The second compound which is prevalent in cigarette smoke is hydrogen cyanide. This noxious gas is detected in significant quantities in the bloodstream of smokers. Its primary effect is at the cellular level, interfering with the enzymatic systems necessary for oxidative metabolism at the tissue level.72
An additional component of tobacco smoke is known as tar. This is the aggregate particulate matter after moisture and nicotine are removed. Many components of tar are carcinogenic and a specific fraction, the polyaromatic hydrocarbons, are known to increase the metabolism of a wide variety of drugs by induction of hepatic microsomal enzymes of the p450 system.10 Patients who are heavy smokers, therefore, may require larger quantities of medications to achieve the desired therapeutic effect, and can develop toxicity to these drugs, when smoking is abruptly discontinued. Only drugs which are metabolized by microsomal enzymes are affected.
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