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Injection (medicine)

life science Maturity 11-13 Next article →

An injection is the process of administering a liquid substance into the body. This is typically done using a needle and a syringe. In medical terms, this is a form of parenteral drug administration. This means the medication does not enter through the digestive tract. Because it bypasses the stomach, the medicine avoids the first pass effect. This effect occurs when the digestive system processes a drug before it reaches the rest of the body. By avoiding this, the medication can be absorbed much more rapidly.

Drawing-syringes-with-needle
Drawing-syringes-with-needle

There are several ways to classify injections. They can be grouped by the specific tissue they enter. They can also be classified by the intended location of the effect. Another way to group them is by the duration of the medicine's effect. Most injections provide a bolus, which is a single, one-time dose. However, some are designed as depot injections. A depot injection is a type of medication designed to release slowly over time. This allows for long-lasting effects within the body.

Many injections are systemic, meaning they affect the entire body. These are used when a patient cannot take medicine by mouth. They are also used if a drug would not be absorbed well by the gastrointestinal tract. The most common systemic method is the intravenous injection, or IV. This involves inserting a needle directly into a vein. This delivers the substance straight into the bloodstream. Because there is no delay for absorption, it provides the quickest onset of effects.

Another common method is the intramuscular injection, or IM. This delivers medication deep into a muscle. The blood vessels in the muscle then absorb the substance into systemic circulation. Common sites for these include the deltoid or the vastus lateralis muscles. Most inactivated vaccines, such as the influenza vaccine, are given this way. Subcutaneous injections, or SC, are administered into the fatty tissue under the skin. This method uses thinner, shorter needles. Absorption from subcutaneous tissue is slower than from a muscle. Insulin is a common example of a drug given almost exclusively this way.

Some injections target very specific layers or areas. An intradermal injection, or ID, delivers substance into the dermis. The dermis is the skin layer located above the fat but below the epidermis. The needle is placed at a shallow angle of 5 to 15 degrees. Because absorption is slow, these are mostly used for sensitivity tests. For example, tuberculin skin tests or allergy tests are often done this way.

Mantoux tuberculin skin test
Mantoux tuberculin skin test

In emergencies, doctors may use an intraosseous injection. This involves inserting a needle into the bone marrow of a large bone, like the tibia. This is used when a patient's veins are difficult to access.

Injections can also be localized to treat a single part of the body. An intra-articular injection goes directly into a joint space. These can include steroids to reduce inflammation from osteoarthritis. They can also include hyaluronic acid to reduce joint stiffness. Other localized types include intravitreal injections, which go into the vitreous humor of the eye. These treat conditions like macular degeneration. By injecting the eye directly, doctors can increase medicine concentration while avoiding side effects in the rest of the body.

Injections are a massive part of global healthcare. In developing and transitional countries, at least 16 billion injections are given every year. Of these, 95% are used for curative care to treat a specific condition. Only 3% are used for immunizations and vaccinations. The remaining injections are used for other purposes, such as blood transfusions. Because injections cause a puncture wound, safety is very important. Medical professionals use aseptic technique to clean the site and prevent infection.

Safety measures are necessary to prevent the spread of bloodborne diseases. Diseases like HIV and hepatitis can spread if needles are reused. To combat this, safety syringes have features to prevent accidental needlesticks. There are also needle exchange programs and safe injection sites. These programs provide sterile needles to discourage reuse. Used needles should always be placed in a puncture-resistant sharps container. This helps protect both healthcare workers and the public from injury.

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File:Drawing-syringes-with-needle.jpg
Drawing-syringes-with-needle.jpg
File:Needle-insertion-angles-1 (edited).png
Needle-insertion-angles-1 (edited).png
File:Mantoux tuberculin skin test.jpg
Mantoux tuberculin skin test.jpg
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