The present invention provides a device for injection of formulations into a patient. In one embodiment the injection is sub-cutaneous. The device is convenient for injecting viscous formulations that would otherwise clog conventional injection devices, for example formulations containing microspheres, suspensions, and other viscous substances. Generally, the device features a needle for piercing the skin, an internal chamber for holding and transmitting fluid, a plunger for applying pressure to the internal chamber, a switch for triggering withdrawal of the needle, a sheath at least partially encompassing the needle and having a flow path within the sheath, and a spring that expands when the switch is triggered, and which thereby at least partially withdraws the needle from the sheath.