Mehta et al Asian Journal of Pharmaceutical Research and Development.

2021; 9(3): 112-117

Available online on 15.06.2021 at http://ajprd.com

Asian Journal of Pharmaceutical Research and Development

Open Access to Pharmaceutical and Medical Research
© 2013-20, publisher and licensee AJPRD, This is an Open Access article which permits unrestricted non-
commercial use, provided the original work is properly cited

Open Access Review Article

Sustained Release Matrix Tablet: An Overview
Mandev Mehta*, H.S Keerthy, Rajkumar Prasad Yadav
Department of Pharmaceutics, Mallige College of Pharmacy, Bangalore-560090, Karnataka, India

ABSTRACT

Sustained Release is also a promising method for reducing medication side effects by preventing the therapeutic concentration
of the drug from fluctuating in the body. The basic rationale of a sustained drug delivery system is to optimise a drug's
biopharmaceutical, pharmacokinetic, and pharmacodynamic properties in order to maximise utility, minimise side effects, and
cure the disease. The drug release rate is regulated by the matrix. HPMC and other release retardants can help with sustained
release, so they are used as a key excipient in the formulation. The method entails compressing a mixture of medication,
retardant material, and additives directly to shape a tablet with the drug embedded in a retardant matrix core; instead,
granulation may be done prior to compression. Hydrophilic, hydrophobic, mineral, and biodegradable matrices may be used. To
assess the drug release rate, in-vitro dissolution tests may be used. The primary goal of continuous release types is to improve
drug therapy, which is determined by the relationship between the advantages and disadvantages of using one.
Keywords: Sustained release, Mechanism of drug release, Matrix tablet, Drug properties

A R T I C L E I N F O: Received 26 Jan. 2021; Review Complete; 20 March 2021 Accepted; 13 May 2021 Available online 15 June. 2021
Cite this article as:
Mehta M, Keerthy H.S, Yadav RP, Sustain Release Matrix Tablet: An overview, Asian Journal of Pharmaceutical Research and
Development. 2021; 9(3):112-117. DOI: http://dx.doi.org/10.22270/ajprd.v9i3.954

*Address for Correspondence:

Mandev Mehta, Department of Pharmaceutics, Mallige College of Pharmacy, Bangalore-560090, Karnataka, India

INTRODUCTION fixed rate while retaining a constant drug level for a set
period of time with the least amount of side effects. The

S
ustained-release pharmaceuticals have become a very
basic premise of a controlled release drug delivery system
valuable tool in medical practice, providing patients
is to maximize a drug's utility by optimizing its
with a wide variety of real and perceived benefits.
biopharmaceutical, pharmacokinetic, and
Sustained release is also a promising way to reduce
pharmacodynamic properties, side effects are eliminated,
medication side effects by stopping the therapeutic
and the disease is cured or controlled in the shortest time
concentration of the drug in the body from fluctuating. The
possible by using the smallest amount of medication
traditional dosage types of drugs are increasingly being
delivered by the most appropriate route.4
phased out in favor of modern and innovative drug delivery
systems .In modern therapeutics, the controlled Sustain release:
release/sustained release dosage forms have become
Sustained-release pharmaceuticals have become a very
extremely popular. The matrix system is a release system
valuable tool in medical practice, providing patients with a
that prolongs and controls the release of a drug that has
wide variety of real and perceived benefits.
been dissolved or dispersed.1The oral route is the most
common route for drug administration, owing to its ease of Oral sustained-release matrix dosage type objectives:
use and the fact that it is the least expensive. The term  To maintain a constant drug concentration for a
"Drug Delivery" encompasses a wide range of techniques specified period of time.
used to deliver therapeutic agents into the human body.  As opposed to traditional drug forms, to minimize the
Drug administration's ultimate goal is to cure patient number of doses administered.
illnesses. Drugs are never given in their pure form; instead,  It should carry the active ingredient directly to the site
they are transformed into a suitable formulation. 3Sustained- of action, with minimal or no side effects.
release dosage forms are designed to release a drug at a
ISSN: 2320-4850 [112] CODEN (USA): AJPRHS
Mehta et al Asian Journal of Pharmaceutical Research and Development. 2021; 9(3): 112-117

 This may necessitate targeting specific receptors or never zero-order. The regulated drug delivery systems are
localization to specific cells or body regions. based on the diffusion of a drug molecule through a
 Potent drugs' safety margins can be improved. polymeric membrane.
 In sensitive patients, the incidence of both local and b. Dissolution-controlled release systems:
systemic adverse side effects can be reduced.
Dissolution-controlled release can be achieved by slowing
Advantages the dissolution rate of a drug in the GI medium,
 Intakes are being reduced in frequency incorporating the drug in an insoluble polymer, and coating
 Side effects should be minimised. drug particles or granules with polymeric materials of
 Drug release that is consistent over time. varying thicknessThe rate limiting step for dissolution of a
drug is the diffusion across the aqueous boundary layer.
 Patient compliance is improved.
The solubility of the substance provides the source of
Disadvantages energy for drug release, which is countered by the stagnant-
fluid diffusional boundary layer. The following equation
 It does not allow for a quick end to therapy
can be used to approximate the rate of dissolution (dm/dt):
 Dose change versatility is restricted.
 The average biological half-life is used to design these dm/dt = ADS/h………….(1)
dosage types. Where,
 They are pricey.
A = Surface area of the dissolving particle or tablet
D = Diffusivity of the drug S = Aqueous solubility of the
drug
h = Thickness of the boundary layer
The two types of dissolution-controlled release are:
Matrix (or monolith) dissolution controlled systems
The medication is suspended in an insoluble matrix of
swellable hydrophobic or hydrophilic materials.
Classification of sustained release drug delivery
Reservoir dissolution controlled systems
system1,3
This mechanism is hollow, with an inner drug core encased
Classification of oral Sustained or Controlled Release
in a water-insoluble polymer membrane.
Systems The controlled release systems for oral use are
mostly solids and are controlled by dissolution, diffusion,
or a combination of both mechanisms. Based on how drugs
are published, these systems are listed as follows:
1. System of continuous release
2. Mechanisms of delayed transit and continuous release
3. Systems with a delayed release
1. Continuous release systems:
Through standard transportation of the dosage type,
continuous release systems release the drug for a prolonged
period of time over the entire length of the gastrointestinal
tract. The following are the different systems that fall into
this category:
a. Diffusion controlled release systems
b. Dissolution controlled release systems
c. Dissolution and diffusion controlled release systems
d. Ion exchange resin- drug complexes
e. pH-independent formulation
f. Osmotic pressure controlled systems.
a. Diffusion controlled release systems:
The rate-limiting step in these systems is the diffusion of
dissolved drug through a polymeric barrier. Since the Figure 2: Matrix system and Reservoir system
diffusional path length increases over time as the insoluble
matrix is steadily depleted of drug, the drug release rate is

ISSN: 2320-4850 [113] CODEN (USA): AJPRHS

Mehta et al Asian Journal of Pharmaceutical Research and Development. 2021; 9(3): 112-117

c. Dissolution and diffusion controlled release systems  Intestinal release systems

The drug centre is encased in a partially soluble membrane  Colonic release systems.
in such systems. Pores are formed when sections of the Various Mechanisms of Medicament Release1
membrane dissolve, allowing aqueous medium into the
centre and thus drug dissolution, as well as the diffusion of 1.Diffusion is rate limiting:
dissolved drug out of the system. Diffusion is the process by which drug molecules travel
d. Ion exchange resin-drug complexes: from a high concentration in the tablet to a lower
concentration in the gastro intestinal fluids. This movement
It is based on the formulation of a drug-resin complex that is determined by the amount of surface area exposed to
forms when an ionic solution comes into contact with ionic gastric fluid, the diffusion pathway, the drug concentration
resins. The drug in this complex is exchanged in the gradient, and the system's diffusion coefficient. We may
gastrointestinal tract and released when there is an excess of use any of the two approaches in operation.
Na+ and Cl present in most cases, an insoluble cross linked
polymer resin is used in this system. They have a salt- The drug is formulated in an insoluble matrix:
forming function group in a polymer chain that repeats. The drug is released through diffusion after the gastric fluid
e. pH-independent formulation: penetrates the dosage form and dissolves the medication.

Because the majority of drugs are weak acids or bases, their The drug particles are coated with a given thickness
release from sustained release formulations is pH- polymer, allowing a portion of the drug to slowly diffuse
dependent. However, a buffer can be added to the through the polymer and retain a constant drug level in the
formulation, such as citric acid salt, amino acid, or tartaric bloodstream.
acid, to help maintain a constant pH by delaying pH- Dissolution is rate limiting:
dependent drug release. Mixing a simple or acidic drug
with one or more buffering agents, granulating with Drugs with low water solubility (BCS class II and IV) have
sufficient excipients, and coating with gastrointestinal fluid a built-in sustained release mechanism. Water-soluble
permeable film forming polymer results in a buffer retain medications, on the other hand. It is possible to use a water
release formulation. As gastrointestinal fluid passes through insoluble carrier to avoid drug dissolution when the drug
the membrane, the buffering agent changes the pH of the particles are covered with this form of material, such as
fluid within, resulting in a steady rate of drug absorption polyethylene glycol. Polyethylene Glycol is a type of
release. plastic. To support delayed release, it is possible to forego
the use of a disintegrating agent.
f. Osmotic pressure controlled systems:
Osmotic pressure is rate limiting:
A semipermeable membrane is placed around the tablet,
particle, or drug solution to allow water to enter the tablet, Osmosis is a process in which liquid flows from a lower
with drug solution eventually being pumped out through a concentration to a higher concentration through a
small delivery aperture in the tablet centered. The following semipermeable membrane that allows only liquid to pass
are two types of osmotic pressure-controlled systems: a. through. The entire drug is covered with a semipermeable
With drug b, Type 1 has an osmotic core. Type 2 contains membrane, with a laser-cut hole on one end of the pill.
the drug in a flexible bag with an osmotic core surrounding Matrix Tablets
it. By optimising the formulation and processing factors, an
osmotic system can be developed to deliver a variety of The active and inactive ingredients in a matrix system are
drugs at a predetermined rate. homogeneously dispersed and mixed in the dosage form.
The matrix systems are by far the most popular oral
Delayed transit and continuous release systems: extended release technology, and their popularity can be
These systems are designed to keep them in the GI tract for attributed to a number of factors. Fick's first law of
a longer period of time after they have been written. This diffusion governs the release of matrix type
category includes mucoadhesive and size-based systems, formulationsMatrix systems are commonly used to achieve
which are designed to detain in the stomach and therefore long-term release. It is the release system that controls and
contain a medication that is stable at gastric pH. prolongs the release of the dissolved or dispersed drug. A
matrix is a well-mixed composite of one or more drugs and
Delayed release systems: a gelling agent, such as hydrophilic polymersThe sustained
Drug release is limited to a specific position in the GIT due release approach allows for therapeutically efficient
to the nature of such systems. The following drugs can be accumulation in the systemic circulation over a longer
contained in such a device: period of time, resulting in greater patient compliance.

 Known to cause gastric distress Classification of Matrix Tablets:12

 Destroyed On the Basis of Retardant Material Used: Matrix tablets can
 Meant to extent local effect at a specific GI sit be divided in to 5 types
 Absorbed from a specific intestinal site The two types
of delayed release systems are:

ISSN: 2320-4850 [114] CODEN (USA): AJPRHS

Mehta et al Asian Journal of Pharmaceutical Research and Development. 2021; 9(3): 112-117

Hydrophobic Matrices (Plastic matrices): Mineral Matrices:

In 1959, the idea of using hydrophobic or inert materials as These are made up of polymers derived from different
matrix materials was introduced for the first time. The drug seaweed plants. Alginic acid, for example, is a hydrophilic
is mixed with an inert or hydrophobic polymer and then carbohydrate derived from algae.
compressed into a tablet in this method of obtaining
On the Basis of Porosity of Matrix14
sustained release from an oral dosage form. The dissolving
drug diffuses through a network of channels that exist In this the drug molecules diffuse across the matrix and
between compacted polymer particles, resulting in produce sustained release. The matrix is further divided into
sustained release .Polyethylene, polyvinyl chloride, ethyl 3 types.
cellulose, and acrylate polymers and copolymers are
examples of materials that have been used as inert or Macro porous systems:
hydrophobic matrices. This type of matrix has pores that are larger than the
Lipid Matrices: diffusant molecule dimension, ranging from 0.1m to 1m.
Drug permeation occurs through these pores in this type of
Lipid waxes and other materials were used to create these system.
matrices. Both pore diffusion and erosion are used to
release drugs from these matrices. As a consequence, the Micro porous systems:
structure of digestive fluid is more susceptible to release Drug molecules pass into pores with diameters ranging
characteristics than a completely insoluble polymer matrix. from 50 to 200 microns.
Carnauba wax has been used in several continuous release
formulations in conjunction with stearyl alcohol or stearic Non-porous systems:
acid retardant base. There are no pores in these structures. Molecule diffusion is
Hydrophilic Matrices: mediated by network meshes. The polymeric phase is
present, but there is no pore phase.
Because of their versatility in achieving a desired drug
release profile, cost effectiveness, and strong regulatory Mechanism of Drug Release from Matrix Tablet: 12
acceptance, hydrophilic polymer matrix systems are The drug in the bathing solution-exposed outer layer
commonly used in oral regulated delivery. The preparation dissolves first, then diffuses out of the matrix. The interface
of medicines in gelatinous capsules or, more often, between the bathing solution and the solid drug moves
tablets.In the field of controlled release, using hydrophilic toward the interior as this step progresses. The following
polymers with high gelling capacities as base excipients is assumptions are made during the creation of the
of particular interest.Infecting a matrix is a well-mixed mathematical model that will be used to explain this
composite of one or more drugs with a gelling agent system:
(hydrophilic polymer). These systems are known as
swellable controlled release systems. Hydrophilic matrices a) During drug release, a pseudo-steady state is maintained;
are made from three different types of polymers. b) the diameter of the drug particles is smaller than the
Cellulose derivatives average distance of drug diffusion through the matrix.
Sodium carboxy methylcellulose; Methylcellulose 400 and c) The bathing solution maintains sink conditions at all
4000cPs; Hydroxy ethyl cellulose; Hydroxy propyl times. The system's release behaviour can be
methylcellulose (HPMC) 25, 100, 4000, and 15000cPs; and mathematically explained using the equation below.
Hydroxy propyl methyl cellulose (HPMC) 25, 100, 4000,
and 15000cPs dM/dh = Co. dh - Cs/2 ……………… (2)
Where,
Non cellulose natural or semi synthetic polymers: Agar-
Agar; Carob gum; Alginates; Molasses; Polysaccharides of dM = Change in the amount of drug released per unit area
mannose and galactose, Chitosan and Modified starches. dh = Change in the thickness of the zone of matrix that has
Biodegradable Matrices: been depleted of drug
These are polymers that are made up of monomers joined Co = Total amount of drug in a unit volume of matrix Cs =
together by functional groups and have a backbone with an Saturated concentration of the drug within the matrix.
unstable linkage. They are biologically degraded or eroded
into oligomers and monomers that can be metabolized or Additionally, according to diffusion theory:
excreted by enzymes generated by surrounding living cells dM = ( Dm. Cs / h) dt........................... (3)
or by no enzymatic processes. Natural polymers like
proteins and polysaccharides, as well as modified natural Where,
polymers and synthetic polymers like aliphatic poly (esters) Dm = Diffusion coefficient in the matrix.
and poly anhydrides, are examples.
h = Thickness of the drug-depleted matrix
dt = Change in time

ISSN: 2320-4850 [115] CODEN (USA): AJPRHS

Mehta et al Asian Journal of Pharmaceutical Research and Development. 2021; 9(3): 112-117

By combining equation 1 and equation 2 and integrating: • Solubility of the drug

M = [Cs. Dm (2Co −Cs) t] ½ ……………… (4) Different Polymers Used in Sustained Release DDS7
When the amount of drug is in excess of the saturation Hydrogels:Polyhydroxy ethyl methyl acrylate (PHEMA),
concentration then: Cross-linked polyvinyl alcohol (PVA) ,Cross-linked
polyvinyl pyrrolidone (PVP), Polyethyleneoxide (PEO)
M = [2Cs.Dm.Co.t] 1/2 ……………………… (5)
Soluble Polymers:Polyethylene glycol (PEG),Polyvinyl
The sum of drug released is related to the square-root of
alcohol (PVA), Polyvinyl pyrrolidone (PVP), Hydroxy
time in equations 3 and 4. As a consequence, if a system is
propyl methyl cellulose (HPMC)
primarily diffusion regulated, a plot of drug release vs.
square root of time is expected to yield a straight line. A Biodegradables Polymers:Polylactic acid (PLA),
porous monolithic matrix allows drugs to be Polyglycolic acid (PGA), Polycaprolactone (PLA),
released.involves drug penetration, dissolution, and Polyanhydrides
leaching out of the drug through tortuous interstitial
Non-Biodegradeble Polymers: Polyethylene vinyl acetate
channels and pores all at the same time. In the case of drug
(PVA),Polydimethyl siloxane (PDS), Polyetherurethane
release from a porous or granular matrix, the volume and
(PEU), Polyvinyl chloride (PVC)
duration of the openings must be taken into account:
Mucoadhesive Polymers: Polycarbophil, Sodium
M = [Ds. Ca. p/T. (2Co – p.Ca) t] 1/2 ……………. (6)
carboxymethyl cellulose, Polyacrilic acid, Methyl cellulose
Where,
Factor affecting of sustained release drug delivery
p = Porosity of the matrix system[1,2,6,7]
t = Tortuosity Biological Factors
Ca = solubility of the drug in the release medium Biological half-life:
Ds = Diffusion coefficient in the release medium. Short-half-life therapeutics are ideal candidates for
sustained-release formulations because they can minimise
T = Diffusional path length
dosing frequency.
For pseudo steady state, the equation can be written as:
Absorption:
M = [2D.Ca .Co (p/T) t] ½ ……………………….. (7)
The absorption rate constant is a fictitious rate constant that
The total porosity of the matrix can be calculated with the should be the drug's release rate constant from the dosage
following equation: form. Sustained-release preparations may be detrimental to
absorptions if a drug is absorbed by active transport or if
p = pa + Ca/ ρ + Cex / ρex ……………………… (8) transport is restricted to a particular region of the intestine.
Where,
Metabolism:
p = Porosity
Slower-releasing dosage types can have poorer
ρ = Drug density bioavailability for drugs that are substantially metabolised
before absorption, either in the lumen or tissue of the
pa = Porosity due to air pockets in the matrix intestine. The majority of intestinal enzyme systems are
ρex = Density of the water soluble excipients saturable. Since the drug is released at a slower rate in these
areas, there is a lower overall dose. During a particular
Cex = Concentration of water soluble excipients time, the drug is exposed to the enzymatic process,
For the purpose of data treatment, equation 7 can be allowing for a more complete conversion of the drug to its
reduced to: metabolite.
M = k. t 1/2 ………………………. (9) Distribution:
Where, Drugs with a large apparent amount of distribution, which
affects the rate of drug removal, are poor candidates for the
k = a constant, so that the amount of drug released versus oral SR drug delivery system, for example. Chloroquine is a
the square root of time will be linear, if the release of drug medication that is used to prevent malaria.
from matrix is diffusion-controlled. The following
parameters are Protein Binding:2
• Initial concentration of drug in the matrix The Pharmacological response of drug depends on drug
concentration drug rather than total concentration and all
• Porosity drug bound to some extent to plasma and or tissue proteins.
• Tortuosity Proteins binding of drug play a significant role in its
therapeutic effect regardless the type of dosage form as
• Polymer system forming the matrix extensive binding to plasma increase biological half-life

ISSN: 2320-4850 [116] CODEN (USA): AJPRHS

Mehta et al Asian Journal of Pharmaceutical Research and Development. 2021; 9(3): 112-117

and thus sometimes SR drug delivery systemis not required In many sustained-release systems, drugs must diffuse
for this type of drug. through a rate-controlling membrane or matrix. The
molecular size of a drug determines its ability to disperse
Margin of safety:
across membranes (diffusion coefficient) (or molecular
As we all know, the higher the therapeutic index rating, the weight). The importance of diffusivity is influenced
better the medication. Due to technical limitations in significantly. In polymers, the letter 'D' represents the
control over release speeds, drugs with a lower therapeutic diffusing species' molecular size.
index are typically poor candidates for formulation of an
Stability:
oral SR drug delivery system. 2
Both acid-base hydrolysis and enzymatic degradation can
Physicochemical factors[2,3,6,7,8,12]
occur when drugs are taken orally. Systems that prolong
Dose Size: distribution over the entire duration of transit in the GI tract
are useful for drugs that are unstable in the stomach.
A single dose of 0.5–1.0 g is generally considered the Compounds that are unstable in the small intestine may
maximum for a traditional dosage type. This is also
have lower bioavailability when delivered from a sustaining
applicable in the case of long-acting medication
dosage type.
formulations. Another factor to consider is the margin of
protection that comes with administering massive doses of CONCLUSION:
a medication with a limited therapeutic range.
This review article focuses on the formulation of sustained-
Ionization, pKa and aqueous solubility: release matrix tablets, patient compliance, and the efficacy
of the dosage form in eliciting the desired therapeutic
The majority of medications are weak acids or bases. Since
response, as well as problems associated with traditional
the unchanged form of a drug preferentially permeates
dosage forms. The term "sustained release" refers to a
through lipid membranes, the relationship between the
drug's gradual release over time. Sustain released
compound's pKa and the absorptive environment is critical. formulations can be controlled or uncontrolled.
The solubility of the drug in the aqueous media will be
critical for delivery systems that depend on diffusion or REFERENCE:
dissolutionMost of the drug will arrive in the small intestine 1. Parashar T, Soniya, Singh V, Singh G , Tyagi S , Patel C , Gupta G.
in solid form for dissolution or diffusion sustaining forms, Novel oral sustained release technology: A concise review. Int. J. Res.
meaning that the drug's solubility can change by several Dev. Pharm. L. Sci. 2013; 2(2):262-9.
orders of magnitude during its release. The solubility of a 2. Rao N. G. R, Raj K. R, P, Nayak B. S. Review on matrix tablet as
sustained Release. Int J Pharm Res All Sci. (2013); 2(3):1-17.
drug formulated in a sustained release system must be less 3. Agarwal G,Agarwal S, Karar P.K, Goyal S. Oral sustained release
than 0.1 mg/ml, according to reports. tablets: An Overview with a Special Emphasis on matrix tablet. Ame J
Adv Drug Deliv. 2017;5(2):64-76.
Partition coefficient: 4. Alli P.R, PratimaB. Bargaje, Nilesh S. Mhaske. Sustained selease drug
delivery system: A Modern Formulation Approach. Asian J Pharm
Compounds with a high partition coefficient are often lipid- Tech Innov. 2016;4(17): 108 –18.
soluble and, as a result, have very low aqueous solubility. 5. Lokhande S.S, Phalke N. N, Badadare S. S. A review On: Sustained
Furthermore, since these compounds can localise in the release technology. World J Pharma Med Res.2019;5(11):60-65
lipid membranes of cells, they can normally remain in the 6. Zalte H.D, Saudagar R.B. Review on sustained release matrix tablet.
Int JPharm Bio Sci.2013;3(4):17-29
body for long periods of time.This means that the drug's 7. Gupta M.M., Ray B. A review On: Sustained release technology. Int J
solubility can change by several orders of magnitude as it is of Thera Appl.2012;8:18 – 23.
released. The solubility of a drug formulated in a sustained 8. Mandhar P, Joshi G. Development ofsustained release drug delivery
release system must be less than 0.1 mg/ml, according to system: A review. Asian Pac. J. Health Sci., 2015; 2(1):179-85.
9. Kambampati S, J. N. Suresh Kumar., C.H Sriram. A Review on
reports. Sustained Release Drug Delivery System.Int J Res Pharma and Nano
Sci. 2013; 2(4):441 - 47.
K = C0/CW 10. Bose s, Kaur A, Sharma S. K. A review on advances of sustained
release drug delivery system. Int J Res Pharm.2013;4(6):1-5.
Where,
11. Patel N, Chaudhary A, Twinkle S, MehulS, Jain H , Upadhyay U.
Co = Equilibrium concentration of all forms of the drug Controlled drug delivery system: A review. Indo Ame JPharm Sci.
2016;3(3):227-33.
e.g. ionized and unionized in an organic phase at 12. Pareek S P, Kumawat S , Sharma V, Sharma D , Rathore D. S ,
equilibrium. Agarwal M. Review on sustained release technology. Int J Pharm Bio
Sci Archive. 2019;7(6): 29-38.
Cw = Equilibrium concentration of all forms in aqueous 13. Patel H, Dhrupesh R. Panchal, Patel U, Brahmbhatt T, Sutha M.
phase. Matrix type drug delivery system: A Review. JPharm Sci Bio Res.
2011;1(3):143-51.
Molecular size and diffusivity: 14. Kumar A.R, Aeila A.S.S. Sustained release matrix type drug delivery
system: An overview. World J Pharm Pharm Sci,2019;8(12):470-80.

ISSN: 2320-4850 [117] CODEN (USA): AJPRHS