BCPS Non-Clinical Practice Test 2026 – Comprehensive All-in-One Guide to Exam Success!

Phenytoin is highly bound to albumin, so when albumin is reduced (as in renal failure), the total phenytoin can underrepresent the amount that actually reaches the tissues. To correct for this, the standard approach uses the Sheiner-Tozer equation: corrected total phenytoin = measured total phenytoin divided by (0.2 × albumin in g/dL + 0.1). The multiplier with albumin is 0.2. This correction increases the reported level when albumin is low, helping to better gauge actual exposure; for example, with higher albumin the denominator grows and the correction is smaller, while with low albumin the denominator shrinks and the corrected value rises. The constant 0.1 accounts for residual unbound drug even when albumin is normal.