Do you have some of the pharmacokinetic information about the drug? If the two drugs have the same quality standards, the two drugs should be interchangeable.

What do you mean by having the same quality standards ? Lets say both drugs x and y contain 10 mg ibuprofen and x and y stands for different brand names ? Can I use any of them ? Both of them if they are in the market will have the same bioavailability ? I mean is it a prerequisite that all brand names should have the same bioavailability or this isn't a requirement ?

So Dr.Andres, when there is a brand name is in shortage, what is the best alternative to use ? Or how can I know the best alternative to use ?

Thanks Dr.Andres, it is just a little bit confusing with regard to OTC product selection as there are many brand names, so as a Pharmacist, one is confused which one would be the best.

I highly recommend not to use brand names but generic names and recommend the medications based on them. After that you could mention which brands with the same generic name are available at the moment at your place and mention your recommendation about the particular medication.

Dr.Maxim, why Generic names and not brand names ?

MR. ANDRES but how did you get the reference for your products which you want to interchange??

I think we need to remember we are treating a patient. If the person really needs a treatment we should not deny them simply because we can't find the same brand. Most of the time the differences between brands are smaller than the differences between individuals, so It is entirely logical to give the patient a trial of a different brand and to watch what happens. So, my recommendation is to switch brands ( my own GP does it all the time) but ensure that the patient knows and is on the lookout for any differences that could be due to a change in pharmacokinetics such as an initially more intense effect (eg: Higher Cmax in an antihypertensive) or delayed effect (Later Tmax).

Mostafa. You can ask the pharmacist which of these brands have bioequivalence study. It might also be indicated in the product insert of the drug. You can also inquire with the drug regulating agency of your country whether or not this particular brand has passed bioequivalence study.

I agree with Zuluaga

Regulations in the US are quite clear on the subject - generic drugs must show bioequivalency. https://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/ApprovalApplications/AbbreviatedNewDrugApplicationANDAGenerics/default.htm.