By Phase III, most clinical trials are being conducted in the United States and Europe, and often are under way farther afield as well, especially as pharma markets are growing in Asia and Latin America.
In this era of global communication and global clinical trials, the location of a CMO isn't necessarily the deal-breaker that it once was, but it's essential that it has been inspected and approved by the appropriate agencies for all countries where the clinical trials will be carried out.
Most reputable vendors have experience with regulations for different areas of the world and have the logistics in place to ship to those locations. The requirements are different in the United States and Europe, and it's important to be aware of these (and be satisfied that the CMO of choice is aware of them, too).
However, there are situations over and above regulatory issues where a local CMO is more important, for example in trials where the comparator drugs are region- or market-specific. Here, the need to manufacture and package locally can be more important, and so will drive CMO choice.