In a move that may hinder companies looking to develop generic Tyvaso, the combination product’s developer is asking the FDA to impose stringent approval requirements on generic competitors.

A citizen petition filed on United Therapeutics’ behalf contends that generic versions of the product — a drug-device combination designed to treat pulmonary arterial hypertension — should not be allowed until they successfully demonstrate efficacy and safety beyond the normal requirements of an ANDA. United Therapeutics says this is needed due to ensure patient safety, since combination products are significantly more complicated to develop than drugs.