The Deadly Swarm.

A group of friends, in dire need of cash, find themselves at a secluded medical trial retreat in what seems like an easy way to earn money but quickly turns into their worst nightmare. Under the guise of a harmless experiment run by the enigmatic Dr. Feldman, they are about to face a horror they never imagined. Unbeknownst to them, Dr. Feldman has unleashed a new terror: a swarm of genetically engineered killer flies, with an insatiable thirst for human blood.