Subcutaneous Injection | Definition and Patient Education

Subcutaneous Injection

What Is a Subcutaneous Injection?

Some medications cannot be given by mouth because acid and enzymes in the stomach would destroy them. Other methods of administration, like intravenous injection, can be difficult and costly. For small amounts of delicate drugs, subcutaneous injection can be a useful, safe and convenient method of getting a medication into your body.

“Subcutaneous” means under the skin. When you perform a subcutaneous injection, you use a short needle to inject a drug into the tissue layer between the skin and the muscle. This can be used for amounts of medication up to 2 mL. Medication given this way is usually absorbed more slowly than if injected into a vein, sometimes over a period of 24 hours.

Medications Given Using a Subcutaneous Injection

Medications administered using a subcutaneous injection include medications that can be given in small volumes (less than 2 mL). Drugs made of proteins that would be digested in the stomach or other delicate medications than cannot be given in oral form are the most common. Hormones are another example.

Insulin is taken by millions of diabetics all over the world as a subcutaneous injection. Growth hormones are also given this way.

Other drugs that need to be given very quickly can also be administered via subcutaneous injection. Epinephrine comes in an automated injector or “EpiPen” form that is used to quickly treat severe allergic reactions. Some pain medications like morphine and hydromorphone can be given this way as well. Antiemetics like metoclopramide or dexamethasone can be given to a patient that is nauseous and vomiting via the subcutaneous route.

Some vaccines and allergy shots are administered as a subcutaneous injection. Many other vaccines are administered as an intramuscular injection (into muscle tissue rather than subcutaneously).

Patients that cannot take oral medications or who are receiving palliative care may be candidates to receive many different medications as a subcutaneous injection.

How Is a Subcutaneous Injection Given?

The location of injection is important for subcutaneous injections. The drug needs to be injected into the tissue layer just below the skin. Some areas of the body have a more easily accessible layer of tissue, where a needle injected under the skin will not hit muscle, bone, or blood vessels. The abdomen, back or side of the upper arm, and the front of the thigh are the most common sites for injection.

The devices used for subcutaneous injection include syringes with short 5/8-inch-long needles. The width of the needle is usually 25 or 27 gauge. There may be other options for doses more than 1 mL or for children or visually impaired patients.

Vials of liquid medication can be single use or multi-use. Vials can also be filled with a powder to which liquid needs to be added, but this is usually done in a medical or pharmacy setting.

Some medications are available in a “pen” where a short one-use needle is screwed on to the end of a pen-shaped, multi-use vial. The amount of medication needed is then dialed in at the end. As was mentioned earlier, emergency medications like epinephrine can also come in a “pen” form.

You should thoroughly clean your hands before injecting medication subcutaneously. Gloves can also be used. If withdrawing medication from a vial, you need to check to make sure that the correct medication is being given. Professionals often refer to the five “Rights” of medication administration: the right patient, the right medication, the right dose, the right route and the right time. If injecting yourself or a family member, make sure that you are using the correct medication, at the correct dose, at the correct time, and in the right manner. 

Once the correct vial is being used, the cap is removed. If the vial or pen is multi-dose, take a note about when the vial was first opened. The rubber stopper should be cleaned with an alcohol swab. 

A new, sterile syringe will be used each time. The syringe is first filled with air up to the dose level that is about to be used. The cap is removed from the needle. Take care not to touch the needle to keep it sterile. The syringe is pushed through the rubber stopper at the top of the vial. Inject the air into the vial, turn the vial and syringe upside down to the needle points upward and withdraw the correct amount of medication. Practice is important to learn to remove any bubbles out of the syringe with tapping.

A pen needle is a more simple procedure of attaching the pen needle to the pen vial. A prime dose is loaded and expelled (usually 2 units or 0.02 mL). And then the correct dose is dialed up.

To inject the medication, the skin should first be inspected to make sure there is no bruising, burns, swelling, hardness, or irritation in the area. Sites of injection should be rotated to prevent damage to an area with repeated injections. The skin should be cleansed with an alcohol swab.

The skin should be held in a pinch between thumb and index finger. Thrust the needle into the skin quickly, but without great force. The needle should be held at a 90-degree angle to the skin. If you have very little fat on your body, you may need to learn a different method at a 45-degree angle.

Press gauze to the injection site as the needle is pulled out of the skin. If there is any bleeding, it should be very minor. You may notice bruising later. After injection, the syringe or pen needles need to be capped and disposed of safely in an approved sharps container.

Complications of Subcutaneous Injection

As with any injection procedure, infection at the site of injection is a possibility. Proper sterile technique and rotating the site of injection around the body can help prevent bruising, irritation, and skin changes.

If a patient has poor circulation, absorption from a subcutaneous injection can be slow.

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