full issue - Association of Biotechnology and Pharmacy

Current Trends in Biotechnology and PharmacyVol. 5 (2) 1110-1122 April 2011. ISSN 0973-8916 (Print), 2230-7303 (Online)1119In the present study the influence of oiltype, quantity of oil, type and concentration ofsurfactant on particle size, zeta potential andloading efficiency were studied by using photoncorrelation spectroscopy, HPLC with UVdetector. An essential component of the emulsionis the internal lipid core which constitutes the drugdissolved in oil and is surrounded by a thin layerof non-ionic surfactant. Sesame and olive oils areof vegetarian origin, bio-compatible and being usedas edible oils from ancient times (19, 20).Moreover they are easily available and to ourknowledge carvedilol loaded nano emulsionswere not reported with these oils. Both the oilswere stable at room temperature and they do notbecome rancid like other oils due to the presenceof natural antioxidants. All these reasons motivateto select the sesame and olive oils for the presentstudy. They have blood pressure reducingproperties therefore their quantity was limited to200µl (19). In all the formulations with 100µl ofeither sesame oil or olive oil the drug was depositedat the bottom of the beaker and the drug contentwas found to be less than 50%. This indicatedthat the volume of the oil was not sufficient tohold the entire drug inside. Hence the volume ofoil was increased to 150 µl. In this case no drugwas seen at the bottom of beaker and the drugcontent was drastically increased to 98.93±1.31%which revealed that 150µl of oil was sufficient tohold 6.3mg of carvedilol. With increasing oil phasevolume from 100µl to 200µl, a significant increasein globule size was observed in both the oils andthe results were shown in Fig.1.Surfactants play a major role in thepreparation and stability of NEs. Surfactants forma monomolecular film around the disperseddroplets and there by reduces the interfacialtension and prevent the droplet coalescence. Brij-97 and tween-80 were used as surfactants forthe present study. Though they are non-naturalsurfactants, they do not produce any toxic effectswhen administered orally. The amount ofsurfactant is also important to form rigid filmaround dispersed globules. However use of excessamount of emulsifier can cause decrease inentrapment efficiency, burst release and formationof other colloidal species like liposomes andmicelles and may even cause toxic effects (20).From the table it was evident that with increasingconcentration of surfactant the globule size wasdecreased but the drug content was decreasedand the optimum concentration of surfactant wasfound to be 1.25% in case of brij 97 and 1.5% incase of tween 80.All the nanoemulsion compositions posses’negative zeta potential, this may be due to thenegative charge of fatty acids. The zeta potentialis a measure of the surface charge and isimportant in keeping the droplets in dispersedstate. The particle interactions are also controlledby the magnitude of the apparent surface chargeof the dispersed globules. Torrey et al (2006)reported that, the ZP of particle formulations is avalue of greater than +30mv or lower than -30mvfor ensuring electrostatic stability. However, thissuggested zeta potential cut off point is anexperience based value and cannot be reliablyused to predict the stability of NEs because awide range of absolute zeta potential values (i.e.,1.5, 12.5, 45.5mv) have been reported for SNEDSand NEs (21,22). The zeta potential depends onthe pH of the nanoemulsion. At lower PH valuesthe zeta potential will be positive and at higherpH values it will be negative. The pH of all NEswas in the range of 6.5±0.03 to 6.8±0.03 and wasalso responsible for negative zeta potentials ofNEs.Carvedilol was a poorly soluble and poorlypermeable drug and its Pka at pH 7.4 was 8.8.At this pH the degree of ionization will be almost100% and it is assumed that the rate of solubilityand hence the rate of drug release will beKoteswari Poluri et al