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Indications and Dosage
Oral
Nutritional deficiency Adult: 0.5-1.5 g daily with at least 6-8 glasses of water to prevent cystine renal stones. Parenteral Nutritional deficiency Child: As TPN for infants For use only after dilution in a crystalline amino acid solution. Each 0.5 g should be combined aseptically with 12.5 g of amino acids. Dilute the admixture with 250 ml of dextrose 50% or such lesser volume as indicated.
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Special Precautions
Avoid in children, pregnancy, lactation, nephrolithiasis. Renal impairment.
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Adverse Reactions
May increase zinc absorption. Ascorbic acid may inhibit the oxidation of L-cysteine to L-cystine.
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Lab Interference
Produce a false-positive result in the nitroprusside test for ketone bodies used in diabetes & suspected hepatocellular injury.
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Action
Description: Cysteine is synthesized from methionine via the trans-sulfuration pathway in the adult, but newborn infants lack the enzyme, cystathionase, necessary to effect this conversion. It also serves as a major precursor for synthesis of glutathione in certain conditions eg acetaminophen overdose which deplete hepatic glutathione & subject the tissues to oxidative stress resulting in loss of cellular integrity.
Pharmacokinetics: Absorption: Following ingestion, some cysteine is oxidised to cystine & both are absorbed from the small intestine by active-transport processes. Cysteine absorption is largely sodium-dependent, while cysteine is absorbed by a sodium-independent transport system. Distribution: Distributed to the liver. Unmetabolised cysteine enters the systemic circulation and distributes to various body tissues. Metabolism: Metabolised hepatically to protein, glutathione, taurine & sulfate. |
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MIMS Class
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