I'm also a senior medical director for an insurance company. As for insurance not paying for off label use, that is often true at first, but as the drug becomes more widely prescribed and accepted off-label, insurances very often will, especially when there isn't something being used that is just as good/cheaper.
In the case of B, since there would be nothing comparable that can possibly PREVENT the occurrence of OM - which remember, would be a VERY costly side effect for an insurance company - I suspect that insurances would adopt paying for this quickly in off label uses.
As for the FDA letting docs prescribe off-label whenever they want: Remember, approved meds have already gone through extensive safety testing to get where they are. If something comes up after approval, a drug can then be pulled - or not. An example of not, even in what appears to be an extreme case is some antipsychotics used in psychiatry. It's been discovered over the years that a rare side effect in the elderly can be sudden death (due to cardiac issues). The FDA has not pulled these drugs because they are so beneficial in many populations, but rather has added a "black box warning" to them, specifically warning of this side effect in this population. But, even that doesn't mean a doc is prohibited from prescribing these drugs in the elderly, and many still do. It just means that in addition to informing the patient/family that this is an off-label use, the doc has to also inform them of the black box warning, so they can make an informed consent decision.
