Steroids

Steroids
medicinal chemistry
PREPARED AND PRESENTED BY:
Mr. Dharmendrasinh A Baria,
Assistant Professor
Pharmaceutical Chemistry Department
Smt. S. M. Shah Pharmacy College
Aamsaran, Mahemdabad
Gujarat
DHARMENDRA BARIA, Smt. S.M. Shah Pharmacy College 1

• Steroids comprise a group of cyclical
organic compounds whose basis is a
characteristic arrangement of
seventeen carbon atoms in a four
ring structure linked together from
three 6-carbon rings followed by a 5-
carbon ring and an eight-carbon side
chain on carbon-17 (illustration on
right).
Cyclopentanoperhydrophenanthrene
A B
C D

CHOLESTEROL
• “Cholesterol is the most highly decorated small molecule in biology. Thirteen Nobel
Prizes have been awarded to scientists who devoted major parts of their careers to
cholesterol. Ever since it was isolated from gallstones in 1784, cholesterol has exerted
an almost hypnotic fascination for scientists from the most diverse areas of science
and medicine…. Cholesterol is a Janus-faced molecule. The very property that makes it
useful in cell membranes, namely its absolute insolubility in water, also makes it
lethal.”

• Cholesterol is the most abundant steroid in animals
 Plants have very small amounts (but have related compounds).
 It’s a major component of cell membranes, and affects the fluidity of the membrane due to
its bulky structure.
 Is a precursor for biosynthesis of many other steroids.
• Cholesterol is called a sterol because it contains an alcohol group.
• We can obtain cholesterol from our diet (animal products), but our liver can also synthesize all
the cholesterol that we need.
 The liver synthesizes more cholesterol when dietary intake is low.
 Excessive blood cholesterol is associated with atherosclerosis and formation of gallstones.
DHARMENDRA BARIA, Smt. S.M. Shah Pharmacy College
4

5
CHOLESTEROL IS THE BIOSYNTHETIC
SOURCE OF ALL STEROIDS

STEROID NOMENCLATURE, STEREOCHEMISTRY, AND NUMBERING
• Nearly all steroids are named
as derivatives of cholestane
(C27), androstane (C19),
pregnane (C21), or estrange
(C18).
• The standard system of
numbering is illustrated with
5α-cholestane (the H8 and H9
protons have been omitted
here for clarity).

• The absolute stereochemistry of the
molecule and any substituents is shown
with solid (β) and dashed (α) bonds.
Most carbons have one β bond and one
α bond, with the bond lying closer to the
“top” or C18 and C19 methyl side of the
molecule. Both α- and β-substituents
may be axial or equatorial. This system
of designating stereochemistry can best
be illustrated by the use of 5α-
androstane.

• The stereochemistry of the H at C5 is always indicated in the name. The
stereochemistry of the other H atoms is not indicated, unless it differs from 5α-
cholestane. Changing the stereochemistry of any of the ring juncture or backbone
carbons (shown with a heavy line on 5α-cholestane) greatly changes the shape of the
steroid, as seen in the examples of 5α, 8α-androstane and 5β-androstane.
• The terms cis and trans are occasionally used in steroid nomenclature to indicate the
backbone stereochemistry among rings. For example, 5α-steroids are A/B trans, and
5β-steroids are A/B cis. The terms syn and anti are used analogously to trans and cis for
indicating stereochemistry in bonds connecting rings (e.g., the C9:C10 bond that
connects rings A and C).

• The position of double bonds can be
designated in any of the various ways
shown in Figure. Double bonds from C8
may go toward C9 or C14, and those
from C20 may go toward C21 or C22. In
such cases, both carbons are indicated
in the name if the double bond is not
between sequentially numbered
carbons (e.g., 5α-androst-8(14)-ene or
5α- Δ8 (14)-androstene).

FROM CHOLESTEROL TO STEROID HORMONES
10

CLASSIFICATION OF STEROIDS
Sterol
• Also known as steroid alcohols.
• Occur naturally in plants, animals, and fungi, with the most familiar type of animal
sterol being cholesterol.
TYPES
• Phytosterols – plant sterol (Campesterol, Sitosterol, and Stigmasterol).
• Blocks cholesterol absorption sites in the human intestine, thus helping to reduce
cholesterol in humans.
• Zoosterol – animal sterol (Cholesterol).
• Ergosterol – sterol present in the cell membrane of fungi.

Camptosterol Sitosterol Stigmasterol
Cholesterol
Ergosterol
12

Bile acids
• Are steroid acids found predominantly in the bile of
mammals and other vertebrates.
• Are conjugated with taurine or glycine in the liver,
forming bile salts.
• Primary bile acids are those synthesized by the liver.
• Secondary bile acids result from bacterial actions in
the colon.
functions:
• To remove unwanted cholesterol from the body
• To aid in lipid digestion in the intestine
Taurocholic acid
Glycocholic acid

Cardiac Glycosides
• Are glycosides of mostly C23-steroidal
compounds.
• Are called cardiac glycosides because they
modify heart action.
Medicinal importance
• They are cardiotonics used to treat
Congestive heart failure (CHF).
• They increase force of contraction of cardiac
muscles without increase oxygen
consumption.
Digitoxin
Digoxin

Steroid hormones
• A steroid that acts as a hormone
• Can be grouped into five groups by the receptors to which they bind:
glucocorticoids, mineralocorticoids, androgens, estrogens, and
progestogens.
Steroid hormones help control
• Metabolism, inflammation, immune functions, salt and water balance,
development of sexual characteristics, and the ability to withstand illness
and injury.

BIOSYNTHESIS OF STEROID HORMONES
16

Cortisol (Hydrocortisone)
Glucocorticoids
 Glucocorticoids originate in the adrenal cortex and affect
mainly metabolism in diverse ways; decrease
inflammation and increase resistance to stress.
 Cortisol (C-21): dominant glucocorticoid in humans,
synthesized from progesterone in the zona fasciculata of
the adrenal cortex, involved in stress adaptation, elevates
blood pressure and Na+ uptake, numerous effects on the
immune system.
CLASSES OF STEROID HORMONES

Mineralocorticoids
 Mineralocorticoids originate in adrenal cortex and
maintain salt and water balance.
 Aldosterone (C-21) : the principal
mineralocorticoid, produced from progesterone in
the zona glomerulosa of adrenal cortex, raises blood
pressure and fluid volume, increases Na+ uptake.
Aldosterone

ESTROGENS
 Estrogens originate in the adrenal cortex and gonads and
primarily affect maturation and function of secondary sex
organs (female sexual determination).
 The natural estrogenic hormones are estradiol, estrone, and
estriol, produced in the gonads, adrenals, and placenta.
 Estradiol (C-18): an estrogen, principal female sex
hormone, produced in the ovary, responsible for secondary
female sex characteristics.
Estrone
Estratriol
Estradiol

Testosterone
ANDROGENS
 Androgens originate in the adrenal cortex and gonads
and primarily affect maturation and function of
secondary sex organs (male sexual determination).
 Testosterone (C-19): an androgen, male sex
hormone synthesized in the testes, responsible for
secondary male sex characteristics, produced from
progesterone; most potent androgen in blood.

PROGESTINS
 Progestins originate from both ovaries and placenta,
and mediate menstrual cycle and maintain
pregnancy.
 Progesterone (C-21): a progestogen, produced
directly from pregnenolone and secreted from the
corpus luteum, responsible for changes associated
with luteal phase of the menstrual cycle,
differentiation factor for mammary glands.
Progesterone

ADRENAL CORTICOSTEROIDS
• Adrenal corticosteroids are hormones produced in the adrenal glands
(located just above the kidneys).
• Cortisone (a glucocorticoid) raises the blood glucose level by causing tissues
other than the brain to switch to metabolizing fats and proteins; it also
suppresses the immune response and can be used as an anti-inflammatory
anti-allergy medication.
• Aldosterone (a mineralcorticoid) regulates ion balance by promoting re-
absorbtion of Na+, Cl- and HCO3
- by the kidneys.
• Prednisone is a synthetic corticoid used to treat various inflammatory
conditions, such as asthma and rheumatoid arthritis.

CLASSIFICATION OF CORTICOSTEROIDS
1. Mineralocorticoids with high salt retention
Aldosterone
11-Deoxycorticosterone
Fludrocortisone
Cortisone acetateHydrocortisonePrednisone Prednisolone
2. Glucocorticoids with moderate-to-low salt retention

Betamethasone DexamethasoneMethylprednisolone
3. Ophthalmic glucocorticoids
Fluorometholone Loteprednol etabonate
Rimexolone

4. CORTICOSTEROIDS USED FOR THE TREATMENT OF ASTHMA AND ALLERGY
Triamcinolone Beclometasone diproprionate Budesonide
Fluticasone propionate
Mometazone furoate
Flunisolide

ACTIONS OF CORTICOSTEROIDS
• Direct (Intended) Actions
 Anti-inflammatory
 Anti-allergy
 Anti-immunity
• Permissive Actions
 Lipolytic effects
 Effect on BP
 Effect on bronchial muscles

• Glucocorticoids (e.g., prednisolone) used to suppress inflammation, allergy and
immune responses.
• Anti-inflammatory therapy is used in many illnesses (e.g., Rheumatoid Arthritis,
Ulcerative Colitis, Bronchial Asthma, eye and skin inflammations).
• Useful in, say, tissue transplantation and lymphopoiesis (leukemias and
lymphomas).
• Striking improvements can be obtained, but severe adverse, but highly
predictable, effects ensue.

• Hydrocortisone used orally for replacement therapy, i.v. for shock and asthma,
topically for eczema (ointment) and enemas (ulcerative colitis).
• Triamcinolone used for severe asthma and for local joint inflammation.
• Betamethasone and Dexamethasone: Very potent, w/o salt-retaining
properties; thus, very useful for high-dose therapies (e.g., cerebral edemas).
• Beclometasone diproprionate, Budesonide: Pass membranes poorly; more
active when applied topically (severe eczema for local anti-inflammatory
effects) than orally; used in asthma, (aerosol).

MINERALOCORTICOIDS
• Aldosterone is a steroid hormone (mineralocorticoid family) produced by the
outer section (zona glomerulosa) of the adrenal cortex in the adrenal gland.
• It plays a central role in the regulation of blood pressure,
• Increasing reabsorption of ions and water in the kidney,
• Aldosterone is pathogenic and contributes to the development and progression
of cardiovascular and renal disease,
• Aldosterone has exactly the opposite function of the atrial natriuretic
progression of cardiovascular and renal disease,
• Hormone secreted by the heart.

• Fludrocortisone has a very great sodium-retaining effect in relation to its
anti-inflammatory action and only at high doses the nonelectrolyte effects
need to be considered. It is used to replace aldosterone where the adrenal
cortex is destroyed (Addison's disease). Fludrocortisone is also the drug of
choice in most patients with autonomic neuropathy, in whom volume
expansion is easier to achieve than a sustained increase in vasoconstrictor
tone.

SAR OF CORTICOSTEROIDS
Modification in Ring A
i. Contraction of ring A to norcortisol yields and inactive compound.
ii. Ring A can be modified isosterically to a heterocycle like 2-Oxacortisol acetate, which has 25%
activity of the cortisol.
iii.The introduction of unsaturation (a double bond) at C-1 leads to enhanced anti-inflammatory
activity (ex. Betamethasone). Whereas the addition of –OH group leads to the compound
becoming inactive.
iv.The introduction of a 2α-methyl group into cortisol leads to increase in activity, the C-2 bromo
substituent is potent among the halogens.
• Hydrocortisone (cortisol) is the naturally occurring glucocorticoid
with mineralocorticoid activity.

v. The C-3 carbonyl group can be fused with a heterocyclic moiety to yield a
‘soft drug’. C-3 spirofused thiazolidine derivative (1) was found to be active
and this derivative considerably reduced the thinning of the skin, generally
found in corticosteroids. but not essential for anti-inflammatory activity.
Ex. 5α-Pregnane- 3-one.
vi. The Δ4 double bond is important.
vii. Ring A can be fused with a pyrazole ring. Compound (2) has 2000 times
the potency of cortisol, but also lacks mineralocorticoid activity.
OH
OAc
OH
O
N
N
C6H4F
(1)
Cortisone
O
OH
F
H
O
O
CH2OPO(OK)2
O
CH3
CH3
5α-Pregnane-3-one.
OH
OAc
OH
O
N
N
C6H4F (2)

Modification in Ring B
i. Substitution of 6α position with hydrophobic groups like alkyl or halogens (methyl, chloro
and fluoro leads to increase in activity.
ii. Polar substituents such as –OH or =O at 6α position decreases the activity.
iii. 7α and 7β substituents decrease the anti-inflammatory activity. Thus 7α and 7β methyl
cortisol derivatives are less potent than cortisol.
iv. Introduction of –OH group at both 6α and 7α position leads to decrease in activity.
v. 6α and 7α difluoromethylene and 6β and 7β derivatives show enhanced activity.
vi. Introduction of 8(9) double in prednisolone affords compound with lower anti-inflammatory
activity.
vii. Removal of the C-19 angular –CH3 group reduces anti-inflammatory activity.
viii. The H at C-10 should be in β-configuration for the optimal activity.

ix. Anti-inflammatory potency of corticosteroids drastically influenced by the substituents at C-9
position. The groups added were –F, -Cl, -Br, -I, -OH and –CH3. The activity of the compounds
increases with increasing hydrophobic bonding of the C-9α substituents. The function of the
electron withdrawing group at C-9 was to increase the activity of the neighbouring 11β-hydroxyl
group which in turn leads to increase in corticoid activity.
Modification of Ring C
i. The C-11 oxygen group is not essential for anti-inflammatory activity. It can be replaced by groups
like –Cl, which can be converted to the hydroxyl group in vivo.
ii. Ester substituents at C-12 have showed anti-inflammatory activity and the potency is in the
following order: propinyl >butyl >isovaleryl.
Modification in ring D
i. Methyl group at C-15 with α configuration enhances anti-inflammatory activity.
ii. Placement of 16α-hydroxy and 17α-hydroxy groups yields potent compounds. These two groups
36

Modification in the side chain at C-17
i. Acetonide derivatives across the 17, 20-diol arrangement resulted in more
potent analogues compared to free diols.
ii. Hydroxyethanone side chain attached at C-17 in the classical corticosteroid
is not essential for activity. Tipredane, a 17-thioketal is a potent topical anti-
inflammatory drug.
Tipredane
may also form acetonide derivatives, which are more potent than the corresponding 16, 17-
dihydroxy derivatives.
iii. At C-16 introduction of chloro, methyl groups increase activity.
iv. The 17α-OH group is not essential for activity. Ketals and esters yield compounds with improved
potency.
v. Introduction of –Cl, -Br and –F at C- 17α position lowers the activity.

iii. Replacement of the –OH group at C-21 by –Cl, or –F enhances
activity.
iv. Retaining of anti-inflammatory activity of corticosteroids observed
upon ketalization of the C-20 carbonyl group with ethylene glycol.
v. Replacement of the C-21 carbon by sulphur (fluticasone) afforded
21-thioesters, also useful clinically.
vi. The C-21 –OH group can be esterified to afford lipophilic
compounds that are meant for respiratory use.
vii. Introduction of activating groups at C-21, conversion of –CH2OH
group to a –CH3 group (medrysone) yields clinically useful
ophthalmic anti-inflammatory compound with relatively little effect
on intraocular pressure.
Fluticasone
Medrysone

ANDROGENS & ANABOLIC STEROIDS
• The term androgens includes a number of natural and synthetic compounds
that exhibit the masculinizing and anabolic action of testosterone.
• The main physiological, endogenic, and androgenic hormones. Androgen,
commonly referred to as male sex hormones or anabolic steroids, in particular,
testosterone, are produced by male sex glands in the male body.

Common Anabolic Androgenic Steroids

• Testosterone is the natural androgen secreted by the interstitial cells of the
testis; it is necessary for normal spermatogenesis, for the development of the
male secondary sex characteristics, and for the growth, at puberty, of the sexual
apparatus. It is converted by hydroxylation to the active dihydrotestosterone.
• Protein anabolism especially in skeletal muscles is increased by androgens.
Growth of bone is promoted, but the rate of closure of the epiphyses is also
hastened, causing short stature in cases of precocious puberty or of androgen
overdose in the course of treating hypo gonadal children.

PATHWAY OF SYNTHESIS OF TESTOSTERONE
IN THE LEYDIG CELLS OF THE TESTES

METABOLISM OF
TESTOSTERONE TO ITS
MAJOR ACTIVE AND
INACTIVE
METABOLITES

SAR OF ANDROGENS
1. For a substance to have activity, it must contain the androstane skeleton.
2. Oxygen at C-3 and C-17 are not essential for the androgenic activity.
3. The basic nucleus having 5β-androstane which having androgenic activity,
whereas 5α-androstane having no activity.
4. There should not be chain constriction or extension because it leads to
finished the activity.

5. Introduction of 3-hydroxy group and 3-keto group enhance the activity.
6. Hydroxy group at C-17 position has no androgenic or anabolic activity.
7. Halogen substitution produces compounds with decreased activity except when placed
at C-4 or C-9 position. For example, 9-fluoro derivatives produces an anabolic effect 20
times that of 17α-methyl testosterone
Fluoxymesterone
17α-methyl testosterone

8. Halogen introduction will decrease the activity except the C-4 and C-9.
9. Introduction of double bond at C-1 position increases the anabolic activity for example –
methandrostenolone is more active than methyltestosterone.
10. Replacement of carbon atom at C-2 position by oxygen (e.g. Oxandrolone) gives the oral
anabolic activity.
Methandrostenolone Methyltestosterone
Oxandrolone

11. Removal of –CH3 group in testosterone gives 19-nor testosterone with more anabolic activity
and less androgenic activity when compared with testosterone.
12. The introduction of heterocyclic system into the steroid nucleus in ring A improve the
anabolic activity. For example, stanozolol are found to possess more anabolic activity,
possessing pyrazole.
19-nor testosterone Stanozolol

ESTROGENS
• Estrogen are a group of steroid compounds that function as the primary female sex
hormones.
• Three naturally occuring estrogen are estradiol,estriol and estrone, In the body these
are all produced from androgens through enzyme action.
SOURCE:-
• Estrogen are produced by developing follicles in the ovaries, the corpus luteum and
the placenta, some estrogens are also produced in smaller amounts by other tissues
such as liver, adrenal glands and the breasts .
• These secondary source of estrogen are especially important in post menopausal
women.

THE BIOSYNTHETIC PATHWAY FOR THE ESTROGENS
49

CLASSIFICATION OF ESTROGENS
1. STEROIDAL ESTROGENS
Estradiol Estrone Estriol
Ethinyl estradiol Mestranol

2. NON STEROIDAL OR SYNTHETIC ESTROGENS
Diethyl stilbestrol
Dienestrol Hexestrol
3. ESTROGENS OF PLANT ORIGIN
Coumestrol Genistein

ESTRADIOL
• Estradiol is a human sex hormone and steroid, and the
primary female sex hormone. It is important in the regulation
of the estrous and menstrual female reproductive cycles.
Estradiol is essential for the development and maintenance of
female reproductive tissues but it also has important effects in
many other tissues including bone. While estrogen levels in men
are lower compared to women, estrogens have essential
functions in men as well.
Uses:
• It helps to regulate and subsequent maintence of female sex
organs, certain function of the uterus and all the secondary sex
features and the mammary glands.

SAR OF ESTROGEN
Modification of ring A
• Ring A is aromatic in nature in all oestrogens, which is essential for
oestrogenic activity.
• -OH group at C-3 is also essential for oestrogenic activity. Removal of
this –OH group leads to loss of activity.
• Substitution at C-1 reduces the activity.
• Smaller groups can be substituted at positions C-2 and C-3. Ex. 2-
hydroxyl ethinyl estradiol.
• Presence of steroid nucleus (cyclopentanoperhydrophenanthrene
ring) is essential for pharmacological activity of oestrogen.
Estrone
Estriol

Modification of Ring B
• Presence of unsaturation at positions C-6 and C-7 increase the potency of
drug. Similarly additional double bond between C-8 and C-9 positions further
increase the activity. Ex. equilin, equilenin.
• 7α-substituents show increased activity.
Modification of Ring C
• Substitution of –OH groups at C-6, C-7 and C-11 position reduces the activity.
• Substitution at C-11 β-position with alkyl group or alkoxy groups which has
17-ethinyl group greatly increase affinity for the estrogenic receptor
compared to estradiol. Ex. 11β-methoxy or 11β-ethyl estradiol.
• –CH2Cl group at C-11 with β-configuration shows more potent activity.
• Larger substituents, ex. N,N-dialkyl undecylamides, shows antagonistic
activity.
54
Equilin
Equilenin

Modification of Ring D
• 17β-OH is essential for estrogenic activity.
• Epimerization of 17β-OH to a α-configuration results in the
formation of less active analogues.
• 17α-Ethinyl or 17α-vinyl groups provide greatest activity due to
increase in polarity. Ex. Ethinyl estradiol.
• Reversal of configuration of C-2 or replacement of H for ethynyl in D
ring leads to loss of estrogenic activity or increase in androgenic
activity.
• The distance between C-3 and C-17 –OH groups should be 11-12 Aᵒ,
presence of this hydrophobic scaffolding helps to optimize
estrogenic activity. Ex. All estrogens and diethylstilbestrol.
55
17α-Ethinyl estradiol
Diethyl stilbestrol

PROGESTINS
• They also called luteum hormones, mostly secreted by the corpus luteum
portion of the ovary and the metabolised to various inactive products, e.g.
pregnanediol. The metabolites are essentially excreted through urine.
• The natural progestational hormone is progesterone , which is secreted by
the corpus luteum in the second part of the menstrual cycle.
• Small amounts are also secreted by the testis in the male and the adrenal
cortex in both sex and large amounts are secreted by the placenta.

USES
1. Prevent habitual abortion.
2. For treatment of functional uterine bleeding resulting due to the lack of oestrogens and
progesterone
3. For treatment of dysmenorrhoea or painful menstruation
4. Pregnancy diagnosis,
5. Oral contraceptives,
6. For treatment of an advanced carcinoma of breasts.
7. To treat premature discomfort in the breasts
8. Progesterone can be used to treat catamenial epilepsy.
9. Progesterone also has a role in skin elasticity and bone strength, in respiration, in nerve tissue and
in female sexuality, and the presence of progesterone receptors in certain muscle and fat tissue.

CLASSIFICATION
1. Derivatives of progesterone
Progesterone
17-Hydroxyprogesterone caproate Megestrol acetate
Medroxyprogesterone acetate

2. Synthetic progesterone
Ethisterone Norethisterone Dimethisterone
NoretynodrelDesogestrel
Levonorgestrel

SAR OF PROGESTERONE
• Presence of steroid nucleus (cyclopentanoperhydrophenanthrene
ring) is compulsory for pharmacological activity of progestins.
• Ketone group at C-3 is not essential for the activity of progesterone,
because removal of it retains the progesterone. Ex. Desogestrel.
• Presence of ethyl or ethinyl or diethyl group at C-17 in α configuration
increase bioavailability through oral route, but decreases by
subcutaneous route.
• The l-enantiomer of the compound resulting from substitution of ethyl
group at C-ring junctures found to be active.
• Derivatives of the progestins like 3-oxime-17-ester decreases
androgenic side effect, while retaining progestin activity.
Progesterone
Desogestrel
Ethisterone

• Introduction of halogen or –CH3 at C-6 or C-7 atoms in α
configuration increases hormonal activity of progestins. Ex.
Medroxyprogesterone acetate.
• Presence of methyl at C-19 is not essential for activity because its
removal leads o formation of compound with increased activity.
• Addition of Cl or F at C-21 prevents metabolic hydroxylation, which
also enhances oral effectiveness.
• Unsaturation at ring A and B enhances activity of 19-norethindrone.
Ex. Trimegestone.
• Addition of methyl at 18th position increases the activity.
• In ring D at C-17, acetylation of 17α-hydroxyl group increases the
duration of action.
Medroxyprogesterone acetate
Norethisterone

Mechanism of Steroid Hormone Action
• Steroid hormones are soluble in the
plasma membrane and readily enter
the cytosol.
• Steroids bind to intracellular receptor
either in the cytosol or in the nucleus.
• The hormone-receptor complex acts
as a transcription factor which turns
on / turns off the genes.

REFERENCES
1. J. N. Delgado and W. A. Remers, Wilson & Gisvold's: Textbook of Organic Medicinal and
Pharmaceutical Chemistry, Tenth edition, Lippincott Raven Publishers, Philadelphia, New
York 1998.
2. S. N. Pandeya: A Textbook of Medicinal Chemistry, Vol-2, S.G. Publishers, Varanasi, 2003.
3. Ashutosh Kar, Medicinal Chemistry, 3rd edition, Wiley Eastern, Ltd, New Delhi,2005.
4. Dr V. Alagarsamy, Textbook of Medicinal Chemistry, Vol. II, Elsevier India, 2013.
5. K. D. Tripathi., Essentials of medical pharmacology, Jaypee Brotter Medical Publisher (p) LTD,
5th edition.

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