Molecular dynamics, physical and thermal stability of neat amorphous amlodipine besylate and in binary mixture

In this paper, a stable amorphous solid dispersion of an antihypertensive drug, amlodipine besylate (AMB) was prepared by entrapping it in a polymer matrix, polyvinyl pyrrollidone, in different weight ratios (AMB/PVP 05:95, 10:90, 20:80, 30:70). The glass forming ability of all binary dispersions were studied by means of differential scanning calorimetry and found good correlation between experimental T_g and Fox Flory's prediction. By considering the daily dosage limit of 5 mg, a weight ratio of 05:95 was further considered for the study. The structures of neat and binary of AMB were characterized by density functional theory, Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy and UV-visible spectroscopy. Further, detailed molecular dynamics of both pure and binary were investigated using broadband dielectric spectroscopy to judge the physical stability of the amorphous dispersions. Translation-rotation coupling of AMB possibly explains the dual conductivity and dipolar nature of the secondary relaxation in neat AMB. Thus, the binary dispersion of AMB with commercially acceptable weight ratio with strong glass forming behaviour and better shelf life was prepared and characterized for practical applications.