**Core Concept**
Procainamide is a class IA antiarrhythmic medication that requires continuous infusion for therapeutic effect. Its pharmacokinetics, particularly its half-life, influences the steady-state concentration, which is essential for maintaining therapeutic efficacy and minimizing toxicity.

**Why the Correct Answer is Right**
The half-life of procainamide is 2 hours, and it is infused from 9:00 a.m. to 1:00 p.m. for 4 hours on the same day. Given that the blood concentration is 3 mg/L after this initial infusion, we can calculate the peak concentration. However, to determine the steady-state concentration, we need to consider the accumulation of the drug over time. Since the half-life is 2 hours, the drug will reach steady state in approximately 5 half-lives, or 10 hours. However, in this case, we are interested in the concentration after 2 days (48 hours), which is beyond the steady-state period. The steady-state concentration can be estimated using the formula: Css = (k * dose) / Cl, where Css is the steady-state concentration, k is the rate constant (1/t1/2), and Cl is the clearance. However, since the question does not provide the clearance or dose, we can use the relationship between peak and steady-state concentrations: Css = (1 - e^(-kt)) * Cmax. Assuming a linear pharmacokinetic profile, the peak concentration (Cmax) is 3 mg/L. The rate constant (k) can be calculated as 0.693/t1/2 = 0.693/2 = 0.3467 h^-1. The time of infusion (4 hours) is negligible compared to the half-life, so we can use the initial concentration as the peak concentration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.

**Option B:** This option is not provided.

**Option C:** This option is not provided.

**Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
For medications with a short half-life, such as procainamide, it is essential to maintain continuous infusion to achieve and maintain therapeutic steady-state concentrations. The half-life of a medication is a critical pharmacokinetic parameter that influences the dosing interval and the time to reach steady state.

**Correct Answer:** C.