Basics of Pharmacology : Discovery and Development of New drugs

Basics of Pharmacology : Drug Discovery and Development

Topics Covered: Drug discovery process, preclinical evaluation, clinical trials and phases, bioassays, and assessment techniques.

Drug Discovery and Development

Definition:

Drug Discovery: Identifying potential new drugs from chemical, biological, or natural sources.
Drug Development: Turning discovered compounds into safe and effective medications.

Story:
In the early 1900s, scientists discovered penicillin accidentally when mold killed bacteria on a petri dish. This chance observation led to the first antibiotic, revolutionizing medicine.

Stages of Drug Discovery and Development

Target Identification: Finding a biological molecule (e.g., protein, enzyme) linked to a disease.
Lead Compound Identification: Searching for a compound that affects the target.
Optimization: Refining the compound for safety and efficacy.
Preclinical Testing: Evaluating the drugs on animals before human trials.

Example:
Scientists discovered statins while searching for compounds to reduce cholesterol by targeting the enzyme HMG-CoA reductase.

Preclinical Evaluation Phase

Purpose:

Assess safety, toxicity, and pharmacokinetics (absorption, metabolism, elimination).
Use animal models and in vitro techniques.

Techniques Used:

Toxicity testing (LD50, organ-specific effects).
Efficacy studies in disease models (e.g., testing cancer drugs in tumor-bearing mice).

Story:
Before humans could benefit from insulin, it was tested on diabetic dogs to demonstrate its life-saving potential.

Clinical Trials and Their Phases

Phase	Purpose	Example Activities
Phase I	Test safety in healthy volunteers	Small group (20-100), dosage and side effects
Phase II	Test efficacy in patients	Medium group (100-300), optimal dosage
Phase III	Confirm safety and efficacy in large groups	Large group (1,000+), long-term effects
Phase IV	Post-marketing surveillance	Monitor rare side effects in the general population

Story:
During Phase I trials for a cancer drug, scientists discovered unexpected side effects but adjusted dosages to safely proceed to Phase II.

Concept and Purpose of Bioassay

Definition:

A bioassay measures the potency and effect of a substance by observing its biological response.
Purpose: Ensure drug efficacy, standardization, and quality.

Example:

Testing insulin potency by its ability to lower blood sugar in diabetic rats.

Story:
Before modern analytical tools, digitalis (heart medicine) was standardized using frog heart assays to ensure consistency.

Types of Bioassays

Qualitative Bioassay: Determines the presence or absence of an effect (e.g., testing for antibiotic activity on bacteria).
Quantitative Bioassay: Measures the intensity or amount of an effect (e.g., drug dose-response curves).

Techniques Used:

Graded Response Assay: Measures the degree of response (e.g., blood pressure reduction).
Quantal Response Assay: Measures an all-or-nothing response (e.g., survival rates).

Example:

The ED50 test identifies the dose required to achieve 50% of the maximum effect.

Techniques of Bioassay Assessment

In Vivo: Testing in live organisms (e.g., mice, rats).

Example: Analgesic drugs assessed using the hot-plate test in rodents.

In Vitro: Testing on isolated cells, tissues, or organs.

Example: Measuring muscle contractions in isolated frog legs for neuromuscular drugs.

Ex Vivo: Testing on tissues removed from living organisms.

Example: Uterine tissue assay for oxytocin.

Real-Life Example: Vaccine Development

During the COVID-19 pandemic, rapid drug discovery and bioassay techniques played a critical role.

Preclinical: Animal models confirmed safety and immune response.
Clinical Trials: Phases I–III tested efficacy in humans.
Bioassay: Standardized potency of vaccines by measuring neutralizing antibody levels.

Key Takeaways:

Drug discovery and development are systematic, multi-phase processes.
Clinical trials ensure drug safety and efficacy.
Bioassays are critical for drug standardization and quality control.

END OF THE CHAPTER

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