For a drug following first-order pharmacokinetics, what formula is used to adjust dosage for desired blood levels?

The appropriate formula for adjusting the dosage of a drug that follows first-order pharmacokinetics is based on the need to achieve a desired concentration of the drug in the bloodstream while considering the current steady-state concentration. In first-order kinetics, the rate of drug elimination is proportional to the concentration of the drug.

The formula provided in the correct choice illustrates this relationship effectively. By dividing the current dose by the concentration at steady state, you establish a baseline of how much drug is present in the system at equilibrium. Multiplying this by the desired concentration allows for the calculation of a new dose that would bring the blood levels up to the targeted range. This method ensures that the therapeutic response is achieved without causing toxicity, as it accounts for the relationship between the dosage and the concentration.

In summary, this formula precisely connects the current dosing and steady-state concentration with the target concentration, making it an essential calculation in pharmacotherapy when managing and optimizing drug therapy in patients.