A catheter handpiece apparatus and method for delivering a desired dose with minimal potential for contamination of the injected substance and rapid, accurate delivery of the desired dose. In one embodiment, a carriage assembly affixed to an inner lumen is slidably located within a handpiece housing equipped with an outer lumen. The carriage assembly receives a dose carpule. An actuator knob cocks the carriage assembly and a spring-powered actuator mechanism. After the catheter is maneuvered to a desired injection site and a desired dose is set, depressing a first trigger causes the inner lumen tip to extend beyond the outer lumen into the injection site. Depressing a second trigger causes the actuator mechanism to push the desired dose from the dose carpule through the inner lumen into the injection site. A second embodiment provides a catheter handpiece with a carriage assembly cocking lever and an operator-powered dose delivery mechanism.