• Pharmacokinetic principles
• Drug absorption, distribution,
metabolism and elimination
Jan Juřica, PharmD., Ph.D.
= Action of a drug requires presence of
a certain concentration in the fluid
bathing the target tissue.
Pharmacokinetics
Occupation theory: The intensity of
pharmacological response (E) is
proportional to the conentration of
reversible drug-receptor complex
Pharmacokinetics deals with the processes of
absorption,
distribution,
metabolism
excretion of the drug
And their relationship with their biological
(pharmacological) effect
„WHAT DOES ORGANISM DO WITH THE DRUG“
“ADME“
elimination
A
D
M
E
invasion
permeation across the membranes
lipophilic – difusion (passive)
hydrophilic – through the pores
active transport
What does influence the movements of the drug in the body?
physico-chemical properties
lipophilic/hydrophilic properties, molecule
structure, pKa, charge…
AH  A- + H+ B + H+  BH+
Ionized compounds
tend to be less lipid
soluble.
Non-Ionized
compounds tend to be
more lipid soluble.
permeation across the membranes
lipophilic – difusion (passive)
hydrophilic – through the pores
active transport
bonds of the drugs to:
plasma proteins
blood cells in the circulation
tissue
receptors
perfusion of the tissues
a) brain, heart, liver, kidney
b) fat tissue
What does influence the movements of the drug in the body?
physico-chemical properties
lipophilic/hydrophilic properties, molecule
structure, pKa, charge…
AH  A- + H+ B + H+  BH+
OATP, MDR, MRP
diffusion
active transport via
transport proteins
through the
pores
permeation across the membranes
lipophilic – difusion (passive)
hydrophilic – through the pores
active transport
bonds of the drugs to:
plasma proteins
tissue
blood cells in the circulation
receptors
perfusion of the tissues
a) brain, heart, liver, kidney
b) fat tissue
What does influence the movements of the drug in the body?
physico-chemical properties
lipophilic/hydrophilic properties, molecule
structure, pKa, charge…
AH  A- + H+ B + H+  BH+
11
ABC - ATP-BINDING CASSETTE
12
ABC - ATP-BINDING CASSETTE
 MDR - multi drug resistance
 MRP - multidrug resistance asociated protein
 MXR - mitoxantrone resistance protein
 Pgp - P-glycoprotein pump
permeation across the membranes
lipophilic – difusion (passive)
hydrophilic – through the pores
active transport
bonds of the drugs to:
plasma proteins
tissue
blood cells in the circulation
receptors
perfusion of the tissues
a) brain, heart, liver, kidney
b) fat tissue
What does influence the movements of the drug in the body?
physico-chemical properties
lipophilic/hydrophilic properties, molecule
structure, pKa, charge…
AH  A- + H+ B + H+  BH+
Concentration of free drug
Afinity for binding sites
Conc. of protein
14
• plasma proteins
• tissue
• blood cells in the circulation
• receptors
15
• most of acidic drugs (at pH of 7.4= anions)
are bound on albumin:
– salicylates, sulfonamides, penicillins
• most of alcalic + neutral drugs (at pH of
7.4= cations) are bound on α1- acidic
gylcoprotein and lipoproteins:
– quinidine, digitoxine, TCA, cyclosporine A
16
• Bonds with plsama proteins are
– reversible
– dynamic
– competitive
17
drug % bound
caffein 10
digoxine 23
gentamycine 50
phenytoin 87
digitoxine 95
diazepam 96
warfarin 98
tolbutamide 99
A bound drug has no effect!
Amount bound depends on:
1) free drug concentration
2) the protein (binding sites) concentration
3) affinity for binding sites
% bound: __[bound drug]__________ x 100
[bound drug] + [free drug]
Bonds in peripheral tissues
• specific for some of the drugs
- tetracycline antibiotics - hydroxyapatit
- chloramfenicol – skin
- grisefulvin - skin
- arsenic – in hair
ABSORPTION
Absorption – permeation of the soluted drug into the body fluids
from the site of administration – necessary for the general
(systhemic) effect
topical effect – on the skin, mucous membranes…
mouth, rectum, vagina
- absorption is fault, can cause difficulties, adverse
effects)
(local aenesthetics, corticosteroids)
Rate and extent of absorption are described by the parameters :
C max - max. concentration of the drug in the plasma after single
administration
T max - time after administration, when is Cmax
F - bioavailability (extent of absorption)
time
Plasmatic concentration of
the drug
Bioavailability
• The fraction of the dose of a drug (F) that
enters the general circulatory system,
F= amt. of drug that reach systemic circul.
Dose administered
F = AUCp.o./AUCi.v.
Extravascular route - 0-100% (resp. 0-1).
Intravenous - 100% = 1
If F is 0-20% = 0-0,2 – not suitable route of administration
(in spite of that fact, some drugs are administered, even if the F ˂ 2-5 %, such
as SET, bisphosphonates).
F = AUCpo/AUCiv
(the same drug, same dose, same patient)
Bioavailability
Bioavailability
• A concept for oral (extravascular) administration
• Useful to compare two different drugs or different
dosage forms of same drug
• depends, in part, on rate of dissolution (which in
turn is dependent on chemical structure, pH, partition
coefficient, surface area of absorbing region, etc.) Also firstpass
metabolism is a determining factor
Influence of the various
bioavailability on the
plasmatic levels of the drug
• Is a measure of bioavailability
Area under curve (AUC)
First pass effect, presysthemic elimination
Factors influencing absorption
Drug-dosage form– tbl./ sol./ supp./ TTS/tbl.subling.
Way of administration
Physico-chemical properties of drugs
- absorptive surface area
- concentration gradient
- ionization, lipofility
- interactions
Other factors influencing the absorption
gender, body weight, plasma volume, gastric
amptying rate,
age - pH, bile, enzyme levels and activity
patophysiological state – liver disseases,
inflammation
simultaneously eaten meal –
acceleration/decelaration
chemical incompatibilities
function of the GIT
Factors affecting pharmacokinetics
Drug dosage forms of the 1st and 2 nd generations
hour
= permeation from the body blood to the tissues and site of the action
is dynamic process
rate - depends on:
bonds (with the plasmatic proteins…)
permeation across the membrabes
blood perfusion through the organ
state - distribution equilibrium; the the proportion of the free
(unbounded) fractions of the drug in the blood and in
the tissues are the same
Barriers – the distribution is limited
blood-brain barrier („leaky areas“ – area postrema),
penicilines X aminoglycosides
placental barrier…
Distribution
Volume of Distribution
Vd = D/C
– Vd is the apparent volume of distribution
– C= Conc of drug in plasma at some time
– D = Total quantity (dose) of drug in system
Vd gives one as estimate of how well the drug is
distributed.
Value < 0.071 L/kg indicate the drug is mainly in the
circulatory system. Values > 0.071 L/kg indicate
the drug has gotten into specific tissues.
Volume of distribution – apparent, hypotethical
the proportion of the quantity of the drug and reached plasmatic
concentration
Volumes of the water in
human body
water in general in
whole the body
extracellularintracellular
intersticial plasma
Perfusion through the organs
organ perfusion rate % heart output
(ml/min/g tkáně)
brain 0.5 14
fat 0.03 4
heart 0.6 4
kidney 4.0 22
liver 0.8 27
musculature 0.025 15
skin 0.024 6
ELIMINATION = biotransformation + excretion
• Kinetics of the first order
= rate of elimination is descending with the
descending concentration in the blood
(linear kinetics)
• Kinetics of the zero order
= rate of elimination is constant (nonlinear
kinetics)
Types of Kinetics Commonly
Seen
• Zero Order Kinetics
• Rate = k
• C = Co - kt
• C vs. t graph is LINEAR
First Order Kinetics
• Rate = k C
• C = Co e-kt
• C vs. t graph is NOT
linear, decaying
exponential.
• Log C vs. time graph is
linear.
First Order Kinetics
Biotransformation – metabolism
Sites of biotransformation
anywhere, where the enzymes are present: plasma, kidney, lungh
GIT, brain, but especially liver
Enzymatic
• biodegradation
• bioactivation (prodrug)
enalapril-enalaprilate
codein-morphine
bromhexin - ambroxol
ELIMINATION
1. Phase : oxidation, hydrolysis
Cytochrom P450, dehydrogenases
2. Phase : conjugation – metabolites are more soluble in the water
Metabolite - effective („more / less / in other way“)
- ineffective
- toxic
men
plants
insect
funghi
yeast bacteria
molluscs
animals
CYP 450
CYP 2D6
30%
CYP 1A2
2%
CYP 2C9
10%
other
3%
CYP 3A4
55%
CYP 3A4
CYP 2D6
CYP 2C9
CYP 1A2
other
Genetic polymorphism
Genetic polymorphism = the existence of several
(At least two ) alleles for the gene from which
At least part has a population frequency of at least 1 %
• Pharmacogenetics
focuses on the study of genetically conditioned variability in
the response to a drug
•Pharmacogenomics examines the relationship of drug
effect on the level of the whole genome, respectively
transcriptome
Genetic polymorphism of biotransformation
enzymes
Polymorphism in the gene of N - acetyltransferase
- Inactivation of drugs in the liver : slow x fast acetylators
- Isoniazide , procainamide, hydralazine
- Peripheral neuropathy (prevention - pyridoxine)
Polymorphism of thiopurine S - methyltransferase
- the metabolism of azathioprine
- commercially available genetic test for determining the
polymorphisms, prevention of serious adverse reactions
Genetic polymorphism of CYP2D6
Null alelles
- encode a nonfunctional protein
- In the homozygous state cause the phenotype PM
SNP (point mutations)
a chromosome deletion
mutation leading to loss of the fction of protein, but the length of
protein is maintained
- * 4 allele ( 12-21 % ) in Caucasian populations (most frequent
1846G > A)
- * 5 allele (2-7 % ) causes loss of whole CYP2D6 gene
- allele * 13 and * 16 - 5'- CYP2D7P / CYP2D6-3' hybrid genes ,
deletion of various parts of CYP2D locus
The alleles associated with decreased enzymatic
function
encode an enzyme with reduced activity
in the homozygous state or with the null allele in the
heterozygous state cause the IM phenotype
* 10 (50-70 % Asian, 1-5% of the Caucasian population)
100C > T ( disrupts normal folding of the protein →
enzyme is very unstable and has a lowe affinity to a
substrate
GENETIC POLYMORPHISM OF CYP2D6
The alleles associated with increased enzyme function
- An increase in the number of active gene copy
- Alleles * 1 , * 2 , 35 *
- The frequency of Caucasians 1-5%
GENETIC POLYMORPHISM OF CYP2D6
•CYP2D6 and antidepressants (especially classical) : significant
PK differences, difficult to adjust dose due to slower onset of
effect, long-term drug therapy
• CYP2C9 and oral antidiabetic drugs - derivatives
sulfonylureas ( e.g. glimepiride, glipizide and tolbutamide)
In heterozygotes CYP2C9 * 1 / * 3 , the total clearance of 50 %
homozygotes and CYP2C9 * 3 / 20 * 3 % compared to WT
• CYP2C9 and anticoagulants - (warfarin) in heterozygous
CYP2C9 * 1 / * 3, the total clearance of 70 %, and in
homozygotes CYP2C9 * 3 / 40 * 3 % compared to WT
GENETIC POLYMORPHISM OF CYP
INDUCERS of CYP 450
• dexamethason
• phenobarbital
• rifampicine
• phenytoin
• St. John`s Wort (Hypericum perforatum)
• Ginkgo biloba
INHIBITORS of CYP 450
• antidepressants (fluoxetine, fluvoxamine, paroxetine)
• quinine, quinidine
• chloramphenicol, erythromycin
• ketoconazol, itraconazol
• grapefruit juice
5mg tablet + grepfruit
juice
5 mg tablet
Phase I of biotransformation
hydroxylation -CH2CH3  -CH2CH2OH
oxidation -CH2OH  -CHO  -COOH
O-dealkylation -CH2OHCH2  -CH2OH + -CHO
N-dealkylation -N(CH3)2  -NHCH3 + CH3OH
N-oxidation -NH2  -NHOH
oxidative deamination -CH2CHCH3  -CHCOCH3 + NH3
NH2
Other non-microsomal biotransformations
• hydrolysis of esters in plasma (suxamethonium by cholinesterase)
• dehydrogenation of alcoholic and aldehydic group in cytosol in
the liver (ethanol)
• MAO in mitochondria (tyramine, noradrenaline, dopamine,
amines)
• xanthinoxidase (6-merkaptopurine, uric acid)
• enzymes with distinct function (tyrosine-hydroxylase, dopadecarboxylase,
etc.)
Phase II of biotransformation
CONJUGATION
Glucuronides -OH, -SH, -COOH, -CONH wih glucuronyl acid
(UDP- GlcUAc)
Sulphates: with -OH functional group
Acetylates: acetyl CoA with NH2, -CONH2, s aminoacid- group
with gluthathion with -halogen- or -nitrate functional groups, epoxides
sulphates
tubulární sekrece
glomerulární filtrace
konjugace s aminokyselinami
glukuronidace
acetylace
porod
10 20 30 2 3 4 5 6
dny měsícedays months
tubular secretion
glomerular filtration
acetylation
conjugation with glucuronic acid
conjugation with aminoacids
birth
Excretion
Kidney (urine)
tubular excretion
x tubular reabsorption
liver (bile)
lungh (air)
saliva, skin, hair, breast milk...
Clearance Cl
• Volume of blood in a defined region of the
body that is cleared of a drug in a unit time.
• more useful concept in reality than kel since
it takes into account blood flow rate
• Clearance varies with body weight
• Also varies with degree of protein binding
• MW < 60.000 D (MW albumin = 68.000 D)
• tubular secretion
– organic acids
• furosemid
• thiazide diuretics
• penicilins
• glucuronides
– organic bases
• Morphine
• Atropine
• Histamine…
• tubular reabsorption
Kidney
acidification
acetazolamid (inhibitor of CA)
ammonium chloride
alcalization
sodium bicarbonate
Liver
Billiar excretion, clearance.
enterohepatic circulation
Extraction ratio ER
= proportion of the drug removed durring
the passage through the organ
ER = ca-cv/ca
Mean residence time MRT
= The average total time molecules of a given
dose spend in the body. Thus, this can
only be measured after instantaneous
administration.
Non-compartment PK
MRT = AUMC/AUC
PHARMACOKINETIC PARAMETERS
PRIMARY
• Bioavailability (F)
• Volume of distribution
(Vd)
• Clearance (Cl)
SECONDARY
• elimination half-life (T1/2)
• elimination constant (Ke)
• AUC (area under the
curve)
• Cumulative index
• Extraction ratio
Repeated administration
• increase in effect – accumulation
senzitization
• decrease in effect
- tolerance - changes at the site of receptor
- chnges in pharmacokinetics
- tachyphylaxis
- resistence – „tolerance“ to the drugs inhibiting cell.
growth or cytotoxic drugs
cytostatics, antiinfectives, antiseptics
• drug dependance
axe po opakovaném podávání efedrinu (pokles vlivu na TK)
rinu
E
E E
0 5 10 15 20 25 30
min
Tachyphylaxis after repeted ephedrine administration
(decrease ineffect on blood pressure)
E = ephedrine administration
BASIC PHARMACOKINETIC
PARAMETERS
• C ( Co, Cmax ) concentration in plasma
• Tmax time to reach Cmax
• Vd volume of distribution
• Cl clearence ( Cl lungh , CL kid , Clliv , Cl tot )
• t 0,5 abs half-life of absorption
• t 0,5 ( t 1/2 el, t 50% el ) half-life of elimination
• AUC Area Under the Curve
total amount of the drug during its presence in the
body
• F [ % ] bioavailability
Elimination constant ke = lnc1 – ln c2 / t2-t1
Half-life of the elimination – the drug is completely eliminated
after 4-5 t 0,5
t 0,5 = ln2/ ke = 0,7/ ke
clearance Volume of the blood in a defined region of the
body that is cleared of a drug in a unit time
ClTOT = D/AUC = ke Vd
Elimination (first order)
Kinetics of elimination of the 1st order –
ln (c)
time1 2 3 4 5 time1 2 3 4 5
10
8
6
4
2
5
2.5
1.25
ln ct = lnc0 - ke.t
ct = c0 . e(-k.t)
c
semilog plot
(i.v. admin)
Normal plot
(i.v. admin)
Half-Life
• C = Co e - kt
• C/Co =1/2 in the time of 1 half-life
• Thus: 0.5 = e – k t
• ln 0.50 = -k t ½
• -0.693 = -k t ½
• t 1/2 = 0.693 / k
- Continual drug administration
- Administration of the drug e.g. by the infusion pump
-the plasma concentration increases until the
elimination rate become equal to the drug intake –
→ plasmatic concentration is steady - the plateau
state (Css).
i.v. infusion
I.v. infusion
Time
The Compartment Model
Body = a series of interconnected well-stirred
compartments within which the [drug]
remains fairly constant.
Movement BETWEEN compartments is
important in determining when and for
how long a drug will be present in body.
Vd1
k10
Vd2
k12
k21
A (e.g. GIT)
ka
D
2- compartment model
central
compartment
peripheral
compartment