Question

A 65-year-old male with a history of symptomatic atrial fibrillation presents to the cardiology clinic to optimize his medical regimen. The physician decides to start an oral antiarrhythmic agent to maintain normal sinus rhythm. The selected drug has the following known pharmacokinetic parameters in this patient demographic:

* Volume of distribution ($V_d$): $40$ L
* Systemic clearance ($CL$): $2.5$ L/hr
* Oral bioavailability ($F$): $0.80$ ($80\%$)
* Half-life ($t_{1/2}$): $11.1$ hours

The target average steady-state plasma concentration ($C_{ss}$) for optimal efficacy without toxicity is $4.0$ mg/L. The physician plans to prescribe the medication to be taken orally every $12$ hours.

Based on these pharmacokinetic parameters, what is the appropriate single oral maintenance dose that should be administered every $12$ hours?