A patient who has been taking opioids for several weeks tells the nurse, "The medication doesn't seem to work as well anymore." The nurse recognizes this as a sign of:

Choice A reason: This is incorrect. SQ (subcutaneous) administration involves injecting a drug into the fatty tissue under the skin. This route is slower than IV or IM administration, as the drug has to diffuse through the tissue before reaching the bloodstream.

Choice B reason: This is incorrect. PO (by mouth) administration involves swallowing a drug and absorbing it through the digestive system. This route is the slowest of all, as the drug has to pass through the stomach and the liver before reaching the bloodstream. The drug may also be affected by the first pass effect, which reduces its bioavailability.

Choice C reason: This is correct. IV (intravenous) administration involves injecting a drug directly into a vein. This route is the fastest of all, as the drug enters the bloodstream immediately and reaches the target site quickly. The drug also has 100% bioavailability, meaning none of it is lost or degraded.

Choice D reason: This is incorrect. IM (intramuscular) administration involves injecting a drug into a muscle. This route is faster than SQ or PO administration, as the drug can be absorbed by the capillaries in the muscle. However, it is still slower than IV administration, as the drug has to cross the muscle membrane before reaching the bloodstream.

Choice A reason: This is correct. The liver is the main organ responsible for drug metabolism. The enzymes that the body uses to metabolize drugs are present throughout the body but are most abundant in the liver. The liver can transform drugs into more polar and water-soluble compounds, which can then be excreted by the kidneys or the biliary system.

Choice B reason: This is incorrect. The lungs are not primarily responsible for drug metabolism, although they can play a minor role in some cases. The lungs can metabolize some drugs that are inhaled, such as anesthetics, or drugs that circulate through the pulmonary blood vessels, such as propranolol. However, the lungs have a lower capacity and a lower variety of enzymes than the liver.

Choice C reason: This is incorrect. The heart is not responsible for drug metabolism, although it can be affected by it. The heart is the organ that pumps blood throughout the body, delivering oxygen and nutrients to the tissues and organs. The heart can be influenced by the pharmacokinetics and pharmacodynamics of drugs, which are the processes of drug absorption, distribution, metabolism, and excretion, and the effects of drugs on the body, respectively.

Choice D reason: This is incorrect. The kidney is not primarily responsible for drug metabolism, although it is important for drug excretion. The kidney is the organ that filters the blood and removes waste products and excess fluid as urine. The kidney can excrete drugs that are water-soluble or that are not reabsorbed by the tubules. The kidney can also metabolize some drugs, such as aspirin, but to a lesser extent than the liver.