Drug Metabolism: Importance and Mechanisms
undefined
3- Drug Metabolism
Objectives:
•
Recognize the importance of biotransformation
•
Know the different sites for drug metabolism
•
Define the major phase I and phase II metabolic
reactions.
•
Describe the modulation of liver microsomal
enzymes by inducers and inhibitors
•
Mention two drugs that are known as enzyme
inducers and inhibitors.
•
Know the impact of first pass metabolism on drug
bioavailability.
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Drug
Metabolism:
It
is
the chemical
reactions which occur in
the
body
to change
drugs
from
nonpolar lipid soluble
forms
to
polar
water
soluble
forms
that are
easily
excreted
by
the
kidney.
Importance:
•
Inactivation or termination
of drug action
(most
drugs).
•
Detoxification
Biotransformation
is
required
for
protection
of body
from
toxic
metabolites
.
•
Activation
of
prodrug
*
(convert
inactive
form
of drug
to
active
form)
e.g.
levodopa
- carbidopa,
prednisone
–
prednisolone
*an inactive substance that is converted to a drug within the body by the action
of enzymes or other chemicals.
Organ
sites
of
drug
metabolism:
1- Liver
(the
major
site).
*
2-
kidney
3-
skin
4- lung
5- Intestinal
Mucosa and
Lumen:
Gut
Mucosa
:
M
ono
A
mine
O
xidase (
MAO
)
.
Gut
lumen
(bacterial flora):
Glucouronidase.
6-
Plasma:
*because it is a large organ, and there are
high concentrations of most drug-
metabolizing enzyme systems
2
e.g.
Alcohol
dehydrogenase
**
(NAD
+
→
NADH)
(boy’s
slides)
(
oxidation
of
alcohol)
.
Alcohol
→
Aldehyde
→
Acid
Ethanol
→
acetaldehyde
→
acid
CH
3
CH
2
OH
→
CH
3
CHO
→
CH
3
COOH
*
Is the material or
protoplasm within a
living cell, excluding
the nucleus. So we will
find there a lot of
enzymes that play a
role in the drug
metabolism and one
**
(ADH) (EC 1.1.1.1)
are a group of
dehydrogenase
enzymes that occur in
many organisms and
facilitate the
interconversion
between alcohols and
aldehydes or ketones
with the reduction of
nicotinamide adenine
dinucleotide (NAD+ to
NADH).
There are several
chemicals in this
organelle that plays
an important role in
the drug metabolism,
those are:
1- N-acetyl
transferase
*
:
Introduction of acetyl
group (CH3COO- ) .
2- Monoamine
oxidase enzyme
**
(MAO):
oxidation of
catecholamines as
adrenaline.
*an enzyme that
catalyzes the transfer
of acetyl groups from
acetyl-CoA to
arylamines.
**a family of enzymes
that catalyze the
oxidation of
monoamines
neurotransmitter.
They are found bound
to the outer
membrane of
mitochondria in most
cell types in the body.
•
Microsomal
enzyme
system
=
Cytochrome
P-
450.
•
There
are more
than 20
families
CYP1, CYP2,
CYP3
•
Sub-families
are
identified as
A,
B,
and C
etc.
•
In human:
only 3
isoenzyme
families
are
important
CYP1,
CYP2 and
CYP3
Oxidation –
Cytochrome P-425:
CYP 3A4/5 carry out
biotransformation
of the largest
number (30-50%) of
drugs.
Expressed in the
liver and intestine
(responsible for first
pass metabolism at
this site).
REMEMBER THERE IS AN
ORGAN SITE AND A
CELLULAR SITE. BE CAREFUL.
3
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Types
of
hepatic metabolic
reaction:
Two phases of hepatic metabolism reactions:
After Phase
I: (The metabolites)
1.
Active
=
lipid soluble > Phase
II
2.
Inactive
=
water
soluble
(excreted)
Catechol o-methyl transferase (COMT)
Any drug has the catechol ring will metabolize by the COMT enzyme. This enzyme will add Ch
3
on one
of the OH and remove H, so it will transfer Ch
3
to O atom
Monoamine oxidase (MAO)
1- The MAO enzyme will oxidize the amino group (NH
2
) by remove NH
2
and add O instead, this will
give me aldehyde
2- another enzyme (aldehyde dehydrogenase) will add another O to the aldehyde group to make acid
1
2
aldehyde group
acid
Amine group
4
After Phase
II: (The metabolites)
Inactive
=
water
soluble
(excreted)
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Reduction:
Removal
of
oxygen
or addition of
hydrogen.
•
May
be
microsomal
or
non-microsomal
E.g.:
levodopa
Levodopa(DOPA)
Dopamine
DOPA-
decarboxylase
H
y
d
r
o
l
y
s
i
s
•
Occurs by addition of water molecules in presence of
enzymes as (esterase & amidases)
•
All are
non microsomal
E
s
t
e
r
a
s
e
h
y
d
r
o
l
y
z
e
d
r
u
g
s
t
h
a
t
a
r
e
e
s
t
e
r
s
A
m
i
d
a
s
e
s
h
y
d
r
o
l
y
z
e
d
r
u
g
s
t
h
a
t
a
r
e
a
m
i
d
e
s
Ester + H
2
0
→
Acid +
Alcohol
e.g. Esters as acetylcholine
(neurotransmitter).
Acetylcholine
→
acetate +
choline.
المقصود هنا إن فيه دوا يصير له تكسر من خلال أنزيم اسمه
استريز وهذا الأنزيم خاص للأدوية اللي فيها استر (حمض +
كحول) والأنزيم راح يكسر الدوا من خلال إضافة ماء على الدوا
ويحوله إلى حمض + كحول (المكونات الأساسية للإستر)
A
m
i
d
e
+
H
2
0
→
A
c
i
d
+
a
m
i
n
e
e
.
g
.
A
m
i
d
e
s
a
s
l
i
d
o
c
a
i
n
e
(
u
s
e
d
a
s
l
o
c
a
l
a
n
e
s
t
h
e
t
i
c
)
ب
ع
ض
ا
لأ
د
و
ي
ة
ر
ا
ح
ي
ص
ير
له
ا
ت
ك
س
ر
ب
و
ا
س
ط
ة
أ
ن
ز
يم
ا
سم
ه
أ
م
ا
ي
د
ي
ز
و
ه
و
خ
ا
ص
ل
لأ
د
و
ي
ة
ا
ل
ل
ي
ت
ت
ك
و
ن
م
ن
أ
م
ا
ي
د
(
أ
م
ين
+
ك
ح
و
ل
)
و
لم
ن
ي
ك
س
ر
ه
ا
ا
لأ
ن
ز
يم
م
ن
خ
لا
ل
إ
ض
ا
ف
ة
م
ا
ء
إ
لى
ا
ل
د
و
ا
ر
ا
ح
ت
ت
ح
و
ل
إ
لى
حم
ض
+
أ
م
ين
6
Amid bond
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Phase
I
result
in:
•
Activation
of
pro-drug
e.g.
levodopa to
dopamine.
•
Inactivation of
drug
(termination of
action).
•
Conversion
of
active
drug
to
active
metabolite.
•
Conversion
of
nontoxic
drug
to
toxic
metabolite.
P
a
r
a
c
et
a
m
ol
hepatotoxic
metabolite (hepatic
necrosis)
•
Product
might
undergo
phase
II
Conjugation:
coming
from
(phase I)
with
endogenous
substance
as methyl group, acetyl
group, sulphate, amino acid or glucuronic acid
to produce conjugate
that
is
water
soluble
and
easily
excreted
in
urine
or
bile
.
Types of conjugation reaction:
Phase
II
metabolic reactions
:
•
All
are
non microsomal
except
glucouronidation
•
Glucouronide conjugation
is a
microsomal
process
(the most
common
of
phase II reactions
)
.
•
Deficieny
of
glucouronyl
transferase
enzyme
in
neonates
may
result
into
toxicity
with
chloramphenicol
(Gray
baby
syndrome)
.
7
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Characteristics
of
Phase
II
product:
•
Usually
pharmacologically
inactive
.
•
Polar
•
more
water
soluble.
•
Easily
excreted
in
urine.
Factors
affecting
metabolism
:
•
Genetic polymorphism
:
Metabolism may vary from population to another due to the existence of
different forms of the metabolic enzymes
. E.g.
Isoniazid
(anti- tuberculosis
drug)
Slow
acetylator
phenotype
results in decrease in isoniazid metabolism &
accumulation of isoniazid with risk of
peripheral neuropathy
the enzyme which will metabolize the drug (isoniazid) has genetic problem so the rate of
metabolism is slow that will lead to accumulation of the drug and causes disease (peripheral
neuropathy)
Rapid
acetylator
phenotype
results into excess metabolites produced with risk
of
hepatitis
the enzyme which will metabolize the drug (isoniazid) has genetic problem so the rate of
metabolism is high which will accumulate the drug in the liver and toxics the liver then cause
hepatitis
Enzyme
Induction
&
inhibition:
Liver
microsomal
enzymes
inducers
:
drugs that
increase
activities of liver microsomal
enzymes
&
increase
the metabolism
of
drug
itself
and other drugs
taken
with
the inducer
at
the
same
time.
Liver
microsomal
enzymes
inhibitors
:
drugs that
decrease
activities of liver microsomal
enzymes
&
decrease
the metabolism of the drug
itself
and other
drugs
taken concurrently
8
•
Alcohol
•
Cigarette
smoking
•
Phe
n
obar
b
i
t
one
(hypnotic)
•
Phenytoin
(antiepileptic)
•
Rifampicin
(Anti TB)
•
Grape
fruits
•
Erythromycin
(antibiotic)
•
Cimetidine
(anti-
ulcer)
•
K
et
o
c
o
n
a
z
ole
(antifungal)
Enzyme Induction
*
Enzyme induction may result in:
•
↑ the
metabolism
and excretion of the inducer drug itself and co-administered drugs
.**
•
↓ the
action
of the inducer drug itself & co-administered drugs.
•
Tolerance
:
decrease in the pharmacological action of the drug
by continuous or
repeated administration .
•
Drug interactions: decrease in action of one drug by administration of another drug.
e.g.
oral contraceptives & phenytoin
(An enzyme inducer)
(
Failure of oral contraceptive
(birth control pills)
may lead to pregnancy if combined with phenytoin)
Enzyme In
hibition:
Enzyme inhibition may result in:
•
↓ Delay the metabolism and excretion of the inhibitor drug and co-administered drugs.
•
↑ Prolong the action of the inhibitor drug & co-administered drugs.
e.g.
warfarin & erythromycin
(inhibitor).
(inhibition of warfarin metabolism may lead to increase its anticoagulant effect ‘risk of bleeding’ )
Notes:
*An enzyme inducer is a type of drug that increases the metabolic activity of an enzyme.
**There’s a difference between metabolism & action of the drug.
Explanation: in inhibition, we are blocking the thing that breaks the drug down,
#therefore increasing the action of the drug.
Co-administered: taken at the same time.
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Lippincott corner
The kidney cannot efficiently eliminate lipophilic drugs that readily cross cell
membranes and are reabsorbed in the distal convoluted tubules. Therefore,
lipid-soluble agents are first metabolized into more polar (hydrophilic)
substances in the liver via two general sets of reactions, called phase I and
phase II.
Phase I
Phase I reactions convert lipophilic drugs into more polar molecules by introducing
or unmasking a polar functional group, such as –OH or –NH2. Phase I reactions
usually involve
reduction
,
oxidation
, or
hydrolysis
. Phase I metabolism may
increase
,
decrease
, or have
no effect
on pharmacological activity.
A)
Phase I reactions utilizing the P450 system:
The phase I reactions most frequently involved in drug metabolism are
catalyzed by the cytochrome P450 system (also called microsomal mixed-
function oxidases). The P450 system is important for
(1) the metabolism of many endogenous compounds (such as steroids,
lipids) and (2) the biotransformation of exogenous substances (xenobiotics).
Cytochrome P450, designated as CYP, is a superfamily of heme-containing
isozymes that are located in most cells, but primarily in the liver and GI
tract.
CYP3A4 (3 = family / A = subfamily / 4 = specific isoenzyme)
Considerable amounts of CYP3A4 are found in intestinal mucosa,
accounting for the first-pass metabolism of drugs.
A)
Phase I reactions not involving the P450 system:
These include:
1.
Amine (histamine, catechol) oxidation,
2.
Alcohol dehydrogenation (ethanol oxidation) [remember oxidation means
adding an oxygen or removing a hydrogen],
3.
Esterases (metabolism of aspirin in liver),
4.
Hydrolysis (procaine)
Extra notes
11
Lippincott corner
Phase II
This phase consists of
conjugation
reactions. If the
metabolite from phase I metabolism is sufficiently polar, it
can be excreted by the kidneys. However, many phase I
metabolites are still too lipophilic to be excreted. A
subsequent conjugation reaction with an endogenous
substrate (such as glucuronic acid, acetic acid, or an amino
acid) results in polar, usually more water-soluble
compounds that are often therapeutically inactive.
Glucuronidation is the most common and the most
important conjugation reaction.
[Note: Drugs already possessing an –OH, -NH2, or –COOH
group may enter phase II directly and become conjugated
without prior phase I metabolism.]
The highly polar drug conjugates are then excreted by the
kidney or in bile.
Extra notes
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Qick Quiz
https://www.onlineexambuilder.com/
pharmacology-l3/exam-106298
Helpful video
https://www.youtube.com/watch?v=c
KzBpkiOrZg
12
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Drug metabolism is a crucial process in the body that transforms drugs into forms easily excreted, affecting their efficacy and toxicity. This involves different sites such as the liver, kidney, and plasma, with enzymes in cellular organelles like cytoplasm and mitochondria playing key roles. First-pass metabolism, enzyme modulation, and the impact on drug bioavailability are vital aspects to consider. Recognizing the significance of biotransformation, knowing phase I and II reactions, and understanding enzyme inducers and inhibitors are essential in pharmacology.
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Presentation Transcript
3- Drug Metabolism Objectives: Recognize the importance of biotransformation Know the different sites for drug metabolism Define the major phase I and phase II metabolic reactions. Describe the modulation of liver microsomal enzymes by inducers and inhibitors Mention two drugs that are known as enzyme inducers and inhibitors. Know the impact of first pass metabolism on drug bioavailability. Work until no longer you have to introduce your self Contact us : Pharma436@outlook.com @Pharma436 1
DrugMetabolism: It is the chemical reactions which occur in the body to change drugs from nonpolar lipid soluble forms to polar water soluble forms that are easily excreted by the kidney. Importance: Inactivation or terminationof drug action (mostdrugs). DetoxificationBiotransformation is required for protection of body from toxicmetabolites. Activation of prodrug*(convert inactive form of drug to active form) e.g. levodopa - carbidopa, prednisone prednisolone *an inactive substance that is converted to a drug within the body by the action of enzymes or other chemicals. Organ sites of drugmetabolism: 1- Liver (the major site).* 2- kidney 3-skin 4- lung 5- Intestinal Mucosa and Lumen: Gut Mucosa: MonoAmine Oxidase (MAO) . Gut lumen (bacterial flora): Glucouronidase. 6- Plasma: *because it is a large organ, and there are high concentrations of most drug- metabolizing enzyme systems substrate Enzymes (in the plasma) Catechol O-Methyl Transferase (COMT) catecholamines (e.g. adrenaline) Esterases Esters (acts on drugs as Local Anesthetics) Amidases amides (act on drugs as Local Anesthetics) Contact us : Pharma436@outlook.com @Pharma436 2
REMEMBER THERE IS AN ORGAN SITE AND A CELLULAR SITE. BE CAREFUL. Cellular sites of drug metabolism CYTOPLASM* MITOCHONDRIA MICROSOMES* LYSOSOMES e.g. Alcohol dehydrogenase** (NAD+ NADH) (boy s slides) (oxidation of alcohol). Alcohol Aldehyde Acid Ethanol acetaldehyde acid CH3CH2OH CH3CHO CH3COOH *Is the material or protoplasm within a living cell, excluding the nucleus. So we will find there a lot of enzymes that play a role in the drug metabolism and one **(ADH) (EC 1.1.1.1) are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+ to NADH). Microsomal enzyme system = Cytochrome P- 450. There are more than 20 families CYP1, CYP2, CYP3 Sub-families are identified as A, B, and C etc. In human: only 3 isoenzyme families are important CYP1, CYP2 and CYP3 Oxidation Cytochrome P-425: CYP 3A4/5 carry out biotransformation of the largest number (30-50%) of drugs. Expressed in the liver and intestine (responsible for first pass metabolism at this site). There are several chemicals in this organelle that plays an important role in the drug metabolism, those are: 1- N-acetyl transferase*: Introduction of acetyl group (CH3COO- ) . 2- Monoamine oxidase enzyme **(MAO): oxidation of catecholamines as adrenaline. *an enzyme that catalyzes the transfer of acetyl groups from acetyl-CoA to arylamines. **a family of enzymes that catalyze the oxidation of monoamines neurotransmitter. They are found bound to the outer membrane of mitochondria in most cell types in the body. Contact us : Pharma436@outlook.com @Pharma436 3
Catechol o-methyl transferase (COMT) Any drug has the catechol ring will metabolize by the COMT enzyme. This enzyme will add Ch3 on one of the OH and remove H, so it will transfer Ch3 to O atom Monoamine oxidase (MAO) aldehyde group Amine group 1 acid 2 1- The MAO enzyme will oxidize the amino group (NH2) by remove NH2 and add O instead, this will give me aldehyde 2- another enzyme (aldehyde dehydrogenase) will add another O to the aldehyde group to make acid Types of hepatic metabolic reaction: Two phases of hepatic metabolism reactions: Phase I Phase II * Oxidation Metabolism * Reduction Conjugation * Hydrolysis After Phase I: (The metabolites) 1. Active = lipid soluble > Phase II 2. Inactive = water soluble (excreted) After Phase II: (The metabolites) Inactive = water soluble (excreted) Contact us : Pharma436@outlook.com @Pharma436 4
Oxidation Addition of oxygen or removal of hydrogen Most important drug metabolizing reaction Microsomal Occurs in microsomes E.g. cytochrome P450 enzyme, NADPH, and oxygen Nonmicrosomal Occurs in cytosol or mitochondria Oxidase Dehydrogenases Are required for oxidation of alcohols. E.g Alcohol dehydrogenase (alcohol aldehyde) E.g. Aldehyde dehydrogenase (aldehyde acid) Monoamine Oxidase (MAO) Responsible for the metabolism of catecholamines as adrenaline and serotonin E.g. Moclobemide (MAO inhibitor used as an antidepressant drug by increasing serotonin in the brain) Xanthine Oxidase Required for the oxidation of xanthine. Hypoxanthine xanthine uric acid accumulation of uric acid GOUT E.g. Allopurinol (inhibitor of xanthine oxidase used in treatment of gout) Contact us : Pharma436@outlook.com @Pharma436 5
Reduction: Removal of oxygen or addition of hydrogen. May be microsomal or non-microsomal E.g.: levodopa DOPA- decarboxylase Levodopa(DOPA) Dopamine Hydrolysis Occurs by addition of water molecules in presence of enzymes as (esterase & amidases) All are non microsomal Amid bond Amidases hydrolyze drugs that are amides Esterase hydrolyze drugs that are esters Amide + H20 Acid + amine e.g. Amides as lidocaine (used as local anesthetic) Ester + H20 Acid + Alcohol e.g. Esters as acetylcholine (neurotransmitter). Acetylcholine acetate + choline. ( + ( ) + ) + ) ( + Contact us : Pharma436@outlook.com @Pharma436 6
Phase I result in: Activation of pro-drug e.g. levodopa to dopamine. Inactivation of drug (termination of action). Conversion of active drug to active metabolite. Conversion of nontoxic drug to toxic metabolite. Paracetamol hepatotoxic metabolite (hepatic necrosis) Product might undergo phase II Conjugation: coming from (phase I) with endogenous substance as methyl group, acetyl group, sulphate, amino acid or glucuronic acid to produce conjugate that is water soluble and easily excreted in urine or bile. Types of conjugation reaction: Conjugation reaction Enzyme required glucouronide conjugation Glucouronyl transferase Acetylation (CH3COO-) N-acetyl transferase Sulphation (SO42-) Sulfo transferase Methylation (CH3) methyl transferase Amino acids conjugation Glycine Transferase PhaseII metabolic reactions: All are non microsomal exceptglucouronidation Glucouronide conjugation is a microsomal process (the most common of phase II reactions). Deficieny of glucouronyl transferase enzyme in neonates may result into toxicity with chloramphenicol (Gray baby syndrome). Contact us : Pharma436@outlook.com @Pharma436 7
Characteristics of Phase IIproduct: Usually pharmacologicallyinactive. Polar more watersoluble. Easily excreted in urine. Factors affecting metabolism: The factor The rate of metabolism Decrease ( ) in neonates & elderly. AGE Decrease ( ) in liver diseases. DISEASES Decrease ( ) in binding protein Degree of Protein Binding increase ( ) in the Induction decrease ( ) in the Inhibition Concurrent use of drugs Decrease ( ) in malnutrition Nutrition Genetic polymorphism : Metabolism may vary from population to another due to the existence of different forms of the metabolic enzymes. E.g. Isoniazid (anti-tuberculosis drug) Slow acetylator phenotype results in decrease in isoniazid metabolism & accumulation of isoniazid with risk of peripheral neuropathy the enzyme which will metabolize the drug (isoniazid) has genetic problem so the rate of metabolism is slow that will lead to accumulation of the drug and causes disease (peripheral neuropathy) Rapid acetylator phenotype results into excess metabolites produced with risk of hepatitis the enzyme which will metabolize the drug (isoniazid) has genetic problem so the rate of metabolism is high which will accumulate the drug in the liver and toxics the liver then cause hepatitis Enzyme Induction &inhibition: Liver microsomal enzymes inducers : drugs that increase activities of liver microsomal enzymes & increase the metabolism of drug itself and other drugs taken with the inducer at the sametime. Liver microsomal enzymes inhibitors : drugs that decreaseactivities of liver microsomal enzymes & decrease the metabolism of the drug itself and other drugs taken concurrently Contact us : Pharma436@outlook.com @Pharma436 8
Enzyme Enzyme inducers Enzyme inhibitors Erythromycin Grape fruits Cigarettesmoking Phenobarbitone (hypnotic) Phenytoin Alcohol (antibiotic) Cimetidine (anti- ulcer) (antiepileptic) Rifampicin (Anti TB) Ketoconazole (antifungal) Enzyme Induction* Enzyme induction may result in: the metabolism and excretion of the inducer drug itself and co-administered drugs.** the action of the inducer drug itself & co-administered drugs. Tolerance: decrease in the pharmacological action of the drug by continuous or repeated administration . Drug interactions: decrease in action of one drug by administration of another drug. e.g. oral contraceptives & phenytoin (An enzyme inducer) (Failure of oral contraceptive (birth control pills) may lead to pregnancy if combined with phenytoin) Enzyme Inhibition: Enzyme inhibition may result in: Delay the metabolism and excretion of the inhibitor drug and co-administered drugs. Prolong the action of the inhibitor drug & co-administered drugs. e.g. warfarin & erythromycin (inhibitor). (inhibition of warfarin metabolism may lead to increase its anticoagulant effect risk of bleeding ) Notes: *An enzyme inducer is a type of drug that increases the metabolic activity of an enzyme. **There s a difference between metabolism & action of the drug. Explanation: in inhibition, we are blocking the thing that breaks the drug down, #therefore increasing the action of the drug. Co-administered: taken at the same time. Contact us : Pharma436@outlook.com @Pharma436 9
Extra notes Lippincott corner The kidney cannot efficiently eliminate lipophilic drugs that readily cross cell membranes and are reabsorbed in the distal convoluted tubules. Therefore, lipid-soluble agents are first metabolized into more polar (hydrophilic) substances in the liver via two general sets of reactions, called phase I and phase II. Phase I Phase I reactions convert lipophilic drugs into more polar molecules by introducing or unmasking a polar functional group, such as OH or NH2. Phase I reactions usually involve reduction, oxidation, or hydrolysis. Phase I metabolism may increase, decrease, or have no effect on pharmacological activity. A) Phase I reactions utilizing the P450 system: The phase I reactions most frequently involved in drug metabolism are catalyzed by the cytochrome P450 system (also called microsomal mixed- function oxidases). The P450 system is important for (1) the metabolism of many endogenous compounds (such as steroids, lipids) and (2) the biotransformation of exogenous substances (xenobiotics). Cytochrome P450, designated as CYP, is a superfamily of heme-containing isozymes that are located in most cells, but primarily in the liver and GI tract. CYP3A4 (3 = family / A = subfamily / 4 = specific isoenzyme) Considerable amounts of CYP3A4 are found in intestinal mucosa, accounting for the first-pass metabolism of drugs. Phase I reactions not involving the P450 system: These include: Amine (histamine, catechol) oxidation, Alcohol dehydrogenation (ethanol oxidation) [remember oxidation means adding an oxygen or removing a hydrogen], Esterases (metabolism of aspirin in liver), Hydrolysis (procaine) A) 1. 2. 3. 4. Contact us : Pharma436@outlook.com @Pharma436 10
Extra notes Lippincott corner Phase II This phase consists of conjugation reactions. If the metabolite from phase I metabolism is sufficiently polar, it can be excreted by the kidneys. However, many phase I metabolites are still too lipophilic to be excreted. A subsequent conjugation reaction with an endogenous substrate (such as glucuronic acid, acetic acid, or an amino acid) results in polar, usually more water-soluble compounds that are often therapeutically inactive. Glucuronidation is the most common and the most important conjugation reaction. [Note: Drugs already possessing an OH, -NH2, or COOH group may enter phase II directly and become conjugated without prior phase I metabolism.] The highly polar drug conjugates are then excreted by the kidney or in bile. Contact us : Pharma436@outlook.com @Pharma436 11
Qick Quiz https://www.onlineexambuilder.com/ pharmacology-l3/exam-106298 Helpful video https://www.youtube.com/watch?v=c KzBpkiOrZg Contact us : Pharma436@outlook.com @Pharma436 12
Pharmacology Team : Boys Girls Contact us : Pharma436@outlook.com @Pharma436 13
