Ch.
15 Drugs
• A drug is any substance taken into the body that modifies or affects chemical
reactions in the body.
• There are a variety of different drugs which treat different diseases.
• Some drugs are medicinal drugs that are used to treat the symptoms or causes
of a disease – for example, antibiotics.
• However, some people misuse drugs, so that they cause harm to themselves
and to others around them.
A drug may be taken legally to reduce a symptom like a headache or to treat
a bacterial infection (medicinal drugs).
Drugs can also be illegal. These are taken to provide stimulation, help 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).
What are medicinal drugs?
• Any substance used in medicine to help our bodies fight illness or
disease is called a medicinal drug.
• Antibiotics are good examples for medicinal drug.
Antibiotics:
• Antibiotics are substances that kill bacteria or
prevent their growth, but do not harm other living
cells.
• Antibiotics are chemical substances made by
certain fungi or bacteria.
• 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.
• The first antibiotic to be discovered was penicillin by Sir Alexander
Fleming in 1928. It is made by the fungus Penicillium.
• 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- preventing the production of
peptidoglycan that form the cell wall, due to this cell wall gets weaker
and ultimately ruptures.
➢ 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.
• A mutation occurs in a bacterial cell which makes it resistant to an
antibiotic.
• When that antibiotic is administered, this cell is not killed, whereas cells
which have not become resistant are killed.
• The resistant cell can therefore survive and reproduce, producing more
resistant bacteria.
• Resistance to antibiotics results in antibiotic resistant bacterial
infections in hospitals such as MRSA (methicillin-resistant
Staphylococcus aureus).
• It is therefore important to try and slow down the development
of resistant bacterial strains.
• This can be done by only using antibiotics for serious
infections, and always completing the full course of antibiotics
to make sure that all the bacteria are killed.
Why don’t Antibiotics Affect Viruses?
• 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.
• However, viruses do not carry out any cell functions and do
not have cell walls, cell membranes or any cell organelles
as viruses infect and utilize the machinery of animal cells to
reproduce, which are not affected by antibiotics.
