rate controlled drug delivery system

1. “Sustainedrelease andcontrolledrelease formulations”.
Presented by,
Karthik swamy B.M
Mpharma 1st sem
Dept.of pharmaceutics.
V.L collegeof pharmacy,raichur

2. Content
1.INTRODUCTION
2.BASIC CONCEPT OF SR OR CR FORMULATIONS
3.ADVANTAGES
4.DISADVANTAGES
5.PHYSICOCHEMICAL APPROCHES.

3. INTRODUCTION:
WHAT IS DRUG DELEVERY SYSTEM?
ANS: The term “drug delivery systems”refers to technology utilized
to present the drug to the desired body site for drug release and
absorption
WHAT IS SUSTAINED RELEASE FORMULATIONS?
SRF Is describes the slow release of a drug substances from
a dosage form to maintain the therapeutic responses for extended
period that is for about 8-12 hours of time.
EX: ASPIRIN SR, DEXTRIN SR.
WHAT IS CONTROLLED RELEASE FORMULATIONS?
These are the formulations which delivers the drug at a
predetermined rate, for locally or systematically, for a specified
period of time
EX: PROZOSIN(MINI PRESS) MORPHINE SULPHATE.

4. “DIFFERENCE BETWEENCONTROLLEDRELEASE& SUSTAINEDRELEASE”

5. CONCEPTOF SUSTAINEDRELEASEFORMULATIONS
The therapeutic blood or tissue levels of the
drug is maintained or accomplished by “zero order”
release dosage form, where the drug release is
independent of amount of drug in the delivery system
here the rate limiting step is the release of drug form
dosage form,here kr<<<ka
Dosage form kr target area ke
drug release elimination.
Where as,the first order depends on the release of
active ingredients immediately,and rate limiting step
is absorption of drug form the absorption pool.here
kr>>>ka

6. ADVANTAGES:
1.Improved Patient compliance:
a)less frequent dosing
b)Reduced night time dosing
C)Reduced patient care time.
2.Better drug utilization :
a)Reduction in total amount of drug administration.
b)maximum effect with minimum dose.
3)Improved efficiency in treatment:
A)Cure or control condition more prompt.
b)Decreased fluctuation in drug level
c)Minimised accumulation with chronic use

7. 4)Bioavailability of certain drugs can be enhanced.
5)Decreased local and systemic side effects.
Eg: decreased GI Irritation by SR-ASPIRIN tablets.
6)Increased safety margin of high potency drugs due to
better control of plasma levels.
7)Economy:
a)Reduction in health care costs (patient care)
b)shorter therapy
c)less frequent dosing.

8. Disadvantages:
1)Dose dumping which may lead to toxicity .It may occur
due to food , physiologic or formulation variation.
2) less flexibility in accurate dose adjustments depending
on patients condition.
3)Need for additional patient education like “Do not crush”
or “Do not chew”
4) Retrieval of drug is difficult in case of toxicity poisoning
or allergic reactions
5) Higher cost formulation.
6)patient to patient variation diseased state are not
considered in formulation.

9. •Physicochemical factors affecting cr/sr drug delivery system
sustained or controlled release
dosage systems 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.
physicochemical properties of drugsare:
 Aqueous solubility and Pka .
 Partition coefficient.
 Drug stability.
 Protein binding.
 molecular size and diffusivity.
 Dose size.
 Drug permeability.
 Drug pka and ionization at physiological PΗ.
 Mechanism of site of absorption

10.  A drug with good aqueous solubility,especially if pΗ
independent,serves as good candidate for SR dosage
form.The drug to be absorbed it must firstly dissolve
in the aqueous phase surrounding the site of
administration and then partition into absorbing
membrane.This is governed by two properties i.e ,
aqueous solubility and its pka
 Aqueous solubility influences its
dissolution rate, according to Noyes whitney equation.
 dc/dt=KD A.CS
 Where, dc/dt=dissolution rate.
 kD =Dissolution rate constant
 A=Total surface area,
 CS=aqueous saturation solubility of drug.

11. Aqueous solubility of weak acids and bases is
governed by pka of compound and pΗ of solution.
According to pΗ theory , the unionized form of a drug
will be absorbed preferentially in a passive manner
through membranes.
Thus for acidic drugs absorption is favoured in acidic
environment and for basic drugs in basic environment.
The release of an ionisable drug must be programmed
in accordance with the pΗ variations across the GIT.
Drug existing largely in ionized forms are poor
candidates for sustained release.
Ex: Hexamethonium.

12.  It is defined as the ratio of drug in oil
phase to that in aqueous phase.
 K=CO /CW
 Where,
 CO =equilibrium concentration of drug in
organic phase.
 CW = equilibrium concentration of drug in
aqueous phase.
 Drugs with extremely high partition coefficient(oil
soluble) readily penetrates the membranes,but are
unable to proceed further.But drugs with high aqueous
solubility cannont penetrate the membranes.
 A balance in K is needed to give an optimum
permeation through the biological membranes


13. According to Hansch correlation a parabolic relationship
between log of K with that of the log of its activity or
ability to be absorbed .
log
activity.
log K
 Drugs unstable in gastric pΗ/GI environment cannot be
administered as oral CR formulation because of
bioavailability problems
ex:Nitroglycerine.

14.  orally administered drugs can be
subjected to both acid-base hydrolysis and
enzymatic degradation.
 Hence they may be designed considering their
transit in the GIT.
 Localized delivery can be attained by bioadhesive
drug delivery systems and can act as reservoir of
drugs thus enhancing their bioavailability.
 Drugs may be protected by incorporation in a
polymer matrix.
 Prodrug concept is also used in designing
sustained release drug formulations.

15.  Drug protein binding can serve as a depot
for drug producing a prolonged release profile,
especially if a high degree of drug binding occurs.
 Drugs bound to mucin may increase absorption, if
the bound drug acts as a depot.
 Drugs are plasma protein bound and their
distribution into extra vascular space is governed
by equilibrium process of dissociation of drug
from protein.
 In general charged compounds have a greater
tendency to bind a protein.
Eg; 95% PPB of drugs are Diazepam,Dicoumal.

16. The ability of a drug to diffuse through
membranes is so called diffusivity.
 Diffusivity is directly proportional to
molecular weight and inversely proportional
to molecular volume.
 Large molecular weight-absorption is slower.
 Smaller molecular weight-absorption is
faster.

17. LogD=Sv logV˖Kv
= Sm logM˖Km
Where,
D=Diffusivity
V=Molecular volume
M=Molecular weight
Sv, Kv, Km, Sm = Constant
The normal range of molecular weight is
150-400.

18. For oral dosage form a dose size of
0.5-1.80g is considered maximal. Higher
doses have to be given as liquids.

19.  The three major drug characteristics that determine
the permeability of drugs for passive transport across
intestinal epithelium are:
 Lipophilicity expressed as log k(o/w)
 Polarity of drug which is measured by the number of
unionized drug molecules.
 Molecular size
 The properties interelate with above mentioned
properties which influence drug selection for CDDS

20.  The pka range for acidic drugs whose
ionisation is pH sensitive is 3.0 to 7.5 and
that for basic drugs is 7.0 to 11.0
 For optimum passive absorption, the drug
should be ionised at that site at least to an
extent 0.1 to 5%
 Drug existing largely in ionised forms are
poor candidates for controlled delivery.

21.  Drug absorbed by carrier mediated transport
process and those absorbed through a
window are poor candidates for CDDS
eg:several B vitamins.

22. THANK YOU