Processes and devices provide parenteral delivery of therapeutic fluids, in particular high-viscosity therapeutic fluids (e.g., protein therapeutics), by a chemical reaction that generates a gas. A device may include a first actuation chamber containing a first reagent, a second reaction chamber containing a second reagent, and a third therapeutic fluid chamber containing the therapeutic fluid. In a loaded configuration, a plunger separates the first chamber from the second chamber. In a delivery configuration, the plunger allows the first reagent from the first chamber to communicate and react with the second reagent from the second chamber. The generated gas acts upon a plunger to deliver the therapeutic fluid from the third chamber.