Pen Injector
A reusable or disposable injection device shaped like a pen that holds a multi-dose cartridge and allows the patient to dial their prescribed dose. Pen injectors are the most common delivery device for GLP-1 receptor agonists, insulin, and growth hormone, combining ease of use with precise dose selection.
Technical Context
Pen injectors consist of a pen body (housing), a cartridge (containing multi-dose peptide solution or suspension), a dose-setting mechanism (dial), and a disposable pen needle (attached before each injection). Cartridges typically contain 1.5mL or 3mL of drug product. The dose dial allows selection of specific doses — essential for drugs requiring titration (semaglutide: 0.25, 0.5, 1.0, or 2.0mg). After setting the dose, pressing the injection button drives the plunger forward, expelling the dose through the pen needle. Patients are instructed to hold the needle in place for several seconds after injection to ensure complete dose delivery. Modern pens include electronic dose memory features and Bluetooth connectivity for dose tracking apps.