Drug routes of administration and their uses

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There are many different drug routes of administration. Some are commonly used, while others are rare. Drug administration can be:

• oral, which is when a person swallows a drug
• intraocular, or into the eye
• intraotic, or into the ear
• nasal, or through the nose
• sublingual, or under the tongue
• buccal, between the gums and the mouth cheek
• inhaled through the respiratory system
• enteral, which is when a person receives the drug directly into their digestive tract
• rectal, or through the rectum
• vaginal, or through the vagina
• transdermal, or through the skin
• subcutaneous, or under the skin
• intramuscular, or via an injection into a muscle
• intravenous, or into a vein
• intra-arterial, or into an artery
• intraosseous, or into the bone marrow

This is not a comprehensive list.

Oral drug administration involves a person putting a drug into their mouth and swallowing it. It is one of the most common routes of drug administration, and it is convenient for many as it does not require special equipment. People can use oral administration for a range of medication types, such as pills, capsules, and liquids.

However, one of the downsides of oral administration is that it can be inefficient. The digestive system and liver start to break down drugs via this route before they reach the bloodstream, meaning the concentration significantly reduces. This is known as the “first pass effect.”

Additionally, some oral drugs can have adverse effects on the digestive system, and some people have difficulty swallowing pills.

The intravenous (IV) administration route involves using a needle to inject a drug directly into a vein. The intramuscular route is similar but involves an injection into a muscle instead.

IV administration is suitable for many drugs, particularly in situations where a person needs an urgent, high, or consistent dose, such as during a severe infection. This is because IV drugs bypass the digestive system and take effect quickly.

Intramuscular administration also bypasses the digestive system, allowing the body to get a more potent dose of a drug. Some vaccines and hormone drugs have intramuscular administration options.

The downside of these methods is that they can cause pain, swelling, or irritation around the injection site. For people with needle phobias, they can be distressing. There is also a risk of complications, such as infection, nerve injury, hematoma, and accidental puncturing of a blood vessel.

The nasal administration route involves spraying or sniffing a drug through the nose, where it quickly absorbs into the bloodstream.

This is a route of administration for drugs that work directly on nasal and sinus conditions, such as decongestant sprays. However, doctors can also prescribe it for other types of medical treatment. For example, some vaccines come in nasal forms.

The benefits of administering medications via the nose are that it is painless, delivers a high concentration of the drug, and allows drugs to take effect quickly.

However, only certain drugs work via nasal administration. Additionally, the dose and effect size may have limitations depending on the size and features of a person’s nasal cavity and how they administer it. People may also make more mistakes with dosing nasal administration, affecting the dose they receive.

Another concern is keeping the tip of the applicator clean. If a person does not, they could get recurring infections.

The sublingual administration route is when a person places the drug under the tongue, where it absorbs into the bloodstream. The buccal administration route works in a similar way, but a person places the drug between the gum and the inside of their cheek instead.

Both of these routes are typically simple and painless. The drugs absorb quickly, meaning a medication can start working quickly. They can be good alternatives to oral administration for people who have difficulty swallowing or with digestion.

Sublingual and buccal administration can be difficult if the drug tastes unpleasant. There are also relatively few drugs that are available with this route of administration, and if a person does not allow the drug to dissolve fully, it will affect their dose.

Some people take certain vitamins sublingually. This method can also be useful for delivering immunotherapy for allergies. Buccal administration is the method of delivery for some nicotine replacement products and strong pain medications, such as fentanyl.

Transdermal administration is when a drug enters the body through the skin, such as via a cream, gel, ointment, or patch. Subcutaneous administration is when a person uses a needle to inject the drug underneath the outer layers of the skin.

Transdermal administration is simple, noninvasive, and painless. Uses include nicotine replacement therapy, hormonal medications, and hormonal contraceptives.

However, the downside of this route is that transdermal application can irritate the skin, and not all drugs absorb effectively this way. Additionally, the condition of the skin may affect absorption. For example, if it is dry or has open cuts, it may absorb too much or too little.

Subcutaneous administration is typical for insulin and the anaphylaxis medication known as epinephrine. Because this level of the skin has few blood vessels, this option allows for a slow release of drugs. However, it is invasive and can be painful.

The vaginal administration route involves inserting a drug into the vagina, where it gradually absorbs into the bloodstream. The drug may come in the form of a suppository, cream, gel, or capsule.

Vaginal administration can be useful for medications that act locally, such as antibiotic or antifungal medications for infections or hormone treatments for vaginal dryness or atrophy. It is also a route for some systemic drugs that affect the whole body.

Vaginally-absorbed drugs can be easy to administer and are typically painless, but the drug may cause discomfort if it is a solid suppository. A 2019 study also notes that factors such as vaginal pH and flora could influence the effectiveness of drugs.

Enteral drug administration refers to any method that delivers a medication to the intestines. This includes oral administration, but also other approaches, such as:

• through the nose and into the stomach via a nasogastric (NG) tube
• through the nose into the intestines via a nasointestinal (NI) tube
• through the skin into the stomach via a percutaneous endoscopic gastrostomy (PEG) tube

Another method of enteral administration is inserting a drug into the rectum, such as via a suppository or enema.

Each of these methods has its own uses and risks. NG, NI, and PEG tubes can be essential for drug administration in situations where a person cannot eat, as it allows doctors to deliver oral medications directly into the stomach or intestines.

Some examples of drugs that can require rectal administration include certain laxatives, and diazepam during a seizure. This route can deliver drugs quickly but can also be uncomfortable, and some drugs may irritate the rectum.

There are many routes of drug administration, each with unique benefits and drawbacks that make them suitable for different situations.

Doctors will weigh up the best options to prescribe depending on a person’s unique circumstances and tolerance. Where one route is not available, it may be possible to prescribe another route of administration instead.