Ultra-Rare Disease gets New FDA-Approved Therapy Intended to Make Treatment more Tolerable

US regulators have approved a new product intended to treat an extremely rare disease known as nephropathic cystinosis, a disease that affects fewer than 3,000 patients worldwide and causes a buildup of cysteine in the body that can be fatal if not treated early in life.

The drug, Procysbi, treats the condition by providing a delayed-release formulation that delivers cysteamine to patients in a new method. The drug's sponsor, Raptor Pharmaceuticals, explains on its website that cysteamine is effective at treating and preventing the escalation of the disease, but that patient adherence was "challenging due to frequent dosing and gastrointestinal side effects."

That's where Procysbi reportedly stands to benefit patients the most, Raptor explains. Because the drug is coated by an enteric microbead formulation, it is able to deliver cysteamine more efficiently and in a way that is better tolerated by patients.

Raptor submitted an application for approval to FDA in March 2012 based on clinical data obtained from a non-inferiority trial of Procysbi and Cystagon, a drug approved to treat the condition in 1994.

"On average, the peak white blood cell (WBC) cystine level measured in patients treated with Cystagon was 0.54 ± 0.05 nmol of half cystine/mg protein," Raptor explained. "By comparison, the average peak WBC cystine level measured in patients treated with RP103 was 0.62 ± 0.05 nmol of half cystine/mg protein. The mean difference was 0.08 nmol of half cystine/mg protein, with a 95.8% confidence interval of 0.00-0.16 (one sided p=0.021)."

In other words, the drug showed that it was clinically superior to Cystagon, though the drug was tested in just 41 patients.

The drug's more common side effects were nausea, bad breath, abdominal pain, constipation, indigestion, headache, upset stomach, drowsiness and dizziness. Less common but more serious risks include ulcers, intestinal bleeding, seizures, altered mental state, rashes and allergic reactions.

The US Food and Drug Administration (FDA), which approved the drug on 30 April 2013, added that approximately 500 patients in the US have the disease and could benefit from the drug.

FDA approves Procysbi for rare genetic condition