When administering a subcutaneous or an intramuscular injection, one should gently pull back on the plunger to

Ascertain that the needle is not in a blood vessel

Explanation:

In subcutaneous administration, a small amount of liquid medicine is injected into the subcutaneous tissue below the patient's skin. This type of injection is indicated for the administration of anticoagulants, hypoglycemic agents and vaccines (anti-rabies and anti-measles). The drug is slowly absorbed into the nearby capillaries, giving prolonged effect of the drug.  Intramuscular injections deposit the medication deep into the muscle tissue, which is highly vascularized and can absorb rapidly. This route of administration provides rapid systemic action and absorption of relatively large doses.

Regardless of whether the injection is subcutaneous or intramuscular, one should carefully pull the plunger to make sure that the needle is not in a blood vessel and does not cause bleeding.

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