CYSTEINE HYDROCHLORIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CYSTEINE HYDROCHLORIDE (CYSTEINE HYDROCHLORIDE).
Cysteine hydrochloride serves as a precursor to glutathione, an important antioxidant. It also provides a source of cysteine for protein synthesis and acts as a mucolytic agent by reducing disulfide bonds in mucus glycoproteins, thereby decreasing viscosity.
| Metabolism | Cysteine is primarily metabolized in the liver via cysteine dioxygenase to cysteine sulfinate, which is further converted to taurine, sulfate, and pyruvate. It can also be incorporated into glutathione via gamma-glutamylcysteine synthetase. |
| Excretion | Renal: 40-60% as unchanged drug and metabolites; fecal: <5%; minor biliary elimination; route of administration (e.g., intravenous) influences exact percentages. |
| Half-life | Terminal elimination half-life: 1.5-3 hours in adults with normal renal function; prolonged in renal impairment (up to 8-10 hours in severe cases). |
| Protein binding | Approximately 20-30%; primarily to albumin; binding is low and not clinically significant. |
| Volume of Distribution | 0.3-0.5 L/kg; indicates distribution primarily into extracellular fluid and tissues; higher Vd in neonates. |
| Bioavailability | Oral: 5-10% due to extensive first-pass metabolism; intravenous: 100%. |
| Onset of Action | Intravenous: within 30 minutes; oral: 1-2 hours; onset refers to reduction of acetaminophen hepatotoxicity when used as an antidote. |
| Duration of Action | Duration: 4-6 hours after IV administration; therapeutic effect may persist longer due to restoration of hepatic glutathione stores; clinical monitoring required. |
Intravenous: 0.8-1 g/m²/day divided every 6 hours for acetaminophen poisoning; for parenteral nutrition, 0.66-1.7 g of cysteine/kg/day (as hydrochloride).
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment established; use with caution in severe renal impairment (GFR <30 mL/min) due to potential accumulation of metabolites. |
| Liver impairment | No specific dose adjustment established; however, caution in severe hepatic impairment (Child-Pugh class C) due to altered metabolism. |
| Pediatric use | Acetaminophen overdose: IV loading dose 140 mg/kg, then 70 mg/kg every 4 hours for 17 doses; for parenteral nutrition: 30-50 mg/kg/day (as cysteine hydrochloride). |
| Geriatric use | No specific geriatric dose adjustments; use with caution due to potential renal and hepatic function decline. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CYSTEINE HYDROCHLORIDE (CYSTEINE HYDROCHLORIDE).
| Breastfeeding | No data on presence in human milk. M/P ratio unknown. Caution due to possible cysteine excess. Weigh benefit against potential risk to infant. |
| Teratogenic Risk | Limited human data; animal studies show no teratogenicity at clinically relevant doses. First trimester: insufficient evidence for risk. Second and third trimesters: no known fetal harm. Avoid use unless clearly needed. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to cysteine or any component","Patients with cystinuria (due to potential cystine stone formation)","Severe metabolic acidosis"]
| Precautions | ["Monitor for metabolic acidosis, hyperammonemia, and fluid overload.","Use with caution in patients with renal impairment or hepatic disease.","Cysteine hydrochloride can cause venous irritation and phlebitis at the injection site.","Contains sodium bisulfite, which may cause allergic reactions in sensitive individuals."] |
| Food/Dietary | No specific food interactions known. Ensure adequate nutrition as part of total parenteral nutrition (TPN). |
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| Monitor maternal acid-base status, electrolytes, and renal function during infusion. Fetal monitoring not routinely required unless maternal condition warrants. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies show no reproductive impairment. |
| Clinical Pearls |
| Administer intravenously; monitor for phlebitis and extravasation. Cysteine is unstable in solution; use immediately after preparation. Contraindicated in patients with hypersensitivity to cysteine or components. |
| Patient Advice | This medication is given intravenously; report any burning, pain, or redness at the injection site. · Tell your doctor if you have any allergies, especially to cysteine or similar compounds. · Regular blood tests may be needed to monitor liver function and metabolic status. · Inform your healthcare provider if you are pregnant, planning to become pregnant, or breastfeeding. |