In the field of pharmacology, a drug refers to a chemical substance that, when administered to a living organism, produces a specific biological effect. Medicine refers to drugs that are taken as prescribed to treat, prevent, or diagnose a disease. A drug, also known as a pharmaceutical, refers to a substance that is utilized to prevent, cure, or alleviate the symptoms of a disease or ailment. The term “drug” can also be used to describe an illegal or controlled substance that individuals use for recreational purposes or to achieve a state of intoxication. Let’s focus our discussion on the topic of pharmaceutical drugs.
What are Drugs?
Drugs are substances that can modify or impact the functioning of a living organism when ingested. These substances typically have a relatively small molecular size, ranging from approximately 100 to 500 atomic mass units (u). When these drugs interact with macromolecular targets, they elicit a biological response. Biological responses that are beneficial and therapeutic can be harnessed for medicinal purposes. They are utilized in the diagnosis, prevention, and treatment of various diseases.
Classification of Drugs
The classification of drugs is used to categorize and organize different types of drugs based on their properties, effects, and potential risks.
Drugs are categorized into different groups based on their pharmacological effects, mechanisms of action, chemical structures, and molecular targets. Drug classification is an important process that aims to ensure the optimal and effective prescription and use of medications.
Classification of Drugs By Pharmacological Effect
The impact that medicine has on the body is known as its pharmacological impact. Drugs are divided into several categories based on this effect:
To alleviate pain without inducing drowsiness, analgesics are used. Both narcotic (such as morphine and codeine) and non-narcotic (such as acetaminophen and ibuprofen) analgesics exist.
Antacids are medications used to treat acid indigestion, heartburn, and stomach discomfort by neutralizing stomach acid. Magnesium hydroxide, aluminum hydroxide, and calcium carbonate are a few examples.
Anxiolytics (or anti-anxiety medicines) are pharmaceuticals that alleviate nervousness and anxiety. Diazepam, lorazepam, and alprazolam are only a few examples.
To treat bacterial infections, antibiotics are used. The antibiotics penicillin, tetracycline, and erythromycin are only a few examples.
Antidepressants are medications used to treat major depressive disorder and other mood disorders. Paroxetine, sertraline, and fluoxetine are a few examples.
Histamine is a substance the body produces in reaction to allergens; antihistamines are medications that counteract its effects. They help alleviate allergy symptoms including sneezing and scratching. Diphenhydramine, loratadine, and cetirizine are only a few examples.
Anti-inflammatory medications, or NSAIDs, are pain relievers and swelling suppressants. Conditions like arthritis and asthma can be alleviated with their help. Aspirin, ibuprofen, and naproxen are just a few examples.
An antiseptic is a chemical that kills or inhibits the growth of disease-causing bacteria and other diseases. Antiseptics work by either directly killing the microbes or blocking their growth. Antiseptics have many uses, including cleaning wounds and treating gastrointestinal and urinary tract infections. The 1% solution of iodoform (CHI3) is used as an antiseptic and disinfectant.
Phenol solutions of 0.2% are antiseptic, whereas those of 1% are disinfectants. Hydrogen peroxide’s major function as an antiseptic is in wound cleansing.
Medications are used to manage psychotic conditions like schizophrenia. Among these are chlorpromazine, clozapine, and haloperidol.
Bronchodilators are medications that ease breathing by relaxing the muscles in and around the bronchial airways. Asthma and COPD are just two of the diseases that these are used to treat. Albuterol, salmeterol, and ipratropium are only a few examples.
Classification of Drugs By Drug Action
On the basis of their pharmacological actions, where “drug action” is the term used to describe how a drug actually acts in the body to provide its therapeutic effect. Drugs are categorized according to the following effects:
Agonist and Antagonists
Therapeutic effects can be achieved by the use of a class of medicines known as agonists. Opioid agonists like morphine and beta-2 agonists like albuterol are two such examples.
To counteract the effects of agonists, there are medications known as antagonists. Naloxone, which blocks the effects of opioids, and flumazenil, which blocks the effects of benzodiazepines, are two such drugs.
Enzyme inhibitors, which are medications that prevent enzymes from doing their job in the body. Acetylcholinesterase inhibitors and angiotensin-converting enzyme (ACE) inhibitors are two examples of drugs used to treat various medical conditions.
Ion Channel Blockers
Drugs known as ion channel blockers are used to prevent the passage of ions through their intended cellular membrane ion channels. Hypertension can be treated with calcium channel blockers, while epilepsy can be managed using sodium channel blockers.
Classification of Drugs Based on Molecular Targets
Drug molecules have the ability to interact with various biomolecules, including enzymes and receptors. These biomolecules, commonly known as drug targets, serve as the specific sites where the drug molecules exert their effects. Drug classification can be determined by the specific drug target to which it binds. The level of specificity in this classification is notably higher in comparison to the other classifications. These compounds frequently exhibit a shared mechanism of action due to their common target.
Classifying medications according to their effects on specific target molecules in the body, such as receptors, enzymes, and ion channels, is called drug classification based on molecular targets. A better knowledge of these relationships can aid in the discovery of new medications and the prevention of harmful drug interactions. The following are examples of well-known drug classes defined by their molecular targets: (I) G protein-coupled receptors; (II) Nuclear receptors; (III) Ion channels; (IV) Enzymes; (V) Pathogens
G protein-coupled receptors (GPCRs)
The G protein-coupled receptor (GPCR) family of cell surface receptors mediates several physiologic processes in the body. Significant therapeutic effects, such as pain relief and inflammation reduction, can be achieved with drugs that activate or inhibit GPCRs. Morphine used to treat extreme pain, and epinephrine, used to treat asthma, are both examples of GPCR agonists. Beta-blockers and antihistamines, both used to treat hypertension, are examples of GPCR antagonists.
The prevention or alteration of the course of a disease can be achieved through the use of enzyme inhibitors. Enzymes are molecules that catalyze biological events in the body. It is possible to divide enzyme inhibitors into two classes: those that are reversible and those that are irreversible. Reversible inhibitors bind to the enzyme non-covalently and can be either competitive or non-competitive, while irreversible inhibitors bind to the enzyme covalently and are therefore irreversible. Drugs that block enzyme activity include those that treat Alzheimer’s disease (acetylcholinesterase inhibitors) and HIV (protease inhibitors).
Enzymes as Drug Target
Enzymes serve as viable targets for drug development due to their crucial role in catalyzing biochemical reactions within living organisms. Therefore, the actions of these enzymes are crucial for the proper functioning of the system. If the regular functioning of enzymes is hindered, it will have an impact on the system. This principle is commonly employed to eliminate a wide range of pathogens.
It has been previously established that in enzymatic reactions, the substrate molecule forms a binding interaction with the active site of the enzyme through weak forces, including hydrogen bonding and van der Waals forces. These weak forces arise from the interactions between the amino acids located in the active site and the substrate.
The administration of a drug molecule that possesses a comparable geometry (shape) to the substrate can result in its binding to the enzyme, thereby leading to the inhibition of its activity. In essence, the drug functions as a catalyst inhibitor for the enzyme. These inhibitors are commonly referred to as competitive inhibitors.
Receptors as Targets
Drug targets, known as receptors, play a crucial role in the physiological effects of numerous drugs. These receptors are responsible for binding to specific molecules, thereby initiating cellular responses. The majority of receptors are embedded within the cell membranes, positioning their active sites towards the external region of the membrane. Chemical messengers, also known as compounds responsible for transmitting messages to cells, exhibit a binding affinity towards the active site of these receptors. This process facilitates the transmission of information into the cell.
These receptors exhibit a significant degree of selectivity towards a specific chemical messenger in comparison to other chemical messengers. In order to impede the transmission of a message, it is necessary to employ a pharmaceutical agent that can effectively bind to the specific receptor site associated with the message. By doing so, the drug can effectively hinder the natural function of the receptor, thereby preventing the message from being transmitted. These pharmaceutical substances are commonly referred to as antagonists. On the other hand, there exist pharmaceutical substances that imitate the actions of endogenous messengers by activating the corresponding receptors. These drugs are classified as agonists and are administered in cases where there is a deficiency of a specific chemical messenger.
Pharmacology Classification of Drug By Chemical Structure
Understanding the physical and molecular features of medications, as well as their methods of action and potential adverse effects, is greatly aided by this classification system.
Based on their molecular makeup, the following are some of the most frequent types of drugs:
Alcohol: Compounds with a hydroxyl (-OH) group linked to a carbon atom are called alcohols. Alcohols are utilized in medicine as solvents and antiseptics; ethanol, a component of alcoholic beverages, is one such alcohol.
Amines: Compounds with a nitrogen atom linked to one or more carbon atoms are called amines. Amines are a class of pharmaceuticals that includes many commonly used medications.
Carboxylic acids: Carbon-based molecules with an attached carboxyl (-COOH) group are known as carboxylic acids. Aspirin is a carboxylic acid and a common analgesic and anti-inflammatory medication.
Esters: When alcohol combines with a carboxylic acid, a new molecule called an ester is produced. Esters can be found in a wide variety of medications.
Phenols: Compounds with a hydroxyl (-OH) group linked to an aromatic ring are called phenols. Antiseptics, disinfectants, and anesthetics are only a few of the many medications that are phenols.
- https://byjus.com/chemistry/classification of drugs/