Introduction
The mycophenolate mofetil powder for oral suspension, as an immunosuppressive agent, is widely administered in patients with kidney disorders and following organ transplantation in children [
1]. Currently, the drug powder is not produced in Iran and, due to limitations in its import from other countries, the patients are in dire need of it. In this regard, by the use of available information and the patent of drug (Cellcept®, 5688529A, Roche company, US), we attempted to localize the production of this drug. Since in the patent, many excipients are used, the screening was conducted to assess the role of these excipients including xanthan gum, colloidal silicon dioxide, soy lecithin, sorbitol, citric acid, sodium citrate, methyl, and propyl paraben. The results of screening demonstrated the determining role of xanthan gum and sorbitol in the final quality and stability of the suspension. Sorbitol is widely used as sweetening agent and a viscosity enhancer in the suspension, and provide steric protection against interparticle agglomeration [
2, 3]. The rheological properties of xanthan gum and its ability to provide flocculated suspension, having desired stability in different ranges of pH, temperature, and shaking speed. It can also reduce destabilizing processes of two-phase systems such as Ostwald ripening and Coalescence [
4, 5]. To further evaluate and determine the suitable amounts of these two excipients in the drug, experiments and response surface methodology were employed in this study.
Methods
Central composite design (CCD) was used to study the interaction of xanthan gum (mg) and sorbitol (gr) as independent variables, while F value (sedimentation volume) of suspension, concentration of active pharmaceutical ingredient (API) after preparation and after storage (%) were considered as dependent variables (
Table 1).
The design recommended 13 formulations with 10 g API, 25-75 mg xanthan gum, 10-25 g sorbitol, 500 mg colloidal silicone dioxide, 100 mg soy lecithin, 55 mg citric acid, 500 mg sodium citrate, 45 mg methyl paraben, 5 mg propyl paraben and purified water to adjust the volume to 50 mL.
To prepare the samples, 10 g of API with determined amounts of xanthan gum, colloidal silicone dioxide, soy lecithin, and sorbitol were blended in a cubic blender for 15 minutes and then transferred into Sigma mixer. The water solution containing citric acid and sodium citrate was gradually added to the powder to provide the paste. The content was dried at a room temperature for 24 hours and then passed through an oscillatory granulator to prepare granules. Finally, distilled water containing preservatives and banana flavor was added to the prepared granules and the F value reached 50 mL. The F value of suspension was calculated by dividing final sediment volume by initial sediment volume after keeping suspension still for 3 days. The reversed-phase high-performance liquid chromatography was employed to assess the concentration of API after preparation and after 3 months of storage at 45 ͦC in the oven. The optimization was done based on defined criteria for each dependent variable presented in
Table 1. Selected formulation was prepared three times and analyzed accordingly. The predicted error was calculated for all responses. The mean particle size and poly dispersity index (PDI) of optimum samples were characterized after preparation and storage.
Results
The results of analysis for dependent variables are shown in
Table 2.
The F value varied from 0.3 to 0.9 in prepared formulations. The results of analysis of variance regarding the P values and proposed quadratic model for this variable (F value) demonstrated that the increase in the amount of xanthan gum significantly increased the F value while the volume of sorbitol had no significant effect on the F value (
Table 2). The amount of API was preserved from 80 to 100% after preparation and 75-98% after storage. The suggested quadratic model for these two variables indicated that increase in the amount of xanthan gum significantly improved the preserved percentage of API, while the amount of sorbitol caused no significant improvement in the API preservation (
Table 2).
The optimum sample composed of 68.81 mg xanthan gum and 16.69 gr sorbitol with F value of 0.92, and API concentrations of 100% and 98% after preparation and after storage, respectively. The calculated predicter error was less than 5% for all study variables. The mean particle size and the PDI of optimum sample were 70.25 µm and 0.76 after preparation, and 75.50 µm and 0.94 after storage
Discussion
Formulation and processing of mycophenolate mofetil powder for oral suspensions have several challenges including physicochemical instability, pH-dependent solubility, sedimentation of particles, and effective taste masking [
6]. The increase in the stability of suspension can be performed through inhibiting the system coagulation by inter-particle repulsion and reducing the speed of particle sedimentation by increasing the viscosity of the continuous phase [
7]. Particle sedimentation can be considered as one of the most critical parameters which can affect the dose uniformity of the suspension [
8].
In this study, to prepare the mycophenolate mofetil powder for oral suspension, its different excipients were used of which xanthan gum and sorbitol significantly affected on the quality and stability of the product. Xanthan gum as the viscosity modifier and stabilizer was demonstrated to significantly enhance the F value of suspension and the protection of API concentration both after preparation and after storage for 3 months. The latter could be attributed to Xanthan gum’ ability for providing steric hindrance in particles and inhibiting crystal growth in the suspension [
9]. There was no significant difference in particle sizes after preparation and after 3 months of storage at high temperature. The amount of sorbitol as sweetening agent and stabilizer had no significant effect on the sedimentation volume and protection of API concentration. The stability of the prepared formulation of mycophenolate mofetil powder was better compared to the previously prepared galenic suspension of mycophenolate mofetil using Ora-plus agent having 70% protected API after 28 days of storage at room temperature [
10].
It can be concluded that the proposed formulation of mycophenolate mofetil powder with optimum amounts of xanthan gum and sorbitol has good stability. Higher amount of xanthan gum and moderate amount of sorbitol are recommended for preparing an optimal product.
Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Iran University of Medical Sciences (Code: IR.IUMS.REC.1399.1235). All ethical principles were observed in this study.
Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
Study concept and design: Homa Faghihi, Amin Umrani, Hamed Montazeri Ghods. Acquisition, analysis, or interpretation of data: Homa Faghihi, Amin Umrani, Hamed Montazeri Ghods, Parastoo Mirzabeigi. Drafting of the manuscript: Homa Faghihi, Amin Umrani, Zohreh Mohammadi. Critical revision of the manuscript for important intellectual content: Homa Faghihi, Amin Umrani, Hamed Montazeri Ghods, Ali Rastegari. Statistical analysis: Homa Faghihi. Administrative, technical, or material support: Homa Faghihi, Amin Umrani, Hamed Montazeri Ghods, Parastoo Mirzabeigi. Study supervision: Homa Faghihi, Amin Umrani, Hamed Montazeri Ghods, Zohreh Mohammadi.
Conflicts of interest
The authors declare no conflict of interest.
Acknowledgements
The authors would like to thank the staff of Laboratory of pharmaceutical processes and the Skill lab of Iran University of Medical sciences and the Zahravi pharmaceutical company for their cooperation in checking the quality of prepared samples.