[troy2k]

First, I will admit that I had terrible luck trying to find ANYTHING on this subject. However, here's what I've pieced together on the physiology of the subject.
There are 3 major features underlying inflammatory pain: a change in the peripheral sensitivity of high-threshold nociceptors--ie, increased sensitivity; an alteration in the chemical makeup of the neurons in the nervous system, a change in their properties and function-- called a phenotypic switch; and finally an increase in the excitability or the responsiveness of neurons within the central nervous system, and this represents central sensitization.
More importantly maybe is the proliferation of proteolytic substances, which may be responsible for the destruction (lysing) of opioid and amide receptor sites, inhibiting analgesic response.
As I said, at this point in time I found NO specific references to the phenomenon of decreased analgesia due to local infection. I have however researched this before. At that time there was little if any understanding as to the mechanisms involved. Much of this is still theory on my part, and I'd be glad to hear what others have found.
Now the important stuff: if you have a patient who falls into this category, it becomes a question of priorities. Will his peridontal infection lead to acute endocarditis? Do you want to send the patient away untreated with a regimen of PCN-VK, trusting in PT compliance? I know of at least one medic who did just that...with dire consequences. It may be worth running labs before you let the patient start a week long regimen.
Also worth consideration is the typical stoicism of third world patients. I've seen teeth pulled just as mentioned in the instigative article, ie, sans anesthesia. These are all factors in your patient care decisions.
For the most part however, peridontal infections can be treated safely with PCN (or perhaps Cipro for those with allergies), then a return visit can allow you to remove the tooth with greater patient comfort.