Controlled Dispense Syringe

What is this patent about?

’950 is related to the field of prefilled syringes, specifically addressing the problem of inadvertently dispensing therapeutic product along with air (headspace) when removing air from the syringe prior to injection. This is a common issue because prefilled syringes often contain a small amount of air to account for thermal expansion and manufacturing tolerances. Current methods require healthcare providers to carefully expel the air, risking product wastage or injecting air into the patient.

The underlying idea behind ’950 is to mechanically limit the travel of the plunger within the syringe barrel, preventing the expulsion of the air bubble. This is achieved by incorporating a stop feature on the plunger rod that physically prevents the plunger from fully traversing the barrel. The stop is positioned such that when it contacts the end of the syringe barrel, a defined volume of air remains trapped within the syringe.

The claims of ’950 focus on a syringe with a barrel, a stopper, a plunger rod, and an outwardly projecting stop . The key element is the stop's configuration to engage the end surface of the barrel's open proximal end. This engagement halts the plunger's movement during dispensing, ensuring that the headspace remains within the barrel. The claims also cover a method of filling such a syringe and a method of dispensing a predetermined amount of fluid therapeutic product from the syringe.

In practice, the syringe is pre-filled with the therapeutic product and a defined amount of headspace. The plunger rod is then inserted, with the stop positioned to allow the plunger to travel only far enough to dispense the liquid medication, leaving the air bubble behind. The predetermined length between the stop and the plunger's distal end dictates the dispensed volume, ensuring accurate dosing without air injection. This eliminates the need for healthcare providers to manually remove air, reducing the risk of medication waste and improving injection safety.

This design differentiates itself from prior approaches by integrating a physical stop mechanism directly into the plunger rod. Traditional syringes rely on the user's judgment to avoid expelling air, which is prone to error. By contrast, ’950 provides a fixed, mechanical limit that guarantees a consistent and accurate dose delivery, regardless of the user's technique. This is particularly beneficial for self-injection scenarios where patients may lack the training or dexterity to accurately remove air from the syringe.