Routes of Administration
By Ron Aylor, CPhT
Drugs may be given to patients using a variety of methods. Some drugs are only effective if they are given in a particular dosage form. Other drugs are administered in forms that enhance or decrease their effect, or localize the effects. Routes of administration are classified as either enteral or parenteral.
parenteral literally means to avoid the gut (gastrointestinal tract)
and refers to any route of administration outside of or beside
the alimentary tract.
Thus, parenterals are injectable drugs that enter the body directly and are not required to be absorbed in the gastrointestinal tract before they show their effect. Parenteral routes of administration usually have a more rapid onset of action (show their effects more quickly) than other routes of administration. Parenteral products must be sterile (free from living microbes). The parenteral route of administration does have its disadvantages: it hurts, it is not a convenient route, and once administered the injected drug cannot be retrieved.
The injection of a drug directly into the patient's veins is the most rapid route of administration, resulting in the most rapid onset of action. Much less frequently used is Intraarterial, injecting drug directly into the patient's arteries.
In this route, the drug is injected into the (top few layers) of the skin. Ideally, the drug is placed within the dermis. The intradermal route is used almost exclusively for diagnostic agents.
This route involves the injection of the drug under the skin into the fatty layer, but not into the muscle. Absorption of the drug is rapid. Insulin is normally administered subcutaneously.
The intramuscular route is used when drugs are injected deeply into muscle tissue. If the drug is in aqueous (water) solution, absorption is rapid. However, if the drug is in an oily liquid or in the form of a suspension, it can prolong the release of the drug.
The intrathecal route involves the administration of a drug directly into the spine (subarachnoid space) as in spinal anesthesia. The intrathecal route is used because the blood-brain barrier often precludes or slows the entrance of drugs into the central nervous system.
Most drugs available today can be administered by mouth (orally). Drugs can be orally administered in the form of tablets, capsules, powders, solutions, syrups or suspensions. Drugs administered by the oral route are usually taken for their systemic effect. These medications must pass through the stomach and be absorbed in the intestinal tract. Orally administered medications are usually easy to take and are usually less expensive than other dosage forms.
The sublingual/buccal route of administration is closely related to the oral route; however, in the sublingual/buccal route the dosage form is not swallowed. The tablet is to be dissolved under the tongue (sublingual) or in the pouch of the cheek (buccal). The drugs administered in this manner are rapidly absorbed and have the advantage of bypassing the gastrointestinal tract. Nitroglycerin, for heart patients, in tablet form is more likely the most frequently administered sublingual drug.
Rectal / Vaginal
Drugs administered by the rectal / Vaginal suppository route may have a local effect (such as for hemorrhoids) or a systemic effect (as in the prevention of nausea and vomiting). The rectal route is convenient to use in children or in patients who are unconscious or vomiting. The amount of drug absorbed in the rectal / vaginal route is usually less than if the drug were administered orally. The absorption of drugs administered rectally is unpredictable and can vary among patients.
Inhalation / Inhaler
Inhalation is a means of introducing medications through the respiratory system in the form of a gas, vapor, or powder. Inhalation is divided into three major types: vaporization, gas inhalation, and nebulization. Vaporization is the process by which a drug is changed from a liquid or solid to a gas or vapor by the use of heat (such as in steam inhalation). Gas inhalation is almost entirely restricted to anesthesia. Nebulization is the process by which a drug is converted into a fine spray by the use of compressed gas.
Topical (Dermal, Ophthalmic, Otic)
Topical drugs are applied to a surface area of the body. Topically applied drugs serve two purposes: Local effect and Systemic effect. For local effect, the drug is intended to relieve itching, burning, or other skin conditions without being absorbed into the bloodstream. For systemic effect, the drug is absorbed through the skin into the bloodstream. Examples of topical preparations are ointments, creams, lotions, Transdermal patches, powders, eye drops, ear drops, and shampoos.
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