This document discusses how excipients and other formulation factors can influence drug absorption. It explains that excipients are added to ensure stability, uniformity, and optimal bioavailability. However, excipients can also impact absorption based on their type and amount. Factors like vehicle, diluents, binders, disintegrants and others are described in terms of how they can increase or decrease the rate of drug absorption from different dosage forms. The document emphasizes that proper selection of excipients and dosage form is important to maximize a drug's bioavailability.

1. Diwakar chudal
B.Pharmacy , Institute of Medicine (IOM)

2. Definition
 Drug absorption is defined as the process of
movement of unchanged drug from the site
of administration to systemic circulation.

3.  Excipients.
 Nature and type of dosage
form.
 Storage conditions.

4.  Non-drug components which are added
during formulation of drug are called
excipients.
 Excipients are added during drug formulation
because:
 Ensures physico-chemical stability.
 Gives uniformity to composition.
 Gives optimum bioavailability.
 Gives suitable colouration and taste.

5.  Despite their importance in the drug
formulation, excipients can highly influence
the absorption of drugs.
 More the number of excipients in a dosage
form, more complex the drug becomes and
more likely to show problems in drug
absorption and bio-availability.

6.  Most commonly used excipients during
formulation of dosage form are:
Vehicle, diluents, binders or granulating
agents, disintegrants, lubricants, coatings,
suspending agents, surfactants, buffers,
complexing agents, colorants, sweetning
agents, precipitation inhibitors, etc

7.  Vehicle or solvent system is the major
component of liquid oral and parenteral
dosage form.
 Basically, 3 types of vehicles are used
▪ Aqueous vehicles (water, syrup, etc)
▪ Non-aqueous water-miscible vehicles (propylene,
glycol, glycerol, etc)
▪ Non-aqueous water-immiscible vehicles (vegetable oils)

8.  Aqueous and water miscible vehicles are
miscible with the body fluids so the drugs
from them are rapidly absorbed.
 Absorption of drugs in different vehicles
follows the order :
water-miscible vehicles > aqueous vehicles
>water-immiscible vehicles.

9.  Absorption of a drug from a viscous vehicle is
slower in comparison to non-viscous vehicle.
 Thus, nature of vehicles and viscosity of
vehicles is also one of the factor affecting the
drug absorption.

10.  Diluents are commonly added to tablets and
capsule formulations if the required dose is
inadequate to produce necessary bulk.
Inorganic Organic

11.  Organic diluents:
Starch, lactose, microcrystalline cellulose, etc
 Inorganic diluents:
Dicalcium phosphate (DCP) is most common.
 Sometimes Drug-diluent interactions alters the
absorption of drug.
Example:
Tetracycline and DCP when interacts, divalent
calcium-tetracycline complex is formed which is
poorly soluble and thus unabsorbable.

12.  Granulating agents are the substance which
are used to hold powders together to form
granules.
 It ensures that the tablet remains intact after
compression.
 Starch, cellulose derivatives, gelatin, sugar
solutions,etc are most common granulating
agents.

13.  Large amount of such granulating agents
increases hardness and decreases dissolution
rates of tablets and hence decreases the rate
of absorption.
Example:
PEG 6000 when binds with phenobarbital, it
forms complex compound with very low
solubility.

14.  Disintegrants are the substance which increases the
dissolution of tablets in water.
 When drug comes in contact with water, disintegrants
helps to overcome the cohesive force between drug
molecules and dissolution of tablets takes place in
aqueous medium.
 However, adsorbing disintegrants like bentonite and
vegum should be avoided with low dose drugs like
digoxin, alkaloids and steroids since a large amount of
dose is adsorbed and only a small fraction is available
for absorption.

15.  Lubricants are added to tablets to reduce
interparticle friction and sticking.
 Also called as anti-frictional agents.
 Lubricants are mostly hydrophobic in nature
and thus inhibits the penetration of water
into the tablets.
 Lubricants are applied by coating it over the
surface of tablets.

16. Coating:
 The process of applying one substance on the
surface of another.
 Deleterious effects of various coatings on
drug dissolution from a tablet follows the
order:
▪ Enteric coat > suger coat > non-enteric film coat

17.  Suspending agents are the substance which
stabilize the solid drug particles by reducing
their rate of settling through an increase in the
viscosity of the medium.
 Also called as viscosity imparters.
 Mostly used suspending agents are hydrophilic
polymers like:
▪ Vegetable gums (eg. Acacia)
▪ Semi-synthetic gums(eg. CMC, MC)

18.  An increase in viscosity by some suspending
agents acts as a mechanical barrier to the
diffusion of drug from the dosage form into
the bulk of GI fluid and from GI fluid to the
mucosal lining.
Example:
 CMC forms unabsorbable complexes with
amphetamine.

19.  Surfactants are used in drug formulations as
wetting agents, solubilizers,etc
 Surfactants may either increase or retard the
drug absorption interacting with drug
molecules.
 Surfactants usually increases drug absorption
by increasing membrane permeability of the
drug.

20.  Decrease in absorption of drug in the
presence of surfactant is due to formation of
unabsorbable drug-surfactant complex at
surfactant concentrations above the critical
concentration.
 Thus, higher surfactants concentration
always decreases the rate of drug absorption.

21.  Buffers are the solutions whose PH value
remains almost constant after addition of
small amounts of acids or alkali.
 Buffers are sometimes useful in increasing
the rate of dissolution of drug. Eg.buffered
aspirin tablets.
 But, certain buffer systems containing
potassium cations inhibits drug absorption as
seen in vit B2 and sulphanilamide.

22.  Inhibitory effect of the various buffer cations
on the drug absorption follows the order:
K+ > NH4
+ > Li+ > Na+ >TRIS+

23.  In some drugs, complexing agents are added
to alter the physico-chemical and bio-
pharmaceutical properties of a drug.
 A complexed drug may have different
stability, solubility, molecular size, diffusion
rate, etc
 Examples of complexation which increases
the drug absorption are:

24. Ergotamine tartarate – caffeine complex. (increases
dissolution)
Caffiene-PABA complex. (increases membrane
permeability)
• However, complexation can sometime decrease the
drug absorption due to formation of poorly
absorbable complex
Eg. Complexation of tetracycline with divalent and trivalent
cations like calcium, iron, magnesium, aluminium,etc
decreases absorption.

25.  Colorants are added in drug formulations to
mask the unattractive original colour of a drug.
 But, colourants can also largly affect the drug
absorption.
 Very low concentrations of water soluble dye
can have an inhibitory effect on dissolution rate
of several crystalline drugs
Eg. Brilliant blue dye retards dissolution of
sulpathiazole.

26.  When concentration of free drug increases
above the saturation, it results in
supersaturation which leads to drug
precipitation or crystallization.
 PVP, HPMC, PEG, PVA, etc are some polymers
which prevents drug precipitation by:
Increasing the viscosity of vehicle
Adsorbing on the faces of crystals thus reducing
crystal growth.

27.  The rate of absorption and bio-availability of
certain drug largely depends on the proper
selection of dosage form of that drug.
This is due to the relative rate at which a particular
dosage form releases the drug to the biological
fluids and membrane.
 As a general rule, bio-availability of a drug
from various dosage forms decreases in the
following order:

28.  Solutions > emulsions > suspensions >
powders > capsules > coated tablets >
enteric-coated tablets > sustained-release
tablets.
 Thus, absorption of a drug from solution is
fastest with least potential for bioavailability
problems whereas absorption from
sustained-release product is slowest with
greatest bioavailability risk.

29.  A number of changes in the physico-chemical
properties of a drug can result due to storage
conditions which can adversely affect absorption
and thus bio-availability.
 When shelf-life of the solutions becomes long,
solubility of drug changes and precipitation can
occur.
 Similarly, decrease in rate of dissolution occurs
in suspension dosage form

30.  High temperature and humidity results in
increase in hardness of tablets which
decreases the rate of absorption.
 Therefore, storage conditions and product
age has significant role in the absorption of
drug from different dosage forms.

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