Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge DOI:https://doi.org/10.31351/vol27iss2pp66-76 66 Studying the Effect of Variables on Acyclovir Microsponge Noor Y. Fareed *,1 and Hanan J. Kassab** *Department of Pharmaceutics, College of Pharmacy, University of Basra, Basra, Iraq.  Department of Pharmaceutics, College of Pharmacy, University of Baghdad, Baghdad, Iraq. Abstract The aim of the present investigation was to develop a microsponge delivery system of acyclovir to control its release when applied topically thereby reducing dosing frequency and enhancing patient compliance. The microsponge was produced by oil in oil emulsion solvent diffusion method. The effect of different formulation and process variables such as internal phase volume, polymer type, drug polymer ratio, stirring speed and stirring duration on microsponge production yield, loading efficiency, particle size, and in vitro drug release was evaluated. The results showed that the microsponge F2 prepared from Eudragit RS polymer had optimum physical properties regarding loading efficiency of 99.71±0.7 % and production yield which was 85%. Also, F2 showed 66% drug release through 8 hours. Accordingly, the oil in oil emulsion solvent diffusion method is an effective technique to formulate microsponge with maximum production yields and loading efficiency for acyclovir. Keywords: Microsponge, Acyclovir, Controlled topical release, Oil in oil emulsion solvent diffusion method. ةدراسة تاثير المتغيرات على اسفنجيات االسايكلوفر المايكروي **و حنان جالل كساب 1* ، نور يوسف فريد . العراق، البصرة ،جامعة البصرة، كليه الصيدلة ، فرع الصيدالنيات* .العراق، بغداد ،بغداد جامعة ،الصيدلة كليه ، فرع الصيدالنيات* الخالصة كاسفنجيات مايكرويه للتحكم بتحرر العقار عند وضعه على الغرض من الدراسة المقدمة هو تصنيع وتقييم عقار االسايكلوفير الجلد لغرض تقليل عدد الجرع اليومية وزيادة امتثال المريض للعالج. حضرت االسفنجيات المايكرويه بواسطة طريقة شبه المستحلب رعة الخلط نسبة الدواء إلى البوليمر، سالمتضمن انتشار المذيب إلى المكون الخارجي الزيتي ثم اختبر تأثير متغيرات طريقة التحضير ك ،وحجم المذيب في الطور الداخلي للمستحلب . كما تم تقيم االسفنجيات بالنسبة الى حجم الجسيمات ، نوع البوليمر ، ، مدة الخلط ( أبدت أفضل الخصائص ٢خصائص السطح وتحرر الدواء خارج الجسم. أثبتت النتائج ان التركيبة) ، كفائة التحميل ، الحصيلة اإلنتاجية . كما أن التركيبة % ٨٥وقابلية التحميل التي كانت، % ٧١،99 ± ٧،٠كالقابلية اإلنتاجية بمقدار، الفيزيائية لالسفنجيات المايكروية ساعات . من خالل نتائج الدراسة تبين نجاح طريقة شبه المستحلب المتضمن انتشار ٨خالل % ٦٦( أبدت تحرر للدواء خارج الجسم ٢) المذيب إلى المكون الخارجي الزيتي لتحضير أسفنجيات االسايكلوفير المايكروية بقدرة إنتاجية و كفاءة تحميل عالية. ، االسايكلوفير ، التحكم بتحرير العقار ، طريقة شبه المستحلب المتضمن انتشار المذيب. اسفنجيات:الكلمات المفتاحية Introduction Microsponges are polymeric porous microspheres used for controlled delivery of medications (1) .This technology has been used for topical formulations and recently for oral administration. Microsponges are biologically safe and are believed to contribute towards reducing side effects, improved stability, increased elegance and enhanced formulation flexibility(2). Even though microsponges are very small in size; they are not able to permeate the skin and are not absorbed systemically; therefore, they are considered drug delivery systems for topical use. Microsponges accumulate in the tiny nooks and crannies of the skin, and release slowly the entrapped drug as the skin requires(3). Microsponges MS can be incorporated into a wide variable of pharmaceutical dosage form, like tablets(4), capsules(5), powders, creams(6), topical emulsions (7), gels (8–10) , etc. Acyclovir ACV was the first antiviral to be approved for the treatment of viral infections such as herpes simplex, varicella zoster virus and Epstein Barr infections(11). ACV is hydrophilic in nature having water solubility of 2.5mg/ml at 37° C. The chemical structure of ACV is shown in Figure 1. 1Corresponding author E-mail: nalbassam@ymail.com Received: 8 / 8 / 2018 Accepted: 3 / 10 / 2018 Iraqi Journal of Pharmaceutical Sciences https://doi.org/10.31351/vol27iss2pp66-76 http://bijps.com/index.php/bijps/index Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 67 Topical delivery of ACV is considered to be attractive choice for viral infection of the skin, as targeted therapy is enabled, circulating drug levels and risk of renal insufficiency will be reduced(12). Poor penetration across the skin decreases the therapeutic value of topical ACV marketed creams (13). High potency formulation and five applications per day are required to achieve the desired antiviral effect, which may cause skin irritation and decrease patient compliance. The aim of the present study was to develop ACV microsponges intended for controlled topical delivery of ACV. The o/o emulsion solvent diffusion method was adopted to prepare ACV microsponge due to low solubility of ACV in the external oil phase; the drug loss was minimized leading to an increase production yield and drug loading efficiency. Different formulation variables (internal phase volume, polymer type, drug to polymer ratio) and processing variables (stirring speed and stirring duration) were evaluated to maximize the encapsulation efficiency and optimize release characteristics. Figure 1. The chemical structure of acyclovir Materials and Methods Materials Acyclovir ACV was purchased from Hangzhou Hyper Chemicals limited, China. Eudragit RS 100 and Eudragit RL 100 were from Evonik Rӧhm GmbH, Germany. Light liquid paraffin, acetone, n-hexane, magnesium stearate, potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, and cellulose nitrate filter with molecular weight cut off 8000-14000. Methods All ACV microsponge formulas were prepared by oil in oil quasi-emulsion solvent diffusion method. The internal phase was prepared by dissolving the polymer into acetone by sonication using SONOREX (Bandelin, Berlin, Germany) to obtain a clear polymeric solution. The drug and Mg-stearate were added to the prepared polymeric solution. The internal phase is added drop wise at a rate of 1 ml per min to 100ml of liquid paraffin with stirring at (500, 1000and 1500 rpm) by using mechanical overhead stirrer (RZR 2041 Heidolph TM, Schwalbach, Germany) for (30, 60 and 120 min) at which the organic solvent could evaporate, and the solidified MS precipitated. The MS were collected by filtration using of Büchner filtration device and was washed six times using n- hexane and left to dry over night at room temperature. The composition of various MS formulations is given in Table 1. Table 1 .Composition of ACV loaded microsponges Formula Code Polymer type Drug / polymer ratio Solvent volume (ml) Stirring rate (rpm) Stirring time (min.) F1 ERS 1:1 5 500 60 F2 ERS 1:1 7.5 500 60 F3 ERS 1:1 10 500 60 F4 ERS 1:1 7.5 500 30 F5 ERS 1:1 7.5 500 120 F6 ERS 1:1 7.5 1000 60 F7 ERS 1:1 7.5 1500 60 F8 ERS 2:1 7.5 500 60 F9 ERS 1:2 7.5 500 60 F10 ERL 1:1 7.5 500 60 F11 ERS: ERL 1:1 7.5 500 60 *All microsponges were prepared by using 0.5 g of polymer and 100 ml of liquid paraffin. *Magnesium stearate was added as a percentage weight relative to the acetone volume Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 68 Characterization of microsponges formulation Determination of production yield The production yield of the microsponge was obtained from the weight ratio of filtered and dried microsponge amount of each formulation to total solid material amount in the dispersed phase (drug, polymer and Mg stearate) as given in the following equation: PY(%)= 𝑷𝒓𝒂𝒄𝒕𝒊𝒄𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒕𝒉𝒆 𝑴𝑺 𝐓𝐡𝐞𝐨𝐫𝐞𝐭𝐢𝐜𝐚𝐥 𝐰𝐞𝐢𝐠𝐡𝐭 (𝐝𝐫𝐮𝐠,𝐩𝐨𝐥𝐲𝐦𝐞𝐫 𝐚𝐧𝐝 𝐌𝐠 𝐬𝐭𝐞𝐚𝐫𝐚𝐭𝐞) × 𝟏𝟎𝟎% Determination of loading efficiency LE The drug content was determined in the prepared microsponge by crushing the MS using a porcelain mortar. Accurately weighed 100 mg of this powder was extracted in 100 ml of NaOH. The solution was sonicated for 15 min and left for 24 hours. The solution then was filtered and diluted (if necessary, a sample of 1ml was withdrawn from this solution, diluted to 100 ml with NaOH) and assayed spectrophotometrically at 264 nm (Cecil spectrophotometer CE7200;UK) to determine the ACV content. The loading efficiency was determined according to the following equation: 𝑳𝑬(%) = 𝑨𝒄𝒕𝒖𝒂𝒍 𝒅𝒓𝒖𝒈 𝒄𝒐𝒏𝒕𝒆𝒏𝒕 𝒐𝒇 𝑴𝑺 𝑻𝒉𝒆𝒐𝒓𝒆𝒕𝒊𝒄𝒂𝒍 𝒅𝒓𝒖𝒈 𝒄𝒐𝒏𝒕𝒆𝒏𝒕 𝒐𝒇 𝑴𝑺 × 𝟏𝟎𝟎% Determination of particles diameter The optical microscope (Olympus, Japan) was equipped with graduated eye piece and was used to estimate the average diameter of ACV microsponges, under (10 X) magnification power, in which, 100 MS particles of each batch were examined. The average particle diameter was determined according to the following equation: d av = ∑ 𝒏𝒅 ∑ 𝒏 Where: dav is the average diameter of particles (μm), n is the number of particles per group, and d is the middle value (μm). Scanning electron microscope (SEM) study The surface topology and particle morphology of the prepared microsponge was studied using Carl Zeiss - SUPRA 55VP FE- SEM, Germany. The samples were first loaded on sample stub using a double side carbon tape and sprinkle the powder on it then tight all stubs on the specimen’s holder after simple blowing to remove non-adherent particles. The prepared samples were loaded on SEM via air-lock door which depends on low voltage to avoid charging. Solid state characterization of microsponge DSC, XRD and FTIR were employed to characterize the physical state of the drug in the prepared microsponge and to confirm the absence of interaction within formulation. The pure drug (ACV), polymer (Eudragit RS), Mg- stearate, the physical mixture of all formula components and AVC MS, were investigated individually using each of these techniques. Differential scanning calorimetry (DSC) Thermal analysis was carried out using DSC-600, Shimadzu, Japan by loading 5 mg of the powder into a sealed aluminum pan, which was compared with a sealed blank aluminum crucible as reference. The temperature was raised from 25°C to 300°C in a nitrogen atmosphere at the rate of 10°C per minute. The flow rate of nitrogen was 50 ml per minute. X-ray diffractometry (XRD) An XRD pattern was determined using X-Ray Diffractometer-6000, Shimadzu, Japan. The results were recorded over a range of 5–50° (2θ). The operating conditions were: voltage 40 kV, currente30 mA, scanning speed 8 deg /min. Fourier transform infrared spectroscopy (FTIR) The IR spectrum was recorded using FTIR 600 spectrometer, UK. The sample was crushed with potassium bromide with a porcelain mortar and pestle. The mixture was then compacted to form a translucent pellet with the aid of a mechanical die press to obtain KBr discs. These discs were scanned in frequency range of 4000-400 cm-1. In vitro release studies Drug release rate from ACV microsponge was carried out through dialysis bag technique using USP dissolution test apparatus-II. The dissolution media consisted of 900 ml phosphate buffer having a pH of 7.4. Accurately, weighed samples of ACV microsponge equivalent to 50 mg of the drug was suspended in 5 ml phosphate buffer (pH 7.4) in a dialysis bag and the rotation speed was adjusted at 50 rpm at 37°C. At prescheduled time intervals (30min, 60min, 120min, 180min, 240min, 300min, 360min, 420min, and 480min) 10 ml of the media were withdrawn and replaced by an equal volume of dissolution medium to maintain a constant volume. The samples were filtered through a (0.45 μm, Millipore) filter, suitably diluted (if necessary ,1 ml of filtrate diluted to 10 ml with phosphate buffer solution) and analyzed at 252 nm using a double-beam Cecil spectrophotometer CE 7200; UK. These experiments were conducted in triplicate. Kinetic modeling of ACV release The data obtained from the in vitro release studies were fitted to different Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 69 mathematical expressions to describe the kinetic and mechanism of ACV release from the microsponge selected formula with the aid of DDSolver an Microsoft Excel add-in (14). The kinetic models used were zero order kinetic , first order kinetic , Higuchi model and Korsmeyer - Peppas (15). The model with the highest correlation coefficient was the best fitted model. Statistical analysis Results of each experiment was reported as a mean ± standard deviation and were analyzed according to the one-way analysis of variance (ANOVA) test, using Microsoft Excel Program 2010. Differences were statistically significant at p < 0.05. Results and Discussion In this study. two types of Eudragit polymers (Eudragit RS and Eudragit RL) were used as a matrix forming agent for ACV microsponges. These polymers are known for their release retarding properties (16). The internal phase solvent used in this experiment was acetone. The compatibility of acetone with liquid paraffin system is attributed to the partial polarity of acetone (17). The oil in oil emulsion diffusion method successfully produced microsponge particle having a uniform spherical shape with high production yield and excellent loading efficiency owning to the low drug solubility in the external phase. The rationalization for Mg-stearate use, is the ability of metal stearate to form a protective shell surrounding the sponge particle and of great benefit in decreasing the coalescence and aggregation (18). The microsponge production yield and loading efficiency is summarized in table 2 Table 2. Characterization of acyclovir microsponges Characterization of F1-F3 revealed that the MS were formed when the volume of inner phase ranged from 5 to 10 ml. The particle size significantly (p < 0.05) decreased with increasing the inner phase volume, because the lower inner phase viscosity led to breaking of the emulsion into smaller droplets forming microsponges with small particle size (19). The loading efficiency was found to decrease at larger internal phase volumes because the reduction in the viscosity of the internal phase enhance drug escape to the periphery(20). Accordingly; 7.5 ml of acetone were found to produce microsponge of acceptable properties in term of loading , yield and particle size. Stirring duration was found to have significant effect on microsponge formation and 60 minutes was found to be most effective, while 30 minutes of stirring was insufficient for complete solvent diffusion and resulted in a lower yield. Stirring for 120 minutes did not significantly affect the microsponge particle size or loading efficiency (p > 0.05). The effect of different polymers and polymer combination on ACV microsponge was studied in F2, F10 and F11 prepared from Eudragit RS, Eudragit RL, and Eudragit RS - Eudragit RL at 1:1 drug to polymer. Particle size was found to be insignificantly affected with changing polymer type (p > 0.05) as the viscosity of the employed Eudragit polymers is similar resulting in comparable internal phase viscosity and similar viscosity difference between the internal and external phase (21) . The loading efficiency was significantly lower (p<0.05) with Eudragit RL microsponges because higher content of the ammonium group facilities the diffusion of some of the entrapped drug to the surrounding medium during formation of the microsponges(22). Increasing the ratio of the drug to the polymer resulted in particle size significant reduction (p<0.05), since the amount of the polymer available per each microsponge was relatively lower than microsponge prepared at lower drug to polymer ratio (23). Also, the Loading Formula code Production yield (%) Loading efficiency (%) Particle diameter (um) F1 67 98.77±0.3 47.23±0.75 F2 85 99.71±0.7 32.36±0.85 F3 88 88.59±0.36 26.57±0.51 F4 75.7 98.72±0.54 39.05±0.73 F5 87 99.28±0.2 30.64±0.5 F6 57 99.35±0.2 21.06±0.3 F7 45 97.31±0.5 16.84±0.4 F8 73 96.65±0.47 28.86±0.31 F9 85 94.05±0.23 51.13±0.32 F10 82 90.84±0.28 31.65±1.65 F11 83 98.12±0.35 30.23±1.45 Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 70 Efficiency was significantly reduced (p<0.05) as lower amount of polymer to the drug produced lower viscosity enhancing drug escape to external media thereby reducing loading efficiency and drug entrapment in the MS(24). Increasing the stirring speed reduced the production yield, due to adherence of the polymer to the walls of the glass container as a result of the vigorous turbulence created in the external phase (25). Also, the particle size was significantly decreased (p<0.05) as the stirring speed increased, since high mechanical shear applied, resulting in a rapid splitting of the formed droplets, allowing less chance of coalescing into bigger droplets(26). The most suitable stirring speed was found to be 500 rpm. Scanning electron microscope (SEM) SEM analysis of the selected microsponge formula is shown in Figure (2). MS were spherical in shape, having uniform size distribution with rough surface contains pores and crakes resulted from diffusion of the solvent. Figure 2. SEM of microsponge F2 [A] 1.5KX magnification [B] 1.0KX magnification Solid state characterization of microsponge According to DSC analysis illustrated in Figure 3, ACV displayed a sharp characteristic endothermic peak at 259°C corresponding to the melting point of the drug in the crystalline form, While Eudragit RS thermogram showed one transition only at 65°C which represents the glass transition temperature of the polymer in the amorphous state. The drug peak was obvious in the physical mixture which excludes in-compatibility. The disappearance of the melting point peak of acyclovir from the selected microsponge formula thermogram is explained by the uniform dispersion of the drug into the polymeric matrices (27) . 100.00 200.00 300.00 Temp [C] -10.00 0.00 mW DSC 259.48x100C 176.83x100C 100.00 200.00 300.00 Temp [C] -3.00 -2.00 -1.00 0.00 mW DSC Figure 3. DSC thermograms of [A]pure ACV [B] Eudragit RS100 A B A B Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 71 100.00 200.00 300.00 Temp [C] -10.00 -8.00 -6.00 -4.00 mW DSC 115.50x100C 176.50x100C 257.39x100C 100.00 200.00 300.00 Temp [C] -1.00 0.00 1.00 2.00 mW DSC 176.33x100C 92.40x100C Continued Figure 3. Eudragit RS100 [C] physical mixture [D] microsponge F2 XRD diagrams are shown in Figure 4a,4b Eudragit RS100 showed typical diffraction form of amorphous materials, whereas the pure drug showed the diffractogram pattern of a crystalline material at 2θ of 7.0154 °, 29.1349° and 26.0690°. The physical mixture and the selected microsponge formula showed a diffraction pattern in which ACV characteristic crystalline diffraction peaks present at 2θ are in the same position of the pure sample but with reduced intensity due to the presence of the polymer(28) . Figure 4. a. XRD of pure ACV [A]eudragit RS100 [B] C D A B Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 72 Figure 4b. XRD of Physical mixture [C] microsponge F2 [D]. The FTIR absorption bands of Pure ACV were noticed at 3519 cm-1 (O-H stretching), 3471 cm-1 and 3440 cm-1 (N-H stretching), (2962 cm-1 , 2927 cm-1) (aliphatic C-H stretching a symmetric), 2854cm-1, 2871 cm-1 (aliphatic C - H stretching symmetric), 1485cm-1 (aliphatic C -H deformation), 1716cm-1 (C = O stretching) and 1049. cm-1 ( C- O stretching), while for Eudragit RS100, asymmetric C - H stretching bands appeared at 2993 and 2954 cm-1, while the band at 2850 cm-1 represent symmetric C-H stretching, the carbonyl group C=O of an ester exhibited a stretching vibration at 1732cm-1, as seen in Figure 5. The characteristic absorption bands of the drug were retained in the physical mixture and the selected microsponge formula with no new peaks appearance which confirms chemical computability between the formulation component and the absence of any chemical interaction. C D Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 73 Figure (5): The FTIR spectrum of [A]pure ACV [B] eudragit RS100 [C] physical mixture [D] microsponge F2 Study of ACV release profiles from the microsponge In vitro release study was performed to investigate the effect of different variable on drug release from the microsponges. The effect of changing drug polymer ratio on drug release was illustrated in figure (6). The best retardation is obtained as the amount of polymer to the drug is increased since increased particle size decreases the effective surface area and increasing the path length traveled by the drug molecule (29). Besides , at higher drug ratio , more drug would present near to and on the surface of the microsponge which is in direct contact with the dissolution media accounting for the rapid release(30). The release profile is also affected by varying polymer type as shown in figure 7. ACV release rate increased from 66 % with F2 (ERS) to 80.22 % for F11(ERS: ERL) and 92.99 % for F10 (ERL) for a duration of 8 hours. Eudragit RS was the least permeable of the three formulas and the most capable of sustaining drug release. This is explained by different structural properties of the two polymers in term of percentage of the quaternary ammonium group present which is (10%) in Eudragit RL 100 while Eudragit RS 100 contains only (5%). Thus, Eudragit RL 100 is more permeable and release the drug at a faster rate than Eudragit RS(21). The effect of stirring speed on drug release was evaluated by comparing the release behavior from F2, F6 and F7 prepared at stirring speeds of 500, 1000 and 1500 rpm as provided in Figure 8. Drug release was faster for F7 than F6 and F2 since it has lower particle size resulted from high stirring speed which led to an increase surface area exposed to the dissolution medium and subsequently release rates are faster.(31) . Figure 6. Effect of drug: polymer ratio on % drug release from F2, F8 and F 9. A B C D Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 74 Figure 7. Effect of polymer type on % drug release from F2, F10 and F 11. Kinetic Analysis of ACV Release Data from F2 Microsponge The release of ACV from microsponge F2 obeys zero order release as their R2 values gave the higher result, the release depends on the MS pore size and release of AVC from the pore rather than the concentration of AVC inside the MS. The mechanism of drug release is non - Fickian diffusion Supercase ΙΙ as the release exponent " n " value of F2 microsponges is more than 1. Supercase ΙΙ release behavior meaning that the release depends on polymer relaxation rather than water diffusion inside the microsponge as shown in table 3. Figure 8. Effect of stirring speed on % drug release from F2, F6 and F7. Table 3 . Kinetic analysis of ACV release data from F2 microsponge F o r m u la Mathematical model for drug release kinetics Korsmeyer-Peppas Zero order First order Higuchi Hixson- Crowell F2 K0 R2 K1 R2 Kh R2 kHC R2 R2 KKP n 0.116 0.9386 0.001 0.8965 2.064 0.7570 0.000 0.9115 0.9452 0.047 1.153 Conclusion It can be concluded from the results obtained in this study that the oil in oil emulsion solvent diffusion method is an effective technique to formulate microsponge based delivery system of acyclovir with maximum production yields and drug loading efficiency. The ACV microsponge formulated with the Eudragit RS at drug: polymer ratio of 1:1 is the best formulation among all the prepared batches in terms of capacity of extending drug release behind 8 hours thereby decreasing the number of applications and enhancing patient compliance. References 1. Mohite PB, Khanage SG, Harishchandre VS, Yogita S. Recent advances in microsponges drug delivery system. Journal of Critical Reviews. 2016;3(1):9–16. 2. Tiwari A, Mishra MK, Shukla A, Yadav SK. Microsponge: An augmented drug delivery system. American Journal of PharmTech Research. 2016;6(6):79–95. 3. Junqueira MV, Bruschi ML. A review about the drug delivery from microsponges. American Association of Pharmaceutical Scientist. 2018 4. Charagonda S, Puligilla RD, Ananthula MB, Bakshi V. Formulation and evaluation of famotidine floating microsponges. International Research Journal of Pharmacy. 2016;7(4):62–67. 5. Al-Mosawi JM, Abdul-Razzaq A, Mahmood HS. Formulation and invitro evaluation of clarithromycin floating microsponge capsule A. Kerbela journal of pharmacy and pharmaceutical science. 2016;11:27–35. 6. Li SS, Li GF, Liu L, Jiang X, Zhang B, Liu ZG, et al. Evaluation of paeonol skin-target delivery from its microsponge formulation: In Vitro skin permeation and In Vivo microdialysis. PLoS One. 2013;8(11):1–8. Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 75 7. Nokhodchi A, Jelvehgari M, Siahi MR, Mozafari MR. Factors affecting the morphology of benzoyl peroxide microsponges. Micron. 2007;38:834–840. 8. Panday P, Shukla N, Sisodiya D, Jain V, Mahajan S. Design and characterization of microsponge loaded controlled release epicutaneous gel of lornoxicam. Applied Medical Research. 2015;1(1):16–21. 9. Mehta M, Panchal A, Shah VH, Upadhyay U. Formulation and in-vitro evaluation of controlled release microsponge gel for topical delivery of clotrimazole. International Journal of Advanced Pharmaceutics. 2012;2(2):93–101. 10. Ravi R, Kumar SKS, Parthiban S. Formulation and evaluation of the microsponges gel for an anti acne agent for the treatment of acne. Indian Journal of Pharmaceutical Science and Research. 2013;3(1):32–38. 11. Gnann JW, Barton NH, Whitley RJ. Acyclovir: Mechanism of action, pharmacokinetics, safety and clinical applications. The Journal of Human Pharmacology and Drug Therapy. 1983;3(5):275–283. 12. Seth AK, Misra A, Umrigar D, Vora NV. Role of acyclovir gel in herpes simplex: clinical implications. Medical science monitor. 2003;9(7):193–198. 13. Shaw M, King M, Best JM, Banatvala JE, Gibson JR, Klaber MR. Failure of acyclovir cream in treatment of recurrent herpes labialis. British medical journal. 1985;291:7–9. 14. Zhang Y, Huo M, Zhou J, Zou A, Li W, Yao C, et al. DDSolver : An add-in program for modeling and comparison of drug dissolution profiles. American Association of Pharmaceutical Scientists Journal. 2010;12(3):263–271. 15. Lobo MS, Costa P. Modeling and comparison of dissolution profiles . European Journal of Pharmaceutical Sciences. 2001;13:123–133. 16. Thakral S, Thakral NK, Majumdar DK. Eudragit®: A technology evaluation. Expert Opinion on Drug Delivery. 2013;10(1):131–149. 17. Rizkalla CMZ, Aziz RL, Soliman II. In Vitro and In Vivo evaluation of hydroxyzine hydrochloride microsponges for topical delivery. American Association of Pharmaceutical Scientist. 2011;12(3):989– 1001. 18. Bogataj M, Mrhar A, Grabnar I, Rajtman Z, Bukovec P, Srcic S. The influence of magnesium stearate on the characteristics of mucoadhesive microspheres, Journal of Microencapsulation. 2000; 17(4) : 499-508, 19. Kiliçarslan M, Baykara T. The effect of the drug/polymer ratio on the properties of the verapamil HCl loaded microspheres. International Journal of Pharmaceutics. 2003;252:99–109. 20. Bothiraja C, Gholap AD, Shaikh KS, Pawar AP. Investigation of ethyl cellulose microsponge gel for topical delivery of eberconazole nitrate for fungal therapy. Therapeutic Delivery. 2014;5(7):781–794. 21. Joshi AS, Patil CC, Shiralashetti SS, Kalyane N V. Design, characterization and evaluation of Eudragit microspheres containing glipizide. Drug Invention Today. 2013;5:229–234. 22. Nath B, Nath LK, Kumar P. Preparation and in vitro dissolution profile of zidovudine loaded microspheres made of Eudragit RS 100, RL 100 and their combinations. Acta Poloniae Pharmaceutica - Drug Research. 2011;68(3):409–415. 23. Sonali S, Singh RP, Prajapati SK. Formulation and evaluation of prednisolone loaded microsponges for colon drug delivery: In-Vitro and pharmacokinetic study. International Journal of Pharmaceutical Sciences and Research. 2014;5(5):1994–2005. 24. Dunaka S, Chittipol SK, Vechha M, Ale B. Formulation and In vitro characterization of ramipril microspheres. Indian Journal of Pharmaceutics. 2011;2(2):47–52. 25. Desavathu M, Pathuri R, Chunduru M. Design, development and characterization of valsartan microsponges by quasi emulsion technique and the impact of stirring rate on microsponge formation. Journal of Applied Pharmaceutical Science. 2017;7(1):193–198. 26. Sahoo SK, Behera AL, Patil S V., Barik BB, Safhi MM. Consequences of formulation variables on physicochemical properties of indinavir sulfate microspheres. Jordan Iraqi J Pharm Sci, Vol.27(2) 2018 Acyclovir microsponge 76 Journal of Pharmaceutical Sciences. 2011;4(3):251–260. 27. Deore KL, Thombre NA, Gide PS. Formulation and development of tinidazole microspheres for colon targeted drug delivery system. Journal of Pharmacy Research. 2013;6:158–165. 28. Nhire N, Derle D V. Development and evaluation of drug loaded eudragit rs- 100 microspheres for colon specific drug delivery system. The Pharma Innovation- Journal. 2014;2(12):67–78. 29. Gaur PK, Mishra S, Bajpai M. Formulation and evaluation of controlled-release of telmisartan microspheres: In vitro/in vivo study. Journal of Food and Drug Analysis .2014;22:542–548. 30. Jelvehgari M, Barar J, Valizadeh H, Shadrou S, Nokhodchi A. Formulation, characterization and in vitro evaluation of theophylline-loaded Eudragit RS 100 microspheres prepared by an emulsion- solvent diffusion/evaporation technique. Pharmaceutical Development and Technology. 2011;16(6):637–644. 31. Haznedar S, Dortunç B. Preparation and in vitro evaluation of Eudragit microspheres containing acetazolamide. International Journal of Pharmaceutics. 2004;269:131– 140.