A drug showing linear pharmacokinetics in a one-compartment model follows
Show Hint
Pharmacokinetics describes how the body handles a drug over time. When a drug shows "linear" pharmacokinetics, it means that doubling the dose roughly doubles the drug concentration in a predictable, proportional way.
Step 1: Define linear pharmacokinetics. A drug shows linear (dose-proportional) pharmacokinetics when doubling the dose doubles the plasma concentration and the AUC. This happens when elimination processes are not saturated.
Step 2: One-compartment model basics. In a one-compartment model, the body is treated as a single uniform space. Drug distributes instantly and is eliminated from that compartment.
Step 3: First-order elimination. First-order means a constant fraction of the drug is eliminated per unit time. The rate of elimination is proportional to the current drug concentration. This gives a straight line on a log-concentration vs time plot and a constant half-life.
Step 4: Eliminate the distractors. Zero-order means a constant amount (not fraction) is eliminated per unit time, regardless of concentration; this occurs when elimination pathways are saturated. Capacity-limited and mixed-order are synonymous with saturable (Michaelis-Menten) kinetics seen with drugs like phenytoin.
Step 5: Conclusion. Linear pharmacokinetics in a one-compartment model = first-order elimination. This is a fundamental pharmacokinetics principle.