Therapeutic Action of Different Classes of Drugs


Table of contents


On the basis of therapeutic action, drugs mainly can be classified into following types.

Classification of drug action based on therapeutic agents and their uses are as:


Excess production of Hydrochloric acid in our stomach cause irritation and pain. Sometimes in severe cases, ulcers can also be produced in the stomach. Hence, ‘the substances which neutralize the excess acid and raise the pH to an appropriate level in stomach are called Antacids’.

ExamplesSodium Bicarbonate, magnesium hydroxide etc.

However excessive bicarbonate in the stomach makes it alkaline and rapidly starts the production of even more acid. Therefore, metal hydroxides are better alternatives because they being insoluble do not increase the pH above neutrality.

The secretion of pepsin and hydrochloric acid is stimulated by Histamine. Therefore, the drug cimetidine was developed to stop the interaction of histamine with the receptors that are present in the stomach wall. As a result, less hydrochloric acid is released and the problem of hyperacidity can be solved.

Structure of drug Cimetidine

Fig.1: Structure of drug Cimetidine

Now days, drugs omeprazole and lansoprazole have been widely used as antacid as they prevent the formation of acid in the stomach.

Structure of drug Omeprazole

Fig.2: Structure of drug Omeprazole

Structure of drug Lansoprazole

Fig.3: Structure of drug Lansoprazole


The drugs which combat the effect of histamine a chemical released by certain cells of the body (mast cell) during an allergic reaction is called Antihistamines.

Actually Histamine is a chemical substance released by our body and cause hypersensitivity or allergy to some people towards dust, pollen grains, cat fur, fabric etc. Histamine is potent vasodilator. It contacts with the smooth muscle in the bronchi and gut and relaxes other muscles such as those present in the walls of fine blood vessel, as a result histamine caused allergy.

Antihistamines are widely used for the treatment of hay fever, conjunctivitis, seasonal rhinitis etc. the antihistamine drugs which are widely used are brompheniramine and terfenadine, diphenylhydramine (Benadryl), cetirizine, promethazine.

Structure of brompheniramine structure of terfenadiene

 Fig. 4: Structure of brompheniramine

Fig.5: Structure of terfenadiene

Neurologically Active Drugs

These type of drugs contain Tranquillizers and analgesic.


Drugs which are used for the treatment of stress, fatigue, mild and severe mental diseases are called Tranquillizers. They relieve anxiety, stress, irritability or excitement by inducing a sense of well-being. Tranquillizers are of many types and they work by different mechanisms.

For example, Noradrenaline is one of the several neurotransmitters which play an important role in mood change. If the level of noradrenaline in the body is low for some reason, then the message transfer process becomes slow and the person suffers from depression. In such cases, antidepressant drugs are used. These drugs inhibit the enzymes which catalyse the degradation of noradrenaline. Two important antidepressant drugs are iproniazid and phenelzine.

Structure of Iproniazid Structure of phenelzine
Fig.6: Structure of Iproniazid 

Fig. 7: Structure of phenelzine


Drugs which reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbance or disorder of the nervous system are called Analgesic. These are classified into following two categories;

  • Non-Narcotic Analgesics: Aspirin and paracetamol are the most important examples of non-addictive analgesics. Aspirin inhibits the synthesis of compounds known as prostaglandins which stimulate inflammation in the tissue and cause pain. These drugs are quite effective in relieving skeletal pain such as that due to arthritis.

Aspirin  Paracetamol

Fig.8: Aspirin

Fig.9: Paracetamol

  • Narcotic Analgesics: Drugs which when administered in small doses relieve pain and produce sleep are called narcotics. However in large doses, they produce stupor, laziness, coma, convulsions and may ultimately cause death. Most of these are obtained from opium poppy and hence are called opiates. It contains alkaloids like morphine and codeine which are very effective analgesic. Morphine diacetate commonly known as Heroin is the most widely used analgesic.

Structure of morphine  Structure of heroin

Fig.10.  Structure of morphine

Fig.11: Structure of heroin


Drugs which are used to cure diseases caused by microbes or microorganisms such as bacteria, virus, fungi etc. are called Antimicrobials. All antimicrobials control the microbial disease in the following three ways;

  • By using a bacterial drug

  • By using a bacteriostatic drug

  • By increasing immunity and resistance of a body to infections


Antibiotics are now defined as chemical substances, which in low concentration, either kill or inhibit the growth of microorganisms intervening in their metabolic process.

They are classified in two classes which are:

  1. bactericidal which is used to kill bacteria

  2. bacteriostatic which is used to inhibits the growth of bacteria.

The full range of microorganism attacked by an antibiotic is called its spectrum. Broad spectrum antibiotics are effective against several types of harmful bacteria. Certain antibiotics are specific for certain disease. For example, streptomycin is used in tuberculosis and chloramphenicol in typhoid.

Antiseptics and Disinfectants

The chemical substances which prevent the growth of micro-organisms or may even kill them when applied to living tissues like skin, are called Antiseptic. They are generally applied on the wounds, cut, ulcers and diseased skin surface in the form of antiseptic cream.

Examples of Antiseptic: Some generally used Antiseptic are:

  • ChloroxylenolDettol: It is a mixture of chloroxylenol and terpineol in a suitable solvent. It is widely used for cuts, wounds etc.

  • Savlon: It is also widely used antiseptic. It is a solution of chlorhexidine gluconate in a suitable solvent.

  • Bithional: It is added to the soaps to reduce the odour from the skin produce by bacterial decomposition of organic matter on skin.

  • Iodine: It is used as a tincture of iodine(a 2-3% sol. of iodine in alcohol and water)

The chemical substances which are used to kill harmful micro-organisms but are not safe to be applied to the living tissues are called Disinfectants. They are generally used to kill the harmful micro-organisms present in the drains, toilets, floors etc.

ThymolExamples of Disinfectants: Some generally used disinfectants are:

  • 1% solution of phenol is a disinfectant.

  • High concentration of SO2 gas is used as a disinfectant.

  • Thymol, a phenol derivative is used as a powerful disinfectant.

Antiseptic and Disinfectants both are used to kill harmful micro-organisms. But the main difference between them is: that Antiseptic is used in curing living tissue and there is no harm when applied to living tissue but a Disinfectant should not be applied on living tissue as this may cause a fatal injury to the skin or living tissue.

Example: A 0.2% solution of phenol is used as an antiseptic but 1% solution of phenol is used as a disinfectants.


Antipyretic: These drugs are used to reduce fever.

Antifertility Drugs: These drugs reduces the chances of pregnancy and hence called as antifertility drugs.

Frequently Asked Questions (FAQs)

Q1. What are drugs and its Therapeutic action?

Sol.  Drugs are chemical substances of low molecular mass. They interact with the macromolecular targets (carbohydrates, protein, nucleic acid and lipids) to produce a biological response. If these drugs are useful, and can be used for the treatment, diagnosis and prevention of diseases than these drugs are called Therapeutic drugs or medicines.

However taking higher dose of these drugs can act as a potential poison. Hence drugs can also be defined as “A drug is a chemical substance which also cures the disease but is habit forming, causes addiction and has serious side effects”.

Example: Penicillin and heroin both are drugs because penicillin is an effective antibacterial agent and heroin is a power pain killer. But penicillin is called a medicine since it does not have addictive properties while heroin is called a Drug of its pronounced habit forming and addictive properties.

Q2. What is site of action?

Sol. The site of action of a drug may be termed as that drug interacts with macromolecules like carbohydrates, proteins, nucleic acid and lipids in the cell. These macromolecules perform various function in the body. For example, protein performs several roles in the body:

  • Proteins act as biological catalysts in the body are called enzymes

  • Proteins which are crucial to communicate system in the body are called receptors

  • Proteins which carry polar molecules across the membranes are called carrier proteins

Similarly, nucleic acid have coded genetic information for the cell while lipids and carbohydrates act as structural materials for the cell membranes.

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Therapeutic Action of Different Classes of Drugs


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