Henderson-Hasselbalch Equation
A mathematical expression relating the pH of a solution to the pKa of a weak acid or base and the ratio of ionized to un-ionized species. In pharmacology, this equation predicts the fraction of drug in ionized versus un-ionized form at any given pH, which determines membrane permeability, absorption across biological barriers, and susceptibility to ion trapping in compartments of different pH.
Beispiele
- Predicting aspirin absorption: at stomach pH 1.5 with pKa 3.5, >99% un-ionized (absorbed)
- Urinary alkalinization to trap weak acid drugs (e.g., salicylate) in ionized form for enhanced excretion
- Predicting local anesthetic efficacy: lidocaine (pKa 7.9) is ~25% un-ionized at pH 7.4 for membrane penetration
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A mathematical expression relating the pH of a solution to the pKa of a weak acid or base and the ratio of ionized to un-ionized species. In pharmacology, this equation …