MICROPHERES

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Raghavendra Institute of Pharmaceutical Education and Research - Autonomous
K.R.PalliCross, Chiyyedu, Anantapuramu, A. P- 515721 1
Microspheres
1
A Seminar as a part of curricular requirement
for I year M. Pharm II semester
Presented by
Mr B Venkatesh
(Reg. No. 20L81S0301)
Under the guidance/Mentorship of
Dr CH Pavan Kumar., M. Pharm., PhD
Associate Professor & Head
Dept. of Pharmaceutics

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• Introduction
• Types of microspheres
• Methods of preparation of microspheres
• Evaluation of microspheres
• Applications
• Conclusion
• References
Contents

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MICROSPHERE
• Microsphere are solid spherical particles ranging from
1-1000μm(or 50nm to 2mm).
• They are spherical free flowing particles consisting of proteins or synthetic
polymers.
• In some cases microspheres are also known as micro particles.
• These can be produced from several natural and synthetic polymeric
materials or even from inorganic materials.
Introduction

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There are two types of microspheres;
Microcapsules
Entrapped substance is distinctly surrounded by distinct capsule
Micromatrices
Entrapped substance is dispersing throughout the microspheres
matrix

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Introduction

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Polymersused in microspheres
preparation
Polymers used in the preparationof microspheres
Naturalpolymers
Proteins
Albumin
Gelatin
collagen
Carbodydrates
Starch
Agarose
Chitosan
Synthetic polymers
Biodegradable
Lactides
Glycosides
Non
biodegradable
PMMA
Epoxy polymers

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Types of
Microspheres
Bioadhesive
microspheres
Magnetic
microspheres
Floating
microspheres
polymeric
microspheres
Mucoadhesive
microspheres
Radioactive
microspheres
Typesof Microspheres
Biodegradable
polymeric
microspheres
Synthetic
polymeric
microspheres

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• Enhance solubility of the poorly soluble drug.
• Provide constant drug concentration in blood which can increase patient
compliance.
• Better drug utilization will improve the bioavailability and reduce the
incidence or intensity of adverse effects.
• Controlled release delivery biodegradable microspheres are used to
control drug release rates thereby decreasing toxic side effects, and
eliminating the inconvenience of repeated injections.
• Reliable means to deliver the drug to the target site with specificity.
Advantagesof microspheres

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• The costs of the materials and processing of the controlled release
preparation are substantially higher than those of standard formulations.
• Reproducibility is less.
• The modified release from the formulations.
• Difference in the release rate from one dose to another.
Limitationsof microspheres

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• Process conditions like change in temperature, pH, solvent addition and
evaporation/agitation may influence the stability of core particles
encapsulated.
• The main disadvantage of microspheres, are tend to migrate away from
injection site and lead to potential risk, embolism and further organ
damage.
Limitationsof microspheres

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1. BIOADHESION MICROSPHERES
• Adhesion - sticking of drug to the membrane by using the sticking property
of the water soluble polymers.
• Adhesion of drug delivery device to the mucosal membrane such as buccal,
ocular, rectal, nasal etc can be termed as bioadhesion.
• The term “bioadhesion” describes materials that bind to biological
substrates’, such as mucosal members.

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• Mechanism - Adhesion of Bioadhesive drug delivery devices to the
mucosal tissue offers the possibility of creating an intimate and prolonged
contact at the site of administration which result in enhanced absorption
and in combination with a controlled release of drug.
• Microspheres constitute an important part of these particulate drug
delivery systems by virtue of their small size and efficient carrier capacity.

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2. MAGNETIC MICROSPHERES
• Localises the drug to the disease site.
• Mechanism - Larger amount of freely circulating drug can be replaced
by smaller amount of magnetically targeted drug.
• Magnetic carriers receive magnetic responses to a magnetic field from
incorporated materials that are used for magnetic microspheres are
chitosan, dextran etc.

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• The different types of therapeutic magnetic microspheres are used to
deliver chemotherapeutic agent to liver tumour.
• Drugs like proteins and peptides can also be targeted through this system.

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3. FLOATING MICROSPHERES
• In floating types the bulk density is less than the gastric fluid and so
remains buoyant in stomach without affecting gastric emptying rate.
• The drug is released slowly at the desired rate, if the system is floating on
gastric content, increases gastric residence and fluctuation in plasma
concentration.

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• It also reduces chances of striking and dose dumping and produces
prolonged therapeutic effect.
• Drug (ketoprofen) given through this form.

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4. POLYMERIC MICROSPHERES
• The different types of polymeric microspheres can be classified as :
a) Biodegradable polymeric microspheres
b) Synthetic polymeric microspheres
a) Biodegradable polymeric microspheres:
• Natural polymers such as starch are used with the concept that they
are biodegradable, biocompatible, and also bioadhesive in nature.

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Mechanism - Biodegradable polymers prolongs the residence time when
contact with mucous membrane due to its high degree of swelling
property with aqueous medium, results gel formation.
• The rate and extent of drug release is controlled by concentration of
polymer and the release pattern in a sustained manner.
• Drawback - in clinical use drug loading efficiency of biodegradable
microspheres is complex and is difficult to control the drug release.

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b) Synthetic polymeric microspheres:
• Synthetic polymeric microspheres are widely used in clinical application,
that are also used as bulking agent, fillers, embolic particles and drug
delivery vehicles etc.
• They are proved to be safe and biocompatible.
• Disadvantage of these kind of microspheres, are tend to migrate away
from injection site and lead to potential risk, embolism ,further organ
damage.

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5. MUCOADHESIVE MICROSPHERES
• 1-1000mm in diameter and consisting either entirely of a
mucoadhesive polymer or having an outer coating of it
• Advantages - efficient absorption and enhanced bioavailability of the
drugs due to a high surface to volume ratio, a much more intimate contact
with the mucus layer, specific targeting of drug to the absorption site
• Mucoadhesive microspheres can be adhere to any mucosal tissue
including those found in eye, nasal cavity, urinary and gastrointestinal
tract, thus offering the possibilities of localized as well as systemic
controlled release of drugs.

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6. RADIOACTIVE MICROSPHERES
• Radio emobilisation therapy microspheres sized 10-30 nm are of larger
than capillaries and gets tapped in first capillary bed when they come
across.
• They are injected to the arteries that lead to tumour of interest.
• So these radioactive microspheres deliver high radiation dose to the
targeted areas without damaging the normal surrounding tissues.

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•Different types of radioactive microspheres are α emitters, β emitters,
γ emitters.

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Factors that influencing method of preparation of
microspheres
Particle size requirement
The drug or the protein shouln’t be adversely affected by the process
Reproducibility of the release profile and the method
No stability problem
There should be no toxic products associated with the final product
Methodof preparationof microspheres

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Preparation
of
microspheres
should satisfy
these criteria
The abilityto incorporate
reasonablyhigh
concentrations ofthe drug.
Stabilityofthe
preparation after
synthesis with a clinically
acceptable shelflife.
Release of active
reagent with a good
control over a wide
time scale.
Controlledparticle
size and dispersibility
in aqueous vehicles
for injection.
Biocompatibilitywith a
controllable
biodegradability
Susceptibilityto chemical
modification.

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METHODS OF PREPERATION
1. Emulsion solvent evaporation technique
2. Double Emulsion technique
3. Polymerization technique
4. Phase separation coacervation technique
5. Spray drying - Spray congealing technique
6. Solvent extraction

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1. EMULSION SOLVENT EVAPORATION TECHNIQUE
• The microparticulate carriers of natural polymers, i.e. those of proteins
and carbohydrates are prepared by single emulsion technique.
• The natural polymers are dissolved or dispersed in aqueous medium
followed by dispersion in the non-aqueous medium e.g., oil.
• In the second step of preparation, cross-linking can be achieved either
by means of heat or by using the chemical cross linkers.

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• The chemical cross-linking agents used include glutaraldehyde,
formaldehyde, terephthaloyl chloride, diacid chloride, etc.
• Disadvantage - excessive exposure of active ingredient to chemicals if
added at the time of preparation.
• Cross linking by heat is affected by adding the dispersion to previously
heated oil.
• Disadvantage - not suitable for the thermo labile drugs due to heat
denaturation.

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2. DOUBLE EMULSION TECHNIQUE
• Double emulsion method of microspheres preparation involves the
formation of multiple emulsions or double emulsion of type w/o/w.
• It is best suited to the water soluble drugs, peptides, proteins and the
vaccines.
• This method can be used with both the natural as well as synthetic
polymers.
• The aqueous solution is dispersed in a lipophilic organic continuous
phase.
• This protein solution may contain the active constituents.

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• The continuous phase is generally consisted of the polymer solution
that eventually encapsulates of the protein contained in dispersed
aqueous phase.
• The primary emulsion is then subjected to the homogenization or the
sonication before addition to the aqueous solution of the poly vinyl
alcohol (PVA).
• This results in the formation of a double emulsion.
• The emulsion is then subjected to solvent removal either by solvent
evaporation or by solvent extraction process.

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• The solvent evaporation is carried out by maintaining emulsion at reduced
pressure or by stirring the emulsion so that the organic phase evaporates
out.
• Then, the emulsion is added to the large quantity of water (with or
without surfactant) into which organic phase diffuses out.
• The solid microspheres are subsequently obtained by filtration and
washing.
• A number of hydrophilic drugs like leutinizing hormone releasing
hormone (LH-RH) agonists, vaccines, protein/ peptides are incorporated in
to the microspheres using this method.

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3. POLYMERIZATION TECHNIQUES
• The polymerization techniques conventionally used for the preparation
of the microspheres are normally classified as:
a) Normal polymerization
b) Interfacial polymerization
a) Normal polymerization:
• Normal polymerization proceeds and carried out using different
techniques as bulk, suspension, precipitation, emulsion and miceller
polymerization process.

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• Suspension and emulsion polymerization can be carried out at lower
temperature, since continuous external phase is normally water
through which heat can easily evaporated.
• The two processes also lead to the formation of the higher molecular
weight polymer at relatively faster rate.
• The major disadvantage of suspension and emulsion polymerization is
association of polymer with the unreacted monomer and other
additives.

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b) INTERFACIAL POLYMERIZATION:
• It involves reaction of various monomers at the interface between the
two immiscible liquid phases to form a film of polymer that essentially
envelops the dispersed phase.
• In this technique two reacting monomers are employed; one of which
is dissolved in the continuous phase while the other being dispersed
in continuous phase.
• The monomers present in either phases diffuse rapidly and polymerize
rapidly at interface.

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• Two conditions arise depending upon the solubility of formed polymer
in the emulsion droplet.
• If the polymer is soluble in droplet it will lead to the formation of the
monolithic type of carrier.
• If the polymer is insoluble in the monomer droplet, the formed carrier is
of capsular (reservoir) type.

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The interfacial polymerization is not widely used in the preparation of
the microparticles because of certain drawbacks, which are
associated with the process such as:
✓Toxicity associated with the unreacted
monomer
✓High permeability of the film
✓High degradation of the drug during
polymerization
✓Fragility of microcapsules
✓Non-biodegradability of the microparticles

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4. PHASE SEPARATION COACERVATION TECHNIQUE
• Phase separation method is specially designed for preparing the
reservoir type of the system, i.e. to encapsulate water soluble drugs
e.g. peptides, proteins, etc.,
• However, some of the preparations are of matrix type particularly,
when the drug is hydrophobic in nature e.g. steroids.
• Principle - decreasing the solubility of the polymer in the organic phase to
affect the formation of polymer rich phase called the coacervates.

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5. SPRAY DRYING AND SPRAY CONGEALING
• It is based on drying of the mist of the polymer and drug in the air.
• Depending upon the removal of the solvent or the cooling of the solution,
the two processes are named the spray drying, spray congealing
respectively.
• The polymer is first dissolved in the suitable volatile organic solvent
such as dichloromethane, acetone, etc.
• The drug in the solid form is then dispersed in the polymer solution under
high speed homogenization.

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• This dispersion is then atomized in a stream of hot air.
• The atomization leads to the formation of small droplets or the fine
mist from which the solvent evaporates instantaneously leading to the
formation of microspheres in a size range 1-100µm.
• Microparticles are separated from the hot air by means of the
cyclone separator while the traces of solvent are removed by vacuum
drying.

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6. SOLVENT EXTRACTION
• Solvent extraction method used for preparation of microparticles,
involves removal of organic phase by extraction of organic solvent.
• The method involves water miscible organic solvents such as
isopropanol.
• Organic phase is removed by extraction with water.
• This process decreases the hardening time for the microspheres.

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• This process involves direct addition of the drug or protein to
polymer organic solution.
• The rate of solvent removal by extraction method depends on
the temperature of water, ratio of emulsion volume to the water
and the solubility profile of the polymer.

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Evaluationof microspheres
PHYSIOCHEMICAL EVALUATION
1. Characterization Particle size and shape
• The most widely used procedures to visualize microparticles are
conventional light microscopy (LM) and scanning electron microscopy
(SEM).
• Both can be used to determining the shape and outer structure of
microparticles.
• LM provides a control over coating parameters in case of double walled
microspheres.

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• The microspheres structures can be
visualized before and after coating
and the change can be measured
microscopically.
• SEM provides higher resolution in contrast
to the LM.
• SEM allows investigations of the microspheres surfaces and after particles
are cross-sectioned.

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• FT-IR is used to determine the degradation of the polymeric matrix of the
carrier system.
• The surface of the microspheres is investigated measuring alternated total
reflectance (ATR).
• The ATRFT-IR provides information about the surface composition of the
microspheres depending upon manufacturing procedures and conditions.

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2.Density determination
• The density of the microspheres can be measured by using a multi volume
pycnometer.
Accurately weighed sample in a cup is placed into the multi volume pycnometer.
Helium is introducedat a constantpressure in the chamber and allowedto
expand.
This expansionresults in a decrease in pressure within the chamber.

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Two consecutive readings of reduction in pressure at different initialpressure
are noted.
From two pressure readingsthe density of the microsphere carrier is
determined.

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3. Isoelectric point
• The micro electrophoresis is an apparatus used to measure the
electrophoretic mobility of microspheres from which the isoelectric point
can be determined.
• The mean velocity at different pH values ranging from 3-10 is calculated by
measuring the time of particle movement over a distance of 1 mm.
• By using this data the electrical mobility of the particle can be determined.

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4. Entrapment efficiency/Capture efficiency
Microspheres containingof drug (5mg) were crushed.
Dissolve it in distilledwater with the help of ultrasonic stirrer for 3 hr.
Filter it.
Assay the filtrate by UV-visible spectroscopy.

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• Entrapment efficiency is equal to ratio of actual drug content to
theoretical drug content.

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5. Swelling index
Different solution (100mL) were taken such as distilledwater, buffer solution
of pH(1.2, 4.5, 7.4) were taken.
Microspheres (100mg) were placed in a wire basket and kept on the above
solution.
Swelling was allowedat 37 0C and changes in weight variationbetween initial
weight of microspheres and weight due to swelling was measured by taking
weight periodically andsoaking with filter paper.

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6. Surface carboxylic acid residue
• The surface carboxylic acid residue is measured by using radioactive
glycine.
• The radioactive glycine conjugates is prepared by the reaction of C 14-
glycine ethyl ester hydro chloride with the microspheres.
• The radioactivity of the conjugate is then measured using liquid
scintillation counter.
• Thus the carboxylic acid residue can be compared and correlated.

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7. Surface amino acid residue
• Surface associated amino acid residue is determined by the
radioactive C 14-acetic acid conjugate.
• The carboxylic acid residue is measured through the liquid scintillation
counter and hence the amino acid residue can be determined indirectly.

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8. Angle of contact:
• The angle of contact is measured to determine the wetting property
of a micro particulate carrier.
• It determines the nature of microspheres in terms of
hydrophilicity or hydrophobicity.
• It is measured at the solid/air/water interface.
• The angle of contact is measured by placing a droplet in a
circular cell mounted above objective of inverted microscope.
• Contact angle is measured at 200o C within a minute of deposition of
microspheres.

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Drug release
In vitro methods
• In vitro drug release studies have been employed as a quality control
procedure in pharmaceutical production, in product development etc.
• Sensitive and reproducible release data derived from physico-
chemically and hydro dynamically defined conditions are necessary.

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1. Beaker method
• The dosage form in this method is made to adhere at the bottom of the
beaker containing the medium and stirred uniformly using over head
stirrer.
• Volume of the medium used in the literature for the studies varies from
50-500 ml and the stirrer speed form 60-300 rpm.

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2. Interface diffusion system
• This method is developed by Dearden & Tomlinson.
• It consists of four compartments.
• A represents the oral cavity, and initially contained an appropriate
concentration of drug in a buffer.
• The compartment B representing the buccal membrane, contained 1-
octanol.

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• Compartment C representing body fluids, contained 0.2 M HCL.
• The compartment D representing protein binding also contained 1-
octanol.
• Before use, the aqueous phase and 1-octanol were saturated with each
other.
• Samples were withdrawn and returned to compartment A with a
syringe.

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3. Modified Keshary Chien Cell
• A specialized apparatus was designed in the laboratory.
• It comprised of a Keshary Chien cell containing distilled water (50ml) at 37
0C as dissolution medium.
• TMDDS (Trans Membrane Drug Delivery System) was placed in a glass tube
fitted with a 10# sieve at the bottom which reciprocated in the medium at
30 strokes per min.

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4. Dissolution apparatus
• Standard USP or BP dissolution apparatus have been used to study in
vitro release profiles using rotating elements, paddle and basket.
• Dissolution medium used for the study varied from 100-500 ml and
speed of rotation from 50-100 rpm.

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5. Stability studies
• By placing the microspheres in screw capped glass container and
stored them at following conditions:
• Ambient humid condition
• Room temperature (27±2 0C)
• Oven temperature (40±2 0C)
• Refrigerator (5 0C-8 0C).
• It was carried out of a 60 days and the drug content of the microsphere
was analysed.

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In vivo methods
• Methods for studying the permeability of intact mucosa comprise of
techniques that exploit the biological response of the organism locally or
systemically and those that involve direct local measurement of uptake or
accumulation of penetrate at the surface.
• The most widely used methods include in vivo studies using animal
models, buccal absorption tests, and perfusion chambers for studying
drug permeability.

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1. Animal models
• Animal models are used mainly for the screening of the series of
compounds, investigating the mechanisms and usefulness of permeation
enhancers or evaluating a set of formulations.
• In general, the procedure involves anesthetizing the animal followed by
administration of the dosage form.
• In case of rats, the esophagus is ligated to prevent absorption pathways
other than oral mucosa.
• At different time intervals, the blood is withdrawn and analyzed.

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2. Buccal absorption test
• The buccal absorption test was developed by Beckett & Triggs in 1967.
• It is a simple and reliable method for measuring the extent of drug loss of
the human oral cavity for single and multi component mixtures of drugs.
• The test has been successfully used to investigate the relative importance
of drug structure, contact time, initial drug concentration and pH of the
solution while the drug is held in the oral cavity.

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3. In vitro-In vivo correlations
• Correlations between in vitro dissolution rates and the rate and
extent of availability as determined by blood concentration and or
urinary excretion of drug or metabolites are referred to as “in vitro-in
vivo correlations”.
• Such correlations allow one to develop product specifications with
bioavailability.

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4. Percent of Drug Dissolved In vitro Vs Peak Plasma Concentration
• One of the ways of checking the in vitro and in vivo correlation is
✓to measure the percent of the drug released from different dosage
forms.
✓to estimate the peak plasma concentrations achieved by them.
✓to check the correlation between them.

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• In the analysis of in vitro and in vivo drug correlation, rapid drug
absorption may be distinguished from the slower drug absorption by
observation of the absorption time for the dosage form.
• The quicker the absorption of the drug the less is the absorption time
required for the absorption of the certain amount of the drug.
• The time required for the absorption of the same amount of drug from the
dosage form is correlated.

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1. Microspheres in vaccine delivery
2. Targeting using microparticulate carriers
3. Monoclonal antibodies mediated microspheres targeting
4. Chemoembolisation
5. Imaging
6. Topical porous microspheres
7. Medical application
8. Radioactive microsphere’s application.
Applicationsof microspheres

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• Microspheres are better choice of drug delivery system than many other
types of drug delivery system.
• In future by combining various other strategies, microspheres will find
the central and significant place in novel drug delivery, particularly in
diseased cell sorting, diagnostics, gene & genetic materials, safe,
targeted, specific and effective in vivo delivery and supplements as
miniature versions of diseased organ and tissues in the body.
Conclusion

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1. Chowdary KPR, Yarraguntla SR. Mucoadhesive microsphere for
controlled drug delivery. Biol. Pharm. Bull. 2004; 1717-24.
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References

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