Pharmacology is the study of drug composition, properties and medical applications. The sources of drugs are also studied in pharmacology. Clinical pharmacology was present in the Middle Ages. Early pharmacologists focused on natural substances, mainly plant extracts. Pharmacology developed in the 19th century as a biomedical science. Any substance that, when absorbed into the body of a living organism, alters normal body function is known as a drug. Drugs are broadly classified into two types.
Pharmacology is not synonymous with pharmacy, which is the name used for a profession, though in common usage the two terms are confused.
A pharmaceutical drug or medicinal drug is defined as any chemical substance used in the diagnosis, cure, treatment, or prevention of disease. Some drugs often make person dependent on them, or addicted. These may be called as addictive drugs. By using such drug, the person’s body becomes familiar to it and the user cannot function well without it. In this chapter, we will learn about the functions of pharmaceutical drugs and the dangers of the addictive drugs.
Various diseases have been made easier to treat in recent years by the production of medicinal drugs. Drugs are obtained from the following sources. 1. Synthetic Drugs Such drugs do not occur naturally but are synthesized in laboratory. Pharmaceutical companies produce these drugs e.g. aspirin.
2. Drugs from Plants and Fungi Many important medicines are obtained from plants and fungi. These medicines include antibiotics, cardiotonics and certain analgesics. The antibiotic penicillin comes from a fungus. The cardiotonic, known as digitalis, is used to stimulate the heart. It is made from the leaves of purple flowered plant, foxglove.
Many addictive illegal drugs e.g. marijuana are also obtained from plants.
Researchers of a pharmaceutical company spent two years testing soil from all parts of the world to find new antibiotics. The project resulted in the development of one antibiotic, Terramycin, which is used to treat many infections.
The pain reliever morphine is made from opium, which comes from the juice of opium poppy plant.
3. Drugs from Animals Drugs obtained from animals are usually their glandular products. Fish liver oils, musk, bees’ wax, certain hormones and antitoxins are obtained from animal sources.
4. Drugs from Minerals
Several common drugs are produced from minerals. The mineral iodine is used in making tincture of iodine, a liquid that helps prevent infection when applied to cuts and bruises. The powder form of silver nitrate is applied on wounds to stop bleeding and prevent infection.
5. Drugs from Bacteria
Many antibiotics e.g. streptomycin are obtained from bacteria.
Principle Usage Of Important Medicinal Drugs
Drugs are classified on the basis of their chemical properties and modes of action.
• Analgesics (painkillers) reduce pain e.g. aspirin, paracetamol etc.
• Antibiotics inhibit or kill bacteria and treat bacterial infections e.g. tetracycline, cephalosporin etc.
• Sedatives induce sedation by reducing irritability or excitement e.g. diazepam.
• Vaccines are used to develop immunity against viral and bacterial infections e.g. vaccines against small pox, whooping cough, hepatitis B etc. Animation 18.4: Drugs from Bacteria Source & Credit : leavingbio
Joseph Lister (1827 – 1912) was an English surgeon. He promoted the idea of sterile surgery for the first time. He introduced carbolic acid to sterilise surgical instruments and to clean wounds.
Sir Alexander Flemming (1881 – 1955) was a Scottish biologist. He discovered the antibiotic penicillin from the fungus Penicillium notatum, for which he was awarded the Nobel Prize in 1945.
Medicines can help you feel better. But if medicines are taken incorrectly, they can actually make you feel worse. It is important to:
• Always check the instructions on doctor’s prescription slip and make sure you take the doses of medicine strictly as your doctor prescribed.
• Always check the expiry date printed on the medicine pack. The expired medicines may prove poisonous.
• Never take medicines prescribed for someone else, even if you think you have the same medical problem.
• Some medicines – such as antibiotics – must be taken for a specific number of days. Make sure you take the medicine for the stated time. Otherwise the problem may come back again.
• Always check with your doctor before you stop taking a medicine or consider a new treatment.
• Some medicines are not suitable for children, and there are special children’s dosages for many medicines.
• Do not take medicine in the dark.
• If your prescription medicines are crucial for your health and life, carry medicines and dosage instructions with you, whenever you are out of home.
• Always keep healthcare products out of the reach of children.
• Do not use the medicine if there are signs of tampering. Inform the pharmacist and the manufacturer of the medicine, about it.
The following are major categories of addictive drugs: 1. Sedatives These drugs interact with central nervous system to depress its activities. Sedative drugs induce dizziness, lethargy, slow brain function and depression. Long-term use of sedative induce suicidal thoughts.
Narcotics Narcotics are strong painkillers. These drugs are often prescribed in conjunction with other less potent painkillers (paracetamol or aspirin). These are used to relieve pain for patients with chronic diseases such as cancer. These are also used to relieve acute pain after operations. But some people may abuse narcotics for ecstatic effects. Morphine and codeine are the narcotics, derived from opium (poppy). Morphine acts directly on central nervous system to relieve pain. Morphine has a high potential for addiction. The most commonly abused narcotic i.e. heroin is a semi-synthetic drug from morphine. It affects on central nervous system and causes drowsiness.
In many western countries, heroin is prescribed as a strong analgesic under the name diamorphine. Its use includes treatment for acute pain, such as in severe physical trauma, myocardial infarction, postsurgical pain etc.
3. Hallucinogens Hallucinogens are the drugs that cause changes in perception, thought, emotion and consciousness. The group includes mescaline, which comes from a cactus and psilocin, which comes from a mushroom. Physiologically, hallucinogens affect on the sympathetic nervous system, causing dilation of pupils, constriction of some arteries and rise in blood pressure.
4. Marijuana (Hashish) Marijuana is a hallucinogen, which is smoked. It is obtained from the flowers, stems, and leaves of the marijuana plant (Cannabis sativa and C. indica). Small doses of marijuana result in a feeling of well-being that lasts two to three hours. High doses increase heart rate. It also affects the production of sperms in men and also weakens the short-term memory.
Hallucinations are perceptions that have no basis in reality, but that appear entirely realistic.
Marijuana is one of the most commonly used drugs in the world, following only caffeine, nicotine, and alcoholic beverages in popularity.
Drug Addiction And Associated Problems
Drug abusers go through withdrawal of social contact or communication. Many studies by the experts of social sciences prove that there exists a close relationship between drug addiction and crime. The compulsion for narcotic drug makes every drug addict a law violator and a criminal. Mere possession of a narcotic drug is a violation of the law. Thus, every drug addict is subject to arrest by the police. Most narcotic addicts get involved in various types of crime e.g. robbery, shoplifting, burglary, embezzlement etc.
Drug addicts may commit violent crimes since so many become psychic patients. The addicts are very weak in their social behaviour. They face social stigma i.e. the society dislikes them because of their unpredictable behaviours.
Antibiotics And Vaccines
Two important medicinal drugs are antibiotics and vaccines. 18.3.1 Antibiotics An antibiotic is a drug that kills or retards the growth (reproduction) of bacteria. They are the chemicals produced by or derived from microorganisms (bacteria and fungi).
Bactericidal and Bacteriostatic antibiotics Antibiotics are used to treat many different bacterial infections. Some antibiotics are ‘bactericidal’, meaning that they kill bacteria. Others are ‘bacteriostatic’, meaning that they work by stopping bacterial growth. Three major groups of antibiotics are described below.
1. Cephalosporins Cephalosporins interfere with synthesis of bacterial cell wall and so are bactericidal. Cephalosporins are used to treat pneumonia, sore throat, tonsillitis, bronchitis etc.
Some antibiotics can be used to treat a wide range of infections and are known as ‘broadspectrum’ antibiotics. Others are only effective against a few types of bacteria and are called ‘narrowspectrum’ antibiotics.
2. Tetracyclines These are broad-spectrum bacteriostatic antibiotics and inhibit bacterial protein synthesis. Tetracyclines are used in the treatment of infections of respiratory tract, urinary tract, intestine etc. Tetracyclines are not used in children under the age of 8, and specifically during periods of tooth development.
3. Sulpha Drugs – Sulfonamides Sulpha drugs are synthetic antibiotics that contain sulfonamide group. Sulfonamides are broad spectrum bacteriostatic antibiotics. They inhibit the folic acid synthesis in bacteria. They are used to treat pneumonia and urinary tract infections.
Antibiotic Resistance Antibiotics are extremely important in medicine, but unfortunately bacteria are capable of developing resistance to them. Such bacteria are not affected by commonly used antibiotics. Bacteria have number of ways of developing resistance. Sometimes, their internal mechanism stops the working of antibiotic. Bacteria can also transfer the genes responsible for antibiotic resistance between them. So such resistant bacteria make it possible for other bacteria to acquire resistance Expired drugs can cause damage to kidneys.
The sulfonamide group is also present in other medications that are not antibiotics e.g. thiazide diuretics (medicines for lowering blood pressure).
When bacteria are exposed to the same antibiotics over and over, they can change and are no longer affected by the drug.
Another reason for increasing antibiotic resistance in bacteria is their use in diseases in which they have no efficacy (e.g. antibiotics are not effective against infections caused by viruses). Resistance to antibiotics poses a serious and growing problem, because some infectious diseases are becoming more difficult to treat. Some of the resistant bacteria can be treated with more powerful antibiotics, but there are some infections that do not eliminate even with new antibiotics.
A vaccine is a material containing weakened or killed pathogens and is used to produce immunity to a disease by stimulating the production of antibodies. In 1796, a British physician, Edward Jenner, infected a young boy with cowpox, by injecting pus cells. After the boy had recovered from cowpox, Jenner injected the pus cells from a smallpox patient into him. The boy did not get smallpox. So it became clear that intentional infection with cowpox protected people from smallpox. This method was named “vaccination” and the substance used to vaccinate was called a “vaccine”. The Mode of Action of Vaccines Pathogens contain special proteins called “antigens”. When pathogens enter the body (blood) of host, these proteins stimulate the immune response in host i.e. synthesis of “antibodies”. Antibodies bind to pathogens and destroy them. In addition, “memory cells” are produced, which remain in blood and provide protection against future infections with the same pathogen. When a vaccine i.e. weakened or dead pathogen is introduced into bloodstream, the white blood cells are stimulated. B-lymphocytes recognize the weakened or dead pathogens as enemies and start producing antibodies against them. These antibodies remain in blood and provide protection against pathogens. If real pathogens enter blood, the already present antibodies kill them.The most common method of administering vaccines is by injection, but some vaccines are given by mouth or nasal spray.
Children are required to be vaccinated before attending school. The vaccination of children has resulted in marked decrease of many once-common diseases including whooping cough, polio, smallpox and others.
Some vaccines do not provide lifetime immunity. For example, tetanus vaccines are only effective for a limited period of time. In such cases, booster shots are necessary to maintain continuous protection.