If sickness will result from delaying a dose of medicine, there is nothing wrong with not fasting if the day is long, such as fifteen hours as it is nowadays. There is nothing wrong with taking the tablet that has been prescribed and breaking the fast for that reason, and making up the fast later. You should take the tablet and refrain from eating and drinking, and make up the fast, because you broke the fast because of this tablet, and you should refrain from eating and drinking and make up that day later on. But if it is possible to delay it and you will not be harmed by that, then you have to delay it so that you can take it at night.
But if you cannot do that, there is no blame on you, and you can make up this day on short days, which are the cold days when the fast is less than 12 hours.