Cysteamine bitartrate

Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

Cystagon (Orphan Australia)
50 mg and 150 mg capsules

Indication: nephropathic cystinosis
Cystinosis is inherited as an autosomal recessive trait. The body is unable to remove cystine from lysosomes, so it accumulates. The accumulation of cystine crystals can affect many organs, particularly the kidney (Fanconi's syndrome). Giving patients cysteamine can slow the deterioration in renal function; however, it is unpalatable and cysteamine bitartrate has been developed as an alternative.

Cysteamine, which was once used in the treatment of paracetamol poisoning, works by reacting with the cystine in lysosomes. The reaction produces cysteine which can be transported out of affected cells.

As cystinosis is a rare condition, it is difficult to study its treatment in adequate numbers of patients. Studies that have been done tend to have used cysteamine hydrochloride rather that cysteamine bitartrate. In general, cysteamine can be expected to reduce the concentration of cystinein white blood cells. If these concentrations can be near normal, renal function and growth are likely to be maintained. It is not clear how long this benefit will last and whether or not renal transplant can be avoided.

The children start on a low dose which is gradually increased. The concentration of cystine in the leucocytes is measured 5-6 hours after a dose. Once a maintenance dose is established, cystine concentrations should be checked every 3 months.

The most common adverse effects occur in the gastrointestinal tract. They include vomiting, anorexia and diarrhoea.

As the number of 'orphan' drugs is likely to increase, they will pose a challenge to systems of drug regulation. It will be difficult to balance the need for such drugs with the relative lack of data to support their use.