Basic
Concept
1) Drugs: Drugs are chemical substances of
low molecular mass (~100-500) which interacts with the macro molecular targets
and produce a biological response.
2) Classification of drugs
a) On the basis of pharmacological effect: It is
useful for the doctors because it provides them the whole range of drugs
available for the treatment of a particular type of problem. For example,
analgesics have pain killing effect.
b) On the basis of drug action: It is
based on the action of a drug on a particular biochemical process. For example,
all antihistamines inhibit the action of histamines which causes inflammation
in the body.
c) On the basis of molecular targets: Drugs
usually interact with the biological macromolecules such as carbohydrates,
protein, lipids and nucleic acids called target molecules.
3) Enzymes: Proteins which perform the
role of biological catalysts in the body are called enzymes
a)
Catalytic
action of enzymes
(1) The first
function of an enzyme is to hold the substrate for a chemical reaction.
Sites of enzymes hold the substrate molecule in suitable position, so that it
can be attacked by reagent effectively. Substrate binds to the active site of
enzymes such as ionic bonding, hydrogen bonding and van der.
(2) The second
function of an enzyme is to provide functional groups that will attack the
substrate and carry out chemical reaction.
b)
Drug-enzyme
interaction: Drugs can block the binding site of the enzyme and prevent
the binding of the substrate, or can inhibit the catalytic activity of the
enzyme. Such drugs are called enzyme
inhibitors.
Drugs inhibit the attachment of substrates on active
site of enzymes in two different ways:
i)
Drugs compete with the natural substrate for their
attachment on the active sites of enzymes. Such drugs are called competitive inhibitors.
ii) Some drugs
do not bind to the enzyme’s active site. These bind to a different site of
enzyme which is called allosteric site. This
binding of inhibitor at allosteric site changes the shape of the active site in
such a way that substrate cannot recognise it.
If the bond formed between an
enzyme and an inhibitor is a strong covalent bond and cannot be broken easily,
then the enzyme is blocked permanently. The body then degrades the
enzyme-inhibitor complex and synthesizes the new enzyme.
§ Receptors: Proteins that are crucial to
body’s communication process are called receptors. 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.
In
the body, message between two neurons and that between neurons to muscles is
communicated through certain chemicals. These chemicals, known as chemical messengers are received at the
binding sites of receptor proteins. To accommodate a messenger, shape of the
receptor site changes. This brings about transfer of message into the cell.
Thus, chemical messenger gives message to the cell without entering the cell.
§ Antagonists: Drugs that bind to the receptor
site and inhibit its natural function are called Antagonists. These are useful
when blocking of message is required.
§ Agonists: Drugs that mimic the natural
messenger by switching on the receptor are called agonists. These are useful
when there is a natural chemical messenger.
4)
Neurologically
active drugs: Analgesics and tranquilizers are neurologically active drugs.
These affect the message transfer mechanism from nerve to receptor.
a)
Analgesics:
Drugs which reduce or abolish pain without causing impairment of
consciousness, mental confusion, in coordination or paralysis or some other
disturbances of nervous system are called analgesics. These are classified as
follows:
i)
Non-narcotic
analgesics: These drugs are non-addictive. Aspirin and paracetamol are
important examples of non-narcotic analgesics. These drugs are effective in
relieving skeletal pain such as that due to arthritis. These drugs have many
other effects such as reducing fever and preventing platelet coagulation.
ii)
Narcotic
analgesics: These are the drugs which when administered in small doses
relieve pain and produce sleep. Alkaloids like morphine, codeine and heroin
belong to the class of narcotic analgesics. These are chiefly used for the
relief of postoperative pain, cardiac pain and pains of terminal cancer, and in
child birth.
b)
Tranquilizers:
Tranquilizers are a class of chemical compounds used for the treatment of
stress, fatigue, and mild or even severe mental diseases. These relieve
anxiety, stress, irritability or excitement by inducing a sense of well-being.
Examples:
Tranquilizers like Chloordiazepoxide and meprobamate are used
for relieving tension.
·
Proniazid and phenelzine are used as antidepressant.
·
Barbiturates viz, veronal, amytal, Nembutal, luminal
and seconal are used as hypnotic, i.e.,
sleep producing agents.
·
Equanil is used in controlling depression and
hypertension.
5) Antihistamines: Antihistamines are the drugs
which interfere with the natural action of histamine by competing with
histamine for binding sites of receptor where histamine exerts its effects.
Brompheniramine, terfenadine, pheniramine maleate (avil), cetrizine and
chlolorpheniramine are some examples of antihistamines.
6) Antimicrobial: An antimicrobial tends to destroy
or inhibit the pathogenic action of microbes such bacteria (antibacterial
drugs), fungi (antifungal drugs) or other parasites (antiparasitic drugs)
selectively. Antiseptics, disinfectants and antibiotics are antimicrobial
drugs.
a) Antiseptics: These are the chemical substances
which prevent the growth of microorganism or kill them but are not harmful to
the living human tissues. Antiseptics are applied to wounds, cuts, ulcers and
diseased skin surfaces. 0.2 % solution of phenol, dettol (a mixture of
chloroxylenol and terpeneol), bithional, tincture of iodine ( 2–3 % ) of solution iodine in alcohol – water , hydrogen
peroxide and boric acid solution are some of the common antiseptics.
b) Disinfectants: These are chemical substances
which kill microorganism or stop their growth but are harmful to living
tissues. These are used to kill microorganism present in floors, drains,
toilets, etc. 1% of phenol, chlorine in the concentration of 0.2to 0.4ppm in
aqueous solution and SO2 in
very low concentration are disinfectants.
c) Antibiotics: These are chemical substances
produced wholly or partly by chemical synthesis which in low concentrations
inhibit the growth or destroy microorganisms by intervening in their metabolic
processes. Antibiotics are of two types:
i) Bactericidal
antibiotics. E.g., Penicillin, aminoglycosides, ofloxacin, etc.
ii) Bacteriostatic.
E.g., Erythromycin, tetracycline, chloramphencol, etc.
·
Spectrum: the full range of microorganism attacked by
an antibiotic is called its spectrum. Antibiotics which kill or inhabit a wide
range of Gram-positive and Gram-negative bacteria are called broad-spectrum
antibiotics. Those effective mainly against Gram-positive or Gram-negative
bacteria are narrow spectrum antibiotics. Ampicillin, tetracycline,
amoxycillin, chloramphenical and ofloxacin are broad spectrum antibiotics.
Penicillin G is a narrow spectrum antibiotic.
7) Antifertility drugs: These are
the chemical substances which are used to prevent unwanted pregnancies in
women. For example, norethindrone, ethynyles-tradiol (novestrol) and
mifepristone.
8) Artificial sweetening agents: These are
the chemical compounds which are non-nutritive in natural and are used as
substitutes for sugar in foods and beverages especially soft drinks. Some
common artificial sweeteners are
§ Saccharin (ortho-sulphobenzimide): It is
useful as a sugar substitute for diabetic persons and those who need to control
calorie intake.
§ Aspartame: It is methyl ester of dipeptide
formed from aspartic acid and phenylalanine. Aspartame is used only in cold
foods and soft drinks as it is unstable at cooking temperature.
§ Alitame: It is a highly potency sweetener.
The control of sweetness of food is difficult while using alitame.
§ Sucrolose: It is trichloroderivative of
sucrose. It is stable at cooking temperature.
9) Food preservatives: These are the chemical
substances which are added to the food material to prevent food spoilage due to
microbial growth. The most commonly used preservative include table salt,
vegetable oil, sugar, potassium metabisulphite and sodium benzoate.
10)
Soap: Soaps are
sodium or potassium salts of long chain fatty acids. Soaps containing sodium
salts are formed by heating fat (i.e. ,glyceryl
ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is
known as saponification.
11)
Synthetic
detergents: These are the cleaning agents which have all 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 of three types, namely anionic, cationic and non-ionic.
a) Anionic detergents: These are so named because
a large part of their molecules are anions and it is the anionic part of the
molecule which is involved in the cleansing action. These are sodium salts of
sulphonated long chain alcohols or hydrocarbons. For example, sodium lauryl
sulphate, sodium dodecylbenzene sulphonate. Anionic detergents are used in
household work and in tooth pastes.
b) Cationic detergents: These are so called because
a large part of their molecules are cations and it is the cationic part of the
molecule which is involved in the cleansing action. Cationic detergents are
quaternary ammonium salts of amines with acetates, chlorides or bromides as
anions. Cetyltrimethylammonium bromide is a cationic detergent and used in hair
conditioners. Cationic detergents have germicidal properties and are expensive;
therefore, these are of limited use.
c) Non-ionic detergents: Non-ionic
detergents do not contain any ion. These are esters of high molecular mass
alcohols. One such detergent is formed when stearic acid reacts with
polyethyleneglycol. Liquid dishwashing detergents are non-ionic type.
i) The problem
in the use of detergents is that if their hydrocarbon chain is highly branched.
Then bacteria cannot be degrade this easily. Slow degradation of detergents
leads to their accumulation. This causes water pollution, unbranched chain can
be biodegraded more easily and hence pollution is prevented.
