Cysteamine is a chemical compound that can be biosynthesized in mammals, including humans, by the degradation of coenzyme A. The intermediate pantetheine is broken down into cysteamine and pantothenic acid. It is the biosynthetic precursor to the neurotransmitter hypotaurine. It is a stable aminothiol, i.e., an organic compound containing both an amine and a thiol functional groups. Cysteamine is a white, water-soluble solid. It is often used as salts of the ammonium derivative + including the hydrochloride, phosphocysteamine, and bitartrate. As a medication, cysteamine, sold under the brand name Cystagon among others, is indicated to treat cystinosis.
Medical uses
Cysteamine is used to treat cystinosis. It is available by mouth and in eye drops.
Adverse effects
Topical use
The most important adverse effect related to topical use might be skin irritation.
Oral use
The label for oral formulations of cysteamine carry warnings about symptoms similar to Ehlers-Danlos syndrome, severe skin rashes, ulcers or bleeding in the stomach and intestines, central nervous symptoms including seizures, lethargy, somnolence, depression, and encephalopathy, low white blood cell levels, elevated alkaline phosphatase, and idiopathic intracranial hypertension that can cause headache, tinnitus, dizziness, nausea, double or blurry vision, loss of vision, and pain behind the eye or pain with eye movement. The main side effects are Ehlers-Danlos syndrome, severe skin rashes, ulcers or bleeding in the stomach and intestines, central nervous symptoms, low white blood cell levels, elevated alkaline phosphatase, and idiopathic intracranial hypertension. IIH can cause headache, ringing in the ears, dizziness, nausea, blurry vision, loss of vision, and pain behind the eye or with eye movement. Additional adverse effects of oral cysteamine include bad breath, skin odor, vomiting, nausea, stomach pain, diarrhea, and loss of appetite. The drug is in pregnancy category C; the risks of cysteamine to a fetus are not known but it harms babies in animal models at doses less than those given to people. For eye drops, the most common adverse effects are sensitivity to light, redness, and eye pain, headache, and visual field defects.
Interactions
There are no drug interactions for normal capsules or eye drops, but the extended release capsules should not be taken with drugs that affect stomach acid like proton pump inhibitors or with alcohol, as they can cause the drug to be released too quickly. It doesn't inhibit any cytochrome P450 enzymes.
Pharmacology
People with cystinosis lack a functioning transporter which transports cystine from the lysosome to the cytosol. This ultimately leads to buildup of cystine in lysosomes, where it crystallizes and damages cells. Cysteamine enters lysosomes and converts cystine into cysteine and cysteine-cysteamine mixed disulfide, both of which can exit the lysosome.
Biological function
Cysteamine also promotes the transport of L-cysteine into cells, that can be further used to synthesize glutathione, which is one of the most potent intracellular antioxidants. Cysteamine is used as a drug for the treatment of cystinosis; it removes cystine that builds up in cells of people with the disease.
History
First evidence regarding the therapeutic effect of cysteamine on cystinosis dates back to 1950s. Cysteamine was first approved as a drug for cystinosis in the US in 1994. An extended release form was approved in 2013.
Society and culture
It is approved by the U.S. Food and Drug Administration and the European Medicines Agency. In 2013, the regular capsule of cysteamine cost about $8,000 per year; the extended release form that was introduced that year was priced at $250,000 per year.
