General Principles of Pharmacology

Pharmacology

Pharmacology is a science which deals with the study of drugs and their effects on living organisms.

The term ‘Pharmacology’ has been derived from the two Greek words Pharmakon, which means a drug and Logos, which means study (discourse).

Drug

A drug is a substance used in the prevention, diagnosis, and treatment of diseases.

According to WHO, a drug is any substance or product that is used to modify or explore physiological systems or pathological states for the benefit of the recipients.

Drugs have various categories based on their function:

Curative drugs: Cure or eliminate a disease (e.g., antimalarials).

Suppressive drugs: Control a disease without curing it (e.g., antihypertensive drugs).

Prophylactic drugs: Prevent a disease (e.g., vaccines).

Scope of Pharmacology

The scope of Pharmacology is wide and includes:

1.Study of the history, sources, physical, and chemical properties of drugs.

2.Pharmacokinetics: Study of drug absorption, distribution, metabolism, and excretion.

3.Pharmacodynamics: Relationship of drug concentration, biological effects, site of action, and mechanism of action.

4.Toxicology: Study of adverse effects of drugs.

5.Clinical pharmacology and therapeutics: Application of pharmacological principles in clinical practice.

6.Pharmacovigilance: Characterization and detection of adverse effects.

7.Development of new drugs and formation of clinical guidelines.

Pharmacology: A Basic Science of Medicine

Many functions of the body are controlled by endogenously produced compounds like neurotransmitters, autacoids, hormones, and similar compounds.

Drugs mimic, block, or affect the actions of these compounds, making pharmacology a fundamental science of medicine.

Pharmacology tools: Active compounds influencing physiological and biological processes.

Subdivisions of Pharmacology

1. Pharmacokinetics

Deals with drug absorption, distribution, metabolism, and excretion (ADME).

Clinical pharmacokinetics: Describes ADME in patients regarding drug therapy.

2. Pharmacodynamics

Focuses on biochemical and physiological effects of drugs and their mechanisms of action.

3. Pharmacotherapeutics

Studies therapeutic uses and effects of drugs.

4. Clinical Pharmacology

Scientific study of drugs in humans.

Includes pharmacodynamic and pharmacokinetic investigations in healthy volunteers and patients.

Analyzes cost-benefit and risk-benefit ratios, determines ideal doses, and studies drug utilization patterns.

5. Toxicology

Studies adverse effects of drugs and chemicals on living organisms.

Includes selection of antidotes and treatment for poisoning.

Clinical toxicology: Diagnosis and treatment of poisoning cases.

6. Pharmacy

Science of compounding and dispensing drugs to prepare suitable dosage forms.

Involves collection, identification, isolation, synthesis, standardization, and quality control of medicinal substances.

7. Pharmacovigilance

Process of identifying, evaluating, and responding to adverse drug reactions or any drug-related problem.

Involves surveillance of side effects of medicines after short-term and long-term use.

Crucial for monitoring new drugs and continues throughout their lifecycle.

Important Terms in Pharmacology

1. Orphan Drug

Drugs for rare diseases affecting a small number of people·

Not readily available commercially due to limited sales and unprofitable development and manufacturing costs·

Examples include acetylcysteine for paracetamol poisoning, 4-methylpyrazole for methanol poisoning, Liothyronine (T3), albendazole for hydatid cyst, and coagulation factor IX·

Government often provides assistance in the development of orphan drugs·

2. Xenobiotics

Chemicals foreign to the body causing physiological or pharmacological effects.

Found in food, drugs, poisons, and additives.

Drugs are considered xenobiotics.

3. Pharmacogenetics

Variation of drug response due to genetic factors.

Genetic conditions can affect drug metabolism or interactions.

Example: G-6-PD deficiency leading to haemolysis induced by Primaquine.

INH metabolism variability: Fast and slow acetylators require dose adjustments.

Genetic variations impact drug response.

4. Prototype Drugs

Drugs are categorized into about 70 major groups, each containing several drugs.

Prototype drug: Exhibits major actions of all drugs in a group.

Studying prototype drugs highlights differences among drugs in the group.

Example: Morphine (prototype of opioids) and acetylcholine (prototype of cholinergic drugs).

Sources of Drugs

1. Vegetable Kingdom

Plants are a rich source of drugs·

Examples: Atropine, digoxin, morphine, quinine, reserpine, curare, ephedrine, volatile oils·

Active constituents classified as alkaloids, glycosides, oils, tannins, flavonoids, resins, and gums·

2. Microbes

Many antibiotics derived from fungi, yeast, or bacteria·

Examples: Penicillin, streptomycin, tetracyclines·

3. Animal Kingdom

Drugs include hormones (insulin, renin, thyroxin), sera, honey, heparin, fish liver oil·

4. Mineral Sources

Salts of metals like iron, sodium, calcium, magnesium, iodine·

Also, include liquid paraffin and radioactive pharmaceuticals like radium and cobalt·

5. Synthetic Agents

Most drugs available today are synthetic·

Examples: Sulphonamides, salicylates, barbiturates, tolbutamide·

6. Semi-synthetic Agents

Obtained by chemical modification of naturally occurring compounds·

Example: Semi-synthetic penicillins·

Modifications aim to improve potency, duration of action, and specificity·

7. Biotechnology or Genetic Engineering

Utilizes bacteria, plant, or animal cells for drug production or modification·

Drugs include human insulin, growth hormones, interleukin, erythropoietin, monoclonal antibodies·

Gene therapy used for treating genetic diseases·