Recovery problem

[sastry]

I am encountering the below mentioned problem can any one help me in resolving this.

I am facing problem in the recovery of Loperamide HCl from formulation containing Simethicone during the dissolution studies( dissolution media 0.1N HCl). My assay value is 100%( diluent I used during assay estimation is methanol) but I am getting only 80% dissolution when I conduct dissolution test.
I have conducted recovery experiment in 0.1N HCl dissolution media by spiking solution having known concentration of Loperamide HCl over placebo the % recovery found to be only 80% where as in the absence of placebo my reocvery is 100%.
I don't have any other choice to change my dissolution media because I need to correlate my invito-invivo data only in 0.1N HCl.
Can any one suggest me , does my recovery improve if I change chromatographic parameters like mobile phase/column/flow/wavelength etc. I shall be glad if any one provides me some suggestion.
I have full length of experimental data I can share if any one is interested to reply . This is really interesting If I increase my placebo quantity my recovery is still further reducing .
If I get only 80% recover when I spike direct active material I can guess simethicone is retarding my drug dissolution. In this case though I add solution having known concentration of active I am not getting 100 % recovery.Looking forward for your valuable input.
Thanks & Regards

[Narendra]

Is it pharmacopoeial monograph ? if not Which appratus you used paddle or basket ? What is the concentration of simethicone per tablet ? What is your dissolution time ? Waht is solubility of Loperamide HCL in acidic condition ? At what rpm you do the dissolution ? Can you give more information