In the last article, we have studied medicines in everyday life, like analgesics, antipyretics, antihistamines, tranquilizers, antifertility, and antimalarials. In this article, we shall study, antimicrobials, antibiotics, antiseptics, and disinfectants.

The action of Microbes in the Body:

The living organisms which cannot be seen with the naked eyes (unaided eyes) and can only be observed through a microscope are called microorganisms or microbes. They include bacteria, fungi, algae, and viruses. They are present almost everywhere air, water, soil, inside and on our body. The disease-producing microbes are called pathogens.

Our body has an efficient defense structure against these pathogens. Skin prevents microbes to enter our body. Some secretions like lysosomes in tears, nasal secretions, saliva, fatty acids, lactic acid in sweat, hydrochloric acid in stomach kill these microbes or inhibit their growth. The breach of this defense system allows the pathogens to reach tissues and cause infection in the body. Due to which normal metabolic activities are disturbed.  This results in a disease. Pathogens produce toxins which may affect tissues and organs of the host.

Antimicrobials:

Antimicrobials are drugs which tend to destroy/prevent development or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs), fungi (antifungal agents), virus (antiviral agents), or other parasites (antiparasitic drugs) selectively. Antibiotics, antiseptics, and disinfectants are antimicrobial drugs.

The antimicrobials that kill bacteria are called bactericidal. Those inhibit the growth of bacteria are called bacteriostatic. Some antimicrobial increase immunity of the body. Germbacteriologistist Paul Ehrlich developed the first antimicrobial called arsphenamine (Salvarsan) for treatment of syphilis.

Sulpha drugs like sulphadiazine, sulphathiazole, sulphanilamide, sulphacetamide, sulphafurazole have great antibacterial power.

Antibiotics:

Antibiotics are used as drugs to treat infections because of their low toxicity for humans and animals. Initially, antibiotics were classified as chemical substances produced by microorganisms (bacteria, fungi, and molds) that inhibit the growth or even destroy microorganisms. The development of synthetic methods has helped in synthesizing some of the compounds that were originally discovered as products of microorganisms. Also, some purely synthetic compounds have antibacterial activity, and therefore, the definition of antibiotic has been modified. An antibiotic now refers to a substance produced wholly or partly by chemical synthesis, which at low concentrations inhibits the growth or destroys microorganisms by intervening in their metabolic processes.

The complete range of microorganisms which are attacked by an antibiotic is called a spectrum. The antibiotics effective against several different types of harmful microorganisms are called broad-spectrum antibiotics. e,g, Tetracycline, Chloramphenicol, etc.

In 1929 Alexander Fleming found antibacterial properties of a Penicillium fungus.

By substitution of different R groups, about 6 natural penicillins have been isolated so far. following five are from these 6 types.

Ampicillin and amoxicillin are semi-synthetic modifications of penicillin.

It is absolutely essential to test the patients for sensitivity (allergy) to penicillin or its modifications ampicillin and amoxicillin before it is administered.

In India, penicillin is manufactured at the Hindustan Antibiotics in Pimpri, at Indian Drugs and Pharmaceuticals Limited at IDPL Rishikesh and in private sector industry.

Types of Antibiotics:

Depending Upon Effect:

Antibiotics have either cidal (killing) effect or a static (inhibitory) effect on microbes. Depending upon these effects antibiotics are classified into two types bactericidal and bacteriostatic respectively.

• Examples of bactericidal antibiotics: Penicillin, Ofloxacin, Aminoglycosides, etc.
• Examples of bacteriostatic antibiotics: Erythromycin, Tetracycline,  Chloramphenicol, etc.

Depending Upon Spectrum:

The range of bacteria or other microorganisms that are affected by a certain antibiotic is expressed as its spectrum of action. The complete range of micro-organisms attacked by an antibiotic is called spectrum.

• Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria are said to be broad-spectrum antibiotics. Ampicillin and Amoxycillin are synthetic modifications of penicillin are broad spectrum Antibiotics. Other examples are tetracycline, chloramphenicol, vancomycin, ofloxacin.
• Antibiotics effective mainly against Gram-positive or Gram-negative bacteria are narrow spectrum antibiotics. e.g. Penicillin G5. Antibiotics effective against a single organism or disease, they are referred to as limited spectrum antibiotics.

Some Important Antibiotics:

Chloramphenicol is a broad spectrum antibiotic. It is rapidly absorbed from the gastrointestinal tract and hence can be given orally in case of typhoid, dysentery, acute fever, whooping cough, a certain form of urinary infections, meningitis, and pneumonia.

• Vancomycin and ofloxacin are the other important broad-spectrum antibiotics.
• The antibiotic dysidazirine is supposed to be toxic towards certain strains of cancer cells.
• Streptomycin is used for the treatment of tuberculosis. In low concentration it is bacteriostatic and in high concentration it is bactericidal.
• p-Aminosalicylic acid (PAS) and isonicotinhydrazine or isoniazid (INH) are also used for the treatment of tuberculosis.

Sulpha Drugs:

Sulpha drugs are derivatives of sulphanilamide. They were first introduced as medicine by Gerhard Domagk in 1930.

Sulphapyridine – Cure for pneumonia

Sulphadiazine – Cure for pneumonia, throat infection, meningitis,

Sulphaguanidine – Cure of bacillary dysentery

Sulphathiazole – Useful against staphylococcal infections and bubonic plague.

Succinyl sulphathiazole – Useful in intestinal infections such as bacillary dysentery and cholera)

Sulphaacetamide – Used to cure urinary tract infections.

Antiseptics:

Drugs which are applied to the living tissues to kill the bacteria and to stop their growth in
wound thus preventing its infection are called antiseptics.

Examples: Iodoform, boric acid, dilute solution of phenol, hydrogen peroxide. Dettol, tincture iodine, soframycin, furacine.

Antiseptics prevent the wound from infection. It is to be noted that antiseptics do not heal wounds. 2 to 3 % solution of iodine in alcohol and water is called tincture iodine. It is a powerful antiseptic and is applied to wounds.

Dettol is antiseptic and a mixture of terpineol and chloroxylenol.

Bithional (the compound is also called bithionol) is added to soaps to impart antiseptic properties.

Boric acid in dilute aqueous solution is weak antiseptic for eyes. Antiseptics are mixed with deodorants, face powders, and breath purifiers. Amyl meta-cresol is used as antiseptics in mouthwash or for gargling.

Uses of Antiseptics:

• They are used to dress the wounds.
• They are used to destroy fungal growth.
• They are used to sterilize surgical instruments.
• They are used in anti-infective in deodorants, shampoos and surgical soaps.

Disinfectants:

Drugs which are applied to the nonliving objects to kill the bacteria and to stop their growth are called disinfectants. They are not safe to be applied to living tissues.

Examples: Concentrated solution of phenol, sulphur dioxide, chlorine, Chlorine in the concentration of 0.2 to 0.4 ppm in aqueous solution. Sulphur dioxide in very low concentrations are disinfectants.

Uses of Disinfectants:

• They kill microorganisms on nonliving objects and used on public health floor and
  to sterilize the surgical instruments.

Difference Between Antiseptics and Disinfectants:

Antiseptics:

• Drugs which are applied to the living tissues to kill the bacteria and to stop their growth in wound thus preventing its infection are called antiseptics.
• Antiseptics are applied to the living tissues such as wounds, cuts, ulcers and diseased skin surfaces.

Disinfectants:

• Drugs which are applied to the nonliving objects to kill the bacteria and to stop their growth are called disinfectants.
• Disinfectants are applied to inanimate objects such as floors, drainage system, instruments.

Important Discoveries in the Field of Medicine:

• Fellix Hoffman (German chemist) – Synthesis of Aspirin
• LeoSternbach (Polish Jewish chemist) – Discovered benzodiazepines (A class of tranquilizers)
• Selman Waksman (Jewish American biochemist) – Discovery of Streptomycin
• Alexander Fleming (Scotish pharmacologist) – Discovery of penicillin
• Paul Ehrich (German scientist) – a compound containing arsenic to treat syphilis, Discovered salvarsan and protonsil.

In the next article, we shall study the chemicals in food.

Previous Topic: Analgesics, Antipyretics, Antihistamines, Tranquilizers, Antifertility drugs, and Antimalarials.

Next Topic: Use of Chemicals in Food

Science > Chemistry > Everyday Chemistry > Everyday Medicines 02

The post Everyday Medicines 02 appeared first on The Fact Factor.

In the last article, we have studied the mechanism of action of a drug. In this article, we shall study some everyday medicines like analgesics, antipyretics, antihistamines, antifertility, and tranquilizers.

Antipyretics:

Chemical substances that are used to bring down body temperature with high fevers are called antipyretics. They don’t have any effect on the human body when it is at normal temperature. This causes the body to lose heat and thus the temperature of the body decreases. Aspirin, Paracetamol, Analgin, Phenacetin acts as antipyretics.

Aspirin is common antipyretic. But it has the side effect. on hydrolysis, it gives salicylic acid which causes bleeding in the stomach. It should not be taken on an empty stomach. Some persons are allergic to aspirin. The usual allergic reactions are rashes on the skin, lowering of blood pressure, profuse sweating, intense thirst, nausea, and vomiting.

Calcium and sodium salts of aspirin are more soluble hence are less harmful. Aspirin has anti-blood clotting action. Hence it is used in the prevention of heart attacks. Other antipyretics used are novalgin, phenyl butazone, methacetin and butazolidine.

Chemical Names:

• Aspirin: 2-Acetoxybenzoic acid
• Paracetamol: 4-Acetamidophenol
• Phenacetin: N-(4-Ethoxyphenyl)acetamide
• Methacetin: 4-Methoxy acetanilide.

Preparation of Aspirin:

When salicylic acid is treated with the mixture of acetic anhydride and glacial acetic acid in presence of concentrated sulphuric acid, acetylation of salicylic acid takes place and aspirin is obtained.

Analgesics:

Analgesics are drugs which reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbances of the nervous system.

Note: Aspirin, novalgin, phenacetin and combiflam act both as antipyreic as well as analgesic.

Analgesics are classified as follows:(i) Non-narcotic (non-addictive) analgesics(ii) Narcotic drugs

Non-narcotic (non-addictive) Analgesics:

Aspirin and paracetamol belong to the class of non-narcotic analgesics. Aspirin inhibits the synthesis of chemicals known as prostaglandins which stimulate inflammation in the tissue and cause pain. These drugs are effective in relieving skeletal pain such as that due to arthritis. These drugs have many other effects such as reducing fever (antipyretic) and preventing platelet coagulation. Because of its anti-blood clotting action, aspirin finds use in the prevention of heart attacks.

Some other analgesics are Novalgin, Butazolidine or phenylbutazone, ibuprofen, naproxen and diclofenac sodium or potassium.

Narcotic (addictive) Analgesics:

Morphine and many of its homologues, when administered in medicinal doses, relieve pain and produce sleep. Adverse effects are vomiting, dysphoria, fatigue, mental confusion. In poisonous doses, these produce stupor, coma, convulsions and ultimately death. They are very potent drugs and their chronic use leads to addiction.

Morphine narcotics are sometimes referred to as opiates since they are obtained from the opium poppy. Another source of narcotics is a marijuana plant. These analgesics are chiefly used for the relief of postoperative pain, cardiac pain and pains of terminal cancer, bone fracture, and in childbirth. These analgesic relieve pain but they attack the central nervous system and produce sleep and unconsciousness.

Other narcotic analgesics are codeine, pethidine hydrochloride, methadone, heroin etc.

Tranquilizers or Hypnotics:

Tranquilizers are a class of chemical compounds used for the treatment of stress, mental tension, anxiety, mania ( a disorder of mood), insomnia (sleeping sickness), discomfort feeling and mild or even severe mental diseases. Tranquilizers are also known as psychotherapeutic drugs.

These relieve anxiety, stress, irritability or excitement by inducing a sense of well-being. They form an essential component of sleeping pills.

Reserpine and chlorpromazine, two powerful tranquilizers were introduced simultaneously.

Examples: Equanil (controlling depression and hyper tension), valium (diazepam), veronol, meprobamate (relieving stress), chlordiazepoxide, serotonin etc. are mild tranquilizers. Other examples are amytal, seconal, librium,

Barbiturates:

The derivatives of the barbituric acid obtained by condensation of urea and malonic acid are called barbiturates.  They form another class of tranquilizers. Examples: Veronal, Amytal, Nembutal, luminal. Barbiturates act on the central nervous system and are hypnotic, i.e., sleep producing agents. Hence they are used to control hypertension and depression.

Treatment of Depression:

Noradrenaline is one of the neurotransmitters that play a role in mood changes. If the level of noradrenaline is low for some reason, then the signal-sending activity becomes low, and the person suffers from depression.

In such situations, antidepressant drugs are required. These drugs inhibit the enzymes which catalyze the degradation of noradrenaline. If the enzyme is inhibited, this important neurotransmitter is slowly metabolized and can activate its receptor for longer periods of time, thus the effect of depression is counteracted.

Drugs used are Iproniazid and phenelzine.

Side Effects of Tranquilizers:

They produce side effects like a headache, weight gain, discomfort, blurring of the vision.

Classifications of Drugs Used for Mental Treatment:

• Narcotics: used as analgesics and antidepressants. e.g. heroin, opium, pethidine.
• Hypnotics: used as tranquilizers and to reduce anxiety and mental tension. e.g. Equanil
• Sedatives (depressants): used to reduce the action of the central nervous system. They induce a feeling of relaxation, calmness, drowsiness, and reduces the wildness of the patient. e.g. valium, barbiturates
• Antidepressants: given to patients lacking confidence. They are called mood boosters. It induces a feeling of well being. e.g. Vitalin, Methadrine and cocaine.

Antifertility Drugs:

Antifertility drugs are the chemicals which are used to check pregnancy in women. These drugs control menstrual cycle and ovulation. These drugs are mainly used in the form of oral pills. The active ingredient in the pills acting antifertility agents are steroids.

The birth control pill is a mixture of synthetic estrogen and progesterone derivatives (synthesized steroids). They are more potent than natural hormones. Progesterone suppresses ovulation. Some of the contraceptive pills contain norethindrone (synthetic progesterone derivative) and ethynylestradiol (Novestrol) (synthetic estrogen derivative).

The active component of ‘morning after pill’ is a synthetic steroid mifepristone. It blocks the effect of progesterone and checks pregnancy.

Antacids:

Basic substances which neutralize the excess of hydrochloric acid in the stomach and raises the pH to appropriate level are called antacids

Examples: Magnesium hydroxide, aluminium hydroxide, Ranitidine (Zantac) is commonly used an antacid.

Overproduction of acid in the stomach causes irritation and pain. In severe cases, ulcers are developed in the stomach. The earlier treatment for acidity was the administration of antacids, such as sodium hydrogen carbonate or a mixture of aluminium and magnesium hydroxide.

However, excessive hydrogen carbonate can make the stomach alkaline and trigger the production of even more acid. Metal hydroxides are better alternatives because of being insoluble, these do not increase the pH neutrality.

These treatments control only symptoms, and not the cause. Therefore, with these metal salts, the patients cannot be treated easily. In advanced stages, ulcers become life-threatening and its only treatment is the removal of the affected part of the stomach.

A major breakthrough in the treatment of hyperacidity came through the discovery according to which a chemical, histamine, stimulates the secretion of pepsin and hydrochloric acid in the stomach. The drug cimetidine (Tegamet), was designed to prevent the interaction of histamine with the receptors present in the stomach wall. This resulted in the release of a lesser amount of acid. The importance of the drug was so much that it remained the largest selling drug in the world until another drug, ranitidine (Zintac), was discovered.

Pentaprazole and Omiprazole are the new drugs used to inhibit gastric secretion.

Antihistamines:

Antihistamines are the drugs that diminish or abolish the effects of histamine, a chemical released by most of the cells during an allergic reaction. Antihistamine by competing with histamine for binding sites of receptor where histamine exerts its effect. Basic Antihistamines are amines which are used as drugs to control allergy effects produced by histamine. Histamine is a potent vasodilator. It has various functions. It contracts the smooth muscles in the bronchi and gut and relaxes other muscles, such as those in the walls of fine blood vessels. Histamine is also responsible for the nasal congestion associated with the common cold and allergic response to pollen.

Synthetic drugs, brompheniramine (Dimetapp) and terfenadine (Seldane), act as antihistamines. They interfere with the natural action of histamine by competing with histamine for binding sites of receptor where histamine exerts its effect.

Antihistamines do not affect the secretion of acid in the stomach. The reason is that antiallergic and antacid drugs work on different receptors.

Examples: Synthetic drugs, brompheniramine (Dimetapp) and terfenadine (Seldane),

Other commonly used antihistamines are Diphenhydramine (Benadryl), pheniramine maleate (Avil), Chloropheniramine maleate (zeet), Chlorotheopyllinat (Avomine). They are used in hay fever, mild asthma, insect bites, cold etc.

The action of Microbes in the Body:

The living organisms which cannot be seen with the naked eyes (unaided eyes) and can only be observed through a microscope are called microorganisms or microbes. They include bacteria, fungi, algae, and viruses. They are present almost everywhere air, water, soil, inside and on our body. The disease-producing microbes are called pathogens.

Our body has an efficient defense structure against these pathogens. The skin prevents microbes to enter our body. Some secretions like lysosomes in tears, nasal secretions, saliva, fatty acids, lactic acid in sweat, hydrochloric acid in the stomach kill these microbes or inhibit their growth. The breach of this defense system allows the pathogens to reach tissues and cause infection in the body. Due to which normal metabolic activities are disturbed.  This results in a disease. Pathogens produce toxins that may affect tissues and organs of the host.

Anti-malarials:

Medicines used to bring down the body temperature during malaria fever are called antimalarials. Malaria is a highly widespread infectious disease caused by Sporozoa called plasmodium. Malaria is characterized by periodic fever, anaemia, and enlargement of liver and spleen. The four species Plasmodium vivax (fever on alternate days), Plasmodium malariae (fever once in three days), Plasmodium ovale (fever once in three days), Plasmodium falciparum (fever once in four days) are responsible for malaria in the human being. The choice of drug depends on the point of action of the drug.

Drugs used are

• Primaquine: It destroys sporozoites in the liver. Its long use is not advisable because it is highly toxic.
• Chloroquine, Proquanil, Pyimethamine: These drugs kill the parasite in the blood.

Previous Topic: Mechanism of Action of Drugs

Next Topic: Antimicrobials, Antibiotics, Sulpha Drugs, Antiseptics, Disinfectants

Science > Chemistry > Everyday Chemistry > Everyday Medicines 01

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In this article, we shall study the meaning of the term drug, and the mechanism of actions of drugs.

Drugs:

The word dug is derived from a French word drogue which means a dry herb. Drugs are chemicals of low molecular mass which interact with macromolecular targets and produce a biological response. Drugs may be a single chemical substance or a combination of two or more different substances. Example: Aspirin, Naproxen

Medicine:

When the biological response of a drug is therapeutic and useful, the drugs are called medicines. Medicine is defined as a chemical substance which is used for the purpose of diagnosis, prevention, cure or relief of disease and for reducing sufferings from pain.

Chemotherapy:

The term chemotherapy was coined by Paul Ehrlich. Paul Ehrlich is known as the father of modern chemotherapy. Chemotherapy is a specific treatment of a disease by the administration of chemical compounds used as medicines. The chemicals so used for the cure are called chemotherapeutic agents.

Characteristics of Ideal Drug:

• It should destroy disease-causing organisms without harming the human body.
• It should not disturb physiological processes in the human body.
• It should not injure host tissues.
• It should have minimum side effects.
• It should be localized to the affected site and should not interfere with the working of other parts.
• The cells should not acquire resistance to the drug after some time.

Methods of Administration of a Drug:

• Oral: tablets, syrups, mixtures administered through the mouth.
• Intravenous: injected directly into the bloodstream.
• Intramuscular:  injection in muscles
• Subcutaneous: injection under the skin
• Nasal: inhalation of a drug.
• Topical: local application e.g. oils, ointments.

Classification of Drugs:

Need for Classification of Drugs:

• It helps to select a proper drug for the treatment of a disease.
• It helps in studying the drug and to do research to overcome the side effects of the drug.
• It also helps in the development of new drugs.
• It helps for pharmacists to design a drug most effective for a particular receptive site.

Classification  Based on Pharmacological Effects:

This classification of drugs is based on the choice of drug and its pharmacological effect. This classification gives a whole range of drugs available for the treatment of a particular type of health disorder. Hence this classification is useful for doctors. Examples:

• Analgesics: Painkilling effect
• Antibiotics: To arrest the growth and kill bacteria
• Antiseptics: To arrest the growth and kill bacteria
• Tranquilizers: To reduce mental stress

Classification Based on the Action of Drugs:

These drugs are diseases oriented and have a different biological mode. Examples: painkillers, antiarthritic, antihistamines medicines. All antihistamines inhibit the (stops) action of the compound histamine which produces allergic reactions such as inflammation in the body.

Classification Based on Chemical Structure:

This classification of drugs is based on the assumption that drugs having similar chemical structures are expected to have similar pharmacological properties. Examples: All sulphonamides having a similar type of chemical structure show antibacterial activity.

Classification Based on Molecular Targets:

Drugs interact with biomolecules like carbohydrates, proteins, lipids, nucleic acids, etc. These are target molecules and the drugs are called target-oriented drugs. This classification is useful for medicinal chemists. Examples: Many enzymes and receptors in cells have molecular targets.

Classification of Drugs by Lay Public:

This is not a scientific classification but commonly used by the lay public. This classification is based on the action of the drug and not on the chemistry of a drug or biological action of the drug. Examples: Cough syrups, analgesics, laxatives, and purgatives.

Designing of a Drug:

Drug target and drug metabolism are the two main aspects considered during drug design. Knowledge of drug target and drug metabolism helps medicine chemists to develop new and improved drugs.

Drug Target:

Drugs interact with biomolecules like carbohydrates, proteins, lipids, nucleic acids, etc. These molecules are called target molecules. To obtain a desired therapeutic result the correct choice of a target for a drug is to be done. The site on which the drug acts is called receptor. Usually a protein or proteinaceous material acts as a receptor.

Drug Metabolism:

A drug travels through the human system in order to reach the target. So the drug should be designed in such a way that it reaches the target without being metabolized in between (i.e. site of administration to site of action). After the action of the drug at the receptor site, the side products of the drug (metabolites) should be excreted without causing harm to the body.

After considering the above points a drug is designed from such compounds which are called lead compounds and chosen as starting points for drug designing. Lead compounds may be obtained from natural sources like plants, trees, venoms and metabolites of organisms or they may be synthesized.

Drug-Target Interaction:

Drugs interact with biomolecules like carbohydrates, proteins, lipids, nucleic acids, etc. These molecules are called target molecules. Biomolecular macromolecules perform the following functions.

• The proteins which perform the role of biological catalysts in the body are called enzymes.
• Proteins which are crucial to the communication system in a body are called receptors.
• Proteins which carry polar molecules across the cell membrane are called carrier proteins.
• Nucleic acids have coded genetic information for the cell and lipids.
• Carbohydrates are the structural part of the cell membrane.

Enzymes as Drug Targets:

The enzymes are biological catalysts. They provide active sites which hold the substrate molecule in a suitable position so that it can be attacked by the reagent effectively. The substrate binds to amino acids of the protein present on active site through interactions like ionic bonding, hydrogen bonding, van der Waals’ interaction or dipole-dipole interaction.

Enzyme provides functional groups that will attack the substrate and carry out a chemical reaction. Drugs inhibit the action of enzymes. Such drugs are called enzyme inhibitors. Thus enzyme inhibitors block the binding site and prevent binding of substrate. They also inhibit the catalytic action of enzymes.

Drug – Enzyme Interaction:

Drugs inhibit the attachment of the substrate on the active site of enzymes in two ways.

Competitive inhibitor’s action:

Such inhibitors compete with the natural substrate for the active site. Hence such inhibitors are called competitive inhibitors.2. In such cases, the drug occupies the position available for the substrate and thus prevents the substrate to occupy the active site on the enzyme. Thus the action of the enzyme is inhibited.

Noncompetitive inhibitors action:

Some drugs do not bind to active sites but bind to a different site of enzyme which is called allosteric sites. Doing this changes the shape of the active site.

Due to the change in the shape of the active site, the substrate cannot recognize the active site. These inhibitors are called non-competitive inhibitors.

Note:

If the bond formed between the drug and the enzyme is strong covalent bond and can not be broken easily then the enzyme is blocked permanently. Then the body degrades the blocked enzyme and synthesizes new enzymes.

Receptors as Drug Targets:

Receptors are proteins which are crucial for body’s communication process. Most of them are embedded in cell membranes such that their small part possessing active site projects out of the surface of the membrane and opens outside of the cell membrane. The chemical messages like neurotransmitters and hormones are received at the binding site of the receptor protein.

To accommodate the Messenger the shape of the receptor changes and this message is transferred into the cell without entering into the cell. When the chemical messenger leaves the site, the receptor regains its original shape.

There are large numbers of different receptors in the body and they interact with different chemical messengers. These receptors show the selectivity of one chemical messenger over the other due to their different shape, structure and amino acid composition at binding sites.

Drug – Receptor Interaction:

Drugs may bind to the receptor site and inhibit its natural function, such drugs are called antagonists. Some drugs mimic the natural messenger by switching on the receptor. Such drugs are called agonists. These are used when there is lack of natural messengers.

There are some receptors which interact with a particular messenger but they differ in their binding sites. For example, there are two types of adrenergic receptors namely α adrenergic receptors and β adrenergic receptors. Both of these receptors can bind adrenaline or epinephrine. It is possible to design drugs which will bind better with one type of adrenergic receptor than the other.

The receptors are not distributed uniformly around the body. For example, The heart has more β adrenergic receptors than α adrenergic receptors. Thus the drug designed to interact β adrenergic receptors will act more on the heart rather than on tissues which are rich in α adrenergic receptors.

If the drug binds to more than one type of receptors then it causes side effects. Side effects can also arise if the degradation product of the drug is biologically active and interacts with some other receptors.

In the next article, we shall study medicines in everyday life, like analgesics, antipyretics, antihistamines, antifertility, and tranquilizers.

Next Article: Analgesics, Antipyretics, Antihistamines, Tranquilizers

Science > Chemistry > Everyday Chemistry > Mechanism of Action of Drug

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