Prescriptions from your home country cannot be filled by a pharmacist in Singapore. If you take medicine that requires a prescription, you will need to visit a local doctor when you arrive in Singapore in order to obtain a new one.
To ensure that you receive the same or similar medicine as in your home country, it is recommended that you bring the corresponding prescription with you to show the doctor. It may occur that the exact medicine is not available within Singapore, in which case you will be prescribed an alternative, equivalent medicine.
Refills can be obtained from a doctor or pharmacy.