Drugs and Their Classification

• Chemistry influences every sphere of human life.
• Chemistry is applied to medicines, food materials and cleansing agents.

Drugs and Their Classification

• Drugs are chemicals of low molecular masses (~100 – 500u) that interact with macromolecular targets to produce a biological response.
• Medicines are therapeutic and useful chemicals used in diagnosis, prevention, and treatment of diseases.
• Chemotherapy is the use of chemicals for therapeutic effect.
• Classifying drugs can be done on the basis of:
  • Pharmacological effect
  • Drug action
  • Chemical structure
  • Molecular targets

Drug-Target Interaction

• Target molecules or drug targets are biomolecules such as carbohydrates, lipids, proteins, and nucleic acids, with which drugs interact.
• Medicinal chemists find molecular targets as the most useful classification.

Enzymes as Drug Targets

• Enzymes are proteins that perform the role of biological catalysts in the body.
• Enzymes do two major functions:
  • Holding the substrate for a chemical reaction
  • Providing functional groups that will attack the substrate and carry out chemical reaction
• Drugs inhibit any of the above-mentioned activities of enzymes.
• Enzyme inhibitors block the binding site of the enzyme and prevent the binding of the substrate.
• Competitive inhibitors compete with the natural substrate for attachment on the active sites of enzymes.
• Some drugs bind to a different site of the enzyme, called the allosteric site, which changes the shape of the active site of the enzyme so that the substrate cannot recognize it.

Receptors as Drug Targets

• Receptors are proteins that are crucial to the body's communication process.
• Receptor proteins are embedded in the cell membrane in such a way that their small part possessing active site projects out of the surface of the membrane and opens on the outside region of the cell membrane.
• Chemical messengers are received at the binding sites of receptor proteins.
• To accommodate a messenger, the shape of the receptor site changes, which brings about the transfer of message into the cell.
• The chemical messenger gives message to the cell without entering it.
• Antagonists are drugs that bind to the receptor site and inhibit its natural function, and are useful when blocking of message is required.
• Agonists are drugs that mimic the natural messenger by switching on the receptor, and are useful when there is a lack of natural chemical messenger.

Therapeutic Action of Different Classes of Drugs

• The therapeutic action of a few important classes of drugs includes:
  • Antacids
  • Antihistamines
  • Neurologically active drugs
  • Antimicrobials
  • Antifertility drugs

Antacids

• Overproduction of acid in the stomach causes irritation and pain.
• Antacids such as sodium hydrogencarbonate or a mixture of aluminum and magnesium hydroxide, were previously administered to handle acidity.
• Histamine stimulates the secretion of pepsin and hydrochloric acid in the stomach.
• Cimetidine for example, prevents the interaction of histamine with the receptors present in the stomach wall, resulting in a release of lesser amount of acid.

Antihistamines

• Histamine is a potent vasodilator with various functions.
• They include contraction of the smooth muscles in the bronchi and gut and relaxes other muscles, such as those in the walls of fine blood vessels.
• Histamine is responsible for the nasal congestion associated with the common cold and allergic response to pollen.
• Synthetic drugs, such as brompheniramine and terfenadine, act as antihistamines and interfere with the natural action of histamine by competing with histamine for binding sites of receptor where histamine exerts its effect.

Neurologically Active Drugs

• Tranquilizers and analgesics are neurologically active drugs that affect the message transfer mechanism from nerve to receptor.
• Tranquilizers are a class of chemical compounds used for the treatment of stress, and mild or even severe mental diseases.
• Tranquilizers relieve anxiety, stress, irritability or excitement by inducing a sense of well-being.
• Noradrenaline is one of the neurotransmitters that plays a role in mood changes, and low levels of noradrenaline is associated with depression.
• Antidepressant drugs inhibit the enzymes which catalyse the degradation of noradrenaline.
• Iproniazid and phenelzine are antidepressant drugs.
• Some tranquilizers such as chlordiazepoxide and meprobamate, are relatively mild tranquilizers suitable for relieving tension, while Equanil is used in controlling depression and hypertension.
• Analgesics reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbances of nervous system.
• Analgesics include:
  • Non-narcotic (non-addictive) analgesics (Aspirin and paracetamol)
  • Narcotic drugs (Morphine)

Antimicrobials

• Antimicrobials tend to destroy/prevent development or inhibit the pathogenic action of microbes and include:
  • Antibacterial drugs
  • Antifungal agents
  • Antiviral agents
  • Antiparasitic drugs
• Antibiotics are used as drugs to treat infections because of their low toxicity for humans and animals.
• Paul Ehrlich developed the medicine arsphenamine for the treatment of syphilis.
• Prontosil is an effective antibacterial agent.

Antifertility Drugs

• Antifertility drugs are of use in the direction of family planning.
• Birth control pills essentially contain a mixture of synthetic estrogen and progesterone derivatives.
• It is known that progesterone suppresses ovulation.
• Synthetic progesterone derivatives are more potent than progesterone.
• Norethindrone is an example of synthetic progesterone derivative most widely used as antifertility drug.
• The estrogen derivative which is used in combination with progesterone derivative is ethynylestradiol.

Chemicals in Food

• Chemicals are added to food to preserve it, enhance its appeal and add nutritive value.
• Main categories of food additives are:
  • Food colours
  • Flavours and sweeteners
  • Fat emulsifiers and stabilising agents
  • Flour improvers - antistaling agents and bleaches
  • Antioxidants
  • Preservatives
  • Nutritional supplements such as minerals, vitamins and amino acids

Artificial Sweetening Agents

• Artificial sweeteners are used instead of natural sweeteners to reduce calorie intake .
• Ortho-sulphobenzimide, also called saccharin, is the first popular artificial sweetening agent.
• Aspartame is the most successful and widely used artificial sweetener.
• Alitame is high potency sweetener, although it is more stable than aspartame, the control of sweetness of food is difficult while using it.
• Sucralose is trichloro derivative of sucrose and is stable at cooking temperature.

Food Preservatives

• Food preservatives prevent spoilage of food due to prohibiting microbial growth.
• Commonly used preservatives include table salt, sugar, vegetable oils and sodium benzoate.

Antioxidants

• These are important and necessary food additives as they help in food preservation by retarding the action of oxygen on food.
• Two most familiar antioxidants are butylated hydroxy toluene (BHT) and butylated hydroxy anisole (BHA).

Cleansing Agents

• Two types of detergents are used as cleansing agents: soaps and synthetic detergents.
• These improve cleansing properties of water and help in removal of fats which bind other materials to the fabric or skin.

Soaps

• Soaps are the detergents used since long, Sodium or potassium salts of long chain fatty acids are used for cleaning.
• In saponification, esters of fatty acids are hydrolysed and the soap obtained remains in colloidal form.
• These separate as scum in water and are useless as cleansing agents.

Synthetic Detergents

• Synthetic detergents are cleansing agents which have all the properties of soaps, but which actually do not contain any soap.
• These can be used both in soft and hard water as they give foam even in hard water.
• Synthetic detergents are mainly classified into three categories:
  • Anionic detergents
  • Cationic detergents
  • Non-ionic detergents
• If their hydrocarbon chain is highly branched, then bacteria cannot degrade these easily, this leads to slow degradation of detergents, effluents containing such detergents reach the rivers, and water gets polluted.
• These days the branching of the hydrocarbon chain is controlled and kept to the minimum so that the unbranched chains can be biodegraded more easily and hence pollution is prevented.