# Freeze-Drying Ethlycellulose Microparticles Loaded with
## 3 Results and Discussion
### In Vitro Release Study of the Ethylcellulose Microparticles Loaded with ETO  
The release of ETO from prepared microparticles before and after freeze-drying in 0.1 N HCl at pH 1.2 (simulated gastric fluid without enzymes) and in phosphate buffer at pH 7.4 (simulated intestinal fluid without enzymes) was studied. The results showed that the percentage of drug released from the prepared microparticles was highly affected by the pH of the dissolution medium. The release of ETO from the prepared microparticles without freeze-drying at pH 1.2 (simulated gastric fluid without enzymes) was slow and  
Figure 4: The amount of etoposide encapsulated into 50 mg of ethylcellulose microparticles dried using the freeze-drying technique. Figure 5: FT-IR spectra of the formulated ethylcellulose-loaded etoposide microparticles. From top to bottom: EC, physical mixture of EC-ETO, and ETO. incomplete. More specifically, the percentage of drug released after 1 h was 24, 15, 13, and 0% for microparticles with drug-polymer ratios of 1:1, 1:3, 1:6, and 1:20, respectively, while after 2 h (maximum gastric residence time), the percentage of drug released from the same type of microparticles was 49, 33, 36, and 24%, respectively. These results match the results reported by [PERSON] et al., who showed that drug-loaded EC microparticles' burst release at intestinal pH might be due to the slow and sustained release of the drug that accumulated on the surface of the microparticles. Additionally, the drug and polymer concentrations showed that a decrease in EC concentration assisted in regulating drug release from the microparticles. Furthermore, there was no significant release of drugs at gastric pH, which indicates that the EC polymer is gastro-resistant [35] (Figure 6). Similar release results in simulated gastric and duodenal pH were also obtained by [PERSON] et al., who formulated sustained-release ketoprofen microparticles coated with ethylcellulose and carboxymethyl ethylcellulose [36]. Further, the freeze-dried microparticles were stable in 0.1 N HCl (gastric pH) for 2 h, as no significant release was recorded. The results of the percentage of ETO released from the prepared microparticles at pH 7.4 before freeze-drying showed that all microsphere formulations controlled and reduced the release rate of ETO in comparison with free ETO. The dissolution data showed that the release of ETO after 10 h was only 55 to 70%. Figure 7 shows the percentage of ETO released from the freeze-dried microparticles. From the dissolution data in Table 2, it is evident that the freeze-dried microparticles with drug-polymer ratios of 1:1, 1:3, and 1:6 released approximately 60 to 70% of the ETO within the first 15 min and approximately 100% of the ETO within 30 min at pH 7.4. These results strongly indicate that the use of the freeze-drying technique for the microparticles prepared in this study is a good technique to enhance the solubility of ETO and increase the release rate of ETO at pH 7.4. This finding is in agreement with the previously mentioned study, where the solubility of ibuprofen was significantly enhanced by using the freeze-drying technique [37]. Similar results were obtained by [PERSON] et al., who showed enhanced dissolution of microparticles loaded with poorly soluble drug nanocrystals: the hydroxypropyl cellulose (HPC) polymer used as a matrix carrier had a low viscosity. This enhancement was due to the spray freeze-dried composite particles, which was attributed to the reduction  
Figure 6: Dissolution profiles at pH 7.4 for free etoposide and the ET-ETO microparticles dried using primary drying at different drug–polymer ratios. in particle size of the drug [38]. [PERSON] et al. showed a similar result for a flutamide (FLT) formulation prepared by incorporating immediate-release lyophilized monophasic dispersions and prolonged-release chitosan microparticles.