In his book, The Edge of Evolution; the Search for the Limits of Darwinism, Michael Behe cites work by Barry Hall in support of his view that there are limits fairly narrow limits to what Darwinian evolution can accomplish:
But antibiotics that require multiple changes are far more resistant to Darwinian processes. That's a critical fact to understand, too. Malaria requires several mutations to deal with chloroquine, so it's a far better drug than ones that are stymied by a single mutation. And chloroquine is not the only case. Recently, former University of Rochester microbiologist Barry Hall examined various antibiotics in a class called "carbapenems," which are chemically similar to penicillin. With unusual clarity of thought on the topic of evolution, Hall wrote, "Instead of assuming that [the chief kind of enzyme that might destroy these antibiotics] will evolve rapidly, it would be highly desirable to accurately predict their evolution in response to carbapenem selection" (emphasis added). Using clever lab techniques he invented, he showed that, although most of the antibiotics quickly failed, one didn't. The reason is that neither single nor double point mutations to the enzyme allowed it to destroy the certain antibiotic (called "imipenem"). Wrote Hall, "The results predict, with >99.9% confidence, that even under intense selection the [enzyme] will not evolve to confer increased resistance to imipenem." In other words, more than two evolutionary steps would have to be skipped to achieve resistance, effectively ruling out Darwinian evolution.
 Hall, B.G. 2004. In vitro evolution predicts that the IMP-1 metallo-beta-lactamase does not have the potential to evolve increased activity against imipenem. Antimicrob. Agents Chemother. 48:1032-33.
I haven't read Hall's paper, so I'm taking Behe's word on how to interpret it. If the interpretation is correct, then it sounds like Hall is confirming where Behe thinks the edge of Darwinian evolution is. If correct, this could have profound consequences for medical research. We would only need to find drugs that require more than two evolutionary steps in order to bestow guaranteed resistance to bacteria.
Is Behe's interpretation of Hall correct? If so, is Hall right? Does that make Behe right? I'll be on vacation for a week. Please stay on topic. I'm curious what the critics have to say on this. I'll read it when I get back.