Repeated OPTIONS requests for cors / ajax requests

On my site I have an auto-suggest text input that suggests results as the user types. The results are provided by a AJAX calls to an API on a different domain. This means I have to use CORS to allow the requests.

It is all working quite well, but every time the user types a new character, the browser sends a new OPTIONS request to ensure it is authorized.

Is there a way around all these repeated options requests?

My php script receiving the requests has

header("Access-Control-Allow-Origin: http://ift.tt/14iaul1");

and the requests are all originating from consent.example.com. To be clear, the authorization works just fine, and the request completes successfully, but I don't know why it needs to keep making options calls. It would make sense to me that the browser would cache this.