Factorial Study.

Ritonavir, exhibits low and variable oral bioavailability due to its poor aqueous solubility. Its oral absorption is dissolution rate limited and it requires enhancement in the solubility and dissolution rate for increasing its oral bioavailability. The individual main and combined  (interaction) effects of CDs and Solutol HS15 on the dissolution rate of  ritonavir from tablet formulations was investigated in a series of 22 – factorial experiments. Ritonavir (100mg) formulated in to compressed tablets by wet granulation method employing selected combinations of CDs ( βCD and HPβCD ) and Solutol HS15. All the tablets prepared were of good quality fulfilling the official (I.P) standards with regard to hardness, friability, disintegration time and drug content. Drug dissolution from the tablets formulated followed first order kinetics and gave relatively higher rates of dissolution (K1) and dissolution efficiency (DE30) values when compared to those of ritonavir plain tablets. Formulations R4 and R8, gave much higher dissolution rates when compared to plain tablets, R1. A 21.35 and 16.85 fold increase in K1 was observed respectively with formulations R4 and R8 when compared to formulation R1 (plain tablets). The dissolution efficiency (DE30) was also increased from 7.29% for formulation R1 (plain tablets) to  43.32 % and 39.36 % respectively for formulations R4 and R8. In combination βCD-Solutol HS15 gave 21.35 fold increase in the dissolution rate HPβCD and Solutol HS15 alone gave an enhancement of 4.85 fold and 6.10 fold in the dissolution rate (K1) of ritonavir tablets respectively. Whereas in combination, HPβCD and Solutol HS15 gave a 16.85 fold increase in the dissolution rate.

  Solid dispersion is a widely accepted technique for enhancing the dissolution rate of poorly soluble BCS class II drugs. In the present study starch phosphate- a new modified starch, PVP and PEG 4000 were evaluated as a carriers in solid dispersions for enhancing the dissolution rate and efficiency of nimesulide, a BCS class II drug. Their individual and combined (interaction) effects in enhancing the dissolution rate and dissolution efficiency of nimesulide were evaluated in a 23- factorial study. Among the individual effects PEG 4000 gave highest enhancement in the dissolution rate of nimesulide (14.23 fold), followed by starch phosphate (11.34 fold). Addition of PVP and PEG 4000 to the solid dispersions in starch phosphate has further enhanced the dissolution rate upto 75.70 fold and dissolution efficiency upto 26.67 fold.   Key words: Solid dispersions, Nimesulide, Starch Phosphate, PVP, PEG 4000, Factorial Study.