Drug Absorption, Distribution, Metabolism, and Effects

Intramuscular Drug Administration and Receptor Binding

Explains what a circuit is: a drug that is administered intramuscularly until it reaches the receptor. It exits the bloodstream through the capillary endothelium, traveling through the interstitial fluid, and crosses the cell membrane of its target cells.

Morphine Effects in Elderly Patients

Explains why an old man, who is administered morphine in doses equal to a middle-aged person, may be at increased risk of sleepiness, even after the drug's effects should have worn off. The elderly, like children, have decreased hepatic activity, so the drug takes longer to metabolize and be disposed of by the body, which can cause drowsiness in the case of morphine.

Drug Molecule Characteristics for Barrier Crossing

What physical characteristics should a drug molecule have to cross physiological barriers easily? The non-ionized forms are readily absorbed by simple diffusion. Regarding solubility, lipid-soluble drugs are distributed more easily than water-soluble drugs.

Importance of Plasma Half-Life for Nurses

Why is it important for nurses to know the plasma half-life of a drug? The plasma half-life determines the frequency and the time interval at which a drug should be administered.

The First-Pass Effect

What is the first-pass effect? Since a drug entering the body may be degraded in many ways, it can be said that a portion of the administered dose of most drugs never reaches its destination because it will be inactivated or destroyed before reaching its target cells.

Prodrugs and Their Use

What are prodrugs? What is their use? Prodrugs are substances that are completely inactive, having no pharmacological activity at the time of administration. They need to be metabolized into an active form. Examples include enalapril and losartan.

Factors Affecting Drug Absorption

Drug Administration

• Route of administration: It is important to know the rate of absorption of a drug according to the route used.
• Dose: In general, drugs that are administered in high doses are absorbed more quickly.
• Pharmaceutical form: In oral forms, syrups and suspensions are absorbed faster than tablets.

Physicochemical Properties of the Drug and pH of the Environment

The pH of the immediate environment influences drug absorption due to its ability to ionize the drug's molecules.

Interactions with Other Drugs and Food

Drugs administered orally can have their absorption altered by the presence of other substances in the digestive tract.

Bowel Diseases

Especially those that affect the intestinal mucosa or cause very rapid intestinal transit.

Factors Affecting Drug Distribution

Blood Flow

The amount of blood flow that a tissue receives determines whether it receives a greater or lesser proportion of the drug.

Physicochemical Properties of the Drug

The solubility of a drug is critical for its ability to be distributed and accumulated in different tissues.

Protein Binding

Many drugs bind to plasma proteins (albumin) and form complexes too large to cross the capillary endothelium. Therefore, they cannot leave the circulation to reach target tissues and cells.

Physiological Barriers

These are anatomical barriers that impede the passage of most substances.