Page 42 - Pharmacology Mnemonics and Short Notes

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2. Acquired: e.g., morphine, ethyl alcohol, nitrates, ephedrine, and
amphetamine.

* It is reversible, so cessation of the drug will lead to loss of

tolerance.

* It may develop to some actions only and not to all actions.
Tolerance occurs to analgesia and respiratory depression of
morphine, but not to miosis and constipation.

Special types of tolerance

1) Tachyphylaxis
(Acute acquired tolerance) e.g. ephedrine on B.P.

Reasons

 Intracellular molecules block access to G
protein s  Beta arrestins in case of beta

agonists

 Agonist bound receptor may be internalized
 like morphine receptors

 Continuous activation may leads to depletion
of some essential substrate required for

downstream effects  like depletion of thiol
co-factors in case of tolerance to nitro-

glycerine

2) Cross tolerance (tolerance between related drugs), e.g. between
ethyl alcohol and general anaesthesia.

Variation in drug response may be due to
1. Alteration in drug concentration that reaches the receptors
Contents due to an effect on absorption, distribution or elimination.

Pharmacology Mnemonics and Short Notes By Muhammad Ramzan Ul Rehman