The autoinjector includes a housing extending along longitudinal axis A and configured to receive a medical container having a barrel defining a reservoir for containing a medical product, said barrel having a distal end provided with an injection needle and an opened proximal end configured to receive a plunger rod for pushing a stopper arranged inside the barrel. A needle cover is coupled to and axially movable with respect to said housing between a first extended position, a retracted position, and a second extended position. A cam is rotationally movable around the longitudinal axis A with respect to said housing between a blocking position and a release position, rotation of said cam from the blocking to the release position being caused by the needle cover moving from the first extended position to the retracted position. A plunger rod axially movable inside the housing between an initial position and an injection end position distally located relative to said initial position, under the action of biasing means configured for biasing the plunger rod in a distal direction towards the injection end position. A retainer is arranged for maintaining the plunger rod in the initial position against the action of the biasing means, the retainer being resiliently deformable between a rest position in which the retainer axially abuts against the plunger rod for blocking the plunger rod in said initial position, and a deformed position in which the retainer radially deflect to allow the plunger rod to move in the distal direction. A lock ring is arranged inside the housing for locking the retainer in the rest position. The lock ring is rotatable around the longitudinal axis A between a locking position, in which the lock ring prevents deformation of the retainer, and an unlocking position, in which the lock ring allows for deformation of the retainer, rotation of the lock ring from the locking to the unlocking position being caused by the cam moving from the blocking position to the release position.

Syringe assemblies are provided including a partially pre-filled syringe barrel and a plunger rod that incorporates one or more retention elements on the plunger rod that prevents solution from entering a non-sterile area of the syringe when the plunger rod is pulled back. Methods to manufacture a sterilized partially-filled pre-fill syringe assembly are also disclosed.