Levemir? FlexPen? is a pre-filled, colour-coded, disposable pen containing insulin detemir. Insulin detemir is usually injected with the evening meal or at bedtime. This insulin must be injected, usually once or twice daily. If you are using it twice a day, inject your first dose in the morning and your second dose with the evening meal, at bedtime, or 12 hours after the morning dose, as directed by your doctor.