AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`
`Effect of Nonionic Surfactant on Transport of Surface-Active and Non-Surface-
`Active Model Drugs and Emulsion Stability in Triphasic Systems
`Submitted: June 13, 2000; Accepted: August 17, 2000; Published: September 20, 2000.
`
`N. Chidambaram and D. J. Burgess
`
`INTRODUCTION
`
`Department of Pharmaceutical Sciences, University of Connecticut, Storrs, CT
`ABSTRACT The effect of surfactant concentration
`on transport kinetics in emulsions using surface-
`active (phenobarbital, barbital) and non surface-
`active (phenylazoaniline, benzocaine) model drugs
`is determined. Mineral oil was chosen as the oil
`phase and the nonionic surfactant polyoxyethylene-
`10-oleyl-ether
`(Brij 97) was chosen as
`the
`emulsifier. Model drug transport in the triphasic
`systems was
`investigated using
`side-by-side
`diffusion cells mounted with hydrophilic dialysis
`membranes (molecular weight cutoffs 1 kd and 50
`kd) and a novel bulk equilibrium reverse dialysis
`bag technique. Emulsion stability was determined
`by droplet size analysis as a function of time,
`temperature, and the presence of model drugs, using
`photon correlation spectroscopy. Mineral oil/water
`(O/W)
`partition
`coefficients
`and
`aqueous
`solubilities were determined in the presence of
`surfactant. The transport rates of model drugs in
`emulsions increased with an increase in Brij 97
`micellar concentrations up to 1.0% wt/vol and then
`decreased at higher surfactant concentrations. The
`transport profiles of the model drugs appeared to be
`governed by model drug O/W partition coefficient
`values and by micellar shape changes at higher
`surfactant concentrations.
`
`An emulsion is a thermodynamically unstable system
`consisting of at least 2 immiscible liquid phases, one
`of which is dispersed as droplets in the other. The
`thermodynamic instability of emulsion systems is a
`consequence of the high interfacial free energy that
`exists between the 2 phases. This free energy is the
`driving force for droplet coalescence and eventual
`phase separation. Surfactants are added to improve
`emulsion stability by decreasing interfacial free
`energy and providing a mechanical barrier to droplet
`coalescence and Ostwald ripening (1). Collision of
`dispersed phase droplets with each other or with the
`walls of the container can lead to thinning and
`rupture
`of
`the
`surfactant
`interfacial
`film.
`Consequently, droplet coalescence and eventual
`phase separation will occur. This effect can be
`overcome by the presence of excess surfactant in the
`bulk, which replenishes the interface when the film
`ruptures or thins (2). Therefore, excess surfactant is
`usually present in emulsion systems and may be in
`the form of monomers, micelles, and liquid crystals.
`This excess surfactant may affect drug transport in
`emulsion systems through micellar solubilization and
`change
`in
`emulsion droplet
`interfacial
`film
`characteristics.
`
`Total transport rates of phenobarbital and barbital
`were faster than those of phenylazoaniline and
`benzocaine. Excess surfactant affected the transport
`rates of the model drugs in the emulsions depending
`on drug surface activity and lipophilicity.
`
`Corresponding author: D. J. Burgess, Department of
`Pharmaceutical Sciences, University of Connecticut,
`Storrs, CT 06269. E-mail:dburgess@uconn.edu
`
`Drugs may possess surface-active characteristics and
`associate at the mineral oil/water (O/W) interface.
`Surface-active drugs will reduce interfacial tension
`and consequently may aid emulsion stability. In the
`presence of surfactants, surface-active drugs may
`increase or decrease surface tension, depending on
`the nature of the interaction between the drug and the
`surfactant. A favorable drug/surfactant interaction
`will result in a reduction in interfacial tension, and an
`unfavorable interaction will result in an increase in
`interfacial tension (3). Therefore, in the presence of
`surfactant, surface-active drugs may enhance or
`reduce emulsion stability. To form micelles, surface-
`
`1
`
`APOTEX 1027, pg. 1
`
`

`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`active moieties should possess a minimum of 8
`carbon atoms in the lipophilic part of the molecule.
`Although surface-active drugs may not meet this
`requirement, they may form mixed micelles with the
`surfactant. Hence, surfactant concentration may
`affect
`the
`transport of surface-active drugs
`in
`emulsion systems.
`
`The effect of concentration of a nonionic surfactant
`on surface-active and non surface-active model
`drug
`transport rates and emulsion stability
`in
`triphasic (oil, water, and micellar) systems was
`investigated. Mineral oil was selected as the oil
`phase because it does not contain any surface-active
`components.
`The
`nonionic
`surfactant,
`polyoxyethylene-10-oleyl-ether
`(Brij 97), was
`selected because it forms relatively stable emulsions
`of mineral oil in water (3). Phenylazoaniline (PAA)
`and benzocaine (BZ) were selected as non surface-
`active model drugs for 3 reasons: their molecular
`weights are similar; each contains a benzene moiety;
`and to enable us to compare our data with those of
`Yoon and Burgess (3). Phenobarbital (PB) and
`barbital (B) were selected as surface-active model
`drugs because
`they have molecular weights
`comparable to those of PAA and BZ (Figure 1). All
`the model drugs have different lipophilicities. PAA
`has a molecular weight (MW) of 197.2 dalton and is
`slightly soluble in water. The approximate solubility
`of PAA
`is 29 mg/L, and
`its pKa (negative
`logarithmic values of ionization constant) value is
`4.4. BZ, the ethyl ester of p-aminobenzoic acid, has a
`molecular weight of 165.2 dalton. The pKa value of
`BZ is 2.5, and therefore it exists in the nonionized
`form at pH 7.0. The approximate solubility of BZ is
`0.4 g/L in water at 25 C and pH 7.0. PB has a
`molecular weight of 232.2 dalton and is a weak acid
`with a pKa value of 7.5. B has a molecular weight of
`184.2 dalton and a pKa value of 7.8. The solubilities
`of PB and B are 1.0 and 7.5 mg/mL in water at 25 C
`respectively.
`
`MATERIALS AND METHODS
`
`Materials
`
`Mineral oil, sodium chloride, sodium phosphate
`monobasic, and hydrophilic Spectrapor 7 dialysis
`membranes and dialysis bags (MW cutoffs 1 kd and
`
`Figure 1. Chemical structures of phenobarbital,
`barbital, phenylazoaniline, and benzocaine.
`
`50 kd) were purchased from Fischer Scientific
`(Springfield, NJ). Brij 97 was a gift from ICI
`(Rochester, NY). PAA was purchased from Aldrich
`Chemical Company, Inc (Milwaukee, WI). BZ, PB,
`and B were purchased from Sigma (St Louis, MO).
`All chemicals were used as received without further
`purification. Deionized water, obtained from a
`NANO-pure ultrapure water
`system
`(D4700,
`Barnstead, Dubuque,
`IA), was used
`for all
`experiments.
`
`Preparation of Buffers
`
`A 0.05 mol/L, pH 7.0 phosphate buffer system was
`used in all the studies. The ionic strength of the
`buffer was adjusted to 0.2 mol/L using sodium
`chloride. After preparation, the phosphate buffer was
`filtered through 0.22  m filters to remove any
`impurities.
`
`Emulsion Preparation
`
`Emulsions were prepared in 100 mL batches at room
`temperature. A desired mass of surfactant was added
`to 80 mL of pH 7.0 phosphate buffer and gently
`mixed. The concentrations of surfactant chosen were
`in the range of 1% to 6.2% wt/vol for the critical
`micelle concentration (CMC) and stability studies. In
`all other studies an initial surfactant concentration of
`6.2% wt/vol was used. A known amount of model
`drug (PAA: 65.7 mg, BZ: 40.0 mg, PB: 60.0 mg, and
`B: 41.0 mg) was dissolved in 20 mL of mineral oil.
`
`2
`
`APOTEX 1027, pg. 2
`
`

`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`concentrations
`drug
`selected
`The model
`determined using surface tension measurements.
`their maximum solubilities
`in
`to
`corresponded
`Surface tension measurements were conducted using
`mineral oil at 37 C.
`a microbalance surface tensiometer (K12, Kruss
`USA) in the Wilhelmy plate mode. Surface tension
`was measured for model drugs in surfactant solutions
`(below the CMC of Brij 97).
`
`Emulsion Stability Determination
`
`Emulsion samples (0.5 mL) were sealed in 1 mL
`ampules and placed in temperature-controlled water
`baths 0.5 C at 5 , 25 , 37 , and 60 C. Emulsion
`mean droplet diameters and size distributions were
`determined using an Accusizer Optical Particle Sizer
`(Model 770, Particle Sizing Systems, Inc, Santa
`Barbara, CA) and a Nicomp Submicron Particle
`Sizer (Model 370, Particle Sizing Systems, Inc). The
`Accusizer Optical Particle Sizer operates on the light
`blockage principle that detects particles in the size
`range of 1  m to 500  m. The Nicomp Submicron
`Particle
`Sizer
`is
`a
`photon
`correlation
`spectrophotometer and detects particles in the size
`range of 0.01  m to 1  m. These instruments were
`used in series to cover the entire particle size range
`of the emulsion systems with a single sample. All
`emulsions were prepared in triplicate, measurements
`were repeated 3 times per sample, and mean values
`and standard deviations were calculated.
`
`Model Drug Solubility
`
`Model drug solubilities were measured in phosphate
`buffer (0.05 mol/L, ionic strength 0.2, pH 7.0) at 37
`C. Brij 97 was added to the buffer in concentrations
`of 0% to 2% wt/vol to determine the effect of the
`micellar phase on solubility. The model drug (PAA
`and BZ)/surfactant buffer
`suspensions were
`equilibrated at 37 C for 48 hours, filtered, and
`analyzed spectrophotometrically using a Spectronic
`3000 Array (Milton Roy, Rochester, NY). Buffer
`solution and Brij 97 buffer solutions were used as
`reference solutions in the absence and presence of
`Brij 97, respectively. The absorbance peak values of
`PAA and BZ occurred at 377 nm and 286 nm
`respectively (in the absence of Brij 97 solution) and
`at 398 nm and 294 nm, respectively (in the presence
`of Brij 97 solution). A High-Performance Liquid
`Chromatography
`(Model 440, Waters Assoc,
`Milford, MA) equipped with an ultraviolet (UV)
`
`The 2 phases (80 mL of aqueous phase and 20 mL of
`oil phase) were mixed at low speed using a magnetic
`stirrer to form a coarse emulsion and introduced into
`the reservoir of the microfluidizer (Model 110T,
`Microfluidic, Newton, MA). The emulsion was
`passed through the microfluidizer pneumatically by
`compressed air at 80 psi. The microfluidizer is fitted
`with a 5  m filter to remove any impurities.
`Emulsions were collected after 5 passes and
`immediately used in the stability and transport
`studies. Surfactant concentration was varied by
`addition of extra surfactant dissolved in buffer
`following emulsification, resulting in a 1:1 dilution.
`Emulsion systems, where no excess surfactant was
`added, were diluted 1:1 with buffer only.
`Consequently, all final emulsions contained 10%
`vol/vol oil phase.
`
`CMC Determination
`
`Surface tension measurements were conducted using
`a microbalance surface tensiometer (K12, Kruss
`USA, Charlotte, NC) in the Wilhelmy plate mode.
`The tensiometer was equipped with a Dosimat
`(automatic
`burette; Model
`665, Metrohm,
`Switzerland) for CMC determination. The Wilhelmy
`plate was rinsed with warm NANO-pure distilled
`water and with acetone. The plate was annealed to
`red-hot with a Bunsen burner. The annealing process
`removed impurities, which cannot be removed by
`rinsing, from the platinum surface. Surface tension
`values were determined from the measured force as
`follows (4):
`
`(1)
`where C is the surface tension, F is the measured
`force, P is the wetted length of the plate, and G is the
`contact angle. CMC values of Brij 97 in the presence
`and absence of O/W emulsion systems were
`determined by a membrane equilibrium technique
`and surface tension measurement (3).
`
`Surface Activity Determination
`
`The effect of model drugs on interfacial tension was
`
`3
`
`APOTEX 1027, pg. 3
`
`

`
`Model Drug Transport
`
`Model drug transport rates in emulsion systems were
`investigated using the bulk equilibrium reverse
`dialysis bag and the side-by-side diffusion cell
`technique, and the data were compared. These
`methods have been described in detail previously (5).
`
`Side-by-Side Diffusion Cell Technique
`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`deviations were calculated.
`detector (Model 441, Waters Assoc) and a reverse
`phase column ( Bondapak – C18, 10 mm, 30 cm x
`3.9 mm I.D.; Waters Assoc) was used for PB and B
`analysis because their absorbance peaks overlapped
`with that of Brij 97. The mobile phase, a mixture of
`ultrapure
`deionized water, methanol,
`and
`trifluoroacetic acid (3:1:0.04, vol/vol), was operated
`at a flow rate of 1.3 mL/min. The column eluent was
`monitored at 247 nm with a sensitivity of 0.005
`AUFS (sensitivity unit used for spectrophotometers).
`Peak areas were obtained using Perkin–Elmer
`programs (Omega 2, Norwalk, CT). Mean values and
`standard deviations were calculated from 3 sample
`determinations.
`
`Oil/Buffer Partition Coefficient Determination
`
`Two mL of oil containing model drug was kept in
`contact with 2 mL of pH 7.0 phosphate buffer
`solution at 37 C 0.10C for 48 hours to allow
`equilibration.
`Preliminary
`experiments were
`conducted
`to determine
`the
`time
`to
`reach
`equilibrium. Samples were analyzed at 24 hours, 48
`hours, 72 hours, and 168 hours, and
`it was
`determined that equilibrium was achieved within 48
`hours. After reaching equilibrium, the 2 phases were
`separated, collected, and analyzed for model drug
`content. Aqueous samples were assayed for drug
`content using UV and high-performance
`liquid
`chromatography (HPLC). These experiments were
`repeated 3
`times. Mean values and standard
`deviations were calculated.
`
`Interfacial Rheology Measurement
`
`Interfacial elasticity (mN/m) was determined using
`an oscillating
`ring
`interfacial
`rheometer
`(CIR
`Limited, UK). The platinum duNuoy ring was placed
`at the interface. The ring oscillates and a proximity
`probe transducer measures the amplitude of motion.
`Dynamic surface rigidity and surface viscosity
`moduli were generated concurrently. Temperature
`was controlled to 37 C 0.1. Solutions were
`prepared in phosphate buffer, pH 7.0, over a range of
`surfactant (1% to 6%) and model drug concentrations
`and
`surfactant:drug
`ratios
`(1:10
`–
`10:1).
`Measurements were taken over a 2-hour period, in
`triplicate, using freshly prepared samples for each
`determination. Average values
`and
`standard
`
`4
`
`Briefly, water-jacketed side-by-side diffusion cells
`(glass chambers with a 4 mL volume and an 11-mm-
`diameter circular opening available for diffusion)
`mounted with cellulosic dialysis membranes (MW
`cutoffs: 1 kd or 50 kd) were used for kinetic studies
`of model drug release from emulsions (5). Samples
`were withdrawn from the receiver cells (2 mL) and
`analyzed spectrophotometrically at predetermined
`time intervals (Brij 97 solution PAA: 398 nm, BZ:
`294 nm; Buffer solution PAA: 377 nm, BZ: 286
`nm). PB and B were analyzed by HPLC (Waters
`)equipped with a UV detector (Waters Assoc)and a
`reverse phase column ( Bondapak,Waters Assoc).
`The same volume of buffer or surfactant solution as
`was withdrawn for each sample was replaced into the
`receiver cells
`to maintain volume and sink
`conditions.
`
`Control Studies
`
`(i) Transport study of model drugs from buffer
`solution to buffer solution⎯ Model drugs in buffer
`solution were placed in the donor cells and buffer
`solutions placed in the receiver cells. This study
`allows determination of the permeability coefficients
`of model drugs through the dialysis membranes.
`
`(ii) Transport study of model drugs from surfactant
`solution to surfactant solution⎯ Model drugs in
`surfactant solution were placed in the donor cells and
`surfactant solutions placed in the receiver cells. This
`study allows determination of the effect of the
`micellar phase on permeability coefficients of model
`drugs through the dialysis membranes.
`
`Both control experiments were repeated 3 times, and
`mean values and standard deviations were calculated.
`
`APOTEX 1027, pg. 4
`
`

`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`Bulk Equilibrium Reverse Dialysis Bag Technique
`
`39
`
`Buffer
`Emulison
`
`0.00154, 30
`
`3.08, 30
`
`37
`
`35
`
`33
`
`31
`
`29
`
`27
`
`Surface Tension (dyne/cm)
`
`25
`0.0001
`
`0.001
`
`0.01
`
`0.1
`Concentration (% w/v)
`
`1
`
`10
`
`100
`
`the critical micelle
`Figure 2. Determination of
`concentration of polyoxyethylene-10-oleyl-ether (Brij
`97) in buffer and in 10% vol/vol O/W emulsion systems
`(pH 7.0,
`I = 0.2, 37° C, mean values of three
`determinations);
`the error bars are within
`the
`symbols.
`
`Table 1. The solubilities, log P (log values of O/W
`partition coefficients), and surface tension (γγ ) values
`(mN/M) of model drugs in 0.05 mol/L phosphate
`buffer (pH 7.0, I = 0.2, 37° C, mean values of three
`determinations).
`
`Model Drugs
`
`Barbital
`
`Solubility (
`g/mL)
`7560 121
`
`Log P
`
`0.6 0.002
`
`C (mN/M)
`SD
`41.6 1.1
`
`Phenobarbital
`
`1002 38
`
`1.33 0.03
`
`46.8 2.8
`
`Benzocaine
`
`1190 45
`
`1.80 0.05
`
`69.2 0.4
`
`Phenylazoaniline
`
`29 0.8
`
`3.19 0.09
`
`67.2 0.5
`
`model drugs (0.0001 mol/L, Table 1). PB and B had
`the greatest effect, reducing the surface tension to
`46.8 2.8 mN/m and 41.6 1.1 mN/m, respectively.
`
`Micellar Solubilization and Partition Coefficient
`Studies of Model Drugs
`
`Model drug lipophilicity as determined by oil/buffer
`partition coefficient and solubility studies are ranked in
`the order of PAA, BZ, PB, and B (Table 1). The
`solubilities of PAA and BZ in buffer (pH 7.0) increased
`with increasing Brij 97 concentration (Figure 3). There
`
`Briefly, dialysis bags (cellulosic membranes with
`MW cutoffs of 1 kd or 50 kd) containing the
`continuous phase
`(receiver phase) alone are
`suspended in a vessel containing the donor phase
`(diluted emulsion), and the system is stirred. At
`predetermined time intervals, each dialysis bag is
`removed and the contents are analyzed for released
`drug. The model drug submicron-sized emulsions (5
`mL) were directly placed into 500 mL of a stirred
`sink solution in which numerous dialysis sacs
`containing 2 mL of the same sink solution were
`previously
`immersed. The dialysis sacs were
`equilibrated with the sink solutions for about 30
`minutes prior to experimentation. At predetermined
`time intervals, dialysis bags were withdrawn and the
`contents assayed spectrophotometrically for model
`drug concentration. The
`release studies were
`performed at a fixed temperature of 37 C 0.10C
`under
`constant
`stirring. Measurements were
`conducted 3 times per sample, and mean values and
`standard deviations were calculated.
`
`RESULTS
`
`CMC Determination
`
`The CMC value of Brij 97 in O/W emulsion systems
`could not be measured directly because the oil phase
`would interfere with the various methods available
`for CMC analysis, such as surface
`tension,
`conductivity, and osmotic pressure determination.
`The CMC of Brij 97 in O/W emulsion systems was
`measured using the method of Yoon and Burgess (3),
`which was a membrane equilibrium technique in
`combination with surface
`tension measurement
`(surfactant concentrations well above the CMC were
`dialyzed from the donor to the receiver chamber
`using the side-by-side diffusion cell). The CMC
`values of Brij 97 in buffer and in 10% vol/vol O/W
`emulsion were 0.00154% wt/vol and 3.1% wt/vol,
`respectively (Figure 2).
`
`Surface Activity Determination
`
`The surface tension values of PAA, BZ, PB, and B
`were measured as a function of time at the air/water
`interface (Table 1). The surface tension of pure water
`is 71.32 mN/m, which decreased in the presence of
`
`5
`
`APOTEX 1027, pg. 5
`
`

`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`
`Figure 4. Effect of polyoxyethylene-10-oleyl-ether
`(Brij 97) concentration on oil/surfactant phosphate
`buffer solution partition coefficient of model drugs
`(pH 7.0, I = 0.2, 37° C).
`
`Figure 5. Effect of time on interfacial rheology of A –
`PAA, B – BZ, C – PB, and D – B, Brij 97, and model
`drug/Brij 97 mixture at mineral oil/buffer interface (pH
`7.0, I = 0.2, 25° C, mean values of 3 determinations).
`
`Emulsion Stability Determination
`
`Emulsion stability was evaluated as a function of
`storage time, temperature, and dilution using the
`mean droplet diameters and droplet size distributions
`obtained from Nicomp analysis (Table 2). The effect
`of dilution was investigated because all emulsions
`were diluted prior to the transport studies. Brij 97
`emulsions stored at 5 C, 25 C, and 37 C were
`stable over the 15-day study period because the mean
`droplet sizes, measured at different times during the
`study period, did not vary with normal size
`distribution. However, PAA and BZ samples stored
`
`6
`
`PAA
`BZ
`
`1275
`
`1225
`
`1175
`
`1125
`
`1075
`
`4 3
`
`3 8
`
`3 3
`
`2 8
`
`0
`
`0 . 0 2
`
`0 . 0 4
`
`0 . 0 6
`
`0 . 0 8
`
`0 . 1
`
`0 . 1 2
`
`0
`
`0 . 0 0 5
`
`0 . 0 1
`
`0 . 0 1 5
`
`0 . 0 2
`
`0 . 0 2 5
`
`0.5
`
`1.5
`1
`Brij 97 (% w/v)
`
`2
`
`2.5
`
`3000
`
`2500
`
`2000
`
`1500
`
`1000
`
`500
`
`Amount of model drug (mcg/ml)
`
`0
`
`0
`
`Figure 3. Effect of polyoxyethylene-10-oleyl-ether
`(Brij 97) concentration on
`the solubilities of
`phenylazoaniline (PAA) and benzocaine (BZ) in 0.05
`mol/L phosphate buffer (pH 7.0, I = 0.2, 37° C, mean
`values of three determinations); the error bars are
`within the symbols. Inserts are blown up for a
`magnified view at the Brij 97 critical micelle
`concentration region.
`
`is an apparent change in the slope of the PAA
`solubility versus the Brij 97 concentration plot at
`0.0015% wt/vol Brij 97. Similar
`trends were
`observed for PB and B. The solubilities of PB and B
`in buffer did not change in the presence of Brij 97.
`The model drug partition coefficients between oil
`and surfactant/buffer solutions (KS) were dependent
`on surfactant concentration (Figure 4). KS values
`decreased sharply initially with increase in surfactant
`concentration up to 1% wt/vol Brij 97 and then
`decreased with a shallow slope upon further increase
`in surfactant concentration.
`
`Interfacial Rheology Determination
`
`The interfacial elasticities of model drugs, Brij 97, and
`model drug/Brij 97 mixtures at the mineral oil/buffer
`interface were investigated as a function of time
`(Figure 5). Interfacial elasticity values of the model
`drugs and Brij 97 increased slightly initially and then
`remained constant over the 120-minute study period.
`The interfacial elasticity values of model drug/Brij 97
`mixtures
`increased gradually
`initially and
`then
`reached a value of 27 mN/m for PAA, 24 mN/m for
`BZ, 42 mN/m for PB, and 48 mN/m for B after 120
`minutes. However, the model drugs and Brij 97 alone
`reached values of 10 mN/m for PAA, 12 mN/m for
`BZ, 20 mN/m for PB, 36 mN/m for B, and 8 mN/m
`for Brij 97, during the 120-minute study.
`
`APOTEX 1027, pg. 6
`
`

`
`Table 2. Effect of storage time, temperature, and
`model
`drug
`on
`emulsion
`droplet
`size
`(polyoxyethylene-10-oleyl-ether [Brij 97] emulsions,
`pH = 7.4, I = 0.2). Temp = temperature.
`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`Increase in droplet size above 1  m was confirmed
`by Accusizer analysis. Dilution of emulsion samples
`with surfactant/buffer solution (1:1 dilution) did not
`affect mean droplet size over the 2-week study
`period.
`
`Phenobarbital
`
`barbital
`
`15 days
`94 2
`96 2
`96 2
`97 3
`
`Mean volume diameter (nm) of the emulsion droplets ± SD
`Temp
`(ºC) Phenylazoaniline Benzocaine
`5
`15 days 0 day
`0 day
`15 days 0 day
`15 days 0 day
`111 1 110 1 111 1 112 2 103 2 105 1 92 1
`25
`109 1 109 1 112 1 112 2 103 1 104 2 95 2
`37
`110 1 111 1 111 1 112 1 104 1 105 2 94 1
`60
`110 1 116 2 114 2 118 2 105 2 105 2 95 2
`
`Table 3. The effect of polyoxyethylene-10-oleyl-
`ether (Brij 97) micellar concentration on the
`effective
`permeability
`coefficient
`of
`phenylazoaniline
`(PAA)
`in 10% vol/vol O/W
`emulsion systems through dialysis (MW cutoffs 1
`kd and 50 kd) membranes at 37° C (n = 3).
`
`Effective permeability coefficient
`(cm/h) of PAA using different
`membranes
`1 KD (x 102)
`50 KD (x 102)
`0.030 0.0014
`0.032 0.0017
`0.062 0.0016
`0.087 0.0012
`0.082 0.001
`0.102 0.0028
`0.069 0.003
`0.088 0.0018
`0.051 0.002
`0.076 0.0022
`
`Brij 97
`(% w/v)
`
`0
`0.5
`1
`1.5
`2
`
`Table 4.The effect of polyoxyethylene-10-oleyl-ether
`(Brij 97) micellar concentration on the effective
`permeability coefficients of benzocaine, phenobarbital,
`and barbital in 10% vol/vol mineral oil/water (O/W)
`emulsion systems through dialysis (MW cutoffs 1 kd
`and 50 kd) membranes at 37° C (n = 3).
`Effective permeability coefficients (cm/h) of
`model drugs using different membranes
`Benzocaine
`Phenobarbital
`Barbital
`50 kd (x
`1 kd (x
`50 kd (x
`1 kd
`102) 1 kd (x102) 50 kd
`(x102)
`102)
`102)
`(x102)
`1.72
`2.14
`5.21
`5.41
`6.74
`6.81
`0.17
`0.41
`0.39
`0.05
`0.08
`0.15
`1.91
`2.41
`5.14
`5.36
`6.68
`6.78
`0.12
`0.01
`0.19
`0.28
`0.38
`0.45
`1.46
`1.94
`5.12
`5.34
`6.66
`6.72
`0.05
`0.11
`0.38
`0.16
`0.40
`0.35
`
`0
`
`1
`
`2
`
`97 (%
`wt/vol)
`
`at 60 C deteriorated within 9 to 15 days, as was
`evident from an increase and then a decrease in the
`mean droplet sizes determined using the Nicomp.
`
`7
`
`Transport Studies of Model Drugs in Brij 97 Solutions
`
`The effective drug permeability coefficients of the
`dialysis membranes (MW cutoffs 1 kd and 50 kd)
`under quasi steady-state conditions were calculated.
`These values are calculated from the slope of a plot
`of ln Qd (logarithmic value of drug concentration in
`the donor compartment)(determined using side-by-
`side diffusion cell technique) versus time for each
`model drug using Fick’s first law of diffusion
`equation (Tables 3 and 4). The effective permeability
`coefficients of the model drugs in buffer solution
`decreased as Brij 97 concentration increased. The
`effective permeability coefficients of PB and B in
`buffer systems (pH 7.0) decreased slightly compared
`with PAA and BZ when Brij 97 concentration
`increased.
`
`Effect of Brij 97 Concentration on Transport of
`Model Drugs in Triphasic Systems
`
`The presence of the micellar phase increased the total
`transport rates of PAA, BZ, PB, and B in emulsion
`systems (pH 7.0) at all concentrations studied up to
`1% wt/vol Brij 97 and then decreased with further
`increase in the micellar phase (Tables 3 and 4). The
`effective permeability coefficients of PAA, BZ, PB,
`and B
`increased with
`increase
`in Brij 97
`concentration using either the side-by-side diffusion
`cell or the reverse dialysis bag techniques up to 1%
`wt/vol Brij 97 and then decreased with further
`increase in Brij 97 concentration (Tables 4 and 5).
`Total transport rates of PB and B were faster than
`those of PAA and BZ at all
`the Brij 97
`concentrations investigated. The release patterns of
`the model drugs using the side-by-side diffusion cell
`technique were linear with time, and the total
`amounts of the model drugs released were less than
`those obtained using
`the reverse dialysis bag
`technique. The release patterns of the model drugs
`using
`the reverse dialysis bag
`technique were
`nonlinear with time.
`
`APOTEX 1027, pg. 7
`
`

`
`DISCUSSION
`
`Effect of Brij 97 (Nonionic Surfactant) on Model Drug
`Emulsion Stability
`
`The CMC values of Brij 97 in phosphate buffer and
`in the presence of emulsions (10% vol/vol O/W)
`were calculated from the surface tension data (Figure
`2). The CMC value of Brij 97 increased from
`0.00154% wt/vol in phosphate buffer to 3.1% wt/vol
`in the emulsion systems (10% vol/vol O/W) as a
`consequence of
`the
`large
`interfacial area of
`submicron-sized emulsions. Therefore, it is assumed
`that 3.1% wt/vol Brij 97 was required to form a
`surfactant monolayer at the emulsion (10% vol/vol
`O/W) interface. Consequently, surfactant in excess of
`that amount (added after emulsion formation) would
`be present in the continuous phase as monomers and
`micelles (6,7). This excess surfactant may aid
`emulsion stability (8) and may affect model drug
`transport. All emulsions were prepared with 3.1%
`Brij 97 initially to ensure monolayer coverage, and
`excess surfactant was added later by dilution.
`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`versus Brij 97 concentration above the CMC value of
`Brij 97 for all model drugs investigated (Figures 3
`and 4). In addition, the UV absorbance peaks of PAA
`and BZ shifted bathochromically in surfactant/buffer
`solutions,
`probably
`because
`of micellar
`solubilization. No significant change was seen in the
`solubilities of PB and B in pH 7.0 buffer in the
`presence of Brij 97, suggesting that these molecules
`were not solubilized in the micellar phase. The PB
`and B UV absorbance peaks were not shifted in
`surfactant/buffer solutions, suggesting that they do
`not form a complex with the surfactant. Therefore,
`the solubilities and consequently the transport of PB
`and B are unlikely to be affected by the presence of
`Brij 97 micellar phase.
`
`Amidon et al. (9) described the micellar solubilized
`drug free drug equilibrium distribution coefficient
`for 1:1 stoichiometry, Km as follows:
`
` (2)
`
` (3)
`
` (4)
`
`where Cw is the drug in the aqueous phase, Cm is the
`drug in the micellar phase, and SAA is the micellar
`phase; in other words, [SAA] = total Brij 97
`concentration – CMC of Brij 97, and [CT] is the total
`drug solubility. In the case of PAA, [SAA] = total
`Brij 97 concentration – intercept of X-axis in the
`solubility plot (Figure 3).
`
`The model drug equilibrium distribution coefficient
`between the buffer and surfactant phase (Km) was
`determined from the ratio of the slope of a plot of
`solubility versus surfactant concentration of model
`drug buffer solubility. The slopes of the solubility
`versus surfactant concentration plots for PAA and
`BZ at pH 7.0 (Figure 3) are 645 and 315,
`respectively. The Km values for PAA and BZ are 58
`and 0.25, respectively, indicating that PAA is more
`lipophilic. These results are in agreement with the
`partition coefficient data of the model drugs between
`mineral oil and buffer. It was not possible to
`
`the model drugs was
`The surface activity of
`determined from their capacity to decrease the
`surface tension value of water. Among the model
`drugs investigated, B is the most surface active,
`followed by PB. PAA and BZ are not considered
`surface active because
`they did not cause a
`significant reduction in the surface tension of water.
`PAA was the least soluble and had the highest log P
`value. PB and BZ have similar solubilities; however,
`the log P value of BZ was slightly higher than that of
`PB. The lower log P value of PB may be a result of
`the surface-active nature of PB. B was the most
`soluble and had the lowest log P value as a
`consequence of the increased hydrophilicity of this
`molecule and its greater surface activity.
`
`The solubilities of PAA and BZ in buffer (pH 7.0)
`increased with increasing Brij 97 concentration due
`to micellar solubilization of these hydrophobic model
`drugs (Figure 3). There is an apparent change in the
`slope of PAA and BZ solubility versus Brij 97
`concentration plot at 0.0015% wt/vol Brij 97. This
`correlates with the CMC value of Brij 97 as
`determined from surface
`tension measurements
`(0.00154% wt/vol, Figure 2). A constant slope was
`observed for the plot of all model drugs’ solubility
`
`8
`
`APOTEX 1027, pg. 8
`
`

`
`AAPS Pharmsci 2000; 2 (3) article 30 (http://www.pharmsci.org/)
`drug may also be responsible for a reduction in
`calculate precise Km values for PB and B because
`model drug transport rate. PB and B do not form
`their solubilities did not change significantly with
`complexes with Brij 97; therefore, no bathochromic
`surfactant concentration. The partition coefficient
`shifts were observed in the UV analysis. However,
`values of PAA and BZ between oil and
`their interfacial elasticity values when mixed with
`surfactant/buffer solution (KS) were calculated using
`Brij 97 differ significantly from those of the
`the following equation:
`individual moieties, which is probably due to the
`K
`surface-active nature of these model drugs (Figure
`0
`6). These data imply that all the model drugs
`SAA
`[K+1
`m
`investigated tend to associate at the interface either
`through
`their surface-active nature and/or by
`forming complexes with the surfactant.
`
`=K
`S
`
`
`
`
`
`
`
`]
`
`
`
`(5)
`
`
`
`where K0 is the O/W partition coefficient. O/W
`partition coefficient values decreased sharply with
`increase in surfactant concentration up to 1% wt/vol
`Brij 97 and decreased with a shallow slope, with
`further increase in surfactant concentration (Figure
`5). This change in the partition coefficient value
`with surfactant concentration is caused by change in
`the solubilizing capacity of the micelles in the
`aqueous phase; the change in capacity is a result of
`change in micellar shape from spheres to rods.
`Micellar shape changes were apparent from a
`nonlinear increase in intrinsic viscosity of surfactant
`solution with an increase in concentration of the
`model
`compounds. The
`viscosity
`changes
`associated with micellar shape change may also
`contribute to the change in the partition coefficient
`value. Micellar shape changes usually occur at
`higher surfac