DR.VIJAYA KRISHNAPost graduate student

Department of PharmacologyGANDHI MEDICAL COLLEGE

Hyderabad, AP.

BIOTRANSFORMATION

01 AUG 2012

PLAN OF PRESENTATION

• INTRODUCTION• DEFINITION• SITES OF BIOTRANSFORMATION• PHASES OF DRUG METABOLISM• PHASE-I REACTIONS• PHASE-II REACTIONS• ENZYME INDUCTION• ENZYME INHIBITION• FACTORS AFFECTING DRUG

METABOLISM• REFERENCES

INTRODUCTION

• Biotransformation/Xenobiotic metabolism/ drug metabolism/detoxification.

• Xenobiotics: a wide variety of foreign compounds to which humans get exposed in day to day life.

• It includes unknown compounds, drugs, environmental pollutants, toxins.

• Many xenobiotics can evoke bilogical responses.

DEFINITION

• The biochemical alteration of drug or xenobiotic in the presence of various enzymes that acts as a catalyst which themselves not consumed in the reaction and there by may activate or deactivate the drug is called biotransformation.

Why Biotransformation is necessary?:

• To easily eliminate the drug• To terminate drug action by

inactivating it By changing its physicochemical properties from:

Active /inactiveLipophilic UnionisedNonpolarPlasma protein bound

Inactive /activeHydrophilic IonisedPolarFree

Consequences of Biotransformation

• Active to Inactive: Phenobarbitone----

Hydroxyphenobarbitone• Inactive (prodrug) to Active : L-Dopa ---- Dopamine Parathion -- Paraoxon Talampicillin -- Ampicillin

• Active to equally active: Diazepam -- Oxazepam Amitriptyline -- Nortriptyline Imipramine -- Des-imipramine Codeine -- Morphine

Sites of biotransformation

• In the body: Liver, small and large intestines, lungs, skin, kidney, nasal mucosa & brain.

• Liver is considered “metabolite clearing house” for both endogenous substances and xenobiotics.

• Intestines are considered “initial site of drug metabolism”.

FIRST PASS METABOLISM:

• First pass metabolism or presystemic

metabolism or ‘first pass effect’

• After oral administeration many drugs are absorbed from the small intestine - transported first via portal system to the liver, where they undergo extensive metabolism before reaching systemic circulation.

26

• First pass effect :Liver-90%, Git-9% and Portal circulation-1%

• Partially metabolised drugs - nitroglycerine,propranolol,salbutamol- high oral dose is required.

• Complete first pass metabolism - isoprenaline, hydrocortisone, insulin.

• Liver diease- increased bioavailability of drugs.

Drugs which undergo first pass effect:LI

VER • ISOSORBIDE

DINITRATE• GLYCERYL

TRINITRATE• MORPHINE• PETHIDINE• XYLOCAINE• IMIPRAMINE• AMITRIPTYLIN

E• PROPRANOLO

L

INTE

STIN

AL M

UCO

SA

• L-DOPA• ALPHA

METHYLDOPA• TESTOSTERON

E• PROGESTERON

E• CHLORPROMA

ZINE• CLONAZEPAM• MIDAZOLAM• CYCLOSPORIN

E

BRO

NCH

IAL

MU

COSA • NICOTIN

E• ISOPRIN

ALINE

With in the cell: Endoplasmic reticulum. smooth ER microsomal reactions rough ER protein synthesis

PHASES OF DRUG METABOLISM

PHASE I REACTION

PHASE II REACTION

1.Degradative reaction 1.Synthetic reaction

2.Introduction of functional group ( -OH, -NH2,-SH,-O -,-COOH)

2.Conjugates phase 1 metabolite with glucuronic acid,sulfate,acetyl, methyl groups.

3.Mainly microsomal 3.Microsomal, Mitochondrial & Cytoplasmic

4.Metabolites formed may be smaller, polar/non-polar Active/Inactive

4.Metabolites formed are usually larger,polar,water soluble & Inactive

DRUG METABOLIZING ENZYMESENZYMES REACTIONS

PHASE 1 “OXYGENASES”

CYP 450 C & O OXIDATION,DEALKYLATION,

FMO N, S & P OXIDATION

EPOXIDE HYDROLASES HYDROLYSIS OF EPOXIDES

PHASE 2 “TRANSFERASES”

SULFOTRANSFERASES(SULT) ADDITION OF SULFATE

UDP-GLUCURONOSYLTRANSFERASES(UGT) ADDITION OF GLUCURONIC ACID

GLUTATHIONE-S-TRANSFERASES(GST) ADDITION OF GLUTATHIONE

N-ACETYL TRANSFERASES(NAT) ADDITION OF ACETYL GROUP

METHYLTRANSFERASES(MT) ADDITION OF METHYL GROUP

OTHER ENZYMES

ALCOHOL DEHYDROGENASES REDUCTION OF ALCOHOLS

ALDEHYDE DEHYDROGENASES REDUCTION OF ALDEHYDES

NADPH-QUINONE OXIDOREDUCTASE(NQO) REDUCTION OF QUINONES

MICROSOMAL ENZYMES NON-MICROSOMAL ENZYMES

1.Smooth endoplasmic reticulum of cells of liver,git,kidney,lungs & skin.

1.Cytoplasm, mitochondria of hepatic & other tissues(plasma).

2.Non-specific,inducible. 2.Non-inducible.

3.PHASE-I: most oxidation & reduction, some hydrolysis.

3.PHASE-I: most hydrolysis, some oxidation & reduction.

4.PHASE-II: only glucuronide conjugation.

4.PHASE-II: all except glucuronide conjugation.

5.Mainly MFO’s like CYP 450, FMO’s, EH, UGT

5. Include MAO, esterases, amidases ,transferases , conjugases.

In the Oxido-reductase process 2 microsomal enzymes play a key role

Flavo proteins ,NADPH –cyt p-450 oxido-reductase

Haemoprotein,cyt p-450 serves as terminal oxidase • P450 heme reduction is rate limiting step

CYTOCHROME P450

• Microsomal drug oxidations require p450,p450 reductase, NADPH ,O2

• Very low substrate specificity.High lipid solubility is the only common structural feature of most of substrates.

• P450 isoforms in liver –cyt1A2 ,2A6 ,2B6 ,2C8, 2C9, 2C18, 2C19, 2D6, 2E1,3A4,3A5

Of these isoforms 3A4/5 carry out biotransformation of about 50% of drugs.

P450 enzymes classified into families denoted by numbers -1,2,3 and sub families by A,B,C & D basis of AA sequence and c-DNA . Another number indicates –specific isoenzymes.

Electron flow in microsomal drug oxidizing system

CO

huCYP-Fe+2

Drug

CO

O2

e-

e-

2H+

H2O

Drug

CYPR-Ase

NADPH

NADP+

OHDrug

CYP Fe+3

Drug

CYP Fe+2

Drug

CYP Fe+2

Drug

O2

CYP Fe+3

OHDrug

CYP 450 SUBSTRATES

1A2 Acetaminophen, antipyrine, caffeine, clomipramine, phenacetin, tamoxifen, theophylline, tacrine, warfarin

2A6 Coumarin, tobacco nitrosamines, nicotine

2B6 Artemisin, bupropion, cyclophosphamide, efavirenz, ifosfamide, ketamine, mephobarbital, mephenytoin, nevirapine, propofol, selegiline, sertraline

2C8 Taxol, all-trans-retinoic acid

2C9 Celecoxib, flurbiprofen,hexobarbital,ibuprofen, losartan,phenytoin, tolbutamide, s-warfarin

2C18 Tolbutamide, phenytoin

2C19 Diazepam, s-mephenytoin, naproxen, nirvanol, omeprazole, propranolol.

2D6 Bufurolo, clozapine, debrisoquin, dextromethorphan, encainaide, fluoxetine, haloperidol, metoprolol, selegiline, tamoxifen, tricyclic antidepressants.

2E1 Acetaminophen, chlorzoxazone, enflurane, halothane, ethanol

3A4, 3A5 Acetaminophen , cyclosporine, alfentanyl, cocaine, dapsone, diazepam, erythromycin, lidocaine, lovastatin, methadone ,midazolam, ethinyl estradiol, mifepristone, terfenadine,tamoxifen,saquinavir.

Microsomal: 1.oxidation – a.CYP dependent

b.CYP independent 2.reduction 3.hydrolysis

Non-microsomal: 1.oxidation 2.reduction 3.hydrolysis

PHASE-I REACTIONSReaction Structure Examples

Microsomal(Cyp 450 dependent): Oxidation

1.Aromatic hydroxylations

R- -------- R- -OH

Phenobarbitone, Phenytoin,propranolol, amphetamine, warfarin, 17α - ethenyl estradiol

2.Aliphatic hydroxylations

RCH2CH3-------> RCHOHCH3

digoxin,ibuprofen,secobarbital,chlorpropamide

PHASE-I REACTIONSReaction Structure Examples Microsomal(Cyp 450 dependent): oxidative Dealkylation

3.N-Dealkylation RN(CH3)2------ RNHCH3+CH3CHO

Mephobarbitone,amitriptyline,morphine, caffiene, theophylline

4.O-Dealkylation R-O-CH3------R-OH+HCHO

phenacetin, codiene, paranitroanisole

5.S-Dealkylation R-SCH3---- R-SH + HCHO

6-methylthiopurine

PHASE-I REACTIONSReaction Structure Example

Microsomal(Cyp 450 dependent): N-Oxidation

Primary amines RNH2------>RNHOH

Aniline, Chlorpentermine

Secondary amines R1-NH2-R2----> R1-NOH-R2

2-acetyl aminofluorene, acetaminophen

Tertiary amines NR1R2R3----> R1R2R3-N-O

nicotine, methaqualone

PHASE-I REACTIONS

Reaction Structure Examples

Microsomal(cyp 450 dependent):

S-Oxidation R1-S-R2--->R1 -SO-R2

cimetidine, chlorpromazine, omeprazole, thioridazine

Deamination R-CHNH2-R---->R-COR +NH3

Amphetamine, diazepam

Desulfurisation R1-PS-R2--->R1-PO-R2

Parathion,thiopental

Dechlorination CCl4---> [CCl3-]---> CHCl3 carbontetrachloride

Flavin Monooxygenases

• Also known as zeigler’s enzyme. Neither inducible nor inhibited.

• six families-FMOs(FMO3 being the most abundant in liver.)

• FMO3 is able to metabolize nicotine,cimetidine and ranitidine,clozapine and itopride.

• A genetic deficiency in this enzyme causes the fish-odor syndrome due to a lack of metabolism of trimethylamine N-oxide (TMAO) to trimethylamine (TMA).

EPOXIDE HYDROLASE• Two types: soluble and microsomal

• Drug----------- epoxide-------- inactive metabolite.

• Ex:carbamazepine--carbamazepine-10-11-epoxide--Trans-dihydrodiol

• Valnoctamide,valproic acid inhibit mEH.

cyp EH

•Highly reactive electrophile•Binds to DNA,RNA.PROTEINS•Cell toxicity

PHASE-I REACTIONS

Reaction Structure Examples

Non-microsomal:Oxidation

Mitochondrial oxidation

R-CH(OH)CH2NH2- R-CH(OH)COOH+NH3

Epinephrine

Cytoplasmic oxidation(dehydrogenation)

C2H5OH-CH3CHO-CH3COOH

Alcohol

Plasma oxidative processes

Histamine-Imidazole acetic acidXanthine- Uric acid

PHASE-I REACTIONSReactions Structure Examples

Microsomal reductions

Nitro Reductions RNO2--RNH2 Chloramphenicol

Azo Reductions RN=NR1-RNH2+R1NH2

prontosilsulfasalazine

Keto Reduction R-CO-R1- R-CHOH-R1

cortisone, methadone, metyrapone

Non-microsomal Reductions:

C(Cl)3CH(OH)2- C(Cl)3CH2OH

Chloral hydrate

PHASE-I REACTIONSReaction Structure Examples

Microsomal Hydrolysis

Pethidine, Lidocaine

Non-Microsomal Hydrolysis

Procaine---PABAAtropine-- atropic acidPenicillin-GProcainamide

Non-Enzymatic Biotransformation

• Skeletal muscle relaxants like ATRACURIUM are metabolised in the plasma spontaneously through molecular rearrangement without involvement of any enzyme action.

ENZYME INDUCTIONXenobiotics can influence the extent of drug metabolism 1.by activating transcription 2.by inducing expression of genes

Mechanism of enzyme induction:

Aryl hydrocarbon Receptor(AHR):

• Induces CYP1A1,1A2,1B1--> activates procarcinogens

• Omeprazole is ligand.

• AHR is a member of super family of transcription factors (PERIOD,SIMPLEMINDED,HIF).

• AHR has regulatory role in the development of mammalian CNS – modulating the response to chemical & oxidative stress.

Pregnane X Receptor:

• Structurally similar to steroid hormone receptors.

• Induces CYP3A4 ,Drug Transporters, SULT’s, UGT’s

• LIGANDS: Pregnanolone-16-carbonitrile, Rifampin, Troleandomycin, Nifidipine, Mevastatin, troglitazone, Ritonavir, paclitaxel, hyperforin.

• Basis for contraceptive failure.

Constitutive Androstane Receptor(CAR):• Can activate genes even in absence of their

ligands.• LIGANDS: Pesticide 1,4-bisbenzene, 5-pregnane-3,20-dione.• Induces CYP2B6, 2C9, 3A4, GST, UGT, SULT,

Drug & endobiotic transporters.• Inverse agonists-androstanol,

clotrimazole,meclizine PXR & CAR exhibits species differenceEx: 1.Rifampicin activates human PXR but not that of Rat.

2.Pregnanolone-16-carbonitrile- activates mouse,rat PXR.

3.Meclizine inhibits human CAR but activates mouse CAR.

Peroxisome Proliferator Activated Receptor α(PPARα):

• Highly expressed in liver & kidney.

• LIGAND: 1.fibrates(gemfibrozil, fenofibrate), 2. hypoglycemic drugs(rosiglitazone, pioglitazone)• Induces 1.enzymes- fatty acids(Arachidonic

acid) 2.CYP4A - oxidation of FA & drugs with FA side chain(leukotiene analogues)

• PPARα does not induce xenobiotic metabolism

Enzyme induction by decreased enzyme degradation(substrate s):

Troleandomycin, clotrimazole induces CYP3A Ethanol induces CYP2E1 Isosafrole induces CYP1A2

ENZYME INHIBITION

• It is basis for several drug interactions. It is a rapid process.

• Microsomal: 1.Reversible – cimetidine & ketoconazole binds tightly to cyp450 heme iron and inhibits metabolism of testosterone.

• Troleandomycin & Erythromycin--> CYP3A4--> cyp3A4-metabolite complex.

• Proadifen(SKF-525-A)--> bind tightly to heme iron and partially irreversibly inhibits enzyme.

2. Irreversible(suicidal inhibitors)- intermediate metabolite bind covalently with P450 apoprotien.

Ex: spironolactone, ethinyl estradiol, ritonavir But Secobarbital inhibits CYP2B1 by binding to

heme & protein moieties.

Non-microsomal:DRUG ENZYME INHIBITED

ALLOPURINOL XANTHINE OXIDASE

NSAIDS CYCLO-OXYGENASE

THEOPHYLLINE PHOSPHODIESTERASE

DISULFIRAM ALDEHYDE DEHYDROGENASE

PHASE-II REACTIONSGLUCURODINATION(microsomal): UDP-GA + substrate(Phase-I metabolite)

Glucuronides(glucopyranosiduronic acids)

Decojugated substrate

Ex: morphine, acetaminophen, diazepam, N-hydroxydapsone, digitoxin.

UGT

ALCOHOL & PHENOLIC HYDROXYL groupsCARBOXYL, SULFURYL, CARBONYL moietiesPrimary, Secondary & tertiary AMINE linkages.

Bacterial glucuronidase

• UGT are encoded by 19 genes(9genes on UGT1 locus-chr.2 & 10genes on UGT2 locus-chr.4)

• UGT1- Glucuronidation of Bilirubin-rate limiting step.

• UGT2 have greater specificity for endogenous substances(steroids) glucurodination.

PHASE-II REACTIONSSULFATION(cytosolic):Sulfotransferase(SULT) conjugates sulfate-

PAPS to the hydroxyl groups & less frequently to aromatic and aliphatic amine groups (acetaminophen, hydroxycoumarins).

SULT has 13 isoforms.SULT play an important role in normal

human homeostasis.SULT2B1b –skin-cholesterol-cholesterol

sulfate-regulates keratinocyte differentiation & skin development.

• SULT2A1-fetal adrenal gland -dehydroepiandrosterone - DHEA sulfate-essential for placental Estrogen biosynthesis during 2nd half of pregnancy.

• SULT1A3- highly selective for catecholeamines.

• SULT1E1-sulfates endogenous & exogenous steroids. Ex:-Estrogen(17-estradiol)-estrogen sulfate.

• In humans significant fractions of circulating catecholamines,estrogens,iodothryronines, DHEA are exist in sulfate form.

PHASE-II REACTIONSGLUTATHIONE CONJUGATION : Glutathione(GSH) is a tripeptide of glycine - glutamic acid - cysteine.• GSH exists in cell as oxidized form(GS-SH)

and reduced form(GSH).• GSH:GSSH ratio is critical in maintaining

cellular environment to be in reduced state.• GSH + Electrophilic compound

Electrophile-GlutathioneGST otherwise react with –O,-N,-S atoms leading to cell damage

GLUTATHIONE-S-TRANSFERASE(GST): • exists in 20 isoforms.

• Cytosolic GST isoforms -7classes - exogenous drugs & xenobiotics (acetaminophen, ethacrynic acid, bromobenzene)

• Microsomal GST isoforms-endogenous leukotrienes & prostaglandins.

• GST play an important role in cellular detoxification.

Its activity in cancerous tissue has been linked to development of resistance to chemotherapeutic agents.

Anticancer drug----> JNK &P38---->Apoptosis

-

Inhibition of GST activity sensitises tumour cells to anticancer drugs.

TLK199(GSH analogue) activated by plasma esterase to TLK117(GST inhibitor) which potentiates toxicity of anticancer drugs.

GST over expression In tumour cells

Resistance

N-Acetylation(cytosol):• Substrate- Aromatic amine groups & Hydrazine

group such as sulfonamides,isoniazid,clonazepam, dapsone,etc.

• Co-substrate- acetyl coenzyme A• Enzyme- N-Acetyl Transferase NAT1 & NAT2 – 25 Allelic variants are

identified.

NAT2 mutation – slow & fast acetylation.

Field of pharmacogenetics has established by the identification of “The characterisation of an Acetylator phenotype.”

Methylation(cytosol):

• Substrate: -N, -O, -S atoms containing compounds• Co-substrate: S-Adenosyl Methionine• Enzyme: Methyltransferase

N-Methyltransferases -Nicotinamide NMT- Serotonin, Tryptophan, Nicotinamide, Nicotine

Phenylethanolamine NMT - Norepinephrine

Histamine NMT - Histamine

Catechol-o-methyltransferase–>Dopamine,Norepinephrine, Methyldopa, Ecstasy

Phenol-o-methyltransferase –>Tyrosine metabolism

Thiopurine-s-methyltransferase ->Azathioprine, Thioguanine, 6-MP

Amino acid conjugation(mitochondria):

Substrate: aspirin, benzoic acid, nicotinic acid, deoxycholic acid Co-substrate: Glycine (or) Glutamine Enzyme: acyl coenzyme A-glycinetransferase Riboside & Riboside phosphates: Many purines & pyrimidines form their active

metabolites by forming ribonucleosides and ribonucleotides.

Purines and pyrimidines are used as antimetabolites in cancer chemotherapy.

1. AGE: Neonates-low microsomal enzymes &

glucuronyl transferase enzyme activity. ex: chloramphenicol-poor glucuronyl

conjugation- Gray baby syndrome. Elderly persons- reduced hepatic

blood flow. Ex: propranolol & pethidine

FACTORS AFFECTING DRUG METABOLISM

• Sex: male rats metabolise the drugs much faster than female rats and prepubertal male rats.

male rats sleep for a shorter duration

than female rats after receiving hexobarbital. In Humans similar sex differences exist

for propranolol, ethanol, estrogens, salicylates.

FACTORS AFFECTING DRUG METABOLISM

• Species: Rabbits metabolise Atropine faster than man as they have high Atropine esterase activity in the liver and plasma.

• Race: Chinese- high alcohol dehydrogenase activity & low Aldehyde dehydrogenase activity- high plasma aldehyde conc.- headache, palpitation after consuming alcohol.

FACTORS AFFECTING DRUG METABOLISM

• Diet and environment: Low carbohydrate-high protein diet- metabolism. High carbohydrate-low protien diet- metabolism. Starvation – enzyme inhibition. Charcoal- broiled foods & cruciferous vegetables induce CYP1A. Grapefruit juice inhibit CYP3A. Cigarette smokers metabolise some

drugs more rapidly than non-smokers

• Genetic polymorphism: Autosomal recessive traits. PHASE-I: CYP2D6DRUG PHENOTYPE EFFECT

debrisoquin PM orthostatic hypotension

codeine PM dec. analgesic effect.

UM inc. respiratory depression

tramadol PM inc. seizure risk

nortriptyline PM inc. ADR

UM dec. therapeutic effect.

• PHASE-I: CYP2C19DRUG PHENOTYPE EFFECT

amitriptyline PM dec. clearance. inc. ADR

citalopram PM inc. GIT side effects

omeprazole EM inc. therapeutic effect

tamoxifen EM inc. endoxifen. inc. efficacy. reduces risk of relapse.

tamoxifen(cyp2d6)

PM dec. endoxifen- dec. therapeutic efficacy.

chlorproguanil EM inc. therapeutic efficacy.

• PHASE-I: CYP2C9DRUG PHENOTYPE EFFECT

CELECOXIB, DICLOFENAC

PM INC. ADR

WARFARIN PM INC. BLEEDING RISK

TOLBUTAMIDE PM CARDIOTOXICITY

PHENYTOIN PM NYSTAGMUS, DIPLOPIA, ATAXIA.

• PHASE-II:Genetic polymorphism

Drug Effect

Pseudocholine esterase

Succinylcholine Succinylcholine apnea

N-Acetyl transferase 2

Slow Acetylation

Isoniazid Pheripheral neuropathy

Sulfonamide Autoimmune response

Bicyclic Aromatic Amines

Bladder cancer

Fast Acetylation

Isoniazid Hepatotoxicity

PHASE-II:Genetic polymorphism

Drug Effect

Thiopurine-s-methyltransferase (TMPT)

Azathioprine6-MercaptopurineThioguanine

Thiopurine induced fatal Hematopoietic toxicity

UDP-Glucuronosyl transferase

Bilirubin Crigler-Najjer syndromeGilbert syndrome

Irinotecan Bone marrow toxicityLife threatening diarrhoea.

Glutathione S transferase(GST)

Acetaminophen Acetaminophen toxicity- hepatic necrosis.

Drug – Drug interaction during metabolism:

Enzyme inducer Drugs with Metabolism

Phenobarbital & other barbiturates

Barbiturates, choramphenicol, chlorpromazine, cortisol, coumarin anticoagulants, digitoxin, doxorubicin, estradiol, itraconazole, phenytoin, quinidine, testosterone, etc.

Phenytoin Cortisol, dexamethasone, digitoxin, itraconazle, theophylline.

Carbamazepine Carbamazepine, clonazepam, itraconazole

Rifampicin Coumarin anticoagulants, digitoxin, itraconazole, glucocorticoids, OC Pills, saquinavir.

St.john’s wort Alprazolam, cyclosporine, digoxin, OC Pills, indinavir, ritonavir, simvastatin, tacrolimus, warfarin

Ritonavir Acutely inhibitor of CYP3A4; Chronicly inducer-midazolam.

Drug – Drug interaction during metabolism:

Enzyme inhibitors Drugs with metabolism

Itraconazole Atorvastatin,cisapride,cyclosporine, diazepam,digoxin,indinavir, phenytoin, quinidine, sildenafil, verapamil, warfarin

Isoniazid,chloramphenicol, Allopurinol

Dicoumarol, probenecid, tolbutamide

Disulfiram Ethanol, phenytoin,warfarin

Chlorpromazine Propranolol

Grapefruit juice Alprazolam, atorvastatin, cyclosporine

Ethanol Methnol

Spironolactone Digoxin

Saquinavir Cisapride, ergots, midazolam.

OC Pills Antipyrine.

DISEASES: Liver diseases - chlordiazepoxide &

diazepam

Pulmonary diseases – procainamide, procaine,

antipyrine Hypothyroidism - antipyrine, digoxin,

methimazole, beta blockers

Cardiac diseases - hepatic blood flow – rate of metabolism - amitriptyline, desipramine, isoniazid, labetalol, propanolol, lidocaine, morphine, pentazocine, verapamil.

REFERENCES

• Goodman Gilman - The Pharmacological Basis of

Therapeutics, 12th Edition• Katzung – Basic & Clinical

Pharmacology, 12th Edition• Sharma – Priciples of Pharmacology, 2nd Edition• www.google .com