Question

Which route of drug administration is used with potent and lipophilic drugs in a patch formulation and avoids first-pass metabolism? (A) topical (B) sublingual (C) rectal (D) oral (E) transdermal

Short answer

The transdermal route is used with potent and lipophilic drugs in patch formulations to avoid first-pass metabolism.

Step-by-step solution

Understand Drug Properties

Potent and lipophilic drugs are effective at low doses and are soluble in lipids or fats. These properties influence the choice of drug administration route to ensure effectiveness and proper absorption.

Analyze Routes of Administration

Different routes of drug administration have different effects. Some routes, like oral administration, can lead to first-pass metabolism, where the drug is significantly metabolized in the liver before reaching systemic circulation. Other routes bypass this effect.

Evaluate First-Pass Metabolism

First-pass metabolism refers to the metabolism of a drug whereby concentration is greatly reduced before it reaches systemic circulation. Avoiding it can enhance the efficacy of potent, lipophilic drugs.

Consider Patch Formulation

Patch formulations are designed to deliver drugs through the skin, a method typically used for drugs that require continuous and controlled release over time.

Identify the Suitable Route

Patches are a form of transdermal drug delivery, which allows for the direct absorption of the drug into the bloodstream through the skin, avoiding first-pass metabolism.

Key concepts

Routes of Drug Administration

When administering medication, selecting the appropriate route is crucial for ensuring effectiveness and safety. These routes can be broadly categorized as either enteral or parenteral. Enteral routes, such as oral administration, deliver drugs through the digestive system. Conversely, parenteral routes, like intravenous or transdermal, allow drugs to enter the bloodstream directly, bypassing the digestive tract.

• Oral administration involves swallowing the drug. It's convenient but often less effective for certain drugs due to first-pass metabolism.


• Intravenous administration directly injects the drug into the bloodstream. It provides immediate effects but requires professional administration.


• Transdermal administration uses patches, enabling drugs to be absorbed through the skin and directly into the bloodstream. This route can be advantageous for specific drugs that need to maintain stable blood levels over time.

First-Pass Metabolism

First-pass metabolism is an essential concept in pharmacology. This metabolic process occurs primarily in the liver when oral drugs are significantly metabolized before reaching systemic circulation. As a result, the concentration of the drug is greatly reduced, which can diminish its effectiveness.
Drugs administered orally first pass through the digestive system, then to the liver via the hepatic portal vein. Many drugs are broken down during this journey.
Avoiding first-pass metabolism is advantageous for certain drugs that need to remain at a particular potency or are metabolized extensively, reducing their efficacy. By choosing alternative routes, such as transdermal, drugs can avoid this initial metabolism and act directly on the target system.

Lipophilic Drugs

Lipophilic drugs have a natural affinity for lipids, making them fat-soluble. This property significantly influences their behavior in the body, especially concerning absorption and distribution.
Lipophilic drugs can easily pass through cell membranes, which consist of lipid layers. This quality is particularly beneficial for drugs designed for transdermal patches, as they need to penetrate the skin efficiently.

• The ability to dissolve in lipids allows these drugs to be absorbed more effectively through lipid-rich biological membranes.


• Lipophilicity often enhances the distribution of the drug within the body, ensuring it reaches effective concentrations in target tissues.

This property, combined with specific formulations like patches, optimizes the drug's ability to enter the bloodstream directly.

Patch Formulation

Patch formulation refers to the creation and use of adhesive patches to deliver drugs through the skin. This method of drug delivery, known as transdermal delivery, provides a controlled, continuous release of medication into the bloodstream, which can be especially beneficial for chronic or long-term treatments.
Transdermal patches are designed with several layers. Typically, they include a backing layer, a drug reservoir, a control membrane to regulate release, an adhesive that sticks to the skin, and a protective liner.

• The backing layer provides structural support and protection for the remaining layers.


• The reservoir contains the medication, while the control membrane ensures consistent delivery rates.

Using transdermal patches avoids first-pass metabolism entirely. Consequently, this method can maintain stable drug levels, reducing fluctuations and enhancing drug efficacy.