What pH adjustment enhances the extraction of an acidic drug with a pKa of 6.5 from urine?

To enhance the extraction of an acidic drug with a pKa of 6.5 from urine, the urine pH should be adjusted to a value that is above the pKa of the drug. The pKa indicates the pH at which half of the drug is in its ionized form and half is in its non-ionized form. For acidic drugs, when the pH is increased above the pKa, more of the drug exists in the ionized form, which is typically more soluble in urine.

In this case, adjusting the pH to 8.5 will maximize the ionization of the drug because it is well above the pKa of 6.5. As a result, this increases the solubility of the acidic drug in urine, facilitating its extraction.

Lowering the pH, such as in options like 6.5, 5.5, or 4.5, would result in more of the drug remaining in its non-ionized form, which is less soluble in urine. Consequently, these lower pH adjustments would not enhance extraction as effectively as raising the pH to 8.5. Thus, the choice that best promotes the efficient extraction of the acidic drug is to set