What is dissolution? Dissolution is a process in which a solid substance get solubilizes in a particular solvent to yield a solution i.e. mass transfer from the solid surface to the liquid phase.

1. The
Factor Affecting
Dissolution Rate
Presented By
Mohammad Zishan Ibrahim

2. What is Dissolution?
Dissolution is a process in which a solid substance
solubilizes in a given solvent to yield a solution
i.e. mass transfer from the solid surface
to the liquid phase.

3. Importance of Dissolution in Solid Dosage Form

4. Dissolution Rate
Dissolution rate is the amount of drug substance
that converts into solution per unit time under
standardized condition of temperature and
pressure.
*The rate of dissolution is given by Noyes and
Whitney:
𝒅𝒄
𝒅𝒕
= 𝒌 𝑪𝒔 − 𝑪𝒃

5. Factors Affecting Dissolution Rate
• Factor related to Physicochemical Properties of Drug
• Factors related to Drug Product Formulation
• Processing Factor
• Factors Relating Dissolution Apparatus
• Factors Relating Dissolution Test Parameters

6. Particle Size
Surface area increases with decrease in particle
size, higher dissolution rates may be achieved
through reduction of particle size.
Factor related to Physicochemical Properties of Drug

7. Drug Solubility
• Aqueous solubility of drug leads to the higher
dissolution rate.
• Dissolution rate is directly proportional to their
respective solubility.
Example :
• Poorly Soluble drug ; griseofulvin,
spironolactone
• Hydrophilic drug : neomycin

8. Solid State Characteristics
Anhydrous : forms dissolve faster than hydrated
from because they are thermodynamically more
active than hydrates.
E.g. Ampicillin anhydrate faster dissolution rate
than trihydrate.
Amorphous : forms of drug tend to dissolve
faster that crystalline materials.
E.g. Novobiocin, Grisefulvin.

9. Salt Formation
• It is one of the common approaches used to
increase drug solubility and dissolution rate.
E.g. sodium and potassium salts of penicillin G,
phenytoin, barbiturates, tolbutamide, etc

10. Binders
• The hydrophilic binders like gelatin increase dissolution
rate of poorly wettable drug.
• Non aqueous binders such as ethyl cellulose retard the
drug dissolution.
• Phenobarbital tablet granulated with gelatin solution
provide a faster dissolution rate in human gastric juice
than those prepared using Na – carboxy methyl
cellulose or polyethylene glycol 6000 as binder.
FACTORS RELATED TO DRUG PRODUCT FORMULATION

11. Disintegrates:
“Disintegrating agent added before & after the
granulation affects the dissolution rate.“
A Microcrystalline cellulose is a very good
disintegrating agent but at high compression
force, it may retard drug dissolution.

12. Lubricants
• Lubricants are hydrophobic in nature (metallic
stearates) and prolong the tablet disintegration time by
forming water repellent coat around individual granules.
This retarding the rate of dissolution of solid dosage
forms.
• Both amount and method of addition affect the
property. It should be added in small amount (1% or less)
and shouldbe tumbled or mixed gently for only very
short time. Prolonged mixing affect the dissolution time.

13. Surfactants
• They enhance the dissolution rate of poorly
soluble drug. This is due to lowering of
interfacial tension, increasing effective surface
area, which in turn results in faster dissolution
rate.
E.g Non-ionic surfactant Polysorbate-80, increases
dissolution rate of phenacetin granules.
• The increase was more pronounced when the
surfactant was sprayed on granules than when
it was dissolved in granulating agent.

14. Complexing Agents
• A complexed drug may have altered stability,
solubility, molecular size, partition coefficient
and diffusion coefficient.
E.g. Enhanced dissolution through formation of a
soluble complex of ergotamine tartarate-caffeine
complex and hydroquinone-digoxin complex.

15. Granulation
• Wet granulation has been shown to improve the
dissolution rate of poorly soluble drugs by imparting
hydrophilic properties to the surface of granules.
• A newer technology called as APOC “Agglomerative
Phase of Comminution” was found to produce
mechanically stronger tablets with higher dissolution
rates than those made by wet granulation. A possible
mechanism is increased internal surface area of
granules produced by APOC method.
PROCESSING FACTORS

16. Agitation
• Speed of agitation generates a flow that continuously
changes the liq/solid interface between solvent and
drug.
• In order to prevent turbulence, The sustain
reproducible laminar flow, which is essential for
obtaining reliable results, agitation should be
maintained at a relatively low rate. Thus, in general
relatively low agitation should be applied.
1. BASKET METHOD- 100 rpm
2. PADDLE METHOD- 50-75 rpm24
FACTORS RELATED TO DISSOLUTION APPARATUS

17. Temperature
• Drug solubility is temperature dependent, therefore
careful temperature control during dissolution process
is extremely important.
FACTORS RELATING DISSOLUTION TEST PARAMETERS
Vibration
• The excessive vibration of dissolution apparatus
increases dissolution rates.
pH of Medium
• Weak acids, dissolution rate increases with increase in
pH where as for weak beses, increase with decrease in
pH

18. Do You Have Any Question?