Medication Summary
The medications required to correct abnormalities due to the renal loss of various substances are listed in Medical Care. In this section, the use of drugs designed to correct the causes of the syndrome are addressed. These drugs are confined to only 2 of the conditions associated with Fanconi syndrome, cystinosis, and Wilson disease.
Cystine-lowering Agents
Class Summary
Numerous compounds have been found to decrease the levels of cystine in cultured cells, but only a few were proven effective in clinical trials. Prominent among the effective drugs is cysteamine, which has been shown to decrease the tissue levels of cystine, delay the progression of renal disease, and improve linear growth, particularly when treatment is started in children younger than 2 years. However, no effect on the Fanconi syndrome was documented. Cysteamine bitartrate (Procysbi), a delayed-release formula that can be given every 12 hours, is approved by the US Food and Drug Administration (FDA) for management of nephropathic cystinosis in children aged 1 year and older and adults. A randomized controlled crossover trial showed the delayed-release product was safe and effective in reducing WBC cystine levels in patients with cystinosis. [26] Approval for children as young as 1 year is based on a long-term, prospective, open-label study that enrolled 17 people living with nephropathic cystinosis, including 15 children between the ages of 1 and 5 years old, who had not previously been treated with cysteamine therapy. Children enrolled in the study experienced lowering of white blood cell (WBC) cystine levels from poor controlled to well controlled at 12 and 18 month measurements. Additionally, they experienced measured improvements in growth milestones including weight and height. [27]
Cysteamine bitartrate (Procysbi)
Cysteamine bitartrate is used off-label to reduce cystine levels, potentially delaying kidney and other damage associated with Fanconi syndrome. The delayed-release product is used in the management of nephropathic cystinosis, a rare genetic condition, in adults and children aged 1 year or older. It was granted an orphan product designation.
Chelating agents
Class Summary
These agents inhibit a toxin by reacting with it to form less active or inactive complex.
D-penicillamine (Cuprimine, Depen)
Recommended for removal of excess copper in patients with Wilson disease. In vitro, 1 atom of copper combines with 2 molecules of penicillamine; 1 g of penicillamine is expected to cause excretion of approximately 200 mg of copper. In practice, however, only about 1% of this amount excreted. Determine dosage by measurements of urinary copper excretion and free copper in the serum.
Trientine hydrochloride (Syprine)
Use in patients who are intolerant to penicillamine. Clinical experience limited. Unlike penicillamine, does not contain a sulfhydryl group, making it unable to chelate cystine; therefore, use only to treat Wilson disease. Administer on empty stomach and swallow capsules whole with water.
Tyrosine Degradation Inhibitor
Class Summary
In addition to dietary treatment, some advise the use of NTBC, which is a highly potent inhibitor of the enzyme 4-hydroxyphenylpyruvate dioxygenase. NTBC prevents formation of fumarylacetoacetate from tyrosine. Results from an international study initiated in 1992 resulted in US Food and Drug Administration (FDA) approval in January 2002.
An open-label study of 207 patients (aged from birth to 21.7 y, median age 9 mo) revealed an improved overall survival rate compared with historical control subjects (29% vs 88% survival probabilities at 4 y) when patients who were younger than 2 months presented with hereditary tyrosinemia type I and were treated with nitisinone and dietary restriction. [28]
Nitisinone (Orfadin)
Used adjunctively to dietary restrictions to treat hereditary tyrosinemia type-1. Highly potent reversible inhibitor of the enzyme 4-hydroxyphenylpyruvate dioxygenase. Prevents formation of fumarylacetoacetate from tyrosine.
