Pharmacology Basics

Drug Responses in the Body

• Drug receptors are specific sites where drugs form chemical bonds.
• Pharmacodynamics involves interactions between drugs and receptors and the resulting pharmacologic response.
• Agonists stimulate a response by interacting with a receptor.
• Antagonists attach to a receptor but do not stimulate a response.

Routes of Drug Administration

• Enteral routes involve the gastrointestinal tract, including oral, rectal, and nasogastric methods.
• Parenteral routes bypass the GI tract through subcutaneous, intramuscular, and intravenous injections.
• Percutaneous routes involve absorption through the skin and mucous membranes.
• Percutaneous routes include inhalation, sublingual, and topical applications.

Drug Stages After Administration

• LADME describes the stages of drug administration: Liberation, Absorption, Distribution, Metabolism, and Excretion.
• Liberation refers to the release of a drug from its dosage form.
• Absorption depends on the administration route.
• Distribution relies on circulation to transport the drug throughout the body.
• Metabolism is influenced by enzyme systems.
• Excretion depends on the GI tract and kidneys.

Liberation

• Drugs are released from their dosage form and dissolved in body fluid.
• Food and water intake can influence the process of converting oral drugs.

Absorption

• Drugs are transferred from the entry site into the body's circulating fluids.
• Absorption rate is affected by the route of administration, blood flow, and drug solubility.
• Subcutaneous and intramuscular injection absorption is influenced by circulation.
• Intravenous medications are absorbed fastest.
• Topical medication absorption can be influenced by skin thickness and hydration.

Distribution

• Body fluids transport drugs throughout the body to action sites.
• Protein binding and fat solubility impact distribution.
• Organs with the largest blood supply receive the most distributed drug rapidly.
• Some drugs are unable to pass through the blood-brain or placental barriers.

Metabolism

• The body inactivates drugs through metabolism.
• The primary organ for metabolism is the liver, with the GI tract and lungs also involved.

Excretion

• Drug metabolites and some active drugs are eliminated from the body through excretion.
• The kidneys are the major organ for excretion; some drugs are excreted in feces.

Half-Life of Drugs

• Various factors modify the quantity of a drug reaching its site of action after a single oral dose.

Drug Actions

• Onset of action occurs when drug concentration at the site of action is sufficient to start a physiologic response.
• Peak action is the time when the drug reaches highest concentrations on target receptor sites.
• Duration of action refers to how long the drug has a pharmacologic effect.

Drug Blood Level

• A blood sample may be drawn and tested to determine the amount of drug circulating in the blood.
• Monitoring drug blood levels is important for drugs like anticonvulsants.
• Dosage may be adjusted based on drug blood levels: increased if low, reduced if high.

Adverse Effects of Drugs

• Desired action is the intended therapeutic effect of a drug.
• Side effects are unintended effects that can occur with drug use.
• Adverse effects include common and serious reactions.
• Idiosyncratic reactions are unusual or abnormal responses occurring when the drug is first administered.
• Allergic reactions occur in patients previously exposed to a drug, resulting in antibody development.

Drug Interactions

• It takes place when one drug's action is altered by another.
• May occur when combined agents increase the action of one or both drugs.
• May occur when combined agents decrease the effectiveness of one or both drugs.

Changes in Absorption

• GI tract is where most drug interactions altering absorption occur.
• Antacids increase gastric pH and can inhibit the dissolution of ketoconazole tablets.
• Separating administration times can manage many alterations in absorption.

Changes in Distribution

• Interactions causing distribution changes usually affect the binding of a drug to an inactive site.
• Unbound drugs represent the pharmacologically active portion.
• Drugs "bound" to proteins in the blood during transportation.
• A drug that is highly protein-bound is less available to the circulation.
• Some medications can cause the binding or unbinding of another medication, which can increase or decrease its effect.

Changes in Metabolism

• Drug interactions commonly result from altered metabolism, involving enzyme inhibition or induction.
• Inhibited metabolism due to concurrent drug use often leads to increased serum drug levels.

Changes in Excretion

• Drug interactions affecting excretion usually act in kidney tubules by altering pH to enhance or inhibit excretion.

Drug Interaction Types

• Additive effect
• Synergistic effect
• Antagonistic effect
• Displacement
• Interference
• Incompatibility