What is the difference between intravenous (IV) and subcutaneous injection?

From the Guidelines

Intravenous (IV) injection is generally not recommended for routine insulin administration, whereas subcutaneous injection is the preferred method, with the abdomen having the fastest rate of absorption, followed by the arms, thighs, and buttocks 1. When considering the differences between IV and subcutaneous injection, it's essential to prioritize the method that provides the most stable and consistent absorption rates.

• Subcutaneous injection allows for slower absorption, which can help maintain a steady insulin level, reducing the risk of hypoglycemia and hyperglycemia.
• The rate of absorption from subcutaneous injection sites can be influenced by factors such as exercise, which increases blood flow to the skin, and areas of lipohypertrophy, which can show slower absorption 1.
• In contrast, IV injection delivers the substance directly into the bloodstream, resulting in faster absorption, but this method is not typically recommended for routine insulin administration due to the potential for rapid changes in blood glucose levels.
• It's crucial to rotate injection sites to prevent lipohypertrophy or lipoatrophy, with rotation within one area (e.g., the abdomen) recommended rather than rotating to a different area with each injection 1.
• The choice between IV and subcutaneous injection ultimately depends on the specific clinical context, with subcutaneous injection being the preferred method for routine insulin administration due to its more stable and consistent absorption rates.

From the FDA Drug Label

Heparin sodium is not effective by oral administration and should be given by intermittent intravenous injection, intravenous infusion, or deep subcutaneous (intrafat, i.e., above the iliac crest or abdominal fat layer) injection. The intramuscular route of administration should be avoided because of the frequent occurrence of hematoma at the injection site. When heparin is given by continuous intravenous infusion, the coagulation time should be determined approximately every four hours in the early stages of treatment. When the drug is administered intermittently by intravenous injection, coagulation tests should be performed before each injection during the early stages of treatment and at appropriate intervals thereafter. After deep subcutaneous (intrafat) injections, tests for adequacy of dosage are best performed on samples drawn four to six hours after the injection.

The main difference between intravenous (IV) and subcutaneous injection is the route of administration and the timing of coagulation tests.

• Intravenous injection is given directly into a vein, and coagulation tests should be performed before each injection.
• Subcutaneous injection is given under the skin, and coagulation tests should be performed 4 to 6 hours after the injection. Key points to consider:
• Administration route: IV injection is given into a vein, while subcutaneous injection is given under the skin.
• Coagulation testing: IV injection requires coagulation tests before each injection, while subcutaneous injection requires tests 4 to 6 hours after the injection. 2

From the Research

Difference between Intravenous (IV) and Subcutaneous Injection

• Intravenous (IV) injection involves administering medication directly into a vein, typically in the arm, whereas subcutaneous (SC) injection involves administering medication under the skin, but not into a muscle or vein 3.
• The choice between IV and SC injection depends on various factors, including the type of medication, patient characteristics, and the desired effect of the treatment 3, 4.
• Some medications are better suited for SC administration, such as trastuzumab, rituximab, and antitumor necrosis factor medications, while others are better suited for IV administration, such as ketamine and vitamin K1 3.
• Patient preference and pharmacoeconomics also play a role in the choice between IV and SC injection, with SC injections often being more convenient and less invasive than IV injections 4.
• The safety and efficacy of IV and SC injections are also important considerations, with IV injections typically being more rapid and effective, but also carrying a higher risk of adverse reactions 5, 6.
• Subcutaneous antibiotic therapy is also a viable option in certain situations, such as in patients with poor venous access or swallowing disorders, although further clinical studies are needed to assess its benefits and risks 6.
• In palliative care, subcutaneous injection can be a useful route of administration for certain medications, including midazolam, morphine, and fentanyl, although further studies are needed to confirm its safety and efficacy 7.