Sanofi and partner Isis Pharmaceuticals are celebrating after regulators in the USA gave the green light to Kynamro for an inherited cholesterol disorder.

The US Food and Drug Administration has approved Kynamro (mipomersen), a 200mg weekly subcutaneous injection for patients with homozygous familial hypercholesterolaemia. It can be used as an adjunct to lipid-lowering medications and diet.

HoFH is a rare inherited condition that makes the body unable to remove LDL, or 'bad' cholesterol, from the blood, causing abnormally high levels of circulating LDL cholesterol. In the USA, HoFH occurs in one in one million individuals and sufferers often face heart attacks and death  before the age of 30.

However, Kynamro will carry a boxed warning "on the serious risk of liver toxicity", the FDA said, because it is associated with liver enzyme abnormalities and accumulation of fat in the liver. It has been approved with a risk evaluation and mitigation strategy (REMS) and the agency is also insisting on four postmarketing studies.

Isis chief executive Stanley Crooke said Kynamro is "the first systemic antisense drug to reach the market and is the culmination of two decades of work to create a new, more efficient drug technology platform". The approval triggers a $25 million milestone payment to Isis.

The approval comes a month or so after advisors to the European Medicines Agency recommended against approving Kynamro after noting that a high proportion of patients stopped taking the drug within two years, mainly due to side effects such as flu-like symptoms, injections site reactions and liver toxicity. At the time, Sanofi's Genzyme unit said it planned to request a re-examination.

The approval comes a month after the FDA approved Aegerion Pharmaceuticals' HoFH drug Juxtapid (lomitapide).