Embodiments may include a method of delivering a drug. The method may include removing or releasing a structure from a patch-pump assembly. The patch-pump assembly may include a sealed prefilled drug-reservoir, a fluid passageway, a cannula-containing assembly, and a penetrator. The method may also include penetrating the sealed prefilled drug-reservoir containing the drug to establish fluid communication between the sealed prefilled drug-reservoir and a fluid passageway by removing or releasing the structure. The method may further include flowing the drug from the prefilled drug-reservoir to the fluid passageway. In addition, the method may include flowing the drug from the fluid passageway to a cannula-containing assembly. Furthermore, the method may include delivering the drug subcutaneously to a subject using the cannula-containing assembly.