Difference Between Subcutaneous Intramuscular and Intravenous Injection

The key difference between subcutaneous intramuscular and intravenous injection is that in subcutaneous injection, the drug is injected under the skin, while in intramuscular injection,  the drug is delivered deep into the muscles, and in intravenous injection, the drug is given directly into a vein.

Subcutaneous, intramuscular, intravenous and intradermal injections are four different types of injections that deliver drugs. As the names suggest, subcutaneous tissue is selected in subcutaneous injection, whereas a muscle is selected in intramuscular injection, and a vein is selected in intravenous injection. Intravenous injection delivers the drug immediately into the blood when compared to intramuscular and subcutaneous injections.

CONTENTS

1. Overview and Key Difference
2. What is Subcutaneous Injection
3. What is Intramuscular Injection
4. What is Intravenous Injection
5. Similarity Between Subcutaneous Intramuscular and Intravenous Injection
6. Side by Side Comparison – Subcutaneous vs Intramuscular vs Intravenous Injection in Tabular Form
7. Summary

What is Subcutaneous Injection?

Subcutaneous injection is a type of injection administered under the skin into the tissue layer located between the skin and the muscle. In other words, subcutaneous injection is administered into the subcutis or subcutaneous tissue. Subcutis is the layer of skin that lies below the dermis and epidermis. The drug given by the subcutaneous injection is absorbed slowly over a period of time since the subcutaneous layer does not contain a lot of blood vessels. The absorption is slower than both intramuscular and intravenous injections.

Insulin is the most commonly administered subcutaneous injection. Heparin and monoclonal antibodies are also injected subcutaneously. These medications cannot be administered orally since they are too large to be absorbed in the intestine. Prior to the administration of the subcutaneous injection, the area of the skin should be sterilized. When selecting an injection site, specific sites with inflammation or damaged skin should be avoided. Figure 01 shows the injections sites for subcutaneous injection. Some subcutaneous injections may leave a specific scar, while some injections may cause fever or rash.

What is Intramuscular Injection?

Intramuscular injection is a type of injection that delivers a drug into a muscle. A muscle is rich with blood vessels. Hence, the absorption of the drug is faster than in a subcutaneous injection. The deltoid muscle of the upper arm and the gluteal muscle of the buttock are the common intramuscular injection sites. In infants, the vastus lateralis muscle of the thigh is the commonly used intramuscular injection site. When selecting a site for intramuscular injection, the muscles with signs of infection or muscle atrophy should be avoided.

Disadvantages related to intramuscular injection involve the requirement of skill and technique, pain from injection, anxiety or fear, and difficulty in self-administration. However, compared to intravenous injection, intramuscular injection is less invasive, can be done within less time, and has a large injection site (a muscle). Most inactivated vaccines are given as IM vaccines.

What is Intravenous Injection?

Intravenous injection is a type of injection that delivers a drug into a vein. It is the fastest way of giving medication. The needle is inserted into a vein, and then the drug is directly delivered into the bloodstream. Since the drug enters the blood immediately, the effect of the drug is quick in comparison to other injections.

Intravenous injections can be used for the administration of nutrition in parenteral nutrition. They may also be used for recreational drugs. The common side effects of intravenous injections are infections and inflammation. An IV catheter, a peripheral intravenous catheter or a central venous catheter can be used in repeated intravenous injections.

What are the Similarities Between Subcutaneous Intramuscular and Intravenous Injection?

• Subcutaneous, intramuscular and intravenous injection are three types of techniques used to deliver a drug to a patient.
• All three techniques use a needle.
• The injection site must be cleaned prior to all three types of injections.

What is the Difference Between Subcutaneous Intramuscular and Intravenous Injection?

The subcutaneous tissue layer is the injection site of subcutaneous injection, while a muscle is the injection site of intramuscular injection. The site of intravenous injection, on the other hand, is a vein. So, this is the key difference between subcutaneous intramuscular and intravenous injection. Generally, the needle is inserted at an angle of 45⁰ during the subcutaneous injection. The angles of needle insertion are 90⁰ and 25⁰ for intramuscular and intravenous injections, respectively. Thus, this is another significant difference between subcutaneous intramuscular and intravenous injection.

Below is a summary of the difference between subcutaneous intramuscular and intravenous injection in tabular form.

Summary – Subcutaneous vs Intramuscular vs Intravenous Injection

The subcutaneous injection delivers a drug into the subcutaneous tissue under the skin. Meanwhile, the intramuscular injection delivers the drug into a muscle. But, the intravenous injection delivers the drug directly into a vein. Hence, this is the key difference between subcutaneous intramuscular and intravenous injection. The drug delivered via intravenous injection enters the blood immediately in comparison to the other two injections.

Reference:

1. “Administering Drugs via a Subcutaneous Injection.” Nursing Times, 10 Feb. 2021, Available here.
2. “Intramuscular Injection.” Wikipedia, Wikimedia Foundation, 7 Jan. 2021, Available here.
3. Case-Lo, Christine. “About Intravenous Medication Administration.” Healthline, Healthline Media, 30 Nov. 2016, Available here.

Image Courtesy:

1. “Injection Sites Subcutaneous” By BruceBlaus – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Im-deltoid” By British Columbia Institute of Technology (BCIT). Download this book for free here (CC BY 4.0) via Commons Wikimedia
3. “ICU IV 1” By Calleamanecer – Own work (CC BY-SA 3.0) via Commons Wikimedia