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Indian Journal of Pharmaceutical Education and Research Association of Pharmaceutical Teachers of India
INTRODUCTION
Topical preparations pertain to medicaments applied to the
surface of a part of the body and is a term used to describe
formulations that have effects only in a specific area of the
body and are formulated in such a manner that the systemic
absorption of the medicament is minimal. The methods
involved in conventional topical drug delivery basically
involve either assisting or manipulating the barrier function of
the skin (topical antibiotics, antibacterials, emollients,
sunscreen agents) or breaching the horny layer at the
molecular scale so as to direct drugs to the viable epidermal
and dermal tissues without using oral, systemic or other
therapies.
There has been a revolution in the last two decades in the
utilization of microemulsion systems in a variety of chemical
and industrial processes. Microemulsions have shown a wide
range of applications starting with enhanced oil recovery in
the 70's, expanding to a wide range of chemicals and entering
the pharmaceutical and cosmetic formulation area a decade
1
ago .
Microemulsions have advantages over both colloidal systems
under investigation and conventional emulsions, suspensions
and micellar solutions and may provide alternative drug
2
carriers . They are promising delivery systems which allow
sustained or controlled drug release for percutaneous, peroral,
topical, transdermal, ocular and parenteral administration of
medicaments. They offer the advantage of spontaneous
fo rma ti on, ease o f manu fac tu rin g an d sc al e-u p,
thermodynamic stability, improved drug solubilization of
hyd r opho b ic dr u gs and b ioav a ilab i lit y. Al so,
microemulsions that have inverse micellar structure may be
3
less comedogenic than either creams or solutions .
4
Hoar and Schulman introduced the word microemulsion,
which they defined as a transparent solution obtained by
titrating a normal coarse emulsion with medium-chain
alcohols. Microemulsions are thermodynamically stable
isotropic systems in which two immiscible liquids (water and
oil) are mixed to form a single phase by means of an
appropriate surfactant or its mixture. The short to medium
chain alcohols are generally considered as co-surfactants in
the microemulsion system. The presence of surfactant and co-
surfactant in the system makes the interfacial tension very
low. Therefore microemulsions form spontaneously, with an
5
average droplet diameter of 10 to 140 nm .
Microemulsions have the ability to deliver larger amounts of
water and topically applied agents into the skin than water
alone or other traditional vehicles such as lotions or creams
because they act as a better reservoir for a poorly soluble drug
6
through their capacity for enhanced solubilization .
The main difference between macroemulsions and
microemulsions lies in the size and shape of the particles
dispersed in the continuous phase: these are at least an order of
magnitude smaller in the case of microemulsions (10-200 nm)
than those of c onventional emulsions (1-20 m).
Macroemulsions consist of roughly spherical droplets of one
phase dispersed into the other whereas microemulsions
constantly evolve between various structures ranging from
droplet-like swollen micelles to bicontinuous structures,
making the usual “oil in water” and “water in oil” distinction
sometimes irrelevant.
In topical formulations, microemulsions have been proved to
Microemulsions For Topical Use– A Review
Nirmala Grampurohit, Padmini Ravikumar* and Rashmi Mallya
Dr. Bhanuben Nanavati College of Pharmacy, Gate No.1, Mithibai College Campus, V.M. Road,Vile Parle (West), Mumbai - 400 056.
Microemulsions have emerged as novel vehicles for drug delivery which allow sustained or controlled release for percutaneous, peroral, topical,
transdermal, ocular and parenteral administration of medicaments. They offer the advantage of spontaneous formation, ease of manufacturing
and scale-up, thermodynamic stability, improved drug solubilization of hydrophobic drugs and bioavailability. While microemulsions are used in
several fields, this article focuses on the reported investigations for topical applications which exhibit minimal systemic absorption.
KEYWORDS : Microemulsion, topical delivery , co-surfactant, antioxidant.
Revised: 19/9/2009
Submitted: 20/7/2009 Accepted: 1/4/2010
Address for Correspondence:
Padmini Ravikumar, Dr. Bhanuben Nanavati College of Pharmacy, Gate No.1, Mithibai
College Campus, V.M. Road,Vile Parle (West), Mumbai - 400 056.
E- mail: pdmnravikumar@yahoo.com
100
ABSTRACT
Ind J Pharm Edu Res, Jan-Mar, 2011/ Vol 45/ Issue 1
increase the cutaneous absorption of both lipophilic and
hydrophilic medicaments when compared to conventional
vehicles (emulsions, pure oils, aqueous solutions). In an
7
extensive review of this type of applications, Kreilgaard et al
attribute this performance to a generally higher solubility of
the medicaments in microemulsions, generating an increased
concentration gradient towards the skin. The role of
penetration enhancers played by the amphiphilic components
of the microemulsion and the internal mobility of the drug
within the vehicle also contribute to the overall performance
of microemulsions in dermal or transdermal drug delivery.
While microemulsions are used in several fields, in this
review an attempt has been made to emphasize on the
reported studies for topical applications which exhibit
minimal systemic absorption.
Formulation Considerations
The challenges in formulating topical microemulsions are:
1. Determining systems that are non-toxic, non-irritating,
non-comedogenic and non-sensitizing.
2. Formulating cosmetically elegant microemulsions.
The microemulsion formulation must have low allergic
potential, good physiological compatibility and high
biocompatibility.
The components involved in the general formulation of
microemulsions include (a) an oil phase (b) an aqueous phase
containing hydrophilic active ingredients [preservatives and
buffers may be included] (c) a primary surfactant [anionic,
non-ionic or amphoteric] (d) secondary surfactant or
cosurfactants.
Generally non-ionic surfactants are chosen because of their
good cutaneous tolerance, lower irritation potential and
toxicity. Microemulsions can be formulated using single-
chain surfactants or double chain surfactants. Single chain
surfactants do not lower the oil water interfacial tension
sufficiently and hence cosurfactants are required. Double
chain ed sur factants like sulfosuccinates can form
microemulsions in the absence of cosurfactants but are too
8
toxic for general pharmaceutical applications . The
cosurfactants even though being indispensable in the
formulation of microemulsions, have exhibited toxicity e.g.
9
medium chain length alcohols . Hence judicious choice of
surfactants and cosurfactants is of great importance. The use
of polyoxyethylenealcohol ethers has been reported as
10 , 1 1 , 1 2
co surfaca nt s . M icroemu ls ions p re pared fr om
phospholipids such as lecithins are preferred over synthetic
13,14
surfactants from the toxicity point of view . The
biocompatibility requirements of the amphiphiles are
fulfilled by lecithins and non-ionic surfactants (Brijs, Arlacel
1
186, Spans, Tweens and AOT) .
The following examples are commonly used formulations
components of microemulsions
- Oil: Ethyl oleate, Mineral oil, Isopropyl myristate,
Decanol, Oleic acid, Vegetable oils (Coconut oil, Safflower
oil, Soyabean oil, Olive oil), Medium chain length
triglyceride (Mygliol 812).
- Surfactant: Polysorbate (Tween 80 and Tween 20),
Lauromacrogol 300, Lecithins, Decyl polyglucoside
(Labrafil M 1944 LS), Polyglyceryl-6-dioleate (Plurol
Oleique), Dioctyl sodium sulfosuccinate (Aerosol OT), PEG-
8 caprylic/capril glyceride (Labrasol).
-Co -su rfact ant : So rbi tan mo noo le ate , Sorb ita n
monoste arate, Propyle ne glycol, Propyle ne glycol
monocaprylate (Capryol 90), 2-(2-ethoxyethoxy)ethanol
(Transcutol P) and Ethanol.
Applications Of Microemulsions
15,16
Microemulsions are promising delivery systems that
allow sustained or controlled drug release for percutaneous,
peroral, topical, transdermal, ocular and parenteral
administration. Enhanced absorption of drugs, modulation of
the kinetics of the drug release and decreased toxicity are
several advantages in the delivery process. The following is a
compilation of reported literature for topical microemulsions.
Antifungal
Superficial mycoses usually respond to topical therapy. In the
settling of eczema, topical antifungal agents such as
ketoconazole are used to reduce the fungal infection caused
by Pityrosporum ovale or Malassezia furfur.
Antifungal agents e.g miconazole, ketoconazole, and
itraconazole being lipophilic in nature have been formulated
as microemulsions to impart to them the advantages like
ease of preparation due to spontaneous formation,
thermodynamic stability, transparent and elegant appearance,
increased drug loading, enhanced penetration through the
biological membranes, increased bioavailability compared to
17, 18
conventional dosage forms. .
Microemulsions of poorly water soluble antifungal drugs
miconazole, ketoconazole, and itraconazole were designed
19
and developed by Puranajoti et al using either mineral oil or
Padmini et al.: Microemulsions For Topical Use– A Review.
101
Ind J Pharm Edu Res, Jan-Mar, 2011/ Vol 45/ Issue 1
olive oil as an oil phase. Various combinations of surfactant
®
and cosurfactant were used, including Labrafil M 1944 CS
® ® ®
and Plurol Oleique (1:1); Labrafil M 1944 CS and Plurol
® ®
Oleique (1:2); or Labrafil M 1944 CS, Capmul MCM C-8,
®
Pluro Oleique, and dehydrated ethyl alcohol (3:3:1:1).
Microemulsions of poorly water-soluble antifungal agents
were successfully developed with in vitro release rates
comparable to that of the gel formulation. The results of the
work done on miconazole nitrate formulated as positively
charged microemulsions indicate optimized drug targeting
without a concomitant increase in systemic absorption. L-
alanine benzyl ester, an ester of a natural amino acid, is an
20
appropriate ionic charge-inducing agent .
Microemulsion based gels for vaginal delivery of
clotrimazole and fluconazole were developed and compared
with the marketed clotrimazole gel (Candid-V® gel) by in
vitro methods. These microemulsion based gels showed
significantly higher in vitro bioadhesion, antifungal activity
as compared to that of Candid-V® gel. Fluconazole
21,22
microemulsion based gel did not exhibit vaginal irritation .
Antiviral
A study was done to investigate and evaluate microemulsion
and microemulsion-based hydrogel as a topical delivery
system for penciclovir in comparison with a commercial
cream. The results of permeation test in vivo in mice showed
that as compared with the commercial cream, microemulsion-
based hydrogel and microemulsion could significantly
increase the permeation of penciclovir into both epidermis
and dermis. Stability tests showed that microemulsion-based
hydrogel stored at 4 °C for 3 months had no significant change
in physicochemical properties. Skin irritation test in rabbits
demonstrated that single application or multiple applications
of microemulsion-based hydrogel did not cause any erythema
or edema. Thus, it can be concluded that microemulsion-
based hydrogel could be a promising vehicle for topical
23
delivery of penciclovir .
water:dimethylsulfoxide
Acyclovir containing microemulsion-based formulations for
to pi ca l d el iv er y w er e developed using isopropyl
myristate/Captex 355/Labrafac as an oil phase, Tween 20 as
s u r f a c t a n t , S p a n 2 0 a s c o s u rf a c t an t , a nd
(1:3) as an aqueous phase.
Transcutol, eucalyptus oil, and peppermint oil were used as
permeation enhancers. In vitro permeation studies through
mice skin were performed using Franz diffusion cells. The
optimum formulation containing 2.5% Transcutol as the
penetration enhancer showed 1.7-fold enhancement in flux
and permeation coefficient as compared to marketed cream
and ointment formulation. In vivo antiviral studies performed
in female mice against induced herpes simplex virus I
infection indicated that a single application of
microemulsion formulation containing 2.5% Transcutol, 24
hours post-injection resulted in complete suppression of
24
development of herpetic skin lesions .
Anti acne
Novel drug delivery strategies like microemulsions can play a
pivotal role in improving the topical delivery of antiacne
agents by enhancing their dermal localization with a
25
concomitant reduction in their side effects Microemulsions
.
of azelaic acid, a bioactive molecule used in many skin
disorders, prepared using the monosodium salt (AZA-Na)
have been evaluated as delivery vehicles. Dialysis membrane
experiments showed decreasing permeability to AZA-Na,
and this was related to its partition at the microemulsion
interface. The results suggested that microemulsions
containing AZA-Na could be used to optimize drug targeting
26
in acne treatment
.
To increase the solubility of azelaic acid in the dispersed oil
phase of microemulsion containing polysorbate 20, butanol,
decanol:dodecanol (2/1) and water, the pH of aqueous phase
was lowered and propylene glycol was added. An increased
partitioning into the lipophilic phase was noted as propylene
glycol concentration was increased. Microemulsion thus
provided a vehicle in which azelaic acid was dissolved rather
than suspended as in a cream. Moreover, reservoir effect
achieved by partitioning into the oil could prolong its release
over several hours. It showed a 10 fold increase in the amount
of drug released (upto 27-30% of initial amount) from the
microemulsion when compared to a cream clinically used in
27
treatment of skin disorders .
Antioxidants
Antioxidants have been used in dermatological and cosmetic
products because of their property of scavenging and
destroying aggressive oxidizing agents and free radicals that
are involved in various skin conditions.
In animals, topical application of alpha-tocopherol has shown
to exert photoprotective effects by reducing the number of
sunburn cells, UV B induced damage and inhibiting
photocarcinogenesis. An o/w or w/o microemulsion of
vitamin E delivered the vitamin predominantly to the
epidermis avoiding accumulation in organs other than the
skin. The cream or lotion preparations of the same amount of
Padmini et al.: Microemulsions For Topical Use– A Review.
102
Ind J Pharm Edu Res, Jan-Mar, 2011/ Vol 45/ Issue 1
28
vitamin results in excessive accumulation in the organs .
Newer studies show that combined applications of various
antioxidants can increase their potency as compared with a
29
single antioxidant alone. Branka Rozman et al have
developed a temperature-sensitive microemulsion gel as an
effective and safe delivery system suitable for simultaneous
topical application of a hydrophilic vitamin C and a lipophilic
vitamin E. By changing water content of liquid o/w
microemulsion, a gel like microemulsion with temperature-
sensitive rheologic al propert ies was forme d. The
temperature-driven changes in its microstructure were
confirmed by rotational rheometry, viscosity measurements
and droplet size determination. The release studies have
shown that the vitamin release at skin temperature from gel-
like microemulsion were comparable to those from o/w
microemulsion and were much faster and more complete than
from o/w microemulsion conventionally thickened with
polymer (carbomer).
Non-thickened (o/w, w/o and gel-like) and thickened (with
colloidal silica) microemulsions were studied as carriers for
vitamin C and E using reconstructed human epidermis
(RHE). The amounts of these vitamins accumulated in and
permeated across the RHE were determined, together with
factors affecting skin deposition and permeation. Notable
differences were observed between formulations. The
absorption of vitamins C and E in RHE layers was in general
enhanced by microemulsions and the vitamins incorporated
in the outer phase of the microemulsion exhibited greater
absorption than that when vitamins were in the inner phase.
Addition of thickener enhanced the deposition of vitamins E
30
and C in the RHE .
Various delivery systems of alpha-tocopherol (1%) were
formulated, which included simple solution, gels, emulsions,
and microemulsions. The hydroalcoholic gel delivered
significantly higher amounts of alpha-tocopherol into the
receptor than the other gels used. A microemulsion containing
isopropyl myristate emerged as the best delivery system for
31
alpha-tocopherol amongst all the systems studied .
Microemulsions of w/o and o/w type for topical application
containing sodium ascorbyl phosphate (hydrophilic
derivative of ascorbic acid) were formulated and compared
with topical application of ascorbyl palmitate which is a
lipophilic derivative of vitamin C. To obtain liquid
microemulsions appropriate for topical application, their
viscosity was increased by adding thickening agents.
Colloidal silica 4% (w/w) was chosen as a suitable thickening
agent for w/o microemulsions and 0.5% (w/w) xanthan gum
for the o/w microemulsions. The presence of thickening agent
and the location of sodium ascorbyl phosphate in the
microemulsion influenced the in vitro drug release profiles.
When incorporated in the internal aqueous phase, sustained
release profiles were observed. This study confirmed
microemulsions as suitable carrier systems for topical
32
application of sodium ascorbyl phosphate .
33
Spiclin et al studied the stability of o/w and w/o type of
microemulsions for topical use containing ascorbyl palmitate
and sodium ascorbyl phosphate which are derivatives of
ascorbic acid that differ in stability and hydrophilic and
lipophilic properties. The stability of the less stable derivative
ascorbyl palmitate was tested under different conditions to
evaluate the influence of initial concentration, location in
microemulsion, dissolved oxygen and storage conditions.
High concentrations of ascorbyl palmitate reduced the extent
of its degradation. In contrast, sodium ascorbyl phosphate
was stable in both types of microemulsion and was shown to
be convenient as an active ingredient in topical preparations.
In the case of ascorbyl palmitate, long-term stability in
selected microemulsions was not adequate.
Investigation on the amphiphilic antioxidant ascorbyl
palmitate and its effectiveness against free radical formation
34
was proven by Polona Jurkovic et al . When applied on the
skin, ascorbyl palmitate decreased the level of formation of
free radicals. Its effectiveness depended significantly on the
carrier system, the type of microemulsion and its
concentration while the time of application had no influence
on its effectiveness. Oil in water microemulsions delivered
ascorbyl palmitate to the skin significantly better than water
in oil microemulsions. In both types of microemulsions, the
effectiveness increased at higher concentrations of ascorbyl
palmitate..
In order to develop alternative formulations for topical
35
administration of retinoic acid, Michele Trotta et al
evaluated microemulsions as delivery vehicles. Oil in water
and water in oil microemulsion formulations were prepared
using water, isopropyl myristate, lecithin, caprylyl–capryl
glucoside and ethanol or 1,2 hexanediol. The results
suggested that o/w microemulsions containing a counter ion
can be used to optimise drug targeting without a concomitant
increase in systemic absorption.
Miscellaneous skin conditions:
The following are examples depicting the use of
microemulsions in varied skin conditions:
Padmini et al.: Microemulsions For Topical Use– A Review.
103
Ind J Pharm Edu Res, Jan-Mar, 2011/ Vol 45/ Issue 1
An o/w microemulsion formulated using lecithin and an alkyl
glucoside as mild, non-irritant surfactants was proposed as a
cosmetic vehicle for arbutin and kojic acid which are
naturally occurring whitening agents. The photostability to
UVB irradiation of both whitening agents was determined in
aqueous solutions and in microemulsions, and also in the
presence of the perfumed compositions. The stability of
arbutin and kojic acid was higher in microemulsions than in
36
aqueous solutions .
37
Subramanian et al studied the topical delivery of celecoxib
using microemulsion as the vehicle for the treatment of UV B
induced skin cancer. Various oil to cosurfactant ratios were
studied to identify t he formula tion varia bles for
microemulsion formation. The effect of these variables on
skin permeation of celecoxib was evaluated. Topical anti-
inflammatory effect of celecoxib was assessed and it showed
higher permeation rate and significant anti-inflammatory
activity. The studied microemulsion formulations have a
prospect for use as a potential vehicle for treatment of UV B
induced skin cancer.
38
Baroli developed and evaluated alternative microemulsion
formulations for topical administration of 8-Methoxsalen
and rel a ted furo cum a rin s for the t rea tmen t of
hyperproliferative skin diseases in association with long-
wavelength UVA light using water, isopropyl myristate
(IPM) and Tween 80: Span 80: 1,2-Octanediol (3:1:1.2 w/w )
and results suggest that the studied microemulsion system is
suitable.
A combination of inhibitors of cyclo-oxygenase-2 and 5-
lipoxygenase applied via a microemulsion delivery system
was proven to be effective in topically inhibiting skin
carcinogenesis. The results clearly showed that topical
treatment with microemulsions containing celecoxib alone or
celecoxib plus zileuton significantly inhibited skin
carcinogenesis and that a combination of both agents had the
39
best results .
Temozolomide acid hexyl ester used in the treatment of skin
cancer has poor solubility and instability. Microemulsion
systems were formulated with either oleic acid or isopropyl
myristate as the oil phase and tocopheryl polyethylene glycol
1000 succinate as a surfactant. Topical formulations of oleic
acid or isopropyl myristate demonstrated beneficial
solubilising ability and provided a stable environment for the
drug. In permeation studies, the isopropyl myristate
microemulsion systems with inclusion of isopropyl alcohol
(IPA) as a co-surfactant significantly increased permeation of
temozolomide acid hexyl ester through silicon membranes
and rat skin resulting in less drug retention within the skin,
while oleic acid microemulsion systems demonstrated higher
solubilising ability and a higher concentration of
40
temozolomide acid hexyl ester retained within the skin .
The abilities of an o/w microemulsion of ethyl oleate with
Tween 80 as emulsifier and n-pentanol as a co-emulsifier
were investigated to inactivate suspensions of vegetative cells
of Salmonella spp. Escherichia coli Pseudomonas
ae rug inosa , St aphyl oco ccus a ureus and Li ste ria
monocytogenes and was found to be effective against all five
microorganisms. The abilities of these microemulsions to
reduce preformed biofilms of the five bacteria were also
41
investigated and was found to be effective .
A microemulsion gel-based system of babchi oil (Psoralea
corylifolia) was studied for the treatment of psoriasis which
could provide improved permeation of the drug through the
skin and increased patient compliance. The chief constituent
of babchi oil is psoralen, a photoactive furocoumarin which
reduces cell proliferation. Moreover, babchi oil, in addition to
providing psoralen also acts as an oily phase for
microemulsion system. The presence of surfactant and
cosurfactant increases the permeation. Eight marketed
samples of babchi oil were used for the preparation of
microemulsions which were subjected to different
thermodynamic stability tests and characterized for droplet
size, viscosity and refractive index. In vitro skin permeation
of babchi oil through rat abdominal skin was determined by
the Franz diffusion cell. The in vitro skin permeation profile
of a formulation consisting of 1.67% v/v of babchi oil, 8.33%
v/v of oleic acid, 55% v/v of Tween 80: Transcutol-P (1:1) and
35% v/v of distilled water was significant when compared
with other microemulsion formulations. This formulation
was converted into microemulsion gel by adding 1%
Carbopol-940 and was tested for its in vivo antiinflammatory
effects determined by footpad edema. The results suggested
that microemulsion gel is a potential vehicle for improved
topical delivery of psoralen and that microemulsion gels are
potential vehicles for improved topical delivery of babchi
42
oil .
Microemulsions containing Aerosol OT, Tween 85, isopropyl
myristate and water were observed to possess a potentially
improved skin bioavailability of cyclosporine A for topical
delivery against autoimmune skin disorders. In animal studies
the amount of drug deposition into the skin and subcutaneous
fat was respectively almost 30 and 15-fold higher than the
concentrations compared with oral administration. The
Padmini et al.: Microemulsions For Topical Use– A Review.
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Ind J Pharm Edu Res, Jan-Mar, 2011/ Vol 45/ Issue 1
systemic distribution in blood, liver and kidney was much
lower following topical administration as compared to oral
administration. The study indicated that because of high
local concentrations and minimal distribution to other organs
via the circulation, topical microemulsion is a suitable
43
vehicle for cyclosporin A .
Ocular
Eye drops account for 90% of the available ophthalmic
formulations due to their simplicity and convenience.
However, rapid precorneal loss caused by drainage and high
tear fluid turnover is amongst the major problems associated
with topical ophthalmic drug delivery. Only 5% of the applied
drug in eye drops penetrates the cornea and reaches the
intraocular tissues with the rest of the dose undergoing
transconjunctival absorption or drainage via the nasolacrimal
duct before transnasal absorption. This results in loss of drug
into the systemic circulation and provides undesirable
systemic side effects Accordingly, microemulsions provided
a promising alternative with improved ocular retention,
increased corneal drug absorption and reduced systemic side
effects whilst maintaining the simplicity and convenience of
the dosage form as eye drops.
44
Judy Chan et al evaluated microemulsion based phase
transition systems for ocular delivery of pilocarpine
hydrochloride (a model hydrophilic drug). They used two
no n- ionic surf ac tants sorb it an mono l au ra te and
polyoxyethylene sorbitan mono-oleate with ethyl oleate (oil
component) and water. These systems undergo phase change
from microemulsions to liquid crystalline and to coarse
emulsion with a change in viscosity depending on water
content. Incorporation of pilocarpine hydrochloride did not
affect the phase behaviour. Thus, phase transition
microemulsion is promising for ocular drug delivery as it
provides the fluidity with its viscosity being increased after
application and increasing ocular retention while retaining
the therapeutic efficiency.
45
Fialho and da Silva-Cunha aimed to develop and
characterize an oil-in-water microemulsion containing
dexamethasone, and evaluate its ocular irritation and the
pharmacokinetics. The developed system showed an
acceptable physicochemical behavior and presented good
stability for three months. The ocular irritation test used
suggested that the microemulsion did not provide significant
alteration to eyelids, conjunctiva, cornea or iris. This
formulation showed greater penetration of dexamethasone in
the anterior segment of the eye and also release of the drug for
a longer time when compared with a conventional preparation
that could allow for a decreased number of applications of eye
drops per day.
Microemulsions composed of Span 20, Tween 20, isopropyl
myristate and water were investigated as potential drug
delivery systems for eye drops containing chloramphenicol
46
by Lv F.F. et al Chloramphenicol in the conventional eye
.
drops hydrolyzes easily to glycol whereas in the
microemulsion it was trapped into the oil-in-water system.
The results revealed that the content of the glycols in the
microemulsion formulation was much lower than that in the
commercial eye drops at the end of the accelerated stability
experim ents. It im plied that the stabil ity of the
chloramphenicol in the microemulsion formulations was
increased remarkably. The microemulsion was found to be
almost free of toxicity and irritation.
Spermicidal
47
O.D'Cruz de scribed a for mulation of novel gel-
mi cr oe mulsions (GM ) a s nontoxic, d ua l- function
intravaginal spermicides, which could be used as delivery
vehicles for lipophilic drug substances targeting sexually
transmitted pathogens. These GMs comprising oil-in-water
microemulsion and polymeric hydrogels were designed to
solubilize lipophilic antiviral/antimicrobial agents and
exhibited rapid spermicidal activity in human semen and was
compared against nonoxynol-9-based detergent spermicide
(Gynol II). Spermicidal GM has shown unprecedented
potential as dual function microbicidal contraceptives to
impro ve vag inal bioav ailab ility of poorly soluble
antimicrobial agents without causing significant vaginal
damage.
Cosmetics
There is growing recognition of the potential benefits of
microemulsions in the field of cosmetics in addition to drug
delivery. They are now being widely investigated for
preparing personal care products with superior features such
as having improved product efficiency, stability, appearance
and minimal irritation. They are well suited for the
preparation of various cos metic products such as
moi s t uriz i n g and s o o thin g a gent s , suns c r eens ,
antiperspirants, body cleansing agents, hair conditioners and
after shave formulations. Microemulsions are also suitable in
48
perfumery so as to minimize the quantity of organic solvents .
CONCLUSION
Microemulsions are commercially feasible, simple and
Padmini et al.: Microemulsions For Topical Use– A Review.
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Ind J Pharm Edu Res, Jan-Mar, 2011/ Vol 45/ Issue 1
convenient novel vehicles for delivery of medicaments which
can enhance drug absorption with reduced systemic side
effects. They can be used to optimise drug targeting without a
concomitant increase in systemic absorption. Appropriate
excipient selection and safety evaluation especially of the
cosurfactants is crucial in the formulation of microemulsions.
They can be potential drug delivery systems for the delivery
of more than one medicament simultaneously.
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