Routes of Administration of Drugs

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The route of drug administration is the pathway utilized by the drug to enter into the body. The drug may be present in ionized or unionized form.

Classification of Routes of Drug Administration:

Enteral route
Parenteral route
Inhalation route
Topical route

Enteral Route:

Enteral route involves the alimentary canal, including either oral, sublingual or rectal route

Oral Route:

The most common route of drug administration is via the oral route. Neutral drugs are given through this route. Tablets, capsules, syrup, emulsions or powders may be given by this route.

This is the cheapest route, being safe and easy to use, thus is the most convenient route available. Drugs given by this route may cause gastric irritation, absorption process may be slow and less amount of drug reaches the target tissues. Some drug may be destroyed by gastric juices as well. Taste may be objectionable and discoloration of teeth may occur as well.

Hepatic metabolism of drugs occurs known as first pass effect, when given through the oral route.

Sublingual Route:

When tablets are placed under the tongue or between cheeks, the route utilized is known as sublingual route. The drugs given by this route need to be lipid soluble and small.

This route is advantageous as rapid absorption takes place and drug enters blood directly. First pass metabolism is also less.  Irritation of mucous membranes may occur by this route

Rectal Route:

Suppositories or enema are given by this route. Local or systemic effects may occur after absorption. Nausea and vomiting may be avoided by this route. Irritant drugs may be given by this route. This route is also preferable for unconscious or old patients.

Drugs given by this route undergo first pass metabolism.

Parenteral Route:

Injections given by parenteral route may be given:

Intra muscular
Intra venous
Intra-arterial
Intra-cardiac
Intra-thecal
Intraosseous
Intrapleural
Intraperitoneal
Intra-articular
Intradermal/Intracutaneous
Subcutaneous route/Hypodermic

Rapid effect of drugs takes place. Injections are suitable for unconscious or uncooperative patients. First pass effect is also avoided and bioavailability is 100%.

Classification:

Subcutaneous:

Arm, forearm, thigh and subscapular space may be utilized for subcutaneous injections. Insulin is given by this route.

Intramuscular route:

Intramuscular injections are given in buttock, thigh or deltoid. Absorption occurs more rapidly than subcutaneous route. Possibility of damage to nerve or vein has to be kept in mind when using this route.

Intravenous injections:

Cubital, basilic and cephalic veins may be used for giving intravenous injections. Rapid onset of action takes place, so is the preferred route in emergency. First pass metabolism does not take place. Infection may occur by this route.

Intraarterial route:

Chemotherapy and angiography are done by this route.

Intradermal route:

Diagnostic tests are done by this route.

Intracardiac route

In case of cardiac arrest, injections are applied directly into the heart.

Intrathecal route:

Subarachnoid space is involved in intrathecal route. Lumbar puncture, spinal anesthesia or other diagnostic tests may be performed.

Intra-articular route:

Injection is applied directly into the joint cavity. Corticosteroids are given by this route.

Intraperitoneal route:

Peritoneal dialysis is done by intraperitoneal route.

Hypospray/Jet Injection:

This is done by applying pressure over the skin. A fine jet of solution emerges from the ‘gun’ (a container containing the drug solution) and penetrates the skin and subcutaneous tissue. This method is expensive and special skills are required. Cuts may result.

Inhalation:

Drugs reach the lungs directly by this route. Aerosols like salbutamol are given by this route. Onset of action is rapid and with minimum side effects. First pass effect does not occur. Special apparatus is required for this route and airway needs to be patent.

Topical route:

Topical route includes enepidermic, epidermic, insufflations, instillation, irrigation and swabbing.

Enepidermic route –drug is applied to the outer skin

Epidermic route –drug is rubbed into the skin

Insufflation –drug in finely powdered form is blown into the body cavities or spaces with special nebulizer

Instillation –drug is poured by a dropper into the conjunctival sac, ear, nose and wounds

Irrigation or Douching –washing a cavity

Painting/Swabbing –lotion form

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The writer enjoys medical education and has special interest in community medicine.