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Cysteine


Pronunciation

 (SIS te een)


Synonyms

 Cysteine Hydrochloride


Generic Available

 Yes


Use

 Supplement to crystalline amino acid solutions, in particular the specialized pediatric formulas (eg, Aminosyn® PF, TrophAmine®) to meet the intravenous amino acid nutritional requirements of infants receiving parenteral nutrition (PN)


Contraindications

 Hypersensitivity to cysteine or any component of the formulation; patients with hepatic coma or metabolic disorders involving impaired nitrogen utilization


Warnings/Precautions

 Use with caution in patients with renal dysfunction and hepatic insufficiency. Metabolic acidosis has occurred in infants related to the "hydrochloride" component of cysteine; each 1 mmol cysteine (175 mg) delivers 1 mEq chloride and 1 mEq hydrogen ion; to balance the extra hydrochloride ions and prevent acidosis addition to the PN solution of a 1 mEq acetate electrolyte salt for each mmol (175 mg) of cysteine may be needed; each 40 mg cysteine (equal to every 1 g amino acid when used in the recommended ratio) adds 0.228 mEq chloride and hydrogen.


Adverse Reactions

 Frequency not defined.

Central nervous system: Fever

Endocrine & metabolic: Metabolic acidosis

Gastrointestinal: Nausea

Renal: Elevated BUN, azotemia


Stability

 Avoid excessive heat, do not freeze; when combined with parenteral amino acid solutions, cysteine is relatively unstable; it is intended to be added immediately prior to administration to the patient; infusion of the admixture should begin within 1 hour of mixing or refrigerated until use; stable 24 hours in PN solution; opened vials must be used within 4 hours of entry


Mechanism of Action

 Cysteine is a sulfur-containing amino acid synthesized from methionine via the transulfuration pathway. It is a precursor of the tripeptide glutathione and also of taurine. Newborn infants have a relative deficiency of the enzyme necessary to affect this conversion. Cysteine may be considered an essential amino acid in infants.


Dosage

 Neonates and Infants: I.V.: Added as a fixed ratio to crystalline amino acid solution: 40 mg cysteine per g of amino acids; dosage will vary with the daily amino acid dosage (eg, 0.5-2.5 g/kg/day amino acids would result in 20-100 mg/kg/day cysteine); individual doses of cysteine of 0.8-1 mmol/kg/day have also been added directly to the daily PN solution; the duration of treatment relates to the need for PN; patients on chronic PN therapy have received cysteine until 6 months of age and in some cases until 2 years of age


Administration

 Parenteral: Use only after dilution into PN solution; dilute with amino acid solution in a ratio of 40 mg cysteine to 1 g amino acid: eg, 500 mg cysteine is added to 12.5 g (250 mL) of 5% amino acid solution


Monitoring Parameters

 BUN, ammonia, electrolytes, pH, acid-base balance, serum creatinine, liver function tests, growth curve


Additional Information

 Addition of cysteine to PN solutions enhances the solubility of calcium and phosphate by lowering the overall pH of the solution.


Dental Health: Effects on Dental Treatment

 No significant effects or complications reported


Dental Health: Vasoconstrictor/Local Anesthetic Precautions

 No information available to require special precautions


Dosage Forms

 Injection, solution, as hydrochloride: 50 mg/mL (10 mL, 50 mL)


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