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7/23/2019 Drugs and Their Classification
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PROJECT REPORT
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ACKNOWLEDEMENT
I take this opportunity to thank several persons who were a great
help in making this project a success.
It is my foremost duty to express my deep regards & gratitude to
my Chemistry teacher Mrs. under whose guidance &
supervision I am able to undertake this project. It is her who has
been my primary source of inspiration and who motivated, guided
and encouraged me at different stages to shape this project.
!"I#$ %I'%(
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1. DRUGS AND MEDICINES
)rugs are chemicals of low molecular masses *+-- /--u0. hese
interact with macromolecular targets and produce a biological response.
1hen the biological response is therapeutic and useful, these chemicals
are called medicines and are used in diagnosis, prevention and treatment
of diseases. If taken in doses higher than those recommended, most of
the drugs used as medicines are potential poisons. 'se of chemicals for
therapeutic effect is called chemotherapy.
. Drugs can be classifie !ainl" #n cri$eria #u$line as f#ll#%s2
.. 3n the basis of pharmacological effect
his classification is based on pharmacological effect of the drugs. It is
useful for doctors because it provides them the whole range of drugs
available for the treatment of a particular type of problem. 4or example,
analgesics have pain killing effect, antiseptics kill or arrest the growth of
microorganisms.
..5 3n the basis of drug action
It is based on the action of a drug on a particular biochemical process. 4or
example, all antihistamines inhibit the action of the compound, histamine
which causes inflammation in the body. here are various ways in which
action of histamines can be blocked.
..6 3n the basis of chemical structure
It is based on the chemical structure of the drug. )rugs classified in this
way share common structural features and often have similar pharmacological activity. 4or example, sulphonamides have common
structural feature, given below. 7tructural features of sulphonamides
..8 3n the basis of molecular targets
)rugs usually interact with biomolecules such as carbohydrates, lipids,
proteins and nucleic acids. hese are called target molecules or drug
targets. )rugs possessing some common structural features may have
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the same mechanism of action on targets. he classification based on
molecular targets is the most useful classification for medicinal chemists.
1.& DRUG'TARGET INTERACTION
Macromolecules of biological origin perform various functions in the body.
4or example, proteins which perform the role of biological catalysts in the
body are called en9ymes, those which are crucial to communication
system in the body are called receptors. Carrier proteins carry polar
molecules across the cell membrane. #ucleic acids have coded genetic
information for the cell. :ipids and carbohydrates are structural parts of
the cell membrane. 1e shall explain the drug;target interaction with the
examples of en9ymes and receptors.
1.&.1 En("!es as Drug Targe$s
.5.. Catalytic action of en9ymes
4or understanding the interaction between a drug and an en9yme, it is
important to know how do en9ymes catalyse the reaction *7ection /.5.80.
In their catalytic activity, en9ymes perform two major functions2
he first function of an en9yme is to hold the substrate for a chemical
reaction. ctive sites of en9ymes hold the substrate molecule in a
suitable position, so that it can be attacked by the reagent effectively.
7ubstrates bind to the active site of the en9yme through a variety of
interactions such as ionic bonding, hydrogen bonding, van der 1aals
interaction or dipole;dipole interaction *4ig. <.0.
he second function of an en9yme is to provide functional groups
that will attack the substrate and carry out chemical reaction.
.5..5 )rug ;=n9yme Interaction
)rugs inhibit any of the above mentioned activities of en9ymes. hese
can block the binding site of the en9yme and prevent the binding of
substrate, or can inhibit the catalytic activity of the en9yme. 7uch drugs
are called en9yme inhibitors. )rugs inhibit the attachment of substrate on
active site of en9ymes in two different ways 2
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)rugs compete with the natural substrate for their attachment on the
active sites of en9ymes. 7uch drugs are called competitive inhibitors
*4ig. <.50.
7ome drugs do not bind to the en9yme>s active site. hese bind to a
different site of en9yme which is called allosteric site. his binding of
inhibitor at allosteric site *4ig.<.60 changes the shape of the active
site in such a way that substrate cannot recognise it. If the bond
formed between an en9yme and an inhibitor is a strong covalent
bond and cannot be broken easily, then the en9yme is blocked
permanently. he body then degrades the en9yme;inhibitor complex
and synthesises the new en9yme.
1.&.& Rece)$#rs as Drug Targe$s
%eceptors are proteins that are crucial to body>s communication process.
Majority of these are embedded in cell membranes *4ig. <.80. %eceptor
proteins are embedded in the cell membrane in such a way that their
small part possessing active site projects out of the surface of the
membrane and opens on the outside region of the cell membrane *4ig.
<.80.
In the body, message between two neurons and that between neurons to
muscles is communicated through certain chemicals. hese chemicals,
known as chemical messengers are received at the binding sites of
receptor proteins. o accommodate a messenger, shape of the receptor
site changes. his brings about the transfer of message into the cell.hus, chemical messenger gives message to the cell without entering the
cell *4ig. <./0.
here are a large number of different receptors in the body that interact
with different chemical messengers. hese receptors show selectivity for
one chemical messenger over the other because their binding sites have
different shape, structure and amino acid composition. )rugs that bind to
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the receptor site and inhibit its natural function are called antagonists.
hese are useful when blocking of message is re?uired. here are other
types of drugs that mimic the natural messenger by switching on the
receptor, these are called agonists. hese are useful when there is lack of
natural chemical messenger.
1.* T+ERA,EUTIC ACTION O- DI--ERENT CLASSES O- DRUGS
he therapeutic action of a few important classes of drugs are as follows 2
1.*.1 An$acis
n antacid is any substance, generally a base or basic salt, which
neutrali9es stomach acidity. hey are used to relieve acid indigestion,
upset stomach, sour stomach, and heartburn.
ntacids perform a neutrali9ation reaction, i.e. they buffer gastric acid,
raising the p" to reduce acidity in the stomach. 1hen gastric hydrochloric
acid reaches the nerves in the gastrointestinal mucosa, they signal pain to
the central nervous system. his happens when these nerves are
exposed, as in peptic ulcers. he gastric acid may also reach ulcers in the
esophagus or the duodenum.
"yperacidity or acid dyspepsia simply means increase of acidity in the
stomach. he human stomach secretes hydrochloric acid which is
necessary for the digestion of food. 1hen the stomach contains an
excessive amount of hydrochloric acid, then the condition is called as
hyperacidity. 7ometimes, hyperacidity is confused for a simple bellyache.
his is because people with hyperacidity generally get pains in their
stomach with similar symptoms as bellyaches. his confusion is morerampant in children who cannot differentiate between different kinds of
stomach ailments. "owever, hyperacidity can be found out with the sour
belching and after taste of the already eaten food in the mouth.
"yperacidity symptoms are observed a couple of hours after eating, when
the food has been digested and still excess acids are left within the
stomach. t this stage, the following symptoms are seen
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typical feeling of restlessness
4eeling of nausea *wanting to throw up0 and actual vomiting
7our belching with an after taste of the already;eaten food
7tiffness in the stomach, which is called as atonic dyspepsia
:ack of desire for any other type of food
Indigestion
Constipation
'ntil @A-, only treatment for acidity was administration of antacids, such
as sodium hydrogencarbonate or a mixture of aluminium and magnesium
hydroxide. "owever, excessive hydrogencarbonate can make the
stomach alkaline and trigger the production of even more acid. Metal
hydroxides are better alternatives because of being insolubleB these do
not increase the p" above neutrality. hese treatments control only
symptoms, and not the cause. herefore, with these metal salts, the
patients cannot be treated easily. In advanced stages, ulcers become life
threatening and its only treatment is removal of the affected part of the
stomach. major breakthrough in the treatment of hyperacidity came
through the discovery according to which a chemical, histamine,
stimulates the secretion of pepsin and hydrochloric acid in the stomach.
he drug cimetidine*egamet0, was designed to prevent the interaction of
histamine with the receptors present in the stomach wall. his resulted in
release of lesser amount of acid. he importance of the drug was so much
that it remained the largest selling drug in the world until another drug,ranitidine *antac0, was discovered.
7ome drugs used as antacids are 2
luminium hydroxide
Magnesium hydroxide
Calcium carbonate
7odium bicarbonate
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!ismuth subsalicylate
"istamine
Cimetidine
%anitidine
3mepra9ole
:ansopra9ole
OME,RAOLE
1.*.& An$i/is$a!ines
1hen body comes into contact with whatever the allergic trigger is ;;
pollen, ragweed, pet dander, dust mites, for example ;; it makes
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chemicals called histamines. hey cause the tissue in nose to swell
*making it stuffy0, nose and eyes to run & eyes, nose and sometimes
mouth to itch. 7ometimes there is also an itchy rash on your skin, called
hives.
ntihistamines reduce or block histamines, so they stop allergy
symptoms. ntihistamines work well to relieve symptoms of different types
of allergies, including seasonal *hay fever 0, indoor and food allergies, but
they canDt relieve every symptom. o treat nasal congestion, doctor may
recommend taking a decongestant. 7ome drugs combine an
antihistamine and decongestant.
7ynthetic drugs, brompheniramine *)imetapp0 and terfenadine *7eldane0,
act as antihistamines. hey interfere with the natural action of histamine
by competing with histamine for binding sites of receptor where histamine
exerts its effect.
ntihistamines come in different forms, including tablets, capsules, li?uids,
nasal sprays, and eyedrops. =xamples of prescription antihistamines
include2
stelin, stepro *a9elastine0 nasal sprays
tarax, $istaril *hydroxy9ine0
Clarinex *desloratadine0
Cyproheptadine *generic only0
=madine *emadastine0 eyedrops
:ivostin *levocabastine0 eyedrops
3ptivar *a9elastine0 eyedrops
Ealgic *carbinoxamine0
Fy9al *levocetiri9ine0
=xamples of 3C antihistamines2
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llegra *fexofenadine0
!enadryl *diphenhydramine0
)imetane *brompheniramine0
Claritin, lavert *loratadine0
avist *clemastine0
Chlor;rimeton *chlorpheniramine0
yrtec *certiri9ine0
=yedrops likes =madine and :ivostin treat symptoms of eye allergies,
including itchy, watery eyes. 7ome medications, like llegra;), Claritin;),
and yrtec;), combine an antihistamine and a decongestant to relieve
congestion.
7ide =ffects of ntihistamines
ntihistamines can cause side effects, and some cause more side effects
than others. )rugs such as !enadryl, Chlor;rimeton, and avist and
belong to an older group known as Gfirst;generationG antihistamines. hey
tend to cause more side effects, particularly drowsiness.
#ewer;generation antihistamines such as llegra, Clarinex, and yrtec
and have fewer side effects, so they may be a better choice for some
people.
7ome of the main side effects of antihistamines include2
)ry mouth
)rowsiness
)i99iness
#ausea and vomiting
%estlessness or moodiness *in some children0
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rouble urinating or not being able to urinate
!lurred vision
Confusion
ALLERGA'D
1.*.* Neur#l#gicall" Ac$i0e Drugs
1.3.3.1 ran?uili9ers
ran?uili9ers and analgesics are neurologically active drugs. hese affectthe message transfer mechanism from nerve to receptor. ran?uili9er is a
drug that acts on the central nervous system and is used to calm,
decrease anxiety, or help a person to sleep. 3ften called depressants
because they suppress the central nervous system and slow the body
down, they are used to treat mental illness as well as common anxiety
and sleeplessness.
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here are two types or classes of tran?uili9ers2 major tran?uili9ers and
minor tran?uili9ers. he former are antipsychotic drugs and the latter are
considered antianxiety drugs. ntipsychotic drugs are used to treat
patients with a severe mental illness, like schi9ophrenia. ntianxiety drugs
are given to patients with emotional problems, like anxiety. here are
various types of tran?uili9ers. hey function by different mechanisms.
#oradrenaline is one of the neurotransmitters that play a role in
mood changes. If the level of noradrenaline is low for some reason,
then the signal;sending activity becomes low, and the person suffers
from depression. In such situations, antidepressant drugs are
re?uired. hese drugs inhibit the en9ymes which catalyse the
degradation of noradrenaline. If the en9yme is inhibited, this
important neurotransmitter is slowly metabolised and can activate its
receptor for longer periods of time, thus counteracting the effect of
depression. Ipronia9id and phenel9ine are two such drugs.
chlordia9epoxide and meprobamate, are relatively mild tran?uili9ers
suitable for relieving tension.
=?uanil is used in controlling depression and hypertension.
)erivatives of barbituric acid vi9., veronal, amytal, nembutal, luminal
and seconal constitute an important class of tran?uili9ers. hese
derivatives are called barbiturates. !arbiturates are hypnotic, i.e.,
sleep producing agents.
7ome other substances used as tran?uili9ers are valium and
serotonin.
MEPROBAMATE PHENELZINE (NARDIL)
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I,RONIAID ALIUM ERONAL
1.3.3.2 nalgesics
nalgesics reduce or abolish pain without causing impairment of
consciousness, mental confusion, in coordination or paralysis or some
other disturbances of nervous system.
hese are classified as follows2
#on;narcotic *non;addictive0 analgesics
spirin and paracetamol belong to the class of non;narcotic
analgesics. spirin is the most familiar example. spirin inhibits the
synthesis of chemicals known as prostaglandins which stimulate
inflammation in the tissue and cause pain. hese drugs are effective
in relieving skeletal pain such as that due to arthritis. hese drugs
have many other effects such as reducing fever *antipyretic0 and
preventing platelet coagulation. !ecause of its anti blood clotting
action, aspirin finds use in prevention of heart attacks.
AS,IRIN
#arcotic drugs
Morphine and many of its homologues like heroin, codeine, when
administered in medicinal doses, relieve pain and produce sleep. In
poisonous doses, these produce stupor, coma, convulsions and
ultimately death. Morphine narcotics are sometimes referred to as
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opiates, since they are obtained from the opium poppy. hese
analgesics are chiefly used for the relief of postoperative pain,
cardiac pain and pains of terminal cancer, and in child birth.
1.*.2 An$i!icr#bials
)iseases in human beings and animals may be caused by a variety of
microorganisms such as bacteria, virus, fungi and other pathogens. n
antimicrobial tends to destroyHprevent development or inhibit the
pathogenic action of microbes such as bacteria *antibacterial drugs0, fungi
*antifungal agents0, virus *antiviral agents0, or other parasites
*antiparasitic drugs0 selectively. ntibiotics, antiseptics and disinfectants
are antimicrobial drugs.
1.3.4.1 ntibiotics
ntibiotics are used as drugs to treat infections because of their low
toxicity for humans and animals. Initially antibiotics were classified as
chemical substances produced by microorganisms *bacteria, fungi and
molds0 that inhibit the growth or even destroy microorganisms. he
development of synthetic methods has helped in synthesising some of the
compounds that were originally discovered as products of
microorganisms. lso, some purely synthetic compounds have
antibacterial activity, and therefore, definition of antibiotic has been
modified. n antibiotic now refers to a substance produced wholly or partly
by chemical synthesis, which in low concentrations inhibits the growth or
destroys microorganisms by intervening in their metabolic processes.
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he search for chemicals that would adversely affect invading bacteria but
not the host began in the nineteenth century. Eaul =hrlich, a erman
bacteriologist, conceived this idea. "e investigated arsenic based
structures in order to produce less toxic substances for the treatment of
syphilis. "e developed the medicine, arsphenamine, known as salvarsan.
Eaul =hrlich got #obel pri9e for Medicine in @-J for this discovery. It was
the first effective treatment discovered for syphilis. lthough salvarsan is
toxic to human beings, its effect on the bacteria, spirochete, which causes
syphilis is much greater than on human beings. t the same time, =hrlich
was working on a9odyes also. "e noted that there is similarity in
structures of salvarsan and a9odyes. he s K s linkage present in
arsphenamine resembles the # K # linkage present in a9odyes in the
sense that arsenic atom is present in place of nitrogen. "e also noted
tissues getting coloured by dyes selectively. herefore, =hrlich began to
search for the compounds which resemble in structure to a9odyes and
selectively bind to bacteria. In @65, he succeeded in preparing the first
effective antibacterial agent, prontosil, which resembles in structure to the
compound, salvarsan. 7oon it was discovered that in the body prontosil is
converted to a compound called sulphanilamide, which is the real active
compound. hus the sulpha drugs were discovered. large range of
sulphonamide analogues was synthesised. 3ne of the most effective is
sulphapyridine.
7:$%7# E%3#37I:
7':E"#I:MI)= 3)L=
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)espite the success of sulfonamides, the real revolution in antibacterial
therapy began with the discovery of lexander 4leming in @5@, of the
antibacterial properties of a Penicillium fungus. Isolation and purification of
active compound to accumulate sufficient material for clinical trials took
thirteen years. ntibiotics have either cidal *killing0 effect or a static
*inhibitory0 effect on microbes. few examples of the two types of
antibiotics are as follows2
!actericidal !acteriostatic
Eenicillin =rythromycin
minoglycosides etracycline
3floxacin Chloramphenicolhe range of bacteria or other microorganisms that are affected by a
certain antibiotic is expressed as its spectrum of action. ntibiotics which
kill or inhibit a wide range of ram;positive and ram;negative bacteria
are said to be broad spectrum antibiotics. hose effective mainly against
ram;positive or ram;negative bacteria are narrow spectrum antibiotics.
If effective against a single organism or disease, they are referred to as
limited spectrum antibiotics. Eenicillin has a narrow spectrum. mpicillin
and moxycillin are synthetic modifications of penicillins. hese have
broad spectrum. It is absolutely essential to test the patients for sensitivity
*allergy0 to penicillin before it is administered. In India, penicillin is
manufactured at the "industan ntibiotics in Eimpri and in private sector
industry.
Chl!"m#henicl$ isolated in @8A, is a broad spectrum antibiotic. It is
rapidly absorbed from the gastrointestinal tract and hence can be given
orally in case of typhoid, dysentery, acute fever, certain form of urinary
infections, meningitis and pneumonia. %"ncm&cin and 'l"cin are the
other important broad spectrum antibiotics. he antibiotic &*i"+i!ine is
supposed to be toxic towards certain strains of cancer cells.
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E=#CI::I# C":3%ME"=#IC3:
ofoxacin
.6.8.5 ntiseptics and )isinfectants
ntiseptics and disinfectants are also the chemicals which either kill or
prevent the growth of microorganisms. Antiseptic(s) are antimicrobial
substances that are applied to living tissue/skin to reduce the
possibility o inection, sepsis, or putreaction. hese are not ingested
like antibiotics.
Some common antiseptics are
Alcohols, most commonly ethanol (6!"#$, %&propanol (6!'#$and &propanol/isopropanol ('!)#$ or mixtures o thesealcohols, are commonly reerred to as *surgical alcohol*, and areused to disinect the skin beore in+ections are given, oten alongith iodine (tincture o iodine$ or some cationic suractants (ben-alkonium chloride .!.#, chlorhexidine .!.# oroctenidine dihydrochloride .%!.#$.
0oric acid is used in suppositories to treat yeast inections o thevagina, in eyeashes, as an antiviral to shorten the duration o
cold sore attacks, in creams or burns, and trace amounts in eyecontact solutions.
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1odine is usually used in an alcohol solution (called tincture oiodine$ or as 2ugol3s iodine solution as a pre& and postoperativeantiseptic.
Sodium chloride (salt$ is used as a general cleanser and as an
antiseptic mouthash. 1ts eak antiseptic e4ect is due tohyperosmolality o the solution above ."#.
Commonly used antiseptic, dettol is a mixture of chloroxylenol and
terpineol.
!ithionol *the compound is also called bithional0 is added to soaps to
impart antiseptic properties.
Iodine is a powerful antiseptic. Its 5;6 per cent solution in
alcoholwater mixture is known as tincture of iodine. It is applied on
wounds. Iodoform is also used as an antiseptic for wounds.
!oric acid in dilute a?ueous solution is weak antiseptic for eyes.
Disinfectants are antimicrobial agents that are applied to non&living ob+ects to destroy microorganisms that are living on theob+ects.5% 7isinection does not necessarily kill allmicroorganisms, especially resistant bacterial spores8 it is lesse4ective than sterili-ation, hich is an extreme physical and/orchemical process that kills all types o lie.
A wide range of different substances are used as disinfectants, including alcohols (also usedas antiseptics), aldehydes, such as ortho-phthalaldehyde, bleaches based on chlorine
compounds, hydrogen peroxide and also iodine (also another traditional antiseptic) and
potassium permanganate solution. Phenolic compounds also have anti-bacterial activity and
are often used in disinfectants bought for use in the home, and in disinfectant hand-washes
and soaps.
Different disinfectants wor in different ways. !ydrogen peroxide, which reacts to produce
free oxygen radicals and bleaches that are based on chlorine compounds are very powerful
oxidising agents. "hey oxidise the complex molecules present on the surface of bacteria,
causing their cell walls and cell membranes to disrupt. "he proteins on the surface become
irreversibly damaged and start to stic together forming clumps. "his happens very #uicly $
a strong solution of sodium hypochlorite solution that is used to disinfect a toilet, for
example, ills bacteria within seconds. "he bacterial cell cannot respond to the damage
#uicly enough and the whole cell simply splits open and dies.
7ame substances can act as an antiseptic as well as disinfectant byvarying the concentration.
4or example, -.5 per cent solution of phenol is an antiseptic while itsone percent solution is disinfectant.
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Chlorine in the concentration of -.5 to -.8 ppm in a?ueous solution
and sulphur dioxide in very low concentrations, are disinfectants.
C":3%3FL:=#3: =%EI#=3: !I"I3#3:
1.*.3 An$ifer$ili$" Drugs
ntibiotic revolution has provided long and healthy life to people. he life
expectancy has almost doubled. he increased population has caused
many social problems in terms of food resources, environmental issues,
employment, etc. o control these problems, population is re?uired to be
controlled. his has lead to the concept of family planning. ntifertility
drugs are of use in this direction.
he basic aim of antifertility drugs is to prevent conception or fertili9ation.hese control the female menstrual cycle and ovulation. he birth control
pills are essentially a mixture of synthetic esterogen and progesterone
derivatives which are more potent than the natural hormones.
It is known that progesterone suppresses ovulation. 7ynthetic
progesterone derivatives are more potent than progesterone.
#orethindrone is an example of synthetic progesterone derivative most
widely used as antifertility drug.
he estrogen derivative which is used in combination with progesterone
derivative is ethynylestradiol *novestrol0.
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NORET+INDRONE ET+4N4LESTRADIOL 5NOESTROL6
Mifepristone is a synthetic steroid which blocks the effects of
progesterone and is used as a Gmorning after pillG in many countries.
MI-E,RISTONE