Answer:
When talking about medical ethics, the first thing that must be taken into account is that there are four major basic principles that direct medical practice, and in general, the practice of all healthcare professionals. These are: autonomy, justice, beneficence and non-maleficence. These four are the core principles that ensure that a doctor will always do the best he can in regards to the patient, and for the benefit of the patient.
Unfortunately, these principles do not always apply to the pharmaceutical industry, whose ideas are set more on making profit, while at the same time procuring chemical compounds that benefit the health of patients. However, they do not take into consideration the means a patient may, or may not have, to acquire the elements.
In the case of the doctor, however, this is another matter altogether as he must seek to do what is best for the patient, given the four major principles of medical ethics. In particular, the doctor must apply here, in this case, the principles of beneficence and non-maleficence and he must prescribe the expensive drugs to a patient who have less means if he considers that they are absolutely the best for the health of the patient, and that there is absolutely no other choice when looking at pharmaceutical options. He must first evaluate if a cheaper medication could not achieve the same results, and benefit both the health situation, and income situation, of the patient. If these two are considered, and the answer is: there are no other possibilities, then I say it is ethical. If the decision is taken based on anything other than the benefit of the patient, then, it would be absolutely unethical.