In physiology, physiological tolerance or drug tolerance is commonly encountered in pharmacology, when a subject's reaction to a drug (such as an opiate painkiller, benzodiazepine or other psychotropic drug) decreases^[1] so that larger doses are required to achieve the same effect. Drug tolerance can involve both psychological drug tolerance and physiological factors. Characteristics of drug tolerance: it is reversible, the rate depends on the particular drug, dosage and frequency of use, differential development occurs for different effects of the same drug. Physiological tolerance also occurs when an organism builds up a resistance to the effects of a substance after repeated exposure. This can occur with environmental substances, such as salt or pesticides.

Tachyphylaxis is a medical term referring to the rapid decrease in response to a drug after repeated doses over a short period of time.

[edit] Mechanisms

There are two major mechanisms for tolerance:

• Dispositional tolerance: occurs because of a decreased quantity of the substance reaching the site it affects.
• Reduced responsiveness: the response to the substance is decreased by cellular mechanisms.^[2]

[edit] See also

• Desensitization
• Physical dependence
• Mithridatization
• Reverse tolerance
• Cross-tolerance
• Drug resistance
• Tachyphylaxis
• Multidrug tolerance

[edit] References

v • d • e Medication > Pharmacology Pharmacokinetics ADME: Absorption • Distribution • Metabolism • Excretion (Clearance) Loading dose • Volume of distribution (Initial) • Rate of infusion Compartment • Bioequivalence • Bioavailability Onset of action • Biological half-life • Plasma protein binding Phase 1 reaction • Phase 2 reaction Therapeutic index (LD50/ED50) Pharmacodynamics Toxicity (Neurotoxicology) • Dose-response relationship (Efficacy, Potency) Antimicrobial pharmacodynamics: Minimum inhibitory concentration/Bacteriostatic • Minimum bactericidal concentration/Bactericide Agonism and antagonism Agonist: Inverse agonist • Irreversible agonist • Partial agonist • Superagonist • Physiological agonist Antagonist: Competitive antagonist • Irreversible antagonist • Physiological antagonist Other Drug tolerance: Tachyphylaxis Drug resistance: Antibiotic resistance • Multiple drug resistance Related fields/subfields Pharmacogenetics • Pharmacogenomics • Neuropsychopharmacology (Neuropharmacology, Psychopharmacology)

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