Final answer:
The correct statement regarding drug absorption is that most drugs need to enter the systemic circulation to be effective. Oral medication absorption can be influenced by meals, and mucous membranes allow for substance absorption, contrary to the belief that they are impermeable.
Step-by-step explanation:
The statement that correctly characterizes drug absorption is: Most drugs must enter the systemic circulation to have a therapeutic effect. This is because the systemic circulation is what delivers the drug throughout the body, allowing it to reach the site(s) where it can exert its therapeutic actions. It's important to note that oral medications, while convenient, may not always be absorbed quickly when taken with meals; in fact, this can sometimes slow down the process depending on the specific properties of the medication and the type of meal consumed.
Furthermore, mucous membranes are not impermeable; they can actually facilitate relatively rapid absorption for certain medications taken through routes such as sublingual or buccal. When comparing subcutaneous and intramuscular injections, the absorption rate depends on various factors including the blood flow to the tissue, but it is not correct to universally state that one is absorbed faster than the other without considering specific drug properties and site of injection.