Distribution functions, steady-state plasma

Ofloxacin - Maximum serum concentrations are achieved 1 to 2 hours after an oral dose. Steady-state concentrations are achieved after 4 doses. Ofloxacin is widely distributed to body tissues and fluids. Elimination is mainly by renal excretion 4% to 8% is excreted in the feces. A longer plasma half-life of about 6.4 to 7.4 hours was observed in elderly subjects, compared with 4 to 5 hours for young subjects. Dosage adjustment is necessary for patients with impaired renal function (Ccr 50 mL/min or less). 

If the half-life is 1.8 hours, the plasma concentration should approach steady state after 8 hours (more than four half-lives). As indicated by the equation used in question 9, the steady-state concentration is a function of dosage and clearance, not volume of distribution. If the plasma level is less than predicted, the clearance in this patient must be greater than average. (In questions of this type, do not assume errors of analysis or administration as answers, unless all other possible answers can be positively ruled out.) The answer is (B). 

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