Pharmacology: Drug Absorption and Administration

• Pharmacology is the study of drugs and their effects on living organisms.
• It encompasses how drugs are absorbed, distributed, metabolized, and excreted.
• Pharmacology also includes understanding a drug's mechanism of action.
• Also covered are therapeutic effects, and adverse effects.

Drug Absorption

• Drug absorption refers to the process by which a drug moves from the site of administration into the bloodstream.
• Various factors influence drug absorption, including the route of administration.
• Other factors that influence drug absorption include the drug's formulation, and its chemical properties.
• Also of importance are the physiological characteristics of the patient, such as age, disease state, and genetic makeup.

Routes of Administration

• Oral administration involves swallowing a drug, which is then absorbed from the gastrointestinal tract.
• Intravenous (IV) injection delivers a drug directly into the bloodstream, bypassing absorption.
• Subcutaneous injection places a drug under the skin, allowing for slower absorption.
• Intramuscular injection places a drug into a muscle, which usually results in faster absorption than subcutaneous.
• Transdermal administration involves applying a drug to the skin for systemic absorption.
• Inhalation involves breathing in a drug, which is then absorbed through the lungs.
• Other routes exist such as: rectal, sublingual, and topical.
• Each route affects the rate and extent of drug absorption.

Mechanisms of Absorption

• Passive diffusion involves the movement of a drug across a membrane from an area of high concentration to an area of low concentration.
• Facilitated diffusion is similar to passive diffusion, but requires a carrier protein.
• Active transport requires energy to move a drug across a membrane, often against a concentration gradient.
• Endocytosis involves the engulfment of a drug by a cell membrane.

Bioavailability

• Bioavailability refers to the fraction of an administered dose of a drug that reaches the systemic circulation.
• Drugs administered intravenously have 100% bioavailability.
• Drugs administered by other routes may have lower bioavailability due to incomplete absorption or first-pass metabolism.
• First-pass metabolism refers to the metabolism of a drug in the liver or gut wall before it reaches the systemic circulation.

Mechanism of Action

• The mechanism of action (MOA) describes how a drug produces its effects at the molecular level.
• Drugs typically interact with specific targets in the body, such as receptors, enzymes, or ion channels.
• Receptors are proteins that bind to drugs and initiate a cellular response.
• Enzymes are proteins that catalyze chemical reactions; drugs can inhibit or activate enzymes.
• Ion channels are proteins that allow ions to pass through cell membranes; drugs can block or open ion channels.

Receptor Interactions

• Agonists are drugs that bind to a receptor and activate it, producing a response.
• Antagonists are drugs that bind to a receptor and block it, preventing activation by other drugs or endogenous substances.
• Partial agonists are drugs that bind to a receptor and activate it, but produce a smaller response than a full agonist.
• Inverse agonists are drugs that bind to a receptor and produce an effect opposite to that of an agonist.

Enzyme Interactions

• Enzyme inhibitors are drugs that bind to an enzyme and decrease its activity.
• Enzyme activators are drugs that bind to an enzyme and increase its activity.

Drug Interactions

• Drug interactions occur when the effects of one drug are altered by the presence of another drug, food, or other substance.
• Drug interactions can be pharmacokinetic or pharmacodynamic.
• Pharmacokinetic interactions affect the absorption, distribution, metabolism, or excretion of a drug.
• Pharmacodynamic interactions occur when two drugs have additive, synergistic, or antagonistic effects.

Types of Drug Interactions

• Additive effects occur when two drugs with similar mechanisms of action produce a combined effect that is equal to the sum of their individual effects.
• Synergistic effects occur when two drugs produce a combined effect that is greater than the sum of their individual effects.
• Antagonistic effects occur when two drugs produce a combined effect that is less than the sum of their individual effects, or when one drug reduces the effect of another drug.

Mechanisms of Drug Interactions

• Enzyme induction occurs when one drug increases the expression or activity of an enzyme that metabolizes another drug, leading to decreased drug levels.
• Enzyme inhibition occurs when one drug decreases the expression or activity of an enzyme that metabolizes another drug, leading to increased drug levels.
• Competition for binding sites can occur when two drugs bind to the same protein, such as albumin, leading to altered drug distribution.
• Altered gastric pH can affect the absorption of drugs that are weak acids or bases.

Side Effects

• Side effects are unwanted or unintended effects of a drug.
• Side effects can range from mild to severe.
• Side effects can be predictable or unpredictable.
• Predictable side effects are those that are known to occur based on the drug's mechanism of action.
• Unpredictable side effects are those that are not related to the drug's mechanism of action and may be due to individual patient factors.

Common Side Effects

• Nausea and vomiting are common side effects of many drugs.
• Diarrhea or constipation can also occur with certain medications.
• Drowsiness or insomnia are frequent side effects, depending on the drug.
• Dry mouth is a common side effect of drugs that have anticholinergic effects.
• Headache is a frequent side effect of many different types of medication.

Serious Side Effects

• Allergic reactions can range from mild rash to life-threatening anaphylaxis.
• Organ damage, such as liver or kidney damage, can occur with certain drugs.
• Bone marrow suppression can lead to decreased production of blood cells.
• Cardiovascular events, such as heart attack or stroke, can be associated with some medications.

Dosage Forms

• Dosage forms refer to the physical form of a drug product.
• Various dosage forms exist, including tablets, capsules, solutions, suspensions, creams, ointments, and injections.
• The choice of dosage form depends on the properties of the drug.
• The choice depends on the desired route of administration.
• The choice depends on the patient's condition.

Types of Dosage Forms

• Tablets are solid dosage forms that are typically made by compressing powdered or granulated drug.
• Capsules are solid dosage forms in which the drug is enclosed in a gelatin shell.
• Solutions are liquid dosage forms in which the drug is dissolved in a solvent.
• Suspensions are liquid dosage forms in which the drug is dispersed but not dissolved in a solvent.
• Creams are semisolid dosage forms that are typically used for topical application.
• Ointments are semisolid dosage forms that are typically used for topical application.
• Injections are sterile solutions or suspensions that are administered by injection.

Factors Affecting Dosage

• Patient's age, weight, and medical condition play a role.
• Kidney and liver function are important considerations.
• Severity of the condition being treated is a factor.
• Other medications the patient is taking can impact dosage.
• Route of administration must also be considered.