[This post results from a query to one of my posts on LinkedIn Network (link), I think visitors of my website would also find it a useful read]
I believe your view/confusion is valid and understandable considering the current state of drug product evaluation practices. Note that this confusion occurs from considering or mixing drugs and drug products as the same. You are not alone with this confusion; even the regulatory authorities are confused with it, in fact indirectly extending it. For example, for generic product evaluations US FDA requires ANDA (abbreviated new DRUG application, in Canada ANDS), which is an incorrect terminology and in reality these are new PRODUCT applications (link). Your confusion also appears to be arising from the same mix-up i.e., not differentiating the drugs from drug products.
My post is regarding PRODUCTs, where one hardly ever conducts clinical tests/studies especially at the commercial production stage. Safety and efficacy studies/evaluations of DRUGS are done in the beginning, sometimes decades ago (e.g., consider the examples of aspirin, acetaminophen, ibuprofen, and others perhaps most drugs). From these clinical studies dose levels are set based on their safety and efficacy profiles.
At the production stage these drugs as PRODUCTS are manufactured worldwide without any further clinical evaluation. At the production/manufacturing stage objective is to produce PRODUCTs of the drugs which must contain the required dose and they must also be capable of providing (often described with terminologies of releasing/delivering/bioavailability) expected amount of the drug in the human body whichever route of drug administration is suggested (often time it is oral, but could be others IV, dermal, sublingual etc.). There would not be any concern or focus here for the safety and efficacy of the drug, along with other non-actives or excipients, which have been already established. In the generics cases, these are assessed often by bioavailability or bioequivalence assessments which is also usually one time shot and often at the pre-production stage. The point being that at the production stage there is hardly any (clinical) safety and efficacy assessment.
On the other hand, at the production stage safety and efficacy refer only to the ability of the product to release drug/dose as expected and this becomes quality metric for the product. If a product does not deliver/release the drug/dose as expected it would not be of quality which mean (equal to) it would not be efficacious and/or safe. This is where equality comes from (you may consider it as mathematical relationship if you like which may not be incorrect either), however, we are dealing with yes/no, pass/fail, or equal/not-equal situation.
So, in short, at the production stage of the PRODUCTs, quality is equal to safety and efficacy.
