Pluronic F-127 gels as a vehicle for topical formulations of indomethacin and rheological behaviour of these formulations.

Topical gel formulations containing a non-steroidal anti-inflammatory drug, indomethacin (IND), were prepared using 20% w/w Lutrol PF-127 as a gel-forming agent, and 16, 20 and 24% w/w Hexylene glycol (HG) or polyethylene glycol 300 (PEG) as solvents. 1% w/w Tween 80 and 1% w/w PVP 25 were added as excipients. The effects of the amounts of solvent and excipients on the physical characteristics of IND gel such as consistency, appearance, crystallization, pH and viscosity were studied. The results indicated that 1% w/w IND is able to form a structural gel. The viscosity values were calculated from the rheograms which were determined by a Haake Rotovisco sensor at a shear rate of 10,000 l/s. Viscosities corresponding to shear rates of 1000, 3000, 6000 and 9000 l/s were also calculated. Yield points were approximated from the rheograms. Although all IND gels maintained their pseudoplastic flow behaviour, their viscosities decreased markedly with increasing shear rates. Furthermore, increasing the amount of HG or PEG gave a more viscous gel except for the 24 w/w% HG gels which turned a jelly with or without either Tween or PVP. The difference in viscosities was explained by the changes in the gel compositions. 20% of PEG-1% PVP ranked first in viscosity followed by 16% PEG-1% PVP, 16% PEG-1% Tween, 24% PEG, 20% PEG-1% Tween and 16% HG-1% PVP. The results indicate that the excipients influence the physical characteristics of the gels. The optimum concentration for gels manifesting as strength of gel was 20% PEG in combination with 1% PVP which had the highest viscosity and yield value at a low shear rate.