o Henderson-Hasselbalch equation Weak acid drugs: PH-pKa=log(a/Had pKa-pH=log(田HA/[A1) Weak base drugs pKa-PH=log( bh|/BD) PH-pKa= log(b/BiD)Henderson-Hasselbalch equation Weak acid drugs: pH - pKa = log ( [A- ] / [HA] ) pKa - pH = log ( [HA] / [A- ] ) Weak base drugs: pKa - pH = log ( [BH+ ] / [B] ) pH - pKa = log ( [B] / [BH+ ] )