteral nutrition, it is considered a "semi-essential" or "conditionally essential" amino acid. It is related to other sulfur-containing amino acids like Methionine, though it does not require the same metabolic conversion steps that Methionine does, making it safer for neonatal use.
Common questions about Cysteine Hydrochloride
Cysteine is primarily used as a nutritional additive in Total Parenteral Nutrition (TPN) for newborn infants and children. It provides a source of sulfur-containing amino acids that are essential for protein synthesis, growth, and the production of glutathione, a major antioxidant. Because premature infants often cannot produce enough cysteine on their own, healthcare providers add it to their IV nutrition to prevent deficiencies. It helps support the development of healthy tissues and protects cells from oxidative damage. Your doctor will determine the exact amount needed based on your child's weight and nutritional requirements.
The most common side effects of Cysteine administration in an IV setting include metabolic acidosis, which is an imbalance in the blood's pH, and electrolyte changes like low potassium or high phosphorus. Because Cysteine is often given as a hydrochloride salt, the extra chloride can lead to an acidic environment in the blood of small infants. You might also see redness or irritation at the site where the IV is inserted. In some cases, it can cause a temporary rise in blood urea nitrogen (BUN) or ammonia levels. Most of these effects are managed by adjusting the other components of the TPN solution.
While there is no known direct chemical interaction between Cysteine and alcohol, Cysteine is almost exclusively used in hospitalized patients, often infants, who are receiving nutrition through an IV. For adults who might be on home TPN containing Cysteine, alcohol should generally be avoided because it can stress the liver and kidneys, which are already working hard to process the IV nutrition. Alcohol can also interfere with the underlying gastrointestinal or hepatic conditions that made TPN necessary in the first place. Always consult your healthcare provider regarding lifestyle choices while on specialized nutritional therapy.
Cysteine is classified as FDA Pregnancy Category C, meaning there is limited data from controlled studies in pregnant women. However, Cysteine is a naturally occurring amino acid that is necessary for fetal development. If a pregnant woman requires Total Parenteral Nutrition (TPN) due to severe illness or inability to eat, Cysteine is often included to ensure the fetus receives adequate sulfur-containing amino acids. The main concern during pregnancy is ensuring that the mother's metabolism of the amino acids does not lead to high ammonia levels, which could affect the baby. Your medical team will monitor blood levels closely to ensure safety for both mother and child.
Cysteine begins to work at the cellular level immediately upon entering the bloodstream through the IV. However, the visible clinical benefits, such as steady weight gain, improved muscle mass, and stabilized blood protein levels, are typically observed over several days or weeks of consistent administration. It is not a medication designed for immediate symptom relief but rather a nutritional component for long-term growth and recovery. Healthcare providers track its effectiveness through daily weight checks and regular blood tests to ensure the body is utilizing the amino acids correctly.
Cysteine is usually stopped when a patient is ready to transition from IV nutrition to oral or tube feeding. Stopping it suddenly while still requiring TPN could lead to a deficiency in sulfur-containing amino acids, which might slow down growth or reduce the body's antioxidant capacity. The transition is typically done gradually under the supervision of a dietitian and doctor to ensure the patient's digestive system can handle protein from food. If the IV nutrition is stopped for any reason, the medical team will monitor the patient closely for any signs of nutritional or metabolic imbalance.
In a hospital setting, Cysteine is part of a continuous IV infusion, so a "missed dose" usually only happens if the IV bag runs out or is delayed. If you are administering TPN at home and notice a delay, contact your home infusion pharmacy or nurse immediately. Do not try to speed up the infusion or add more Cysteine to the next bag yourself, as this can cause dangerous metabolic imbalances or cause the minerals in the bag to clump together (precipitate). The medical team will provide specific instructions on how to safely restart the infusion at the correct rate.
Yes, Cysteine is intended to support healthy weight gain in patients who cannot eat enough food by mouth. As an amino acid, it is a building block of protein, which is essential for growing muscle, skin, and organs. In premature infants, the addition of Cysteine to TPN is a key factor in helping them reach a healthy weight and developmental milestones. However, this is "healthy" weight gain associated with growth and recovery, not the type of weight gain associated with excess fat or certain hormonal medications. Your doctor will monitor growth curves to ensure the weight gain is appropriate.
Cysteine can be taken with many other medications, but it is highly sensitive to the environment inside the IV bag. It should not be mixed with alkaline (high pH) drugs because they can cause the Cysteine to become insoluble and form dangerous crystals. When Cysteine is in your IV nutrition, the pharmacist checks all your other IV medications for "Y-site compatibility" to make sure they can safely enter the same vein. Always provide your doctor with a full list of all medications, including over-the-counter supplements, to prevent any chemical or metabolic interactions.
Yes, L-cysteine hydrochloride injection is available as a generic medication and under brand names like Elcys. Generic versions are required by the FDA to have the same quality, strength, and purity as the brand-name products. Because it is a specialized product used primarily in hospitals or by home infusion pharmacies, you won't typically find it on a standard pharmacy shelf. The cost and availability will depend on your hospital's formulary or your insurance provider's coverage for parenteral nutrition supplies.
Other drugs with the same active ingredient (Cysteine)