That's quite strange, the Pinelabs (white) machine should take Amex, I've not seen failure/declined transactions with that one till date. Next one which works is like
@plastikman mentioned, Paytm machines.
HDFC POS have a few different ones, some are supported, some need special approvals to enable Amex (they use ancient methods to approve using forms, etc..). Unless that medical shop is a branded franchise, I wouldn't bet on them supporting Amex yet.