Doctors want to do whatever they think is best for patients. Yet there’s lots of evidence that shows doctors don’t always follow the best available evidence.

Doctors will tell you this is because no two patients are the same, so you can’t always rely on existing studies. Often you have to follow your instinct. On the other hand doctors who have a financial incentive to perform a procedure will perform it more often than those who don’t, suggesting that the patient’s best interest isn’t the sole motivator for all docs.

Insurance companies, for their part, have a financial incentive to keep costs down. So they sometimes require doctors to get authorization before prescribing certain drugs or doing certain procedures. This drives doctors and their patients up the wall.

In his WSJ.com column today, Ben Brewer writes of an arthritis patient he’s been treating for 11 years. The man hasn’t been helped by over-the-counter painkillers, and Brewer wants to prescribe Celebrex, a Pfizer pain drug that costs $120 a month.

The insurance company wouldn’t allow the prescription unless Brewer faxed them a form explaining why he thought it necessary. He wasn’t pleased.

They want me to incur the overhead and frustration that comes with trying to prove to a non-doctor that I know my patient and what I’m talking about. They want to cut costs, and they don’t really care about how it affects my patients or my practice. If they make the process hard enough, they hope I’ll just give up.

The day the Celebrex prescription was denied, Brewer saw 28 patients. He didn’t manage to find the time to get the prescription approved.