Not in medical field, but nicotine is generally biotoxic and used as a pesticide so i'm not at all surprised. Detriments to any symbiotic microorganisms aside, regularly spraying the lungs and other airways with a light coating of biotoxic film seems a good way to generally inhibit replication or damage any negative bioparticles, so long as the damage doesn't overwhelmingly interfere with the smoker's own biological functions and weaken the overall system ...