Maarg Manthan · Topic 7.2

Chemistry of Pharmaceuticals

Science & Technology › Chemistry in Daily Life and Biomolecules · Topic 7.2

Pharmaceutical chemistry deals with the design, making and action of medicines. A drug is a chemical that affects the body to prevent, treat or diagnose disease. Most drugs act by binding to a target in the body, such as an enzyme, a receptor or a transport protein. Enzyme inhibitors block an enzyme, receptor agonists activate a receptor, and antagonists block it. Drugs are grouped by their effect, such as analgesics for pain, antipyretics for fever, antiseptics, antibiotics, antacids, antihistamines, tranquillisers and antidiabetic drugs. Paul Ehrlich proposed the idea of a magic bullet and introduced salvarsan for syphilis in 1909. New drugs go through preclinical studies and clinical trials in phases I to III before approval, and phase IV monitors safety after approval.

5 min read · UPSC Prelims · Science & Technology · Chemistry in Daily Life and Biomolecules

At a Glance

Magic bullet Paul Ehrlich, 1909
Pain relievers Aspirin, paracetamol, morphine
Antiseptic Used on living tissue
Disinfectant Used on objects
Trial phases I, II, III, IV
Exam link UPSC Prelims, Science & Technology: Chemistry in Daily Life and Biomolecules

Where Does It Fit?

This is the second topic of the macro on chemistry in daily life and biomolecules. It links the earlier health macro on diseases and drugs to the chemistry of the medicines themselves. Previous topic: Polymers and Biopolymers. Next topic: Carbon and Its Allotropic Forms.

Which Classes of Drugs Should You Know?

Class	Examples and action
Analgesics	Reduce pain. Non-narcotic such as aspirin and paracetamol, and narcotic such as morphine and codeine, which act on the nervous system and can cause dependence
Antipyretics	Reduce fever, such as paracetamol and aspirin
Antiseptics	Applied on living tissue to kill or stop microbes, such as dilute iodine tincture, boric acid, hydrogen peroxide and phenol at 0.2 per cent
Disinfectants	Used on non-living things such as floors and instruments, such as chlorine, bleach and phenol at 1 per cent
Antibiotics	Kill or stop bacteria. Narrow-spectrum drugs act on few kinds, and broad-spectrum on many, as in Antibiotic Medications and Antimicrobial Resistance (AMR)
Antacids	Neutralise excess stomach acid, such as magnesium hydroxide, aluminium hydroxide and sodium bicarbonate. Ranitidine and omeprazole reduce acid production
Antihistamines	Block histamine in allergy, such as cetirizine
Tranquillisers	Calm anxiety, such as diazepam, and antidepressants
Antidiabetic drugs	Insulin and metformin, as in Lifestyle Diseases: Diabetes Mellitus and Other Non-Communicable Diseases

How Are Drugs Discovered and Tested?

Sources: many drugs come from plants, such as aspirin from willow bark, quinine from cinchona and morphine from opium poppy, from microbes, such as penicillin, or are designed in laboratories.
Target-based design: chemists use knowledge of the shape of the target to design molecules that fit, with computers helping to screen millions of compounds.
Preclinical studies: tests on cells and animals for effect and toxicity.
Clinical trials: phase I tests safety in a small group, phase II tests effect and dose, phase III confirms benefit in large groups, and phase IV follows safety after sale.
Regulation: in India the Central Drugs Standard Control Organisation approves drugs and trials under the New Drugs and Clinical Trials Rules, 2019.
Drug development time: often 10 years or more and costly, as in Drug Cost Structure and Pricing in India.

What Else Should You Remember?

Aspirin: acetylsalicylic acid, first sold by Bayer in 1897. It reduces pain, fever and inflammation, and in low doses thins blood, but can irritate the stomach.
Paracetamol: reduces pain and fever but not inflammation, and overdose damages the liver.
Sulpha drugs: the first broad antibacterial medicines, found by Gerhard Domagk in the 1930s.
Food additives: preservatives such as sodium benzoate, antioxidants such as BHA and BHT, artificial sweeteners such as saccharin, aspartame and sucralose, and colours, regulated by FSSAI.
Soaps and detergents: soaps are sodium or potassium salts of fatty acids, made by saponification of fats with alkali, and they form scum in hard water. Synthetic detergents work in hard water, and non-biodegradable ones cause foaming and pollution.
Active pharmaceutical ingredients: the main chemical in a medicine. India is the largest supplier of generic medicines but imports many ingredients, and the Government has launched production-linked incentives for bulk drugs.
Misuse: self-medication, overuse of antibiotics and painkillers and drug abuse carry risks, and the Narcotic Drugs and Psychotropic Substances Act, 1985 controls narcotics.
Chiral drugs: the same molecule can exist in mirror-image forms with different effects, as in the tragedy of thalidomide.
Pharmaceuticals industry: the pharmaceuticals industry in India is the third largest in the world by volume, and it makes about a fifth of the global supply of generic medicines.
Antiseptics: antiseptics used in homes include dilute Dettol, tincture of iodine and hydrogen peroxide, and each has a specific concentration for safety.
Preservatives: food preservatives such as salt, sugar, vinegar and sodium benzoate slow the growth of microbes.

Why Does It Matter for the Exam?

Classification questions: drug with its category, and antiseptic versus disinfectant.
Trial questions: what each phase tests and who regulates.
Policy link: bulk drug parks, generics and drug quality.
Everyday chemistry: soaps, detergents and food additives.
Common errors: mixing antiseptics with disinfectants or calling all painkillers addictive.

As an analytical point, a good drug is selective, effective and safe. Knowing the target explains both the benefits and the side effects.

Why Is This Topic Important?

Facts Drug classes asked
Process Trial phases
Everyday Soaps and additives

What Came Next?

The next topic covers carbon and its allotropic forms. Next topic: Carbon and Its Allotropic Forms.

Key People and Terms

Analgesic Pain reliever
Antiseptic Applied on living tissue
Antacid Neutralises stomach acid
Saponification Making soap from fat and alkali
Receptor Target protein for a drug
API Active pharmaceutical ingredient

Exam Corner

Points to Remember

Aspirin: Bayer, 1897.
Ehrlich: salvarsan, 1909.
Phenol 0.2% antiseptic; 1% disinfectant.
Soap by saponification.
Trial phase III confirms benefit.

Do Not Confuse With

Antiseptic and disinfectant On living tissue versus on objects
Narcotic and non-narcotic analgesic Morphine versus aspirin
Soap and detergent Fatty acid salt versus synthetic cleanser

Memory Hook

Analgesic pain, antipyretic fever; antiseptic on skin, disinfectant on floor; trials four phases, saponification soap.

Mains Angle

Questions link drug chemistry with regulation and daily life. These points add depth.

Classes Drug types
Process Discovery and trials
Daily life Additives and cleaners

A Question You May Face

An original practice question, not a past paper question.

“Describe the main classes of drugs with examples and explain how new drugs are developed and tested.”

How to Answer

Target How drugs act.
Classes Examples.
Trials Phases.
Regulation CDSCO.

GS Relevance

Prelims: drug classes and examples, antiseptic versus disinfectant, trial phases, soaps and detergents. GS Paper 3: science and technology, health.

Frequently Asked Questions

What is the difference between an antiseptic and a disinfectant?

An antiseptic is a chemical applied to living tissue such as skin or wounds to kill or stop the growth of microbes, as with dilute iodine or 0.2 per cent phenol. A disinfectant is used on non-living things such as floors and instruments, as with chlorine or 1 per cent phenol, and is too harsh for the body.

What are analgesics?

Analgesics are drugs that reduce pain without causing loss of consciousness. Non-narcotic analgesics such as aspirin and paracetamol also reduce fever, while narcotic analgesics such as morphine and codeine act on the brain, are strong and can cause dependence, so their use is controlled by law.

How do antacids work?

Antacids are weak bases such as magnesium hydroxide, aluminium hydroxide and sodium bicarbonate that neutralise excess hydrochloric acid in the stomach and relieve heartburn. Other medicines such as ranitidine and omeprazole reduce the production of acid instead of neutralising it.

What are the phases of clinical trials?

Phase I tests the safety and dose of a new drug in a small group of healthy volunteers or patients. Phase II tests whether it works and the best dose in a few hundred patients, phase III confirms benefit and safety in large numbers, and phase IV monitors long-term effects after the drug has been approved for sale.

How is soap made?

Soap is made by saponification, in which a fat or oil is heated with a strong alkali such as sodium hydroxide, giving sodium salts of fatty acids, which are soap, and glycerol. Soaps form scum with the calcium and magnesium salts of hard water, while synthetic detergents do not.

PYQ Practice — Statement Analysis

1 Aspirin is a non-narcotic analgesic.

True

It also reduces fever.

2 A disinfectant can be safely applied on living tissues.

False

That is an antiseptic.

3 Paul Ehrlich introduced the idea of a magic bullet.