i imagine you can get some variability from batch to batch since drug companies buy their raw materials from different sources and sometimes subcontract with other manufacturers.
here's a very interesting thread if what the poster says is true
I agree with Dr. Brendel but moreover there are additional issues involving creep in many ways, lets take the worst cases using the simpliest example, an immediate release drug. It is far more complex to consider extended release or similar drugs but you can see how it applies in these examples....
CREEP 1 -- Generic drugs are approved with approximately 12-24 people take the generic drug and actual branded drug and usually switch during the middle of the study. The blood levels of drugs are taken and compared to each other using a confidence interval of 90% and the actual amounts need to be within 80% to 125% (notice 80%!). Sometimes the branded drug goes away because of generic competition then the first or Agency's choice generic becomes the "New branded" medication. Now the second generation generic drug gets approved using that first generation generic (assume the branded drug is off market). So doing the math, that drug could be... 0.8 x 0.8 = 0.64 --> 64% of what the original medication is and still be acceptable!!!
CREEP 2 -- Now I have yet to include manufacturing creep, most drugs are regulated to have active ingredients assay 90% to 110% in each batch, some are tighter (e.g., 95-105) but lets not assume that. So if you include that creep 0.64 x 0.9(branded drug) x 0.9(first generic) x 0.9(second generic) = 0.46% - roughly HALF of the first branded drug. If you add a bit of manufacturing changes during the 10-20 years... who knows how far you can deviate.
Now am I saying that generic drugs are half the potency of the branded drug - no. I am saying that they can be quite far off in blood levels and still be approved. Now does your drug need a minimum blood concentration threshold to work or just sustained amount....
Oct 3, 2012