Title:  Medication delivery pen

United States Patent:  6,277,099

Assignee:  Becton, Dickinson and Company (Franklin Lakes, NJ)

Filed:  August 6, 1999

A medication delivery pen includes a housing having an actuator disposed in the proximal end of the housing for setting and administering a dosage of medication, a medication-containing cartridge assembly having a cartridge with a pierceably sealed distal end, an open proximal end removably attachable to the distal end of the housing, and a piston in sliding, fluid tight engagement within the cartridge. A drive mechanism is coupled between the actuator and the cartridge to exert an axial force on the piston to inject the set dosage of medication. The actuator triggers the drive mechanism to administer the injection of medication held in the cartridge and a processor is coupled to the actuator to determine a value equal to the dosage set by the actuator. The drive mechanism includes a pair of half nuts in rotational engagement with the actuator, a non-rotatable lead screw having a distal end for exerting the axial force on the piston to inject the set dosage of medication, a proximal end, and threads extending between the proximal and distal ends. The nuts open and close radially to selectively engage with the threads of the lead screw for axially advancing along the lead screw upon rotation of the actuator.

SUMMARY OF THE INVENTION

The subject invention relates to an electronic medication delivery pen which has mechanical features that reduce the amount of priming that must be performed, eliminates the need for an interlock mechanism to prevent overdosing, increases the reliability of the drive mechanism, and ensures that the full dosage of medication is delivered upon injection.

In accordance with the present invention, a medication delivery pen includes a housing having opposing proximal and distal ends. An actuator is disposed in the proximal end of the housing for setting and administering a dosage of medication. A medication-containing cartridge assembly includes a cartridge having a pierceably sealed distal end, an open proximal end removably attachable to the distal end of the housing, and a piston in sliding, fluid tight engagement within the cartridge. A drive mechanism is coupled between the actuator and the cartridge to exert an axial force on the piston to inject the set dosage of medication. The actuator triggers the drive mechanism to administer the injection of medication held in the cartridge. A processor is coupled to the actuator to determine a value equal to the dosage set by the actuator and a memory device is coupled to the processor to store the dosage value determined by the processor. The drive mechanism includes a pair of half nuts in rotational engagement with the actuator, a non-rotatable lead screw having a distal end for exerting the axial force on the piston to inject the set dosage of medication, a proximal end, and threads extending between the proximal and distal ends. The nuts open and close radially to selectively engage with the threads of the lead screw for axially advancing along the lead screw upon rotation of the actuator.

Because the half nuts advance along the lead screw, thus eliminating the need for a rotatable lead screw, the inventive medication delivery pen advantageously reduces the likelihood that components will improperly engage with one another due to their misalignment during operation.

In accordance with another aspect of the invention, a first spring is provided in the housing to bias the lead screw in the distal direction so that the lead screw remains in contact with the cartridge piston when the cartridge assembly is attached to the housing. This feature advantageously reduces the amount of priming that must be performed upon installation of a new cartridge.

In accordance with yet another aspect of the invention, a release nut is provided to engage with the lead screw at a location distally of the half nuts. The release nut is located at a first axial position when the cartridge is attached to the housing and a second axial position when the cartridge is removed from the housing. The release nut activates the processor so that the processor is in an operational state when the release nut is in the first axial position and is in a disabled state when the release nut is in the second axial position. Accordingly, since the pen will be automatically disabled when the cartridge is not properly inserted, the present invention advantageously avoids the need for a separate interlock mechanism.

In accordance with yet another aspect of the invention, at least one dial stop element couples the distal ends of the half nuts to the release nut so that the axial travel of the half nuts is limited to a minimum value, thereby limiting the injectable dosage of medication to a minimum value. Likewise, the dial stop element may also limit the axial travel of the half nuts to a maximum value, thereby limiting the injectable dosage of medication to a maximum value.

In accordance with another aspect of the invention, the actuator includes a rotatable knob and a plunger in rotational engagement with the rotatable knob. The plunger has a plurality of axial splines located on its distal end that define slots therebetween. The housing has at least one radially extending boss that aligns with the slots in select rotational states of the plunger to allow axial motion of the plunger and misaligns with the slots in other rotational states of the plunger to prevent axial motion of the plunger. The select rotational states of the plunger aligning with the boss correspond to an integer number of dosage units. This feature of the invention advantageously ensures that the user can only inject a whole number of units of medication.

Claim 1 of 23 Claims

What is claimed is:

1. A medication delivery pen, comprising:

a housing having opposing proximal and distal ends;

an actuator disposed in the proximal end of the housing for setting and administering a dosage of medication;

a medication-containing cartridge assembly having a cartridge with a pierceably sealed distal end, an open proximal end removably attachable to the distal end of the housing, and a piston in sliding, fluid tight engagement within said cartridge;

a drive mechanism coupled between the actuator and the cartridge to exert an axial force on the piston to inject the set dosage of medication, wherein the actuator triggers the drive mechanism to administer the injection of medication held in the cartridge;

a processor coupled to the actuator to determine a value equal to the dosage set by the actuator; and

means for disabling the processor when the cartridge is removed or not properly inserted in the housing,

wherein the drive mechanism includes: a pair of half nuts in rotational engagement with the actuator; a non-rotatable lead screw having a proximal end, a distal end for exerting the axial force on the piston to inject the set dosage of medication, and a set of threads extending between the proximal and distal ends, said half nuts being radially openable and closable to selectively engage with the threads of the lead screw for axially advancing along the lead screw upon rotation of the actuator.

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