What is the ruling on working as a sales representative for a pharmaceutical/infant formula company that offers money to doctors to increase its sales?

It is not permissible to work in a field that involves assisting in what is unlawful, and paying bribes to doctors to promote the company's products is prohibited. If it is possible to work with the company while avoiding these prohibitions, then that is required; otherwise, it is not permissible. Remember the words of Allah Almighty: "And whoever fears Allah – He will make for him a way out And will provide for him from where he does not expect."