Routes of Drug Administration: Types and Differences

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There are many routes of drug administration, with each drug generally having a primary pharmaceutical form and being typically administered via one or two routes to achieve the desired therapeutic effect.

The Main Routes of Administration

The routes of drug administration refer to the pathways through which an active ingredient is introduced into the body to reach the site of action and produce the desired therapeutic effect. Selecting the appropriate route is pivotal in pharmacology, as it significantly impacts the entire pharmacokinetic process of the drug. Let’s explore the available options.

Enteral Route

The enteral route involves drug absorption through the oral cavity and gastrointestinal tract and includes several types:

  • Oral: This is the most commonly used method due to its convenience, safety, and cost-effectiveness. However, it is the most complex and least efficient in terms of delivering drugs to tissues. Drugs can be administered as liquids, capsules, tablets, or chewable tablets.
  • Sublingual: Allows the drug to diffuse through the capillary network directly into the systemic circulation without metabolic inactivation. The drug is placed under the tongue, where it quickly dissolves and is absorbed. This route is advantageous for drugs that are active in low doses and highly fat-soluble.
  • Rectal: Offers the advantage of avoiding inactivation or alteration by intestinal enzymes or the low pH of the stomach. It is suitable for drugs that might irritate the gastric mucosa and can be beneficial when oral administration is impractical.

Parenteral Route

The parenteral route typically enables rapid drug effects, administration of drugs unsuitable for oral use, prompt intervention in emergencies, and delivery of nutritional solutions to patients unable to consume food orally. It is the preferred method for medications requiring swift action or for administering to unconscious patients.

The specific routes are:

  • Endovascular: is the most common method and offers all the standard advantages of parenteral administration. Unlike oral methods where drug recall with vomit or activated charcoal is possible, endovascular administration involves introducing the active ingredient, solubilized in an aqueous vehicle, directly into the circulatory system.
  • Intramuscular: Involves formulating the active ingredient appropriately and then dissolving it in either an aqueous or oily liquid. The solution is then injected into specific muscle areas of the body, typically targeting the buttocks, shoulder deltoids, or thigh muscles.
  • Subcutaneous: This route involves administering the drug into the subcutaneous tissue layer. Subcutaneous administration can achieve both local effects, such as with local anesthetics, and systemic effects.

Other Routes of Drug Administration

In addition to the most common routes of administration, there are other possibilities:

  • Inhalation: involves the introduction of a drug into the airways during the act of inhalation. It ensures a certain speed by exploiting the large surface area of the mucous membrane of the respiratory and pulmonary tract and is used for certain drugs in a gaseous state. The active ingredient then passes through the upper respiratory tract until it reaches the alveolar level, which is the deepest point of the respiratory system.
  • Topical: drugs for topical, i.e. local, use are applied directly to the skin or mucous membranes such as the oral, nasal, rectal, vaginal and conjunctival. They are usually ointments, powders, creams, ointments, gels or pastes. This category also includes transdermal patches, i.e. adhesive strips containing active ingredients that are absorbed by the skin.
  • Intrathecal and intraventricular: the drug is injected into the spinal canal. This route of administration is used when the drug is to have a rapid or local effect on the brain, spinal cord or the layers of tissue covering them to treat infections of these structures.

What is the route of administration to choose?

The selection of the route of administration depends on the drug’s characteristics, including its fat-solubility, water-solubility, desired speed of action, bioavailability, and patient compliance. This decision is crucial as it significantly influences the absorption, distribution, metabolism, and elimination of the active substance.

Each route has its own advantages and disadvantages; therefore, it should be customized based on the drug’s characteristics, therapeutic requirements, and patient preferences to optimize the efficacy and safety of the treatment.