6 Factors affecting drug absorption 4th

Physiological
factors
Formulation
factors
Physicochemical
factors
Drug
absorption
factors

PHYSICOCHEMIC
AL FACTORS
Physicochemical factors

 Drug solubility & dissolution rate
 Particle size & effective surface area
 Polymorphism & amorphism
 Pseudopolymorphism (hydrates/solvates)
 Salt form of the drug
 Lipophilicity of the drug (pH- Partition-
hypothesis)
 pKa of drug & gastrointestinal pH
 Drug stability

Drug Solubility & Dissolution rate
Disintegration
Deaggregation
ionic drug
Non ionic drug
Fine particle
Drug in
solution at
absorption site
Granules
Solid dosage
form
GI lumen GI barrier


Absorption of a drug is possible only when it
is present in the solution form,
Absolute Solubility or intrinsic solubility is
defined as…
“ The maximum amount of solute
dissolved in the given solvent under standard
conditions of temperature, pressure & pH.


The rate limiting steps in absorption of orally
administered drugs are: 1. Rate of dissolution
2. Rate of drug permeation

Dissolution is the rate limiting step for hydrophobic
& poorly aqueous soluble drugs.
E.g. Griesiofulvin & Spironolactone.

Permeation is the rate limiting step for hydrophilic
& high aqueous soluble drugs.
E.g. Cromolyn sodium OR Neomycin.

Dissolution :is the mass transfer from solid
surface to the liquid phase.
Theories of drug dissolution:-
1. Diffusion layer model/film theory
2. Danckwerts’s model/penetration theory
3. Interfacial barrier model/limited solvation
theory

Particle Size & Surface Area

Particle size plays a major role in drug absorption & this case is
important when the drug is poorly soluble (aqueous solubility).
Dissolution rate of solid particles α surface area

Smaller particle size, greater surface area then higher will be
dissolution rate, because dissolution is thought to take place at the
surface area of the solute( Drug).

Particle size reduction has been used to increase the absorption of a
large number of poorly soluble drugs
E.g. Bis-hydroxycoumarin, digoxin, griseofulvin


Types of surface area
1) Absolute surface area
2) Effective surface area

In absorption studies, the effective surface area is of much important
than absolute.

To increase the effective surface area, we have to reduce the size of
particles up to 0.1 micron. So these can be achieved by “micronisation
process’’.

But in these cases, one of the most important thing to be kept in mind
that what type of drug is need to be micronised if it is………
a) HYDROPHILIC OR b) HYDROPHOBIC

a) HYDROPHILIC DRUGS:

In hydrophilic drugs the small particles have higher energy
than the bulk of the solid resulting in an increased interaction
with the solvent.

Examples,
1.Griesiofulvin – Dose reduced to half due to micronisation.
2.Spironolactone – the dose was decreased to 20 times.
3.Digoxin – the bioavailability was found to be 100% in
micronized tablets.

After micronisation, it was found that the absorption
efficiency was highly increased

b) HYDROPHOBIC DRUGS:
 In this, micronization techniques results in decreased effective surface
area & thus fall in dissolution rate.
 Reasons for such change involves:
 Drug Adsorb air onto their surface– inhibit their wettability
 Reaggregate due to high surface free energy – float or settle
 Absolute SA of hydrophobic drug can be converted to effective SA by:
a) Use of surfactant as a wetting agent (tween 80)
- decreases the interfacial tension.
- displaces the absorbed air with the solvent. (Ex: Phenacetin)
b) Add hydrophilic diluents like PEG, PVP, dextrose etc.
(which coat the surface of hydrophobic drug particles.)

Internal structure of
compound
Molecular adducts
Non crystalline (amorphous)
Crystalline
Polymorphs
(single molecules)
Enantiotropic Monotropic
Solvate
stoichiometric
Complexes
pseudopolymorphs
Non stoichiometric
complexes
Hydrate
Polymorphism

Polymorphism

The polymorphs differ from each other with
respect to their physical properties such as
solubility, melting point, density, hardness
and compression characteristics. Thus, these
change in physical properties affect the
dissolution properties and hence the
absorption.

Polymorphism
 Polymorps are of two types:
a) Enantiotropic polymorph(reversible) E.g. Sulfur
b) Monotropic polymorph (unstable) E.g.Glyceryl stearates.
 Polymorphs have different stabilities and may
spontaneously convert from a metastable form (unstable
form) to the stable form at a particular temperature.
 Polymorphism has profound influence on formulation
development as it may exhibit different solubility,
dissolution rate, compactibility, hygroscopicity,etc.

AMORPHISM:
 Some drugs can exist in amorphous form (i.e. having no internal crystal
structure). Such drug represents the highest energy state.
 They have greater aqueous solubility than the crystalline forms
because a energy required to transfer a molecule from the crystal
lattice is greater than that required for non-crystalline (amorphous
form).
Ex: : the amorphous form of Novobiocin is 10 times more soluble
than the crystalline form.
dissolution order: Amorphous > Meta-stable > stable

Pseudopolymorphs
 When the solvent molecules are entrapped in the
crystalline structure of the polymorph, it is known as
pseudo-polymorphism.
1.Solvates
“where the solvent molecules are incorporated in the
crystal lattice of the solid are called as the solvates, and the
trapped solvent as solvent of crystallization.”
2.Hydrates (most common)
“when the solvent in association with the drug is water
, the solvate is known as a hydrate.”
 Ex: n-pentanol solvates of flurocortisone and succinyl-
sulfathiazole

 Anhydrous form greater aqueous solubility than
hydrate
Eg: anhydrous form of ampicillin have higher aqueous
solubility than trihydrate form.
 Solvate form greater aqueous solubility than
nonsolvate
Eg :the chloroform solvate of griseofulvin more water
soluble than nonsolvate form.

Salt forms of drug
 One of the easiest approach to enhance solubility and
dissolution by converting a drug into its salt form.
 While considering the salt form of drug, pH of the diffusion
layer is important not the pH of the bulk of the solution.
Example: in the Salt form of weak acid the pH of the
diffusion layer will be higher than that observable with the
free acid form of drug, which promotes the solubility and
dissolution of a weak acid and absorption is bound to be
rapid.

Fig: Dissolution and absorption of an acidic drug administered in a salt form
Diffusion
of soluble
drug
particles
Soluble
form of the
drug
rapid
dissolution
drug in
solution
diffusion layer
higher pH(5-6) Bulk of
solution
relatively
lower pH(1-3)
GI Lumen
GI Barrier
Blood
Drug in
blood
fine precipitate
of weak acid
Salt forms of drug

Salt forms of drug
 Other approach: Formation of in – situ salt formation
i.e……
“increasing in pH of microenvironment of drug by
incorporation of a buffering agent.” (E.g. aspirin, penicillin)
 But sometimes more soluble salt form of drug may result
in poor absorption.
(Ex: Sodium salt of phenobarbitone viz., its tablet
swells and did not get disintegrate, thus dissolved slowly and
results in poor absorption)

pH Partition Hypothesis
 The theory expresses the interrelationship of Dissociation Constant &
Partition Co-efficient of the drugs with the pH of GIT for predicting the
drug absorption.
 It states that……
“for drug compounds of molecular weight more than 100, which
are primarily transported across the bio-membrane by passive diffusion”
the process of absorption is governed by:
1. The dissociation constant pKa of the drug.
2. The lipid solubility of the un-ionized drug.
3. The pH at the absorption site.

A) Drug pKa and GI pH:
 Amount of drug that exists in un-ionized form and in ionized form
is a function of pKa of drug and pH of the fluid at the absorption
site, and it can be determined by Handerson-Hasselbach equation:
 For weak acids,
pH = pKa + log [ionized]
[un-ionized] ..(1.1)
% Drug ionized = 10pH-pKa x 100 … (1.2)
1+10pH-pKa
 For weak bases,
pH = pKa + log[un-ionized]
[ionized] …(1.3)
% Drug ionized = 10pKa-pH x 100 …(1.4)
1+10pKa-pH

2.5 7.5 8
pKa for weak acid
Very weak acid
Unionized at all pH
value
Eg: phenytoin
Affected by change
in Ph
best absorbed in the
stomache eg: NSAID
Stronger acid
Ionized in the entire
ph range
Poorly absorbed
Eg cromolyn Na
11 5
pKa for weak base
Very weak base
Unionized at all pH
value
Eg: diazepam
Affected by change in
Ph
best absorbed in the
intestine eg: morphie
Stronger base
Ionized in the entire
ph range
Poorly absorbed
Eg guanethidine

B) Lipophilicity & drug absorption:
 The lipid solubility of the drug is determined from its oil/water
partition co-efficient (PCo/w) value, whereby the increase in this value
indicates the increase in % drug absorbed.
PCo/w = Distribution of the drug in the organic phase (octanol)
Distribution of the drug in the aqueous phase
 Nowadays, the calculation is done by the value in log & mostly n-
octanol vs water as partitioning medium.
Log PC values Interference on absorption Examples
Less than 0 (polar) Poor intestinal absorption Gentamycin
0 to 1 Good GI absoption Minoxidil
About 3 Appreciable GI absorption Chlorpromazine
More than 5 (highly nonpolar) Poor intestinal absorption Pimozide (antipsychotic)

Limitation of pH partition Hypothesis:
1.Presence of virtual membrane pH
2.Absorption of ionized drug.
 Due to large lipophilic group in the structure.
3.Influence of GI surface area and residence time of
drug.
 Both acidic and basic drugs are more rapidly
absorbed from intestine (due to large SA and
long residence time)
4.Presence of aqueous unstirred diffusion layer
 Drug having large partition coefficient can rapidly
penetrate the lipid membrance but diffusion
through unstirred water layer is rate limiting in
their absorption.

Drug Stability
 A drug for oral use may destabilize either during
its shelf life or in the GIT.
 Two major stability problems resulting in poor
bioavailability of an orally administered drug are
 degradation of the drug into inactive form
Ex: Penicillin G (enzymatic degradation)
 interaction with one or more different
component(s) either of the dosage form or
those present in the GIT to form a complex
that is poorly soluble or is unabsorbable.

1) Disintegration time
(tablets/capsules)
2) Dissolution time
3) Manufacturing variables
4)Pharmaceutical ingredients
(excipients/adjuvants)
5) Nature & type of dosage form
6) Product age & storage condition

1. Disintegration time:
Rapid disintegration is important to have a rapid
absorption so lower D.T is required.
 Now D.T of tablet is directly proportional to
- Amount o f binder
- Compression force .
And one thing should be remembered that in vitro
disintegration test gives no means of a guarantee of
drugs bioavailability because if the disintegrated drug
particles do not dissolve then absorption is not possible.
 Coated tablet especially sugar coated ones have long
DT.

2. Manufacturing variables: -
- Manufacturing processes
- excipients
Manufacturing processes
a. Method of granulation
b. Compression force.
a) Method of granulation:
Wet granulation yields a tablet that dissolves faster
than those made by other granulating methods. But
wet granulation has several limitations like
 formation of crystal bridge.
 chemical degradation due to presence of liquid.
 Drying step may harm the themolabile drug
also, this method involved large number of steps

 Other superior recent method called as
Agglomerative phase of communication
(APOC), which involves grinding of basic
drug in ball mill and produce micronized
drug, which undergoes spontaneous
agglomeration, which then can be punched
with little addition of dry excipients.
 The tablet of this method
• Stronger and show rapid rate dissolution
The reason attributed to it was an
increase in the internal surface area of
the granules prepared result in high
dissolution.

b) Compression force:
The compression force employed in tableting
process influence:
 Density.
 Porosity.
 Hardness.
 disintegration time and
 dissolution of tablets.

Higher compression force
 increases the density and hardness of tablet
decrease porosity and hence penetrability of the
solvent into the tablet retard wettability.
 cause deformation, crushing or fracture of drug
particle into smaller one or convert a spherical
granule into disc particle with a large increase in
the effective surface area lead to increase
dissolution rate.
A B C D
Dissolution
rate
Compression force

3. Pharmaceutical ingredients / Excipients:
 More the no. of excepients in dosage form, more
complex it is & greater the potential for absorption
and Bioavailability problems.
Commonly used excipients in various dosage forms
are vehicle ,binder, diluent …..etc

a) Vehicle:
Rate of absorption – depends on its miscibility with
biological fluid. Miscible vehicles (aq or water
miscible vehicle) –rapid absorption e.g. propylene
glycol.
Immiscible vehicles - absorption –depends on its
partitioning from oil phase to aq body fluid.
b) Diluents:
 Organic Hydrophilic diluents-form the hydrophilic
coat around hydrophobic drug particles –thus
promotes dissolution and absorption of poorly
soluble hydrophobic drug.eg starch, lactose
 Non organic Eg dicalicium phosphate DCP
DCP-TC poor absorption

c) Binders & granulating agent :
Hydrophilic binders e.g. starch, gelatin,
PVP
– imparting hydrophilic properties to
granule surface – better dissolution of
poorly wettable drug. e.g. phenacetin.
More amount of binder – increases
hardness of tablet – decrease dissolution
& disintegration rate.

d) Disintegrants :
 Mostly hydrophilic in nature.
Decrease in amount of disintegrants –
significantly lowers Bioavailability.
e) Lubricants :
Commonly hydrophobic in nature –
therefore inhibits penetration of water into
tablet and thus dissolution and
disintegration.

g) Surfactants :
 Widly used in formulation as wetting agent ,
solubilizer …etc
 Their effect on absorption very complex
May enhance or retards drug absorption by
interacting with drug or membrane or both.
 Increase absorption:
 Promotion of wetting
 Better membrane contact of drug for
absorption
 Enhance membrane permeability of the
drug.
 Decrease absorption:
 Formation of unabsorbable drug-micelle
complex (above cmc)
 Laxative action (large conc)

Colourants:
Even a low concentration of water
soluble dye can have an inhibitory
effect on dissolution rate of several
crystalline drugs.
The dye molecules get absorbed onto
the crystal faces and inhibit the drug
dissolution.
e.g: Brilliant blue retards dissolution
of sulfathiazole.

4. Nature and type of dosage form:
disintegration
dissolution of shell
deaggregation
biomembrane
faster
Tablets
Fine particle
capsules
powders
suspension
emulsion
solution
granules
absorption
dissolution
Drug in
solution
Drug-blood

5. Product age and storage conditions :
A number of changes especially in the
physicochemical properties of a drug in
dosage form
Can result due to aging and alteration in
storage conditions which can adversely affect
Bioavailability of the drug.
e.g:
 precipitation of drug in solution.
 Change in particle size of suspension .
 Hardening of tablet.

1. Age
2. Gastric emptying time
3. Intestinal transit time
4. Gastrointestinal pH
5. Disease states
6. Blood flow through
the GIT
7. Gastrointestinal
contents:
 Food- drug interactions
 Fluids
 Other normal GI
contents
8. Presystemic
metabolism by:
 Luminal enzymes
 Gut wall
enzymes
 Bacterial
enzymes
 Hepatic enzymes

 In children & Infants:
 Gastric pH is high,
 Intestinal surface and blood flow to GIT is low resulting
in altered drug absorption pattern in comparison to
adult.
 in Elderly patient: causes of impaired drug absorption:
 altered gastric emptying,
 decrease intestinal surface area,
 decrease gastric blood flow & higher incidence of
achlorhydria and bacterial overgrowth in small intestine.
1.age


the passage from stomach to small intestine, called as gastric
emptying (1-5 hr)

Rate limiting step in absorption because the major site of drug
absorption is intestine.
Rapid gastric emptying is advisable where:
 Rapid onset of drug is desired eg: sedatives.
 Drugs are not stable in gastric fluids eg: penicillin G.
 Dissolution occuring in intestine eg: enteric coated forms.
The drug is best absorbed from the distal part of small
intestine eg Vit B12.
2.Gastric emptying time


For better drug dissolution and absorption
the gastric empting can be promoted by
taking drug on empty stomach.

Gastric empting of drug is delayed by co-
administering food because, unless the gastric
contents are fluid enough or size of the solid
particles is reduced below 2mm its passage
through the pylorus into the intestine is not
possible .

 Delay in gastric emptying is recommended where:
 Food promotes drug dissolution and absorption
eg: griseofulvin.
 The drugs dissolve slowly eg: griseofulvin.
 Disintegration and dissolution of dosage form is
promoted by gastric fluids.
 Drugs are absorbed from proximal part small
intestine VIT B2
 Several parameters used to quantify gastric emptying
:
Gastric emptying rate: speed at which stomach
contents empties into intestine.
Gastric emptying time: time required for gastric
contents to empty into small intestine.

FACTORS AFFECTING GASTRIC
EMPTYING:
1.Volume of meal:
 larger the bulk of meals, longer the gastric
emptying time.
2.Composition of meal:
Empting rate: carbohydrates > proteins > fats
Delayed gastric emptying with fatty meal, is beneficial
for the absorption of poorly soluble drugs like
griseofulvin.

3.Physical state and viscosity of meal:
 Liquid :less than hour
 solid meal : 6 to 7 hours.
 Viscous more than less viscous
4.Temperature:
High or low temperature of ingested fluid(in
comparison to body temp.) reduces the gastric
emptying.
5.Gastro intestinal pH:
 Retarded at low stomach ph and promoted at high
ph.
6.Electrolytes and osmotic pressure: water, isotonic
solutions and solution of low salt concentration
empty rapidly whereas high electrolyte conentration
decreases gastric emptying.

7.Body posture
increase emptying rate.
 Standing
 lying on right side
retard emptying rate.
 Supine.
 lying on left side.
8.Emotional state:
Stress and anxiety promote gastric motility
Whereas depression retard it
9.Exercise vigorous physical training retard gastric
emptying

10.drugs
Drugs that retard gastric emptying include
 Poorly soluble antacids: aluminium hydroxide
 Anticholinergics: atropine
 Narcotic analgesics: morphine
 Tricyclic anti depressents: imipramine
Drugs that stimulate gastric emptying include
 Metoclopromide.
 Domperidone.
 Cisapride.

11.Disease state:
Disease that retard gastric emptying rate
gastroenteritis,
gastric ulcer,
pyloric stenosis
Disease that promote gastric emptying rate
Partial or total gastrectomy
Duodenal ulcer
Hyperthyriodism

Since small intestine is the major site for absorption of
most drugs, long intestinal transit time is desirable for
complete drug absorption.
The residence time depends upon the intestinal motility or
contraction
Intestinal region Transit time
Duodenum 5 min
Jejunum 2 hrs
Ileum 3to 6 hrs
Caecum 0.5 to 1hr
Colon 6 to 12 hrs
3. Intestinal transit:

Delayed transit time is desirable for:
 Drugs that dissolve or release slowly from their
dosage form (sustained release product).
 Drugs that dissolve only in intestine(enteric coated).
 Drugs absorbed from specific sites in the intestine
(several B vit.s).
Intestinal transit time affected by:
 Disease (decreased digestive secretion and
pregnacy retard intestinal transit time wheras
diarrhea promote it )
 Drug:
 Laxatives and metoclopromide :promote the rate of intestinal
transit
 Anticholinergic: retard gastric and intestinal transit promote
absorption of poorly soluble drugs

The GI ph generally increases as one moves down the
stomach to the colon and rectum.
GI fluid pH influence drug absorption in several ways
1.Disintegration: (sometime pH dependent)
 Enteric coated formulations: coat dissolves only in
intestine followed by disintegration.
2.Dissolution:
 weakly acidic drugs: dissolve rapidly in alkaline ph of
intestine.
 Weakly basic drugs: dissolve in acidic ph of stomach
4. Gastro intestinal pH:

3.Absorption: depends on drug pKa and whether its
an acidic or basic drug, GI ph influences drug
absorption by determining amount of drug that
would exist in unionised form at the site of
absorption.
4.Stability: (GI pH also affect chemical stability of
drug)
acidic stomach ph- affect degradation of pencillin G
and erythromycin.
Can be overcome by preparing prodrugs of such
drugs . eg: carindacillin and erythromycin
estolate.

Gastrointestinal diseases:
Gastrointestinal diseases and infections:
 Two of the intestinal disorders related with
malabsorption syndrome that influence drug
availability are celiac disease (destruction of villi and
microvilli) and Crohn’s disease.
 Crohn’s disease that can alter absorption pattern
are altered gut wall microbial flora, decreased gut
surface area and intestinal transit rate.
 GI infections like shigellosis, gastroenteritis, cholera
and food poisoning also result in malabsorption.
5. Disease state:

Gastrointestinal surgery:
Gastrectomy can result in drug dumping in the
intestine, osmotic diarrhea and reduced intestinal
transit time.
Cardiovascular diseases:
Several changes associated with congestive
cardiac failure influence bioavailability of a drug.
(edema of intestine, decrease GIT blood flow..etc)
Hepatic diseases:
Disorders such as hepatic cirrhosis influence
bioavailability mainly of drugs that undergo
considerable first-pass hepatic metabolism.
e.g. propranolol.

 The GIT is extensively supplied by blood capillary
network and the lymphatic system.
 Most drugs reach the systemic circulation via blood.
 Few drugs(low mwt, lipid soluble) removed by
lymphatic system.
 High perfusion rate of GIT helps in maintaining sink
conditions and concentration gradient for drug
absorption by rapidly removing drug from the site
of absorption.
 GIT perfusion rate increase after meal but not affect
drug absorption significantly.
6.Blood flow through GIT:

A number of contents can influence drug absorption as
follows:
1. Food-drug interactions: Presence of food may either
delay, reduce, increase or may not affect drug
absorption.
Food affect drug absorption by:
 Alteration in the GI emptying rate, fluid secretion, ph,
blood flow.
 And/ or physicochemical interaction with the
drug(alteration in dissolution profile, compexation and
adsorption)
Delayed Decreased Increased Unaffected
Aspirin Pencillins Griseofulvin Methyldopa
Paracetamol Erythromycin Nitrofurantoin Propylthiouraci
l
Diclofenac Ethanol Diazepam Sulfasomidine
7. Gastrointestinal Contents:

2.Fluid volume:
Administration of drug with large fluid volume results
in better dissolution, rapid gastric emptying and
enhanced absorption.
e.g: erythromycin (taken with glass of water under
fasting)
3.Interaction of drug with normal GI constituents:
 The GIT contains a number of normal constituents such
as mucin, bile salts and enzymes which influence drug
absorption.
 Mucin a protective mucopolysaccharide that lines the
GI mucosa, interacts with streptomycin and certain
quaternary ammonium compounds and retards their
absorption.
Bile salts aid solubilisation and absorption of
lipophilic drug like griseofulvin and vit A,D,E,K.
Bile salt decrease absorption of neo- and
kanamycin(forming water insoluble complex)

4.Drug-drug interactions in the GIT:
These interactions can be either physicochemical
or physiological.
- Physicochemical interactions are due to :
 Adsorption: antidiarrhoeal preparations
containing adsorbents like kaolin-pectin retard
absorption of number of drugs co-administered
with them.
e.g: promazine, lincomycin.
Complexation: unabsorbable complexes are
formed.
e.g: antacids or mineral substances
containing heavy metals such as Al, Ca+2 , Mg+2
retard absorption of tetracycline by forming
unabsorbable complexes.

-Physiological interactions are due to :
 Decreased GI transit:
Anticholinergics like propantheline retard GI
motility and promote absorption of drugs like ranitidine
and digoxin & delay absorption of paracetemol and
sulphamethoxazole.
 Increased gastric emptying:
Metoclopramide promotes GI motility and
enhances absorption of tetracycline, levodopa.

For a drug administration orally, the 2 main reasons
for its decreased bioavailability are:
a. Decreased absorption and
b. First pass metabolism
The loss of drug through biotransformation by such
eliminating organs during its passage to systemic
circulations called as first pass or presystemic
metabolism.
The 4 primary systems which effect presystemic
metabolism of a drug are:
a. Luminal enzymes b. Gut wall enzymes
c. Bacterial enzymes d. Hepatic enzymes
8.Presystemic metabolism:

a.Luminal enzymes:
These are present in gut fluids and include enzymes
from intestinal and pancreatic secretions. latter
contain hydrolases which hydrolyse ester drugs.
chloramphenicol palmitate active
chloramphenicol, and which split amide linkages and
inactivate proteins.

b.Gut wall enzymes: also called as mucosal enzymes
present in stomach, intestine and colon.
 Alcohol dehydrogenase : enzyme of stomach
mucosa inactivates ethanol.
 Intestinal mucosa: contains both phase I and
phase II enzymes.
eg: sulphation of ethinyl estradiol .
 Colonic mucosa : also contains both phase I
and phase II enzymes.
c.Bacterial enzymes :
eg: sulphasalazine sulphapyridine &
(drug in ulcerative colitis) 5-aminsalicylic acid
hydrolyzation

d.Hepatic enzymes:
several drugs undergo first pass hepatic metabolism,
the highly extracted ones being propranolol,
nitroglycerine, diltiazem, lidocaine, morphine etc.

REFERENCES
1. Brahmankar D.M., Jaiswal S.B., First edition, “Absorption of
Drugs” Biopharmaceutics and Pharmacokinetics – A treatise,
Vallabh Prakashan, Delhi 1995.
2. Shargel L., Andrew B.C., Fourth edition “Physiologic factors
related to drug absorption” Applied Biopharmaceutics and
Pharmacokinetics, Prentice Hall International, INC., Stanford
1999.
3. Aulton M.E. Pharmacetutics “The Science of Dosage Form
Design”, 2nd Ed.; Churchill Livingstone.

6 Factors affecting drug absorption 4th

More Related Content

What's hot

Similar to 6 Factors affecting drug absorption 4th

More from Dr Ahmad Abdulhusiaan Yosef

Recently uploaded

6 Factors affecting drug absorption 4th