Why does digoxin, a drug with a narrow therapeutic index, exhibit variable plasma concentrations between patients even when administered at the same weight-normalized dose?

💡 Explanation

Variable digoxin plasma concentrations arise primarily because renal clearance is highly variable among individuals; this variation is due to differences in kidney function and drug transporter activity. Therefore, digoxin clearance is a key determinant, rather than solely hepatic metabolism or receptor binding, because digoxin is primarily eliminated renally, making kidney function the dominant factor.

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