The invention relates to a pump unit (1), replaceably attachable to a reusable backend (6) of an injection arrangement (7) for delivering a liquid medicament, the pump unit (1) comprising a medicament inlet (1.1), a medicament outlet (1.2) and a pump (2) for delivering the liquid medicament from the inlet (1.1) to the outlet (1.2), wherein a medicament container (4) is arranged in the pump unit (1), wherein a fluid communication between the medicament container (4) and the pump (2) is establishable when the pump unit (1) is attached to the reusable backend (6).
