Final answer:
Lidocaine and some nitroglycerines are not administered orally due to inactivation by gastric acids, which prevents their proper absorption into the bloodstream, making them ineffective for therapeutic use.
Step-by-step explanation:
Lidocaine and some nitroglycerines are not administered orally because they are inactivated by gastric acids. These drugs would be rendered ineffective before they could be absorbed into the bloodstream. For example, the hydrolysis process that occurs in the gastrointestinal (GI) tract can degrade certain drugs, as seen with medications like procaine. In the case of lidocaine, an effective local anesthetic, its role as a Na+ channel blocker requires its direct presence at the target site, which is compromised if inactivated by gastric acids. With nitroglycerines, the high first-pass metabolism by the liver could significantly reduce their potency if taken orally. Instead, these drugs are often given by parenteral routes such as intravenous or intramuscular injections, which allow them to bypass the GI tract and deliver a quick and effective therapeutic effect.