To my knowledge, this version of the drug is not commonly available in the US. I found a couple of articles that state "Sandimmun Neoral" is the microemulsion or "modified" version of Sandimmun.
http://rheumatology.oxfordjournals.o...tract/39/2/156
http://ndt.oxfordjournals.org/cgi/co...tract/16/2/373
Based on this, I think "Sandimmun" and "Sandimmun Neoral" have different bioavailabilities and shouldn't be used interchangeably. The newer Neoral formulations are better from an absorption standpoint.
Make sure that your father's dosage doesn't exceed 5mg(of drug)/kg(his body weight)/day. Make sure he isn't eating/drinking grapefruits.
Also his cyclopsporine trough level should be measured to make sure it isn't excessive because of interactions with other drugs that he may be taking.
I am not an expert. Just sharing my opinions.