Classification of Drugs: Types, Functions & Chemical Composition

Classification of Drugs: Drugs are artificial compounds that serve definite purposes. These chemicals are specifically designed and produced for treating ailments and diseases which affect the human body under different circumstances. A student of medicine should have detailed information about the various pharmaceutical drugs and their classifications to be able to find remedies for different types of diseases.

Drugs are chemical substances that alter the body’s function, either physically or psychologically, or even both when consumed. Drugs have low molecular masses (around \(150\) to \(500\,{\rm{u}}\)) that interact with macromolecule targets and produce suitable biological responses. When drugs are taken for a useful and therapeutic biological response, they are known as ‘medicines’. This article covers the important aspects of medicinal drugs, their functions and classifications. Read the complete article to know more.

Introduction

A chemical substance that produces a biological effect when administered to a living organism is known as a drug in pharmacology. When these drugs are taken in the prescribed manner to cure, prevent or diagnose a disease, it is known as medicine. Based on the effects of drugs, they are classified into four different classes based on pharmacological effect, drug action, chemical structure, and molecular targets.

Classification of Drugs

Drugs can be classified mainly based on the following criteria:

1. Pharmacological Effect
2. Chemical Structure
3. Drug Action
4. Molecular Targets

1. Based on Pharmacological Effect – Based on the action of drugs on our body, they are classified based on their therapeutic actions. Such as antacids reduce acidity in the stomach, analgesics are pain killers, antiseptics kill microorganisms, etc.
2. Based on Chemical Structure – Based on the common chemical structures, drugs are classified into various classes. As chemical structures, functional groups, etc., are responsible for their chemical properties. Mostly, drugs having similar chemical structures show similar effects on the body. For example, sulphonamide drugs, barbiturates, etc.
3. Based on Drug Action – Drugs are also classified based on their action on molecular targets and effects on our body. For example, histamines are responsible for causing inflammation in the body, and we take anti-histamines to block their actions.
4. Based on Molecular Targets – Some drugs target protein, carbohydrates, etc. Generally, drugs that have similar structures target similar molecules in our body and produce responses accordingly.

Drug Target Interaction

The process of finding a drug to a specific target location that leads to a change in its function is known as drug-target interaction. The most common biological targets in our body are ion channels, nuclear receptors, G-protein coupled receptors, and enzymes.

Pharmacological Classification of Drugs

Drugs are classified into different classes based on their pharmacological effects on the body. Let’s discuss them one by one.

1. Antacids

In our stomach, hydrochloric acid is present that protects it from foreign particles. But sometimes, due to increased levels of this acid level, lots of health issues occur. Thus, we need antacid medicines. Antacids provide us quick relief from acidity in our stomach that causes indigestion, upset stomach, and heartburn.

They are bases that neutralize the increased amount of acids in our stomach. Antacids include salts of aluminium, magnesium, etc. This class of medicine is used to reduce acid reflux, stomach ulcers, or acidity due to indigestion. One of the most popular antacid tablets is ‘Ranitidine’.

2. Neurologically Active Drugs

Neurologically Active Drugs affect the mechanism of transfer of a message from the nerve to the receptor. They are of two types: Tranquilizers and analgesics.

(a) Tranquilizers: Tranquilizers have a calming effect and eradicate both the physical and psychological effects of anxiety, stress, irritability, or fear and help to induce a feeling of well-being. The drugs are recommended for short- and medium-term use. These drugs form an important component of sleeping pills. For example, noradrenaline is one of the neurotransmitters that play a vital role in mood changes.

If the level of noradrenaline is low due to some reason, then the signal-sending activity decreases, and the person suffers from depression. To cure this, antidepressant drugs are required. Some tranquillizers, namely, chlordiazepoxide, meprobamate, and etizolam, are suitable for relieving tension. Equanil is used to control depression and hypertension.

(b) Analgesics: Analgesics are a class of drugs that help us to achieve ‘analgesia,’ i.e. relaxation from pain. They are also known as pain killers.

They are divided into two classes:

1. Non-narcotic Analgesics
2. Narcotic Analgesics

Non-narcotic Analgesics – They are also known as non-addictive analgesics. The most famous examples of this class of drugs are aspirin and paracetamol. Aspirin, chemically known as acetylsalicylic acid, is used to reduce pain, fever, or inflammation.

Paracetamol is also used to treat moderate pain, body aches, and fever. They are also known as ‘antipyretics’. Antipyretics override the secretion of prostaglandin in the hypothalamus to reduce the body temperature, which results in a reduction of fever.

Narcotic Analgesics – Narcotic analgesics interact with specific opiate receptors and produce desired pharmacological effects like they reduce fever and induce sleep. They may prove to be fatal if these drugs are taken in poisonous doses. Morphine narcotics (obtained from the opium poppy) are chiefly used to get relief from postoperative pain, cardiac pain, and pain of childbirth, cancer, and many more.

3. Antihistamines

Most of the allergy symptoms are treated by a class of drugs known as ‘antihistamines’. They are most commonly used by people who are allergic to pollen and other allergens. These drugs help to treat conditions caused by too much histamine (a potent vasodilator) in our body’s immune system. Synthetic drugs like brompheniramine (Dimetapp), hydroxyzine, viruses and antihistamines.

4. Antimicrobials

Antimicrobials are a group of medicines that stop the growth of microorganisms like bacteria, fungi, viruses, etc. For example, antibiotics are used against bacteria, antivirals are used against viruses, and antifungals are used against fungi. Let’s learn about them in detail:

(a) Antibiotics: Antibiotics are taken to fight against bacterial infection in our body. They are widely used due to their low toxicity to human beings and animals. Though various antibiotics were in use earlier, the real revolution in antibacterial therapy was brought by the discovery of antibacterial properties of a Penicillium fungus by Alexander Fleming in \(1929.\)

Based on the range of wars fought against bacteria, antibiotics are classified as broad-spectrum antibiotics (that includes a broad range of Gram-positive and Gram-negative bacteria) and narrow-spectrum antibiotics (that include a narrow range of Gram-positive and Gram-negative bacteria). For example, Ampicillin, Amoxycillin, Chloramphenicol, etc.

(b) Antiseptics and Disinfectants:

Both Antiseptics and disinfectants kill microorganisms, but the primary difference between them is that an antiseptic is applied to the living body. In contrast, disinfectants are applied to non-living surfaces to kill germs. A commonly used antiseptic is Dettol; it is a mixture of chloroxylenol and terpineol. Chlorine and phenol solutions are known as disinfectants.

5. Antifertility Drugs

These drugs are chemical substances that suppress the effect of hormones that promote pregnancy by inhibiting ovulation. These antifertility drugs actually reduce the chances of pregnancy and act as conception. Antifertility drugs are made up of synthetic progesterone derivatives or a combination of derivatives of estrogen and progesterone. These drugs have brought a great revolution in controlling the population. For example, Norethisterone, nostril, etc.

Classification of Antihypertensive Drugs

To treat hypertension (high blood pressure), various antihypertensive medicines which lower blood pressure are:

(a) Diuretics – Excess salt and water from our blood are eliminated through the kidneys with the help of diuretics.

(b) Calcium Channel Blockers – Calcium channel blockers are drugs that are used to lower blood pressure. Calcium movement is slowed down into the cell’s artery walls, which makes it easier for the heart to pump and dilates blood vessels. As a result, the heart doesn’t have to work as hard to pump blood, and blood pressure decreases.

(c) ACE inhibitors – They inhibit the activity of ACE (Angiotensin Converting Enzyme). This enzyme is responsible for converting Angiotensin I to Angiotensin II (vasoconstrictor).

Classification of Drugs Used in Peptic Ulcers

Drugs of peptic ulcers are broadly classified into three categories:

1. Antacids: They neutralize acidity in our stomach. Due to increased acidity in the stomach, stomach walls get eroded causing ulcers.
2. Anticholinergic: They reduce the secretion of gastric acid and decrease gastrointestinal movement and give us relief from stomach cramps.
3. H2 Receptor Antagonist: They suppress the secretion of gastric acid directly.

Drug List

Some of the commonly used drugs approved by the Food and Drug Administration (F.D.A) in the U.S. and other government bodies are:

1. Paracetamol
2. Amoxicillin
3. Metronidazole
4. Quinine
5. Ciprofloxacin
6. Diclofenac
7. LSD
8. Marijuana (Cannabis)
9. Cocaine
10. Nicotine

Strong Anti-Inflammatory Drugs

Anti-inflammatory drugs reduce swelling or inflammation. Some of these drugs are as follows:

1. Ibuprofen 
2. Naproxen
3. Aspirin
4. Meloxicam
5. Celecoxib
6. Indomethacin

Uses of drugs

Drugs have lots of physical benefits when taken in a prescribed amount. They treat diseases both physical and mental and make us fit and fine. Drugs prevent, cure, suppress, and diagnose diseases. We get a feeling of well-being and energy with the help of drugs!

Disadvantages of Drugs

1. Drugs affect our central nervous system negatively.
2. Some drugs are very dangerous for the lungs, blood pressure, etc.
3. Heroin is a neurologically active drug that has severe side effects on blood pressure, bad teeth, constipation, and depression.
4. Dose-related toxicity occurs if a higher dose of drugs is taken.
5. Drugs have long-term complications in our bodies.
6. The tolerance level of a drug increases with its prolonged use.
7. Drug addiction leads to a lot of diseases, and disabilities for individuals that hamper them physically as well as mentally.

Summary

We have learned how important drugs in our lives are. They cure and save us from many diseases due to we can lead a normal and happy life.

Every drug performs a specific function, and on that basis, they are divided into various groups. Like antacids relieves acidity in the stomach, antihistamines treat allergic issues, tranquillizers and analgesics are neurologically active drugs that affect our central nervous system. Thus we can conclude that classification of drugs is necessary for proper treatment and cure of diseases.

Frequently Asked Questions (FAQs) on Classification of Drugs

Q.1: What is an Anti-Inflammatory Drug example?
Ans: Some commonly used NSAIDs (Non-steroidal anti-inflammatory drugs) include aspirin, ibuprofen, and naproxen (such as Naprosyn). NSAIDs drugs help to reduce inflammation, which often helps to relieve pain. In other words, they’re anti-inflammatory.

Q.2: What drugs commonly cause problems, and how do they affect the body?
Ans: Various types of drugs affect your body in different ways. However, they can have both short-term and long-term effects on our body, which can be both physical and psychological, but they can cause side effects that can be problematic in the future. Overuse of drugs can quickly start to affect our health and other aspects of our life. For example, drug addiction (opioids) can cause hallucinations. Common side effects of drugs include constipation, dermatitis, diarrhoea, dizziness, headache, insomnia, and many more.

Q.3: How are drugs classified?
Ans: Drugs are classified into four different classes based on biological responses such as pharmacological effect, drug action, chemical structure, and molecular targets.

Q.4: What are the main Drug Classification Systems?
Ans: Drug classification systems are essential because it provides the ability to assign medications to a structured hierarchy for various categories such as action mechanism, physiological effects, and therapeutic actions. No single classification system can meet all of these needs. Hence, there are multiple criteria by which we can classify drugs such as stimulants, depressants, antacids, antimicrobials, and many more.

Q.5: What are the 5 Classifications of Drugs?
Ans: The major five classifications of drugs are Central nervous system depressants (e.g.alcohol), Central nervous system stimulants (e.g. cocaine), Opiates and Opioids (e.g. heroin), Hallucinogens, and Marijuana (e.g. LSD).