What is a Fixed Dose Combination?

A fixed dose combination (FDC) is a medication which provides two or more active ingredients in fixed dosages available in a single method of delivery. For example, two active ingredients could be combined in a single tablet. Such drugs are designed for people receiving combination drug therapy for conditions like malaria, tuberculosis, and acquired immune deficiency syndrome (AIDS) and there are also some versions available for people with common comorbidities, in which the fixed dose combination treats two different conditions.

Using such drugs is designed to cut down on pill burden. This reduces the number of individual pills which a patient needs to take overall, making it easier for patients to manage their medications. For people taking numerous medications every day, it can be difficult to keep track of their drugs, and a fixed dose combination streamlines the process. In addition, such drug formats also increase compliance; if a patient needs to take two different drugs and they are combined in one dosage, the doctor will know that the patient will take the drugs together as directed.

Fixed dose combination formats are available in varying dosages, to allow doctors to prescribe the dosage most appropriate for the patient. However, sometimes a needed dosage ratio is not available, and the patient will need to take two separate medications. These drugs can also be a problem for patients with allergies because if the patient has a reaction, the active ingredient which caused it is not immediately obvious since the patient is taking two at once.

In order to be marketed, fixed dose combination drugs do need to be approved by regulatory agencies which confirm that they are effective. The drugs should not conflict with each other, but there is a chance that an FDC could react with another drug a patient is taking. It is advisable for patients to make sure that all of the medications they are taking are clearly listed on their medical files and at the pharmacy so that any potential conflicts can be quickly identified, preferably before a prescription is dispensed.

When a doctor prescribes a new medication, even a fixed dose combination which may be doing nothing more than changing the format used to deliver drugs, a patient should ask what the medication is, why it is being prescribed, how it works, and how to use it. Doctors sometimes assume that this information is evident when it is not and this can lead to confusions or lack of compliance on the patient's part because the patient does not understand how to use the drug.