The aim of this study was to prepare and characterize a new nanocarrier for oral delivery of tamoxifen citrate (TMC) as a lipophilic oral administrated drug. This drug has low oral bioavailability due to its low aqueous solubility. To enhance the solubility of this drug, the microemulsion system was applied in form of oil-in-water. Sesame oil and Tween 80 were used as drug solvent oil and surfactant, respectively. Two different formulationswere prepared for this purpose. The first formulation contained edible glycerin as co-surfactant and the second formulation contained Span 80 as a mixed surfactant. The results of characterization showed that the mean droplet size of drug-free samples was in the range of 16.64–64.62 nm with a PDI value of b0.5. In a period of 6 months after the preparation of samples, no phase sedimentation was observed,which confirmed the high stability of samples. TMC with a mass ratio of 1% was loaded in the selected samples. No significant size enlargement and drug precipitation were observed 6 months after drug loading. In addition, the drug release profile at experimental environments in buffers with pH=7.4 and 5.5 showed that in the first 24 h, 85.79 and 100% of the drugwere released through the first formulation and 76.63 and 66.42% through the second formulation, respectively. The in-vivo results in BALB/c female mice showed that taking microemulsion form of drug caused a significant reduction in the growth rate of cancerous tumor and weight loss of the mice compared to the consumption of commercial drug tablets. The results confirmed that the new formulation of TMC could be useful for breast cancer treatment.

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