Define the terms tolerance and tachyphylaxis. (20% of marks) Describe the different mechanisms by which tolerance can develop, and give examples for each. (80% of marks)
Tolerance is the requirement of higher doses of a drug to produce a given response. When this develops rapidly (with only a few administrations of the drug) this is termed tachyphylaxis. Various mechanisms exist by which tolerance occurs and these include cellular tolerance (e.g. neuronal adaptation to opioids or alcohol), enzyme induction and depletion of neurotransmitters. Few candidates knew a comprehensive list or had a classification system for the different types of tolerance. No candidate had a good definition of tachyphylaxis.
It would be important to point out that nowhere in the published literature is there a well-accepted definition of tachyphylaxis, and there is no shame in being unable to generate one at a moments notice during the ten minute SAQ timeframe, particularly when the dividend is a meager 20% of the mark. Similarly, there is very little material out there to classify a "comprehensive list" of tolerance mechanisms. The following list was concocted and classified on the basis of several competing and frequently contradictory textbook entries.
Acquired tolerance: a drug-induced reduction in subsequent drug effect.
Innate tolerance: a genetically determined resistance to the drug effect.
Tachyphylaxis: a rapid decrease in response to repeated doses over a short time period
Mechanisms of tolerance:
There are a few other sub-varieties for acquired tolerance which defeat efforts at classification; one might describe these as tolerance-related phenomena.
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