A patch injector (10) for parenteral administration of a drug to a drug recipient has a drug-cartridge module (14) attached to a power-pack module (12) and to a drug-recipient interface module (16). A compressed, elastic power element (18) disposed in the power-pack module (12) is coupled to a plunger (30) movably disposed in a drug reservoir (22) in the drug-cartridge module (14). An injection needle (24) at the distal end of the drug reservoir (22) is oriented orthogonal to the drug reservoir (22) and generally toward a skin-contact surface (28) extending parallel to the longitudinal drug-reservoir axis (22A). The power element (18) is configured to displace the plunger (20) distally into the drug reservoir (22) and to move the injection needle (24) toward the skin-contact surface (28) when the power element (18) expands distally along the drug-reservoir axis (22A).
