The influence of solid/solvent interfacial interactions on physicochemical and mechanical properties of ofloxacin

Purpose
To investigate the potentials of a simple solvent treatment technique for improving the physicochemical and mechanical properties of ofloxacin.
Methods
Ofloxacin was treated with 5% aqueous ammonia solution at a solid to solvent ratio of 1:3 and treatment time of 4 h in stoppered flasks, then filtered under vacuum. Changes in ofloxacin powder characteristics were monitored using SEM, particle size analysis, IR, DSC, XRD, hydrophilicity, equilibrium solubility, dissolution rate, flowability, and compressibility tests. The effect of PVP K90 and Tween 80 used in two concentrations (0.2% and 2%) was investigated. Crystals of ofloxacin having particle size < 160 μm were included whenever appropriate for comparison.
Results
The treated ofloxacin showed bundles of elongated prisms with a wide particle size range (2 to 39 μm). Average size was reduced from 9.8 to 6.4 and 4.6 μm with 2% Tween 80 and PVP, respectively. Different analytical techniques confirmed that neither structure modification nor additive molecule incorporation in crystal lattice occurred during treatment. The treated powder showed repose angle 39°, bulk density 0.282 g/cm3, tap density 0.319 g/cm3, Hausner ratio 1.13, Carr’s index 11.6%, compact hardness 5–6.45 kg, porosity 13–6.38%, and elastic recovery 4.5–8.8%. The corresponding values for untreated ofloxacin were 59.5°, 0.221 g/cm3, 0.314 g/cm3, 1.42, 29.6%, 3.74–5.27 kg, 15.38–7.22%, and 4.57–8.83%, respectively. Values were further improved by PVP addition.
Conclusions
Treating ofloxacin powder with 5% aqueous ammonia solution in the presence of 2% PVP improves the dissolution, flowability, and compressibility of the drug. The treated powder is suitable for the preparation of tablets with few excipients.