7. Mechanisms of drug transport
Intercellular (transcellular) transport
Passive transport
Passive diffusion
Pore transport
Ion-pair transport
Facilitated diffusion
Active transport
Primary
Secondary
Symport
Antiport
7Absorption of Drug4/13/2018
8. Mechanisms of drug transport
Intracellular (paracellular) transport
Tight junctions of epithelial cells
Persorption
Endocytosis
Pinocytosis
Phagocytosis
8Absorption of Drug4/13/2018
9. Passive diffusion
Non ionic diffusion
Driving force- concentration gradient
Drug movement- kinetic energy of molecule
Energy independent process
Expressed by Fick’s first law of diffusion
The drug molecules moves from a region of higher
concentration to one of lower concentration until
equilibrium is attained and the rate of diffusion is directly
proportional to the concentration gradient across
membrane.
9Absorption of Drug4/13/2018
10. Passive diffusion
Fick’s first law of diffusion
Characteristics of passive diffusion
Downhill transport
Process- energy independent & non saturable
Drug transfer directly proportional to conc gradient
Greater the area & lesser thickness of membrane, faster
diffusion
Process is rapid over short distance and slower over long
distance
)(/
CC
h
DAK
dt
dQ
GIT
wm
10Absorption of Drug4/13/2018
11. Passive diffusion
Fick’s first law of diffusion
Characteristics of passive diffusion
Equilibrium is attained when the concentration on
either side of membrane becomes equal.
Rate of transfer of unionised drug is more than ionised.
Greater partition coefficient of drug, faster the
absorption.
Drug diffusion is rapid- volume of GI fluid is low.
Process id dependent on molecular size of the drug.
)(/
CC
h
DAK
dt
dQ
GIT
wm
11Absorption of Drug4/13/2018
12. Passive diffusion
Fick’s first law – non sink condition
Sink condition
Equation follows first order kinetics hence passive
diffusion process is first order process.
Hydrophobic molecules > Small uncharged polar
molecules> Large uncharged polar molecules
Ions – not absorbed by passive diffusion.
GITPC
dt
dQ
12Absorption of Drug4/13/2018
13. Pore transport
Connective transport/ bulk flow/ filtration
Transport of molecules into the cell through the
protein channels present in the cell membrane.
Characteristics
Driving force- hydrostatic pressure/ osmotic difference
across the cell membrane.
Water flux promotes transport- solvent drag.
Absorption- low molecular size, less than 100.
Water soluble drugs- urea, water, sugars
Chain like or linear compounds absorbed by filtration.
13Absorption of Drug4/13/2018
14. Ion pair transport
Formation of reversible neutral complex with
endogenous ions (mucin).
Complex- liphophilic and water soluble
Absorbed by passive diffusion.
Example- Propranolol- oleic acid, quaternary
ammonium compounds.
14Absorption of Drug4/13/2018
15. Carrier-Mediated transport
Faster than passive diffusion
Carriers- component of membrane
Reversible/ covalent bonding
Carrier-solute complex-
transverse across membrane
dissociation of solute
carrier –returns to original site
Carriers – proteins/ enzymes
A- Passive diffusion
B- Carrier mediated transport
15Absorption of Drug4/13/2018
16. Carrier-Mediated transport
Characteristics
Carrier protein has uncharged outer surface.
Carrier protein soluble in lipid.
Carrier- any direction - work efficiently.
Transport process is structure specific.
System is structure specific.
Limited carrier- competition – similar agents.
System is capacity limited.
16Absorption of Drug4/13/2018
17. Carrier-Mediated transport
Characteristics
Mixed order kinetics
Bioavailability decreases with increasing dose
Example – Vit B1, B2, B12
Absorption window
Two types
Facilitated diffusion
Active transport
17Absorption of Drug4/13/2018
19. Facilitated diffusion
Characteristics
Downhill transport
Faster than passive diffusion
Driving force- concentration gradient
Passive process
Energy independent
Vitamin B1, B2 & B12
Intrinsic factor-B12
19Absorption of Drug4/13/2018
20. Active transport diffusion
Two Types
Primary active transport
Secondary active transport
Primary active transport
Direct ATP requirement
Process transfers only ion/ molecule in one direction
Hence called uniporter
Absorption of glucose
Two types
Ion transporters
ABC transporters
20Absorption of Drug4/13/2018
21. Active transport diffusion
Primary active transport
Ion transporters
ATP driven ion pump- proton pump
Two types
Organic anion transporter
atrovastatin
Organic cationic transporter
diphenhydramine
21Absorption of Drug4/13/2018
22. Active transport diffusion
Primary active transport
ABC (ATP binding cassette) transporters
Transport small molecules (drug and toxins) out of cell.
Exsorption
Efflux pumps
ABC transporter example- p-glycoprotein (P-gp)
P-gp called multidrug resistant protein
Drug- anticancer drugs
22Absorption of Drug4/13/2018
23. Active transport diffusion
Secondary active transport
No direct requirement of ATP
Concentration gradient
Two types
Symport (co transport)
Antiport (counter transport)
23Absorption of Drug4/13/2018
24. Active transport diffusion
Secondary active transport
Symport
Both molecules moves in same direction
Na+ - glucose symporter : uses potential energy of sodium
concentration gradient to move glucose against concentration
gradient.
H+ - coupled peptide transporter – absorption of peptide like
drugs- beta lactam antibiotics.
Antiport
Molecules moves in opposite direction
24Absorption of Drug4/13/2018
25. Active transport diffusion
Characteristics
Uphill transport
Faster than passive diffusion
Energy required
Inhibited by metabolic poison
Fluorides, cyanide,
Endogenous material absorbed.
Drugs- 5 flurouracil, 5-flurobromacil via pyrimidine
transport.
Methyl dopa, levodopa via L-amino acid transport system.
Enalapril via peptide carrier system.
25Absorption of Drug4/13/2018
27. Endocytosis
Engulfing extracellular material.
Fats, starch, insulin, vitamin A, D, E, K.
Drug absorbed in lymphatic system- bypass first pass.
Two types
Phagocytosis (cell eating)
Pinocytosis (cell drinking)
27Absorption of Drug4/13/2018
28. Factors affecting drug absorption
Pharmaceutical factors
Physicochemical properties of drug
Dosage form related factors
Patient related factors
28Absorption of Drug4/13/2018
29. Physicochemical factors
Drug solubility & dissolution rate
Rate determining steps
Dissolution- hydrophobic like griseofulvin, spironolactone
Permeation- hydrophilic like neomycin
BCS- Amidon et al
Class I drug: high solubility/ high permeability
Class II drugs: low solubility/ high permeability
Class III drugs: high solubility/ low permeability
Class IV drugs: low solubility/ low permeability
29Absorption of Drug4/13/2018
30. Physicochemical factors
Drug solubility & dissolution rate
Intrinsic solubility
Maximum amount of solute dissolved in a given solvent under
standard conditions of temperature, pressure and pH.
Static property
Dissolution rate
Amount of solid substance that goes into solution per unit
time under standard conditions of temperature, pH and
solvent composition and constant surface area.
Dynamic process
30Absorption of Drug4/13/2018
31. Physicochemical factors
Theories of dissolution
Dissolution
Solid substance solubilises in a given solvent.
Mass transfer from the solid surface to the liquid phase.
Theories
Diffusion layer model
Surface renewal theory
Limited solvation theory
31Absorption of Drug4/13/2018
32. Physicochemical factors
Diffusion layer model
Two steps
Solution of the solid to form stagnant film or diffusive
layer which is saturated with the drug
Diffusion of the soluble solute from the stagnant layer to
the bulk of the solution; this is RDS in drug dissolution
32Absorption of Drug4/13/2018
33. Physicochemical factors
Diffusion layer model
Diffusion layer or stagnant
film
Formation of thin film or
layer at solid-liquid interface
is diffusion layer
Diffusion layer is saturated
with drug
Rapid step
Diffusion of soluble solute
From stagnant layer to bulk
of the solution
Slower step, hence rate
determining
33Absorption of Drug4/13/2018
34. Physicochemical factors
Diffusion layer model
In dissolution theory, it is assumed that an
Solute molecules exists in the concentrations
from Cs to Cb. beyond the static layer at x
greater than h,
mixing occurs in the solution and the drug is
found in uniform concentration, Cb
throughout the bulk phase.
At x= 0 drug in the solid is in equilibrium
with drug in diffusion layer.
The gradient in the concentration with the
distance is constant as shown in fig.
This is the gradient represented by the term,
(Cs-C)/h.
When Cb is considerably lower than Cs, the
system is represented by Sink conditions
34Absorption of Drug4/13/2018
35. Physicochemical factors
Diffusion layer model
The rate of dissolution is given by Noyes & Whitney
Where,
dc/dt= dissolution rate of the drug
K= dissolution rate constant
Cs= concentration of drug in stagnant layer
Cb= concentration of drug in the bulk of the solution at time t
)( bS CCk
dt
dC
35Absorption of Drug4/13/2018
36. Physicochemical factors
Diffusion layer model
Modified Noyes-Whitney’s Equation
Where,
D= diffusion coefficient of drug.
A= surface area of dissolving solid.
Kw/o= water/oil partition coefficient of drug.
V= volume of dissolution medium.
h= thickness of stagnant layer.
(Cs – Cb )= conc. gradient for diffusion of drug.
bS
OW
CC
Vh
DAK
dt
dC
/
36Absorption of Drug4/13/2018
37. Physicochemical factors
Diffusion layer model
Sink conditions
In the derivation of equation it is assumed that
D and h remains constant
the static diffusion layer thickness is altered by the force of
agitation at the surface of the dissolving tablet.
Surface area A never remains constant as powder, granule or
tablet dissolves and it is difficult to obtain an accurate
measure of A.
SC
h
DA
dt
dC
37Absorption of Drug4/13/2018
38. Physicochemical factors
Diffusion layer model
Sink conditions
This is first order dissolution rate process, for which the
driving force is concentration gradient.
This is true for in-vitro dissolution which is characterized by
non-sink conditions.
The in-vivo dissolution is rapid as sink conditions are
maintained by absorption of drug in systemic circulation i.e.
Cb=0 and rate of dissolution is maximum.
Under sink conditions, if the volume and surface area of the
solid are kept constant, then
38Absorption of Drug4/13/2018
39. Physicochemical factors
Diffusion layer model
Sink conditions
Under sink conditions, if the volume and surface area of the
solid are kept constant, then
This represents that the dissolution rate is constant under sink
conditions and follows zero order kinetics.
K
dt
dC
39Absorption of Drug4/13/2018
40. Physicochemical factors
Diffusion layer model
Dissolution under sink & non sink conditions
Conc.ofdissolveddrug
Time
first order dissolution under non-
sink condition
zero order dissolution under
sink condition
40Absorption of Drug4/13/2018
41. Physicochemical factors
Diffusion layer model
Sink conditions can be achieved by
Bathing solid in fresh solvent from time to time
Increasing volume of dissolution fluid
Removing dissolved drug by partitioning
Adding water miscible solvent
Adding adsorbents
41Absorption of Drug4/13/2018
42. Physicochemical factors
Diffusion layer model
Hixon & Crowell’s cubic root law
takes into account the particle size decrease and change
in surface area,
W0
1/3 – W1/3 = Kt
Where,
W0=original mass of the drug
W=mass of drug remaining to dissolve at time t
Kt=dissolution rate constant.
42Absorption of Drug4/13/2018
43. Physicochemical factors
Danckwert’s Model
Turbulence in dissolution medium exists at solid/liquid
interface
Dankwert takes into account the eddies or packets that
are present in the agitated fluid which reach the solid-
liquid interface, absorb the solute by diffusion and carry
it into the bulk of solution.
These packets get continuously replaced by new ones
and expose to new solid surface each time, thus the
theory is called as surface renewal theory.
43Absorption of Drug4/13/2018
44. Physicochemical factors
Danckwert’s Model
The Danckwert’s model is expressed by equation
Where,
m = mass of solid dissolved
Gamma (γ) = rate of surface renewal
DCCA
dt
dm
dt
dC
V bS )(
44Absorption of Drug4/13/2018
45. Physicochemical factors
Interfacial Barrier model
An intermediate concentration can exist at the interface as a
result of solvation mechanism and is function of solubility
Interfacial barrier model is expressed by equation
Where,
G = dissolution rate per unit area
Ki = effective interfacial transport constant
)( bSi CCKG
45Absorption of Drug4/13/2018
46. Physicochemical factors
Factors affecting drug dissolution and dissolution rate
Physicochemical properties of drug
Dosage form factors
46Absorption of Drug4/13/2018
47. Physicochemical factors
Particle size and effective surface area
Particle size and surface area are inversely related to
each other.
Two types of surface area
Absolute surface area which is the total surface area of any
particle.
Effective surface area which is the area of solid surface
exposed to the dissolution medium.
Effective surface area is directly related to the
dissolution rate.
Greater the effective surface area, more intimate the
contact between the solid surface and the aqueous
solvent and faster the dissolution.
47Absorption of Drug4/13/2018
48. Physicochemical factors
Polymorphism & amorphism
When a substance exists in more than one crystalline
form, the different forms are designated as polymorphs
and the phenomenon as Polymorphism.
Stable polymorphs has lower energy state, higher M.P.
and least aqueous solubility.
Metastable polymorphs has higher energy state, lower
M.P. and higher aqueous solubility.
Eg. Chloramphenicol palmitate B
48Absorption of Drug4/13/2018
49. Physicochemical factors
Polymorphism & amorphism
Amorphous form of drug which has no internal crystal
structure represents higher energy state and greater
aqueous solubility than crystalline forms.
E.g.- amorphous form of novobiocin is 10 times more
soluble than the crystalline form.
Thus, the order for dissolution of different solid forms of
drug is –
amorphous > metastable > stable
49Absorption of Drug4/13/2018
50. Physicochemical factors
Hydrates/ Solvates
The stoichiometric type of adducts where the solvent
molecules are incorporated in the crystal lattice of the solid
are called as the solvates.
When the solvent in association with the drug is water, the
solvate is known as hydrate.
The organic solvates have greater aqueous solubility than the
nonsolvates.
E.g. – chloroform solvates of griseofulvin is more water soluble than
their nonsolvated forms
50Absorption of Drug4/13/2018
51. Physicochemical factors
Salt form of drug
Dissolution rate of weak acids and weak bases can be enhance
by converting them into their salt form.
With weakly acidic drugs, a strong base salt is prepared like
sodium and potassium salts of barbiturates and sulfonamides.
With weakly basic drugs, a strong acid salt is prepared like the
hydrochloride or sulfate salts of alkaloidal drugs.
51Absorption of Drug4/13/2018
52. Physicochemical factors
pH partition hypothesis
Theory states that for drug compounds molecular weight
greater than 100 dalton, primarily transported across
biomembrane by passive diffusion and process of absorption
is governed by:
pKa of drug
Lipid solubility of unionised drug
pH at the absorption site
Most drugs are- weak electrolytes
Ionisation depends on the pH of the biological fluid.
Unionised with sufficient lipid soluble drug cross barrier until
equilibrium is attained.
52Absorption of Drug4/13/2018
53. Physicochemical factors
pH partition hypothesis
Theory is based on following assumptions
GIT is a simple lipoidal barrier
Larger fraction of unionised drug, faster absorption
Greater the partition coefficient of unionised drug, better absorption
Drug pka and GIT pH
Unionised fraction is function of pKa of drug and pH of GIF
Low pKa of acidic drug- strong acid- greater ionisation
Higher pKa of basic drug- strong base- greater ionisation
53Absorption of Drug4/13/2018
55. Physicochemical factors
pH partition hypothesis
Drug pKa and GIT pH
Shore et al
Therapeutic ratio (R) given by
)(
)(
Plasma
Git
a
101
101
C
C
R
acidsFor Weak
pKapH
pKapH
Plasma
Git
)(
)(
b
101
10
R
basesFor Weak
Plasma
Git
pHpKa
pHpKa
Plasma
Git
C
C
55Absorption of Drug4/13/2018
56. Physicochemical factors
pH partition hypothesis
Drug pka and GIT pH
Generalisations regarding ionisation & absorption of acids
Very weak acids (pKa > 8): unionised at all pH values, absorption is
rapid and independent of GI pH. Pentobarbital, hexobarbital,
phenytoin, ethosuximide
Moderately weak acid (Pka, 2.5 – 7.5): absorption is pH dependent,
better absorbed from acidic pH (pH<pKa). Cloxacillin, aspirin,
ibuprofen, phenylbutazone
Strong acid (Pka< 2.5): ionised in the entire pH range of GIT, poorly
absorbed. Disodium cromoglycate
56Absorption of Drug4/13/2018
57. Physicochemical factors
pH partition hypothesis
Drug pka and GIT pH
Generalisations regarding ionisation & absorption of Bases
Very weak bases (pKa < 5): unionised at all pH values, absorption is
rapid and independent of GI pH. Theophylline, caffeine, oxazepam,
diazepam, nitrazepam
Moderately weak bases (Pka, 5 – 11): absorption is pH dependent,
better absorbed from alkaline pH. Morphine, chloroquine,
imepramine, amitriptyline
Strong bases (Pka > 11): ionised in the entire pH range of GIT, poorly
absorbed. Mecamylamine, Guanethidine
57Absorption of Drug4/13/2018
58. Physicochemical factors
pH partition hypothesis
Aqueous Solubility
Total aqueous solubility (St): Sum of concentration of ionised and
unionised drug in solution.
The solubility of unionised form of drug is known as intrinsic
solubility of drug.
For acidic drugs
For basic drugs
]101[SS )(
aT
pKapH
]101[SS )(
bT
pHpKa
58Absorption of Drug4/13/2018
59. Physicochemical factors
pH partition hypothesis
Conclusions and generalisations
For weakly acidic drugs
When pH > pKa, St >> Sa, ionisation of drug increases
When pH = pKa, St = 2Sa, 50 % ionisation
When pH< pKa, St = Sa, drug exists as unionised form
For basic drugs
When pH > pKa, St = Sb, drug exists as unionised form
When pH = pKa, St = 2Sb, 50 % ionisation
When pH< pKa, St >> Sb, ionisation of drug increases
59Absorption of Drug4/13/2018
62. Physicochemical factors
Limitations of pH partition hypothesis
Presence of virtual membrane pH
Absorption of ionised drugs
Influence of surface area and residence time of drug
Presence of aqueous unstirred diffusion layer
62Absorption of Drug4/13/2018
63. Physicochemical factors
Limitations of pH partition hypothesis
Presence of virtual membrane pH
Virtual membrane pH different than luminal pH
pH absorption curve
Basic drugsAcidic drugs
pH of GI Lumen
pHofGILumen
63Absorption of Drug4/13/2018
64. Physicochemical factors
Limitations of pH partition hypothesis
Absorption of ionised drugs
pH absorption curve
Absorption of ionic drugs
Large lipophilic group
Influence of surface area and residence time of drug
Acidic drugs- stomach
Basic drugs- intestine
Area available
Acidic & basic drugs absorbed well in intestine, long residence
64Absorption of Drug4/13/2018
65. Physicochemical factors
Limitations of pH partition hypothesis
Presence of aqueous unstirred diffusion layer
Aqueous GIT fluid
Aqueous unstirred
diffusion layer
Lipoidal biomembrane
Blood
65Absorption of Drug4/13/2018
66. Physicochemical factors
Drug permeability & absorption
Absorption is expressed by
Where
M = amount of drug absorbed
Peff = effective membrane permeability
A = surface area available for absorption
Capp = apparent luminal drug concentration
tres = residence time of drug in GI lumen
Three major properties determine permeability
Lipophilicity
Polarity of drug
Molecular size
resappeff tACPM
66Absorption of Drug4/13/2018
67. Physicochemical factors
Drug permeability & absorption
Rule of five by Lipinski et al
Molecular weight of drug < 500
Lipophilicity of drug, log P < 5
Number of H bond acceptors < 10
Number of H bond donors < 5
67Absorption of Drug4/13/2018
68. Physicochemical factors
Drug stability
Shelf life of drug during storage
Destabilization in GIT
Stereochemical nature of drug
68Absorption of Drug4/13/2018
69. Dosage form factors
Disintegration time
Manufacturing variables
Excipients
Manufacturing processes
Method of granulation
Compression force
Intensity of packing of capsule content
Nature and type of dosage form
Product age and storage condition
69Absorption of Drug4/13/2018
70. Dosage form factors
Method of granulation
Wet granulation
Dry granulation
APOC method
70Absorption of Drug4/13/2018
71. Dosage form factors
Compression force
Rateofdrugdissolution
A B C D
Compression force
71Absorption of Drug4/13/2018
72. Dosage form factors
Intensity of packing of capsule contents
Diffusion of GI fluids into the tightly filled capsules
creates a high pressure within the capsule resulting in
rapid bursting and dissolution of contents.
On other hand, it shows that capsule with finer particles
and intense packing have poor drug release and
dissolution rate due to decrease in pore size of the
compact and poor penetrability by the GI fluids.
72Absorption of Drug4/13/2018
74. Dosage form factors
Nature and type of dosage form
Solutions
Emulsions
Suspensions
Powders
Capsules
Tablets
Coated tablet
Enteric coated tablet
Sustained release tablet
74Absorption of Drug4/13/2018
75. Patient related factors
Gastrointestinal tract
Function
Length 450 cm
Stomach
Small intestine
Large intestine
75Absorption of Drug4/13/2018
76. Patient related factors
Stomach
Structure- bag like
Small surface area
Acidic pH- favors absorption of acidic drugs
Acidic pH – favors dissolution of basic drugs
Limited gastric residence
76Absorption of Drug4/13/2018
78. Patient related factors
Small Intestine
Large surface area (200 sqm)
Length of small intestine (300-500 cm)
Greater blood flow (1 l/min)
Favourable pH range (5-7.5)
Slow peristaltic movement
Prolonged residence time (3-6h)
High permeability
78Absorption of Drug4/13/2018
79. Patient related factors
Large Intestine
Small surface area (0.15 sqm)
Length (110 cm)
blood flow (0.02 l/min)
pH range (6-8)
Residence time (6-12 h)
Important in absorption of poorly soluble drug and SRDF
79Absorption of Drug4/13/2018
80. Patient related factors
Age
Infants
Gastric pH high
Less intestinal surface area
Low Blood flow
Elderly
Altered gastric emptying
Decreased intestinal surface area
Decreased blood flow
Higher incidence of achlorhydria and bacterial overgrowth
80Absorption of Drug4/13/2018
81. Patient related factors
Gastric Emptying
Passage of drug from stomach to small intestine
Rate limiting step for absorption
Rapid gastric emptying increases bioavailability
Rapid gastric emptying is advisable where
Rapid onset of action is desired
Dissolution occurs in intestine
Drug unstable in stomach
Drug best absorbed in intestine
Gastric emptying can be promoted by taking drug on empty
stomach
81Absorption of Drug4/13/2018
82. Patient related factors
Gastric Emptying
Delay in gastric emptying is advisable where
Food promotes dissolution and absorption
Disintegration and dissolution promoted by gastric fluid
Drug dissolves slowly
Drug irritates gastric mucosa
Drug absorbed in proximal part of intestine
Gastric emptying rate
Gastric emptying time
Gastric emptying half life
Barium sulphate is used to determine gastric emptying
82Absorption of Drug4/13/2018
83. Patient related factors
Gastric Emptying
Factors influencing gastric emptying
Volume of meal
Composition of meal
Physical state & viscosity of meal
Temperature of meal
Gastrointestinal pH
Electrolytes & osmotic pressure
Body posture
Emotional state
Exercise
Disease state
Drugs
83Absorption of Drug4/13/2018
84. Patient related factors
Intestinal transit
Peristaltic movement- promotes absorption
Delayed intestinal transit is desirable
SR products
Drugs dissolves in intestine
Absorption window
Slow absorption
84Absorption of Drug4/13/2018
85. Patient related factors
Gastrointestinal pH
Disintegration- Enteric coated
Dissolution
Absorption
Stability
85Absorption of Drug4/13/2018
86. Patient related factors
Disease state
Gastrointestinal diseases
Achlorhydria
Celiac disease
Crohn’s disease
Malabsorption
GI infections
Colonic diseases
GIT surgery
Cardiovascular diseases
Hepatic diseases
86Absorption of Drug4/13/2018
87. Patient related factors
Blood flow to GIT
28% of cardiac output
Sink condition
Food alters blood flow
87Absorption of Drug4/13/2018
88. Patient related factors
GIT content
Food drug interaction
Fluid volume
Large fluid volume results better dissolution, rapid gastric
emptying
Delayed Decreased Increased Unaffected
Aspirin Penicillins Griseofulvin Methyldopa
Paracetamol Erythromycin Diazepam Propylthiouracil
Diclofenac Tetracyclines Vitamins
Digoxin Iron
88Absorption of Drug4/13/2018
89. Patient related factors
GIT content
Normal GI constituents
Mucin decreases absorption of drug
Bile salts increases absorption of lipid soluble drugs
Drug-drug interactions
Physicochemical
Adsorption
Complexation
pH change
Physiological
Decreased GI transit (Propantheline)
Increased gastric emptying (Metoclopramide)
Altered GI metabolism (Antibiotics)
89Absorption of Drug4/13/2018
90. Patient related factors
First Pass Effect
The loss of drug through biotransformation by GIT and Liver
during its passage to systemic circulation.
Luminal Enzymes
Digestive enzymes
Enzymes present in gut fluid include intestinal and
pancreatic secretions.
Hydrolases
Hydrolyses esters
chloramphenicol palmitate to
chloramphenical
Inactivates proteins
90Absorption of Drug4/13/2018
91. Patient related factors
First Pass Effect
Bacterial enzymes
Gut wall enzymes
Alcohol dehydrogenase
Phase I and Phase II enzymes
Hepatic enzymes
91Absorption of Drug4/13/2018
92. Buccal & Sublingual Administration
Sublingual Route
Under tongue and allowed to dissolve
Buccal Route
Between cheek & gum
Barrier for absorption- oral epithelium
Drug absorbed by passive diffusion
Advantages
Rapid absorption
No first pass
92Absorption of Drug4/13/2018
93. Buccal & Sublingual Administration
Factors
Biphasic solubility of drug is required.
pH of saliva (6)
Binding of drug to oral mucosa
Storage compartment
Thickness of oral epithelium
Surface area
Taste of medicament
Antianginals, Antihypertensives, Analgesics,
Bronchodilators
93Absorption of Drug4/13/2018
94. Rectal Administration
Unconscious patients and children
If patient is nauseous or vomiting
Easy to terminate exposure
Absorption may be variable
Good for drugs affecting the bowel such as laxatives
Irritating drugs contraindicated
Dosage- solutions, suppositories
pH (8)
Surface area
Bypass first pass (lower half)
Analgesics, Bronchodilators,
94Absorption of Drug4/13/2018
97. Topical Administration
Skin conditions
Thickness of stratus corneum
Presence of hair follicles
Trauma
Hydration of skin
Age
Skin microflora
Skin pH
Skin surface lipids
Anatomical site
97Absorption of Drug4/13/2018
98. Topical Administration
Composition of topical vehicle
Vehicle/ base
Permeation enhancers
Application conditions
Rubbing
Occulsion
Loss of vehicle
External factors
Environmental humidity and temperature
Grooming
Exposure to chemicals
Chronic use of certain drug
98Absorption of Drug4/13/2018
99. Topical Administration
Drug administered
Nitroglycerine, lidocaine, testosterone
Iontophoresis
Delivery of ionic drug into the body -an electric current
Sonophoresis
Delivery of drug- under influence of ultrasound
99Absorption of Drug4/13/2018
100. Intramuscular Administration
Factors
Vascularity of the injection site
Blood flow to site
Lipid solubility and ionisation
Molecular size of drug
Volume of injection and drug concentration
pH, composition and viscosity of injection vehicle
100Absorption of Drug4/13/2018
101. Pulmonary Administration
Large surface area of alveoli
High perfusion
High permeability
Bronchodilators, steroids, antiallergics
Factors
pH
Lipid soluble- passive diffusion
Ionic, polar- pore transport
Particle/ globule size
101Absorption of Drug4/13/2018
102. Intranasal Administration
Less surface area
High perfusion
High permeability
Peptides, proteins, Bronchodilators, steroids,
antiallergics
Factors
pH (5.5-6.5)
Lipid soluble- passive diffusion
Ionic, polar- pore transport
Molecular size
Mucociliary clearance
102Absorption of Drug4/13/2018
103. Bibliography
D. M. Bramhankar and S. B. Jaiswal. Biopharmaceutics and
Pharmacokinetics A Treatise. Delhi;Vallabh Prakashan. 2010
Jambhekar SS, Breen PJ. Basic Pharmacokinetics. London;
Pharmaceutical Press. 2009.
Shargel L, Wu-Pong S, Yu ABC. Applied biopharmaceutics and
Pharmacokinetics. McGraw Hill. 2007.
4/13/2018 Absorption of Drug 103