A seminar onMULTIPLE EMULSIONS by M. NALINI KRISHNA REDDY (M.Pharm. I Semester) Department of Pharmaceutics BLUE BIRDS COLLEGE OF PHARMACY (Affiliated To Kakatiya University) WARANGAL-506 009
INTRODUCTION • FORMULATION OF MULTIPLE EMULSIONS • PREPARATION OF MULTIPLE EMULSIONS • CHARACTERISATIONOFMULTIPLEEMULSIONS • STABILITY OF MULTIPLE EMULSIONS • STABILITY ASSESSMENT STUDIES • DRUG RELEASE FROM MULTIPLE EMULSIONS • BIOAVAILABILITY • APPLICATIONS • CONCLUSION • REFERENCES CONTENTS
INTRODUCTION An emulsion “is a thermodynamically unstable system consisting of at least two immiscible liquid phases, one of which is dispersed as globules in other liquid phase, stabilized by presence of an emulsifying agent” (Leon et al, 1991). Emulsifying agents are ampiphillic in nature. Emulsifiers assist in formation of emulsions by three mechanisms (Leon et al, 1991). Reduction in interfacial tension. Formation of rigid interfacial film. Electric repulsion.
MULTIPLE EMULSIONS • These are polydispersed system where the drops of the dispersed phase themselves contain even smaller droplets, in most cases identical with a continuous phase. • Based on dispersed media multiple emulsions are of two types (James et al, 2002). • w/o/w multiple emulsion • o/w/o multiple emulsion • According to seifriz even more complex multiple emulsions may occur like, o/w/o/w/o or w/o/w/o/w but the stability is delicate. • Certain multiple emulsions have been termed as liquid membrane systems
FORMULATION OF MULTIPLE EMULSIONS (Shende et al, 2006) Mainly multiple emulsion are composed of : Oils: For pharmaceutical use oils like refined hydrocarbon oils are used. Such as, light liquid paraffin and esters of long chain fatty acids including vegetable oils and mineral oils. Example: ethyl oleate, isopropyl meristate, olive oil, arachies oil, seasem oil. Mixtures of oils can be used. To reduce specific gravity To alter the viscous nature of the oil.
Selection of oil phase can affect various emulsion parameters. Like : • Yield • Release profile • Particle size • Emulsion stability • A novel o/w/o emulsion containing castor oil as internal oil phase and a floro carbon as an external oil phase has been described for pulmonary delivery of the drug. ……..FORMULATION OF MULTIPLE EMULSIONS
…….FORMULATION OF MULTIPLE EMULSIONS Aqueous phase (Sinha et al, 2002): The two aqueous phases of w/o/w emulsions can be Simple aqueous solution of drugs Buffer solutions Aqueous suspensions of drug Gelled aqueous phase and Aqueous phases containing viscosity enhancers Increase and release rate of drug can be modified by changing the pH of two aqueous phases. Increase in difference of pH between two aqueous phases’ leads to instability.
…….FORMULATION OF MULTIPLE EMULSIONS Surfactants (Florence et al, 1982): Reduce interfacial tension between two phases (w/o or o/w interface) At least two surfactants are used for the preparation of multiple emulsions. For w/o/w lipophilic surfactant act as primary emulsifier and hydrophilic as secondary emulsifier in case of o/w/o it is vice versa. The optimum concentration of the surfactant to emulsify given oil can be determined by the use of hydrophilic lipophilic balance (HLB).
…….FORMULATION OF MULTIPLE EMULSIONS Surfactants (Florence et al, 1982): For primary surfactant the HLB valued should be in the range of 2-7 and for secondary surfactant it is between 6-16 for a w/o/w emulsion. Non ionic emulsifiers are preferred due to their low toxicity and they do not react with ionic compounds. Non ionic surfactants like spans and tweens have high HLB range are used.
Two step emulsification or double emulsification method (James et al, 2002): • Multiple emulsions may be prepared in a two stage procedures by the re-emulsification of a primary emulsions. • First step is preparation of primary emulsion. • The second emulsification step is critical, and excess mixing can fracture the drops, resulting in simple emulsion • A low sheer mixer may be employed with 1000 rpm for 15 minutes in first step not more than 600 rpm for 5 minutes for second step. PREPARATION OF MULTIPLE EMULSIONS
PREPARATION OF MULTIPLE EMULSIONS Fig. Preparation of w/o/w type of multiple emulsions by two step method
Phase Inversion or one step method: PREPARATION OF MULTIPLE EMULSIONS Fig. Preparation of multiple emulsions using phase inversion technique
Membrane Emulsification Method (Charcosset et al, 2004) PREPARATION OF MULTIPLE EMULSIONS Fig-Schematic diagram of apparatus used for the multiple emulsion preparation using membrane emulsification technique Y = 5.03X + 0.19 Y-mean globule size X-membrane pore size
Average globule size and size distribution: • Optical microscopy, • Coulter counter method. • Electron microscopy • Average globule size of multiple emulsion ranges from • 2-5 micrometers. • Size distribution studies are done to know the movement of particles i.e., size distribution behaviors with time (coalescence and flocculation). CHARACTERIZATION OF MULTIPLE EMULSIONS (Shende et al, 2006)
The critical size of droplets for setting is given from stokes law. • Rate of setting or creaming = D2/18 ή (dp-dm) g. • D = particle diameter • ή = viscosity of the medium • dp & dm = densities of particles and medium • g = gravitational constant ……CHARACTERIZATION OF MULTIPLE EMULSIONS
Area of interphases: • The average globule diameter determined can be used in the calculation of total area of interphase. • S = 6/D (S – total area of interphase in sq. cm. & D- diameter of globule in cm.) • Number of globules: • Number of globules per cubic millimeter can be measured using haemocytometer cell. • Number of globules/mm3 = number of globules x dilution x 4000 / number of small square counted. • Average droplet size should be in the range of 2-5 µ.m. ……CHARACTERIZATION OF MULTIPLE EMULSIONS
Yield or Entrapment Efficiency (Sinha et al, 2002) • Yield is expressed in two ways • Percentage of multiple droplets relative to simple droplets • Fraction of internal aqueous phase entrapped as multiple droplets. • Factors affecting the yield of multiple emulsions • Primary phase volume ratio • Secondary emulsification time • Mixing speed • Secondary phase volume ratio • Additives ……CHARACTERIZATION OF MULTIPLE EMULSIONS
Determination of entrapment efficiency • Internal phase tracer technique • Dialysis • Centrifugation • Conducirtivty measurements • Per cent of drug entrapped = amount of drug entrapped/total amount of drug X 100. ……CHARACTERIZATION OF MULTIPLE EMULSIONS
Rheology : (Jim et al, 2003) ……CHARACTERIZATION OF MULTIPLE EMULSIONS • By increasing the shear rate and shear time the apparent viscosity increased. • Further shearing caused increase in shear stress of emulsion and induced phase inversion • Reasons of phase inversion: • Increase in volume fraction of oil droplets by entrapment of water molecules • Coalescence of oil droplets upon shearing.
Emulsion stability is a phenomenon which depends upon the equilibrium between water, oil and emulsifier. Unfortunately Multiple Emulsions are thermodynamically unstable (Jim et al, 2003). • Some of the breakdown pathways that may occur in multiple emulsions are • Coalescence of internal droplets • Coalescence of multiple droplets • Expulsion of internal droplets • Shrinkage of internal droplets • The causes for the instability of multiple emulsions are • Migration of emulsifier • Osmotic instability • Creaming STABILITY OF MULTIPLE EMULSIONS
The following methods can be used for stabilization of multiple emulsions (Sinha et al, 2002) : • Use of high viscous oils • Polymerization and complexation of interfacially adsorbed surfactant molecules • Gelation of oil or aqueous phases of the emulsion • Liquid crystal stabilized multiple emulsion • Stabilization in the presence of electrolytes METHODS TO STABILISE MULTIPLE EMULSIONS
Fig; Various approaches to stabilize w/o/w multiple emulsion. A-stabilizing through liquid crystal formation B-stabilization by interfacial polymerization C-stabilization by adsorption of electrolyte or adsorption or covalent anchoring of polymer D-gelation of either internal or external phase or oil core
STABILITY ASSESSMENT STUDIES Stability of multiple emulsions can be assessed in various aspects like Determination of particle size Determination of phase separation Measurement entrapped percentage and viscosity In – vitro release studies: Dialyzing the multiple emulsion packed in a dialysis tube against a suitable dissolution media Conductometric method
Fig: Assembly use for invitro drug release. • In –vivo evaluation: • Blood concentration data in rats and rabbits • Urinary excretion data in man
Release of drug from multiple emulsions occurs from various mechanisms (Pandit et al, 1987). • Diffusion of unionized drugs through the oil layer • Carrier mediated transport • Micellar transport • Rapture of oil membrane • Thinning of oil membrane • Swelling and breakdown behavior DRUG RELEASE FROM MULTIPLE EMULSIONS
The administration of emulsions intravenously, presence of interesting relationship between physicochemical properties and physiological response (Walster, 1993). • The clearance of an emulsion from the blood is determined largely by its interaction with the reteculo endothelial system. It can be stated that: • Fine particle size emulsions are cleared more slowly than coarse particle size emulsions. • Negatively charged and positively charged particles are cleared more quickly than natural particles. • Emulsions stabilized by low molecular weight emulsifiers are cleared more rapidly than those stabilized by high molecular emulsifiers. BIOAVAILABILITY OF MULTIPLE EMULSIONS
Multiple emulsions are formulated for intravenous, topical and oral administration. • Controlled and sustained drug delivery • Improve in the bioavailability • Drug targeting • Vaccine adjuvant • Hemoglobin multiple emulsion • Masking of taste • Drug overdose treatment • Immobilization of enzymes • Tropical and cosmetic use. APPLICATIONS OF MULTIPLE EMULSIONS:
Multiple emulsions are complex polydispersed systems where both oil in water and water in oil emulsion exists simultaneously which are stabilized by lipophillic and hydrophilic surfactants respectively. • The ratio of these surfactants is important in achieving stable multiple emulsions. Among water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) type multiple emulsions; the former has wider areas of applications. • Various factors affecting the stability of multiple emulsions and the stabilization approaches of multiple emulsions were discussed in detail. CONCLUSION
Favorable drug release mechanisms and rate along with in-vivo fate of multiple emulsions make them a versatile carrier. It finds wide range of applications in controlled or sustained drug delivery, targeted delivery, taste masking, bioavailability enhancement, enzyme immobilization, etc. • Multiple emulsions have also been employed as intermediate step in the microencapsulation process and are the systems of increasing interest for the oral delivery of hydrophilic drugs, which are unstable in gastrointestinal tract like proteins and peptides. • With the advancement in techniques for preparation, stabilization and rheological characterization of multiple emulsions, it will be able to provide a novel carrier system for drugs, cosmetics and pharmaceutical agents. CONCLUSION
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