US FDA has a data base on Inactive ingredients that has been used in approved formulations.

http://www.accessdata.fda.gov/scripts/cder/iig/getiigWEB.cfm

The search with dimethyl sulfoxide resulted in three topical formulations and the maximum concentration of DMSO used was 45%w/w.

The commercial product is PENNSAID (diclofenac sodium topical solution) which contains the above strength of DMSO.

http://www.rxlist.com/pennsaid-drug.htm

Thanks @ Naresh Mittapelly for your valuable information. These are useful for me. 

Thanks

As per the ICH guidelines Q3C(R5), DMSO belongs to CLASS III residual solvents, i.e., it is comparatively less toxic than class I and II . As indicated in the guidelines, higher levels of residual solvents may be acceptable in certain cases such as short term (30 days or less) or topical application. However, justification for these levels should be made on a case by case basis.

Please find the attached file. 

Thank you so much @Johirul Islam for the information. It is verymuch useful for me. As you mentioned it might differ case-by-case, I will be trying to get more information in this regard.