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Not tried to do it this way before when we have required antibiotics we have seen the doctor on the ship they do have an extensive range of drugs and this is one way of getting them but they will likely charge upwards of $50 for the consultation plus the medicine, but you will get a receipt and maybe able to claim some of this back depends on the condtions set out in your insurance.
One point I should have said if you need medication take ample with you plus a little extra as we once got stranded on the way home in Boston hit be very heavyt snow that closed the airport.
If your prescriptions are part of a long term treatment plan and they are likely to run out during your cruise, then it would be better to order extra before you leave. If you explain to your surgery why you will need extra they usually comply with your request.
If you become ill on your cruise (as I did during Easter 2008 whilst on Sea Princess) you can go to your medical centre (check opening times) and make an appointment to see a doctor. I got seen immediately by a nurse (after filling in some personal details on a form) and then a doctor who confirmed my suspicions that I had an infection and needed anitbiotics. He prescribed them straight away. Overall, my tests, consultation with doctor and nurse and antibiotics cost me $130 which then worked out as £65. I didn't mind paying that much as I received good quality service. They gave me a form for insurance purposes too (which I didn't bother with as on past experience, with another illness I suffered, they may refuse to pay up if it occurred again).
I'm not quite sure what you are trying to ask, but I hope my information helps. It is always best to go on holiday with all medication for the entire trip.