Correct Answer: (d) The doctor told his patient to continue the same course of medicines for the following week.
Note: (d) The doctor told his patient to continue the same course of medicines for the following week. (Correct)
(a) The doctor told his patient to continued the same course of medicines in the next week. (Verb I form should be used)
(b) The doctor told his patient for continuing the same course of medicines for the next week. (Incorrect preposition for is used)
(c) The doctor told his patient that he may continue the same course of medicines in the following week. (Incorrect word)