DO YOU KNOW❓

3 drugs with delayed recovery are weak bases: Diazepam, Midazolam & Etomidate (pKa ranging from 3-6)

5 drugs which are potent analgesics are strong bases: Morphine, Fentanyl, Ketamine, Bupivacaine, Lignocaine (7.5-8.5)

4 most commonly used drugs are weak acids: Paracetamol, Propofol, Atropine, Thiopentone (7.5-11)

LASI (lasix) and SALI (salicylic acid) are strong acids (3-4)

At pH < pKa, acidic drugs become less ionised:

HA ⇌ H+ + A–

At pH < pKa, basic drugs become more ionised as they accept protons:

B + H+ ⇌ BH+

Drugs cross membranes in the un-ionised state and so their pKa and the pH of the surrounding environment affect their rate of absorption. Hence, acidic drugs will be more readily absorbed in the highly acidic stomach, whereas basic drugs are better absorbed in the intestine where pH is higher.

Note: You can not find from pKa whether a drug is acidic or basic