Pharmacology: Mechanisms and Interactions

• Pharmacology encompasses the study of drugs and their effects on living organisms.
• It includes pharmacodynamics (what the drug does to the body) and pharmacokinetics (what the body does to the drug).
• Understanding pharmacology is crucial for rational drug use and development.

Mechanism of Action

• Mechanism of action (MOA) describes how a drug produces its therapeutic effect at the molecular and cellular level.
• Drugs can interact with various targets, including receptors, enzymes, ion channels, and transporters.
• Receptor interactions can be agonistic (activating the receptor) or antagonistic (blocking the receptor).
• Enzyme inhibition is a common MOA where drugs bind to enzymes and reduce their activity.
• Ion channels can be blocked or modulated by drugs, affecting ion flow and cellular excitability.
• Transporters can be inhibited, preventing the movement of molecules across cell membranes.

Drug Interactions

• Drug interactions occur when one drug affects the activity of another drug when administered together.
• Interactions can be pharmacokinetic (altering absorption, distribution, metabolism, or excretion) or pharmacodynamic (drugs having additive or opposing effects).
• Enzyme induction increases the metabolism of other drugs, potentially reducing their therapeutic effect.
• Enzyme inhibition decreases the metabolism of other drugs, potentially increasing their toxicity.
• Additive effects occur when two drugs with similar actions are combined, increasing the overall effect.
• Synergistic effects occur when the combined effect of two drugs is greater than the sum of their individual effects.
• Antagonistic effects occur when one drug reduces the effect of another drug.
• Drug-food interactions can also affect drug absorption and metabolism.
• Interactions can lead to adverse effects or therapeutic failure.

Dosage Forms

• Dosage forms are the physical forms in which drugs are administered.
• Common dosage forms include tablets, capsules, solutions, suspensions, creams, ointments, and injections.
• Tablets are solid dosage forms prepared by compression or molding, and can be immediate-release, delayed-release, or extended-release.
• Capsules are solid dosage forms in which the drug is enclosed in a hard or soft soluble shell.
• Solutions are liquid dosage forms containing a drug dissolved in a solvent.
• Suspensions are liquid dosage forms containing solid drug particles dispersed in a liquid vehicle.
• Creams and ointments are semisolid dosage forms for topical application.
• Injections are sterile solutions or suspensions administered via various routes (intravenous, intramuscular, subcutaneous).
• Choice of dosage form depends on the drug's properties, the desired route of administration, and the patient's condition.

Drug Absorption

• Drug absorption is the process by which a drug enters the bloodstream from the site of administration.
• Factors affecting absorption include the drug's physicochemical properties, the route of administration, and physiological factors (e.g., gastric pH, intestinal motility).
• Oral administration involves absorption from the gastrointestinal tract, which can be affected by food, other drugs, and gastrointestinal diseases.
• Intravenous administration bypasses absorption, delivering the drug directly into the bloodstream.
• Intramuscular and subcutaneous administration involve absorption from the muscle or subcutaneous tissue, respectively.
• Transdermal administration involves absorption through the skin.
• Bioavailability is the fraction of the administered dose that reaches the systemic circulation.
• First-pass metabolism in the liver can significantly reduce the bioavailability of orally administered drugs.

Side Effects

• Side effects are unintended effects of a drug that occur at therapeutic doses.
• They can range from mild to severe and may be predictable or unpredictable.
• Common side effects include nausea, vomiting, diarrhea, constipation, drowsiness, and dry mouth.
• Allergic reactions are immune-mediated responses to a drug and can range from mild skin rashes to life-threatening anaphylaxis.
• Idiosyncratic reactions are rare and unpredictable drug reactions that are not dose-related.
• Some drugs can cause organ damage, such as liver damage (hepatotoxicity) or kidney damage (nephrotoxicity).
• The risk of side effects depends on the drug, the dose, the duration of treatment, and individual patient factors (e.g., age, genetics, comorbidities).
• Monitoring for side effects is an important part of drug therapy.