Pharmacology Chapter 1

Pharmacology Chapter 1

• General pharmacology, introduction, and scope of pharmacology
• Various drug administration routes: advantages and disadvantages
• Definitions and scope of pharmacokinetics and pharmacodynamics
• Scope of pharmacology: toxicology, effect of poisons, methods for their detection, diagnosis, and treatment
• Chemotherapy, the branch of pharmacology dealing with drugs capable of destroying causative organisms without harming host cells
• Pharmacopoeia defines and describes established drugs and medical preparations
• History of pharmacology (Francois Magendie, 1783-1855 and Rudolf Buchheim, 1820-1879)

Introduction Definition and Scope of Pharmacology

• Pharmacology defined as the study of interactions between drugs and biological systems
• Derivation from Greek words "pharmakon" (drug) and "logos" (study)
• Covers drug history, source, biochemistry, physiological effects, mechanism of action, and uses of drugs
• Pharmacokinetics studies how the body interacts with the drug (absorption, distribution, metabolism, excretion)
• Pharmacodynamics studies how the drug interacts with the body (mechanism of action and pharmacological effect).
• Includes scope of Toxicology, the science of poisons,
• Chemotherapy, the mechanism of destroying causative organisms, and
• Pharmacopoeia, an official code with selected drugs and medical preparations.

Various Routes of Drug Administration

• Routes of drug administration are paths by which drugs enter the body.
• Examples include tablets, capsules, suspensions, ointments, creams, and injections.
• Routes include oral, parenteral, topical.

Oral Route

• Drugs are swallowed with liquid or solid preparations

• Advantages: most medical preparations are consumed orally, economical, convenient for children and adults, less chance of acute reaction

• Disadvantages: can be inefficient for patients, can irritate the gastric mucosa, may cause nausea and vomiting

Rectal Route

• Drugs are administered in suppositories/ enemas via rectal route
• Advantages: useful in children and adults, useful in cases of vomiting, can achieve high drug concentration
• Disadvantages: may cause rectal irritation or inflammation, absorption is often slow and erratic (inconsistent).

Sublingual/ Buccal Route

• Dosage form is placed under the tongue or in the buccal cavity
• Advantages include rapid absorption, avoidance of first-pass metabolism, maintained drug stability, and less chance of infection
• Disadvantages: only small doses can be administered, absorption is sometimes incomplete.

Parenteral Administration

• Routes other than the enteral route (e.g., oral, rectal)
• Includes intravenous (IV), intramuscular (IM), subcutaneous (SC), and inhalational.
• Intravenous: rapid onset of action, 100% bioavailability, best in cases of diarrhea and vomiting
• Intramuscular: rapid onset, suitable for liquids, no GIT factors
• Subcutaneous: self-administration possible
• Inhalational: rapidly absorbed, used for anesthetic gases.

Intravenous route

• Drugs are directly injected into veins.
• Advantages: rapid absorption, high bioavailability, and suitable for emergencies.
• Disadvantages: risk of systemic infection.

Intra-arterial

• Drugs are administered into the arteries
• Advantages: immediate and rapid onset of action, useful for administering anticancer drugs.
• Disadvantage: limited to drugs administered via skin route.

Inhalation

• Drugs are inhaled as aerosols or vapors.
• Advantages: drugs directly absorbed from lungs into circulation, bypasses the first pass effect.
• Disadvantages: only for small particle drugs, unsuitable for insoluble particles.

Drug Absorption

• Absorption is the movement of a drug from administration site into the bloodstream.
• Factors affecting absorption: administration route, surface area of the absorbing surface, aqueous solubility
• Types of absorption: oral, parenteral, topical

Bioavailability

• The rate and extent of absorption.
• Affected by factors such as first-pass metabolism, solubility and degradation in the GI tract.
• Injection of drugs intravenously is almost 100% bioavailable.
• Oral administration may be incompletely absorbed by first-pass metabolism.

Factors affecting drug absorption

• Routes of administration, surface area of absorbing surface, aqueous solubility
• Concentration gradient, vascularity of surface
• Absorption sites like skin, cornea, and mucus membranes.

Drug Distribution

• The extent to which a drug spreads throughout the body.
• Affects by factors including: organ/tissue size and perfusion rate, drug binding to blood components/extracellular components, age, obesity, disease states
• Distribution also influences drug concentration in different organs/tissues.

Metabolism/Biotransformation of Drugs

• Chemical alteration of drugs within the body that changes drug structure and properties.
• Process occurs mainly in the liver.
• Types of metabolism include activation (converting inactive drugs into active ones), inactivation (rendering active drugs less active), and formation of metabolites (conversion into different compounds).
• Factors affecting drug metabolism include age, sex

Excretion

• Removal of drugs and metabolites from the body.
• Routes of excretion include the kidneys (urine), liver (bile), lungs (exhalation), sweat, saliva, and breast milk.
• Many factors affect excretion such as blood circulation, chemical properties of drug, and presence of metabolites.
• Factors include age, disease, and certain drugs.

Factors affecting drug metabolism

• Age, species, sex differences, enzyme induction and inhibition, and stereochemistry of drugs

General mechanisms modifying drug action

• Body size, age, sex, species, genetic predisposition, routes of administration, pregnancy/lactation
• Physiological states (e.g., kidney or liver diseases), dietary and environmental factors, psychological status, bioaccumulation, and tolerance/resistance.