Many places (e.g. Wikipedia) report the action of a drug on the various receptors, transporters, ion channels, and the like in terms of the Ki(nM). (This is for drugs that act primarily through such channels). They really ought to, but usually don't, also tell you whether the mechanism is competitive, uncompetitive, noncompetitive, as these can affect the rate of binding by a factor of 2 (or more?). For purposes of this question, assume we are dealing with competitive binding.
Is there a way to go from drug dosage and these Ki values to the level of binding of particular receptor? For example, suppose we have 100% absorption (or we look at the pharmacokinetics for greater precision). If you know the molecular weight of a drug, and blood volume (average about 5 liters, though you should adjust for body weight) then you can calculate the concentration in nM. (I am guessing that I can neglect the volume of blood cells and leakage into the lymphatic system, though I may be wrong about this). Then I think you can just multiply by the Ki.
My goal is to draw a line between the interactions that matter and those that don't under standard dosage. More precisely, I am trying to compare receptor and transporter bindings for several drugs in the same drug class at the usual prescribed dosage for each. I observe that the range of reported Ki(nM) is often six orders of magnitude or greater. So even if you don't know the binding mechanism, one should still be able to divide the actions into those definitely present, often at near saturation, those that are only trivially present, and those in a range that might be affected by doubling or halving the dose. The difference in magnitude caused by different binding mechanisms should only matter for those in the middle ground.
However, I am not a pharmacist, biochemist, or doctor, and I am very aware that every step in the chain of logic above might be mistaken. This is about trying to think clearly about the effects of related drugs, and the information is not going to be used to set dosage for any animal or human. So I think it is OK for me to look for, and for you to offer, pretty good information that may not have 100% scientific validation.