Exemplary embodiments provide wearable automatic injection devices for administering a therapeutic agent to a patient's body at fast, controlled rates, for example, in a single fast bolus. Exemplary embodiments also provide methods for assembling wearable automatic injection devices for administering a therapeutic agent to a patient at fast, controlled rates. Exemplary embodiments also provide methods for using wearable automatic injection devices for administering a therapeutic agent to a patient at fast, controlled rates.