Fidyah (Arabic: الفدية) and Kaffara (Arabic: كفارة) are religious donations made in Islam when a fast (notably in Ramadan) is missed or broken. The donations can be of food, or money, and it is used to feed those in need. They are mentioned in the Qur'an which distinguishes the two, but unifies them into one idea.
Qadha fast must be performed before the next month of Ranadhan. If you delay it, then there is a Kaffara for the delaying the Qadha fast. It is feeding one poor person for every delayed day of Qadha. Feeding means giving food either ready meal or food grains like wheat or rice etc. The amount is 750 grams per person per day.
Fasting the whole of the month of Ramadan is obligatory unless you are traveling or ill with an illness which is related to fasting or caused or worsened by fasting. If taking the antibiotics is must, then you can try to take it in the period fromMahrib till Fajr. If you need to take it during the day and you can not avoid it, then it will be medically necessary which allows you not to fast but you must keep Qadha of that fast which you missed after the month of Ramadan.
If you did not do the Qadha' of the previous holy month of Ramadhan, and entered into the next Ramadhan, and you were capable of re-doing those days, you will need to pay a Kaffarah.
The Kaffarah is 750grams of flour, or bread, or rice, or dates, or something similar to these items for each day. You select the amount (750grams) of only one of these items, of your choice.
You will also still need to do the Qadha' of those passed days.
And Allah knows best.