CHAPTER # 15
DRUGS
MS. MARRIAM KHAN
DRUGS
• A drug is any substance taken into the body that modifies or
affects chemical reactions in the body
• The drug may be one taken legally to reduce a symptom such as a headache
or to treat a bacterial infection (medicinal drugs)
• But it could also be one taken – often illegally – to provide stimulation or
induce sleep or create hallucinations (recreational drugs).
• Drugs are present in many products such as: tea, coffee and ‘energy drinks’
(caffeine); tobacco (nicotine); and alcoholic drinks (alcohol) which, although
legal, can cause serious effects when taken excessively or over extended
periods of time.
MEDICINAL DRUGS
• Any substance used in medicine to help our bodies
fight illness or disease is called a drug.
ANTIBIOTICS
• Antibiotics are substances which kill bacteria but do not harm other living cells.
• Antibiotics are made by fungi.
• The first antibiotic discovered was Penicillin made by the fungus Penicillium.
• Penicillin kills bacteria by stopping them from making their cell walls.
SOURCES
• The ideal drug for curing disease would be a chemical that destroyed
the pathogen without harming the tissues of the host.
• Most of the antibiotics we use come from bacteria or fungi that live in
the soil.
• One of the most prolific sources of antibiotics is Actinomycetes.
• These are filamentous bacteria that resemble microscopic mould fungi.
• The actinomycete Streptomyces produces the antibiotic streptomycin.
PENICILLIN
• Perhaps the best known antibiotic is penicillin, which is produced by the mould
fungus Penicillium and was discovered by Sir Alexander Fleming in 1928.
• Penicillin is still an important antibiotic but it is produced by mutant forms of a
different species of Penicillium from that studied by Fleming.
• The different mutant forms of the fungus produce different types of penicillin.
• The penicillin types are chemically altered in the laboratory to make them
more effective and to ‘tailor’ them for use with different diseases. ‘Ampicillin’,
‘methicillin’ and ‘oxacillin’ are examples.
• Antibiotics attack bacteria in a variety of ways.
• Some of them disrupt the production of the cell wall and so prevent the
bacteria from reproducing, or even cause them to burst open;
• Some interfere with protein synthesis and thus arrest bacterial growth.
• Animal cells do not have cell walls, and the cell structures involved in
protein production are different.
• Consequently, antibiotics do not damage human cells although they may
produce some side-effects such as allergic reactions.
• Not all bacteria are killed by antibiotics. Some bacteria have a nasty
habit of mutating to forms that are resistant to these drugs.
• For this reason it is important not to use antibiotics in a diluted form, for too
short a period or for trivial complaints.
• These practices lead to a build-up of a resistant population of bacteria. The
drug resistance can be passed from harmless bacteria to pathogens.
• It is important to note that antibiotics are ineffective in the
treatment of viral diseases.
DEVELOPMENT OF RESISTANT BACTERIA
• If a course of antibiotics is not completed, some of the bacteria it is being
used to destroy will not be killed, but will have been exposed to the drug.
• Some of the survivors may be drug-resistant mutants.
• When they reproduce, all their offspring will have the drug resistance, so the
antibiotic will become less effective.
• One type of bacteria that has developed resistance to a number of widely
used antibiotics is called MRSA (methicillin-resistant Staphylococcus aureus).
• These types of bacteria are sometime referred to as ‘superbugs’ because they
are so difficult to treat.
• Staphylococcus aureus is very common and is found living harmlessly on
the skin, the nose and throat, sometimes causing mild infections.
• It becomes dangerous if there is a break in the skin, allowing it to infect
internal organs and causing blood poisoning.
• This can happen in hospitals with infection during operations, especially
if hygiene precautions are not adequate.
• Doctors now have to be much more cautious about prescribing
antibiotics, to reduce the risk of resistant strains developing.
•
Patients need to be aware of the importance of completing a course of
antibiotics, again to reduce the risk of development of resistant strains.
ANTIBIOTICS AND VIRAL DISEASES
• Antibiotics are not effective against viral diseases.
• This is because antibiotics work by disrupting structures in bacteria such as cell
walls and membranes, or processes associated with protein synthesis and
replication of DNA.
• Viruses have totally different characteristics to bacteria, so antibiotics do not
affect them.
Virus
Bacteria