DRUGS

Arms race You have probably never heard of the drug carbapenem. This drug is an antibiotic - a substance that is used to kill bacteria that are causing infections in a person's body. The reason that the name of this antibiotic is not well known is because it a last resort antibiotic. It is only used when bacteria cannot be killed by any other antibiotics. The more that a particular antibiotic is used, the more risk there is that some populations of bacteria will develop resistance to it. This means that antibiotics that were once very effective at curing bacterial infections may no longer work. Doctors therefore try to keep some antibiotics 'in reserve'. If these drugs are hardly ever used, then the chances that any bacteria will develop resistance is much smaller. Then, when the drug is really needed, it is there to be used as an effective weapon. Some of the people who are most vulnerable to infections by bacteria are those who are already and are in hospital receiving long-term care enterobacteria. Until recently, these infections could be treated using carbapenem. But, in 2001, in a hospital in North Carolina in the USA, several patients with enterobacteria infections who were treated with carbapenem did not recover. The bacteria that were making them ill were resistant to carbapenem. Since then, these carbapenem-resistant bacteria have been found in other parts of the USA, and also as far away as Australia. Up to 50% of patients with these infections can die from them. Hospitals are now trying other antibiotics to treat these infections. But it is a constant battle. The more we use antibiotics, the more bacteria become resistant to them. We have to keep finding new antibiotics, to keep one step ahead of the bacteria.

What is a drug? People have always used drugs. Long ago, people discovered that some plants could help to cure diseases or to heal wounds. They also used substances obtained from plants and animals to change their perception of the world around them, inducing hallucinations and feelings of contentment or excitement. Today, many of the drugs we use still come from plants. Without drugs, many people would live much shorter lives, or suffer greater pain. Drugs used in medical care, or to relieve mild pain, are very helpful to us. However, o some people misuse drugs, so that they cause harm to themselves and to others around them.

drug any substance taken into the body that modifies or affects chemical reactions in the body Key definition

Medicinal drugs - Antibiotics Sometimes, a person's body needs help in its fight against a bacterial infection. Until 1944, there was little help that could be given. People died from diseases which we now think quite harmless, such as infected cuts. Then a discovery was made which has had a tremendous effect on our ability to treat diseases. Antibiotics were discovered. Antibiotics are substances which kill bacteria, but do not harm other living cells. Most of them are made by fungi. It is thought that the fungi make antibiotics to kill bacteria living near them - bacteria and fungi are both decomposers, so they might compete for food. We use the chemical welfare system of the fungus to wage our own war against bacteria.

Medicinal drugs - Antibiotics The first antibiotic to be discovered was penicillin. It is made by the fungus Penicillium, which you might sometimes see growing on decaying fruit. Penicillin kills bacteria by stopping them making their cell walls. Since the introduction of penicillin, many more antibiotics have been found. We have to go on trying to find more and more antibiotics, because bacteria evolve to become resistant to them, p.s-eic543ekipettapta.W. The more we use antibiotics, the more selection pressure we put on bacteria to evolve resistance

Medicinal drugs - Antibiotics People did not realise this when antibiotics were first discovered, and used them for all sorts of diseases where they did not help at all, such as diseases caused by viruses. Now doctors are much more careful about the amounts of antibiotics which they prescribe. We should only use antibiotics when they are really needed - then there is more chance that they will work when we need them to. Many antibiotics kill bacteria by damaging their cell walls. Viruses do not have cell walls, so they are unharmed by antibiotics.

Figure 15.2 This Petri dish contains agar jelly on which the bacteria that cause typhoid fever are growing. The three white circles are little discs of filter paper soaked in different antibiotics. You can see how the bacteria are unable to grow close to the discs, showing that these antibiotics are effective against the bacteria.

Misuse of drugs - Heroin Opium poppies produce a substance called opium, which contains a number of different .chemicals. Some of these, especially morphine and codeine, are used in medicine for the relief of pain. Opium is also the raw material from which heroin is produced, which is also used in medicine. Heroin can be addictive. An addictive drug is one which causes a person to become dependent on it - they are not able to stop taking it without suffering severe psychological and physical symptoms. Heroin is a powerful depressant. This means that it slows down many functions of the brain. It reduces pain, and slows down breathing. It also slows down the functions of the hypothalamus. When a person takes heroin, it produces a feeling of euphoria - that is, they feel intensely happy. However, in many people it can rapidly become addictive. They feel so ill when they do not take it that they will do anything to obtain more. As their bodies become more tolerant of the drug, they need to take more and more of it in order to obtain any feelings of pleasure.

Misuse of drugs - Heroin Not everyone who takes heroin becomes addicted to it, but many do. Addiction can develop very rapidly, so that a person who has taken it for only one or two weeks may find that they cannot give it up. A person who has become addicted to heroin may lose any ability to be a part of normal society. He or she may think only of how they will get their next dose. They may not be able to hold down a job, and therefore become unable to earn money, so many heroin addicts turn to crime in order to obtain money to buy their drug. They are not able to help and support their family. Some people take heroin by injecting it into their veins. This can be dangerous as the needles used for injection are often not sterile, and pathogens such as the hepatitis virus can be introduced into the body. The sharing of needles by heroin addicts has been a major method by which HIV has spread from one person to another.

Misuse of drugs - Heroin It is possible for a heroin addict to win the battle against his or her addiction, but it needs a great deal of will-power and much help from others. The withdrawal symptoms that an addict suffers after a few hours without the drug can be extremely unpleasant, and even life threatening In the brain, there are many different neurotransmitters that transfer nerve impulses across synapses from one neurone to another. We have seen that there are receptors on the cell surface membrane of the second neurone, which have a shape into which the neurotransmitter molecules precisely fit. One group of these neurotransmitters is called endorphins. Endorphins help to reduce sensations of pain, affect mood and reduce sensations of hunger and thirst. One situation in which endorphins are produced is when we do exercise - this is why exercise often has a `feel-good' effect. When it enters the brain, heroin is metabolised to morphine. Morphine molecules fit into some of the endorphin receptors. This is why heroin makes people feel good. Unfortunately, taking heroin can reduce the production of natural endorphins, and also affect the brain's production of other important neurotransmitters. Users often find that they have to keep taking more and more heroin to get the same effect and, if they stop using it, will suffer extremely unpleasant withdrawal symptoms.

Misuse of drugs - Alcohol Alcohol is a very commonly used drug in many different countries. People often drink alcoholic drinks because they enjoy the effect that alcohol has on the brain. Alcohol can make people feel more relaxed and release their inhibitions, making it easier for them to enjoy themselves and to mix and interact with other people. Alcohol is quickly absorbed through the wall of the stomach, and carried all over the body in the blood. It is eventually broken down by the liver, but this takes quite a long time. Drinking fairly small quantities of alcohol is not dangerous, but alcohol does have many effects on the body which can be very dangerous if care is not taken. Alcohol lengthen reaction time.

Misuse of drugs - Alcohol Alcohol is a depressant, which means that even small amounts of alcohol slow down the actions of parts of the brain, so alcohol lengthens the time you take to respond to a stimulus. This can mean the difference between life and death - often someone else's death - if the affected person is driving a car. A very high proportion of road accidents involve people who have recently drunk alcohol - either drivers or pedestrians. Most countries in which drinking alcohol is allowed have legal limits on blood alcohol level when you drive. However, we now know that even very small quantities of alcohol increase the risk of an accident, so the only safe rule is not to drink alcohol at all if you drive.

Misuse of drugs - Alcohol can increase aggression in some people Different people react differently to alcohol. In some people, it increases their feelings of aggression, and releases their inhibitions so that they are more likely to be violent or commit other crimes. They may be violent towards members of their family. Research has shown that at least 50% of violence in the home in many countries is related to drunkenness, and that alcohol has played a part in the criminal behaviour of around 60% of people in prison in western countries.

Misuse of drugs - Large intakes of alcohol can kill Every year, people die as a direct result of drinking a lot of alcohol over a short period of time. Alcohol is a poison. Large intakes of alcohol can result in unconsciousness, coma and even death. Sometimes, death is caused by a person vomiting when unconscious, and then suffocating because their airways are blocked by vomit.

Misuse of drugs - Alcoholism Alcoholism is a disease in which a person cannot manage without alcohol. The cause of the disease is not fully understood. Although it is obvious that you cannot become an alcoholic if you never drink alcohol, many people regularly drink large quantities of alcohol, but do not become alcoholics. Probably, there are many factors which decide whether or not a person becomes alcoholic. They may include a person's genes, their personality, and the amount of stress in their lives. An alcoholic needs to drink quite large quantities of alcohol regularly. This causes many parts of the body to be damaged, because alcohol is poisonous to cells. The liver is often damaged, because it is the liver which has the job of breaking down drugs such as alcohol in the body. One form of liver disease resulting from alcohol damage is cirrhosis, where fibres grow in the liver

Misuse of drugs - Alcoholism Excessive alcohol drinking also damages the brain. Over a long period of time, it can cause loss of memory, and confusion. One way in which the damage is done is that alcohol in the body fluids draws water out of cells by osmosis. When this happens to brain cells, they shrink, and may be irreversibly damaged. This osmotic effect is made worse because alcohol inhibits the release of a hormone which stops the kidneys from allowing too much water to leave the body in the urine. So drinking alcohol causes a lot of dilute urine to be produced, resulting in low levels of water in the blood. Misuse of drugs - Alcoholism

Tobacco smoking Everyone knows that smoking damages your health, but still people do it. Figure 15.8 shows the main components of tobacco smoke. There are, in fact, many more substances in tobacco smoke, and researchers are still finding out more about them, and the damage that each of them can do to the smoker's health. One public health concern is that these dangers exist for both smokers and non-smokers. The possible damage is just as real for non-smokers who are in a smokers' environment. They breathe in smoke from burning cigarettes, and from smoke exhaled by smokers. This is termed passive smoking. In many countries, smoking is now banned in all public places. It is also very strongly recommended that parents do not smoke anywhere near their children.

Tobacco smoking Nicotine affects the brain. It is a stimulant, which means it makes a person feel more alert. Nicotine is an addictive drug. This is why smokers often find it extremely difficult to give up. Nicotine damages the circulatory system, making blood vessels get narrower. This can increase blood pressure, leading to hypertension. Smokers have a much greater chance of developing coronary heart disease than non-smokers. Tar contains many different chemicals, some of which are carcinogens - that is, they can cause cancer. The chemicals can affect the behaviour of some of the cells in the respiratory passages and the lungs, causing them to divide uncontrollably. The cells divide over and over again, forming a lump or tumour. If this tumour is malignant, this is cancer. Cells may break away from the first tumour and spread to other parts of the body, where new tumours will grow. Almost everyone who gets lung cancer is a smoker, or has lived or worked in an environment where they have been breathing in other people's cigarette smoke.

Tobacco smoking Smoking cigarettes increases the risk of developing many different kinds of cancer. All forms of cancer are more common in smokers than in non-smokers. Carbon monoxide is a poisonous gas which affects the blood. The carbon monoxide diffuses from the lungs into the blood, and combines with haemoglobin inside the red blood cells. This means that less oxygen can be carried. The body cells are therefore deprived of oxygen. This is not good for anyone, but it is especially harmful for a baby growing in its mother's uterus. When the mother smokes, the baby gets all the harmful chemicals in its blood. The carbon monoxide can prevent it from growing properly. Smoke particles are little particles of carbon and other materials that are present in cigarette smoke. They get trapped inside the lungs. White blood cells try to remove them, and secrete chemicals that are intended to get rid of these invading particles. Unfortunately, the chemicals secreted by the white blood cells can do serious damage to the lungs themselves, resulting in chronic obstructive eulmonary disease (COPD).

Tobacco smoking The delicate walls of the alveoli tend to break down. There is therefore less surface area across which gas exchange can take place. The person is said to have emphysema. They find it difficult to get enough oxygen into their blood. A person with emphysema may not be able to do anything at all active, and eventually they may not even have the energy to walk. Several of the chemicals in cigarette smoke harm the cells lining the respiratory passages. You may remember that these cells clean the air as it passes through, stopping bacteria and dust particles from getting down to the lungs shows how smoking affects this cleaning mechanism.

Smoking and heart disease Smoking increases the risk of developing high blood pressure. As the blood passes through the lungs, it absorbs many substances from cigarette smoke. Some of these make the walls of the arteries get thicker and harder. The walls cannot stretch and recoil as easily as the blood surges through them. Smoking also makes it more likely that a blood clot will form inside blood vessels, including the coronary arteries that supply the wall of the heart with oxygenated blood.

Smoking and lung cancer It was in the 1950s that people first began to realise that there was a link between smoking cigarettes and getting lung cancer. The person at the forefront of this new understanding was a medical researcher called Richard Doll. At that time, doctors were becoming concerned about the rapid rise of lung cancer in the British population. No-one knew why this was happening. Richard Doll interviewed lung cancer patients in 20 hospitals in London, trying to find out if they had anything in common. His initial theory was that this was something to do with the new substance, tarmac, that was being used to build roads. However, it rapidly became clear to him that all of these people were smokers. Very quickly, he himself stopped smoking. Smoking and lung cancer