Medication administration device

A medication administration device comprising:

• a casing having a hollow cylindrical shape;
• a syringe comprising:
• a barrel housed in the casing and filled with a medication, and
• a puncture needle in fluid communication with the barrel and configured to administer the medication to a living body;
• a needle cover having a hollow cylindrical shape, disposed inside the casing, covering a distal end of the syringe, and configured to be displaced toward a proximal end relative to the casing when the needle cover is pressed against a puncture target;
• a plunger disposed inside the casing and configured to eject the medication through the puncture needle upon movement of a distal end of the plunger inside the barrel;
• and
• a cap detachably disposed at a distal end of the needle cover, and configured to be detached before the puncture needle punctures the puncture target;
• wherein:
• an inner peripheral surface of the casing includes at least three guide ribs that extend axially and protrude toward an outer peripheral surface of the plunger that faces the inner peripheral surface of the casing;
• the outer peripheral surface of the plunger includes at least three guide grooves that extend in a moving direction of the plunger, wherein at least a part of each guide rib is inserted into a respective one of the guide grooves;
• and
• between each guide rib and each guide groove, a first clearance is formed in a protruding direction of the guide rib and a second clearance is formed in a direction perpendicular to the protruding direction of the guide rib.

A medication administration device comprising:

• a casing having a hollow cylindrical shape;
• a syringe comprising:
• a barrel housed in the casing and filled with a medication, and
• a puncture needle in fluid communication with the barrel and configured to administer the medication to a living body;
• a needle cover having a hollow cylindrical shape, disposed inside the casing, covering a distal end of the syringe, and configured to be displaced toward a proximal end relative to the casing when the needle cover is pressed against a puncture target;
• a plunger disposed inside the casing and configured to eject the medication through the puncture needle upon movement of a distal end of the plunger inside the barrel;
• and
• a cap detachably disposed at a distal end of the needle cover, and configured to be detached before the puncture needle punctures the puncture target;
• wherein:
• an outer peripheral surface of the plunger includes at least three guide ribs that extend axially and protrude toward an the inner peripheral surface of the casing that faces the outer peripheral surface of the plunger;
• the inner peripheral surface of the casing includes at least three guide grooves that extend in a moving direction of the plunger, wherein at least a part of each guide rib is inserted into a respective one of the guide grooves;
• and
• between each guide rib and each guide groove, a first clearance is formed in a protruding direction of the guide rib and a second clearance is formed in a direction perpendicular to the protruding direction of the guide rib.