Aspects Of Pharmacotherapy
Write A Short Note On Tolerance
Answer:
Tolerance
Tolerance: Tolerance means a requirement for higher doses of a drug to produce a given response.
Drug Tolerance May Be:
- Natural: The species or individual are inherently less sensitive to the drug, for example, black races are tolerant to mydriatics.
- Acquired: Acquired tolerance develops due to repeated use of a drug, for example, tolerance develops to the sedative action of chlorpromazine.
Tolerance develops to the analgesic and euphoric action of morphine.
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Mechanism Of Tolerance
- Change in receptors: It is the conformational change in the receptor.
- Loss of receptors: It is due to a gradual decrease in the number of receptors expressed over the cell surface due to their endocytosis or internalization.
- Exhaustion of mediators: It is the depletion of an essential intermediate substance.
- Altered drug metabolism: Increased metabolic degradation or decreased drug metabolism.
- Physiological adaptation: Nullification by the homeostatic response of the body, for Example. antihypertensive action thiazides are lowered because of activation of the renin-angiotensin system.
- Active extrusion of drug from cells: It is seen with anticancer drugs.
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Tolerance Can Be Of the Following Subtypes
- Pharmacological tolerance: It is due to pharmacokinetic, i.e. increased elimination, or pharmacodynamic mechanisms, i.e. reduced responsiveness of target tissues.
- Behavioral tolerance: It is the adjustment of an individual to compensate for the presence of drugs. Frequent alcohol drinkers may function better under its influence than first-time drinkers.
- Reverse tolerance: Increased sensitivity leads to the user experiencing the effects with less amount of the same drug.
- Cross tolerance: Tolerance to a drug often leads to tolerance to chemically similar drugs, for Example. alcoholics are relatively tolerant to barbiturates and general anesthetics.
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