The document discusses sustained release dosage forms (SRDF), which are designed to provide prolonged therapeutic effect by releasing medication over an extended period after a single dose. It covers various drug release types, suitable drug properties, and the use of various polymers for controlled release mechanisms, along with their advantages and disadvantages. Additionally, it highlights factors affecting drug absorption and safety while providing references for further reading.

1. Sustained Release Dosage
Form [SRDF]
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2. CONTENT
• INTRODUCTION
• RATIONALE
• DRUG PROPERTIES SUITABLE FOR SRDF
• POLYMERS USED IN SRDF
• MECHANISM OF RELEASE OF SRDF
• ADVANTAGES
• DISADVANTAGES
• REFRENCES
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3. INTRODUCTION
• Sustained release, are terms used to identify drug
delivery system that are designed to achieve a
prolonged therapeutic effect by continuously
releasing medication over an extended period of
time after administration of a single dose.
• Sustained release dosage forms provide an
amount of drug initially made available to the body
to cause the desired therapeutic response, followed
by a constant release of medication for maintenance
of activity over a period of time
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4. Different Terminology
On basis of release of drug from dosage form
1. Immediate Release ( IR)
2. Delayed Release (DR)
3. Controlled/Continuous release (CR)
4. Sustained Release (SR)/
Extended release (ER/XL/XR)/Prolonged release
/Repeat action
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5. Immediate Release
• Immediate release dosage form releases drug
immediately after administration of single dose.
• It generally releases 85-90%drug in 15 mins.
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6. Delayed Release
• Term “delayed-release” is used for enteric coated
dosage forms that are intended to delay the release of
medicament until it has passed through the stomach.
• Capsules ,tablets may be coated, or, more commonly,
encapsulated granules coated to resist releasing the
drug in the gastric fluid of the stomach where a delay
is important to alleviate potential problems of drug
inactivation or gastric mucosal irritation.
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7. Controlled Release
• Controlled release dosage forms release drug at
predetermined rate locally, systemically for specified
period of time.
• Controlled release is perfectly zero order release.
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8. 8

9. Rationale for Sustained Release
• Drugs which are often administered repeatedly at
specified time interval to maintain therapeutic level in
blood or body tissues
• uniform drug response achieved by using different
combination of doses and dosage interval
• However, the dosage regimen of an orally
administered drug may be considered to be optimal
when the therapeutic effect is maintained for the
desired duration of the treatment at the lowest
frequency of administration.
• Frequent administration of dose produces side effect
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10. DRUG PROPERTIES SUITABLE FOR SRDF
Physicochemical properties
Aqueous solubility:
Drugs having low solubility at absorption site and are pH dependent
are poor candidates
eg. Tetracycline
Partition coefficient and Molecular Size :
Drugs with high P.C. readily cross memb. While
those with low P.C. can not cross memb.
Large mol. Wt. compounds are poor candidate.
Drug stability:
Drug unstable in 1-7 pH can’t given by GIT.
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11. pKa and Ionization at physiological pH:
• For passive absorption drug should be un-ionized
• Largely ionized drug poor candidate eg. Hexamethonium
• pKarange for acidic drugs is 3.0-7.5 & for basic drug
7-11
Dose:
• Dose must not be greater than 500mg.
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12. BIOLOGICAL FACTORS
Absorption:
• Uniform absorption to maintain constant blood
tissues level
• Orally slowly absorbed drugs are poor candidate
Distribution:
• Affected by binding to tissues and proteins
• Bound portion of drug considered as inactive or unable to
cross membrane.
• Described by apparent volume of distribution
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13. • Biological half life:
Those drugs having short half life are most suitable for
SR. eg. Diphenhydramine
• Side effect:
Those drugs causing GI irritation are selected for
SR, eg. Diclofenac sodium, potassium citrate
• Safety margin:
Drugs having narrow therapeutic index are selected
for SR, eg. Diclofenac sodium
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14. POLYMERS
• Hydrophilic polymer:
Hydroxy propyl methyl cellulose (HPMC)
Hydroxy propyl cellulose (HPC)
Hydroxy ethyl cellulose (HEC)
Sodium Alginate
Poly (ethylene oxide)
Cross linked homopolymer
Copolymer of Acrylic acid
• Hydrophobic polymer
1. Waxes:
Carnauba wax
Bees wax
Candelilla wax
Microcrystalline wax
Paraffin wax 14

15. 2. Insoluble polymer:
Ethyl cellulose
Cellulose acetate
Cellulose acetate butyrate
Cellulose acetate propionate
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16. MATRIX(MONOLITH) SYSTEM
Drug/excipients embeded within a matrix
Dissolution controlled Drug release
 Homogenous dispersion of drug throughout a rate-
controlling medium
 Release rate is controlled by the dissolution rate of the polymer
 Two methods for drug-wax particle preparation
-Aqueous dispersion
-Congealing
 Drug release is often first-order
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17. Dissolution controlled drug release:-
Diffusion controlled drug release:-
Non swellable matrix Swellable matrix
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18. Diffusion controlled Drug release:-
 Drug is dispersed in an insoluble Matrix of rigid non
swellable hydrophobic material or
swellable hydrophilic substances
 Rigid matrix prepared by congealing
 Swellable matrix prepared by drug and gum granulated
then compressed into tablet
 Rate controlling step is diffusion
 From rigid matrix Drug release follows Ficks first order diffusion
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19. RESERVOIR SYSTEM
Drug/ excipients core coated with a polymeric membrane
Dissolution controlled drug release :
 Particles are coated or encapsulated by one of the several
microencapsulation methods, resulting in pellets which are filled in
hard gelatin capsules or compressed into tablets.
 Dissolution of coat depends on solubility and thickness of coating
layer (1-200 micron)
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20. Diffusion controlled drug release
Hollow systems containing an inner core of drug
surrounded in a water insoluble polymer membrane.
 Polymer applied by coating or microencapsulation
 Drug release involves partitioning into memb. and
subsequent release into the surrounding fluid by
diffusion
 Rate controlling factors
- Polymeric content in coating
- Thickness of coating
- Hardness of microcapsule
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21. Advantages
• Employ minimum drug.
• Improves efficacy in treatment
• Avoid patient compliance problems
• Minimizes drug accumulation with chronic dosing
• Minimizes local, systemic side effects
• Less fluctuations in concentration of drug
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22. Disadvantages
• Therapy can not be terminated if there are any side
effects
• Less flexibility to physician in dose adjusting
• Costly
• Dose dumping
• Increased potential for first –pass clearance
• Poor systemic availability
• Unpredictable and often poor in vivo-in vitro
correlations
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23. REFERENCES
1.Remington;The science and practice of pharmacy,20th
ed
,vol-I,p.p.898.
2. Leon Lachaman; The theory and practice of industrial
pharmacy, 3rd
ed,p.p.430-456.
3.Herbart A.Liberman ,Leon Lachaman; Pharmaceutical
dosage form; Tablets,vol-III,2nd
ed,p.p.199-302.
4.Bentley’s Textbook of pharmaceutics,8th
ed,p.p.661-666.
5. Michael E. Aulton; Pharmaceutics, The science of dosage
form design;2nd
ed, p.p.290-291.
6. "http://en.wikipedia.org/wiki/Sustained_release" 23

24. 7. Ashok Katdale; Excipient development for pharmaceutical
biotechnology & drug delivery,p.p.12,185-187 .
8. D. M. Brahmankar, Sunil B. Jaiswal,; Biopharmaceutics and
pharmacokinetics, A Treatise, pp. 335-370.
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