pt 4 effects of chronic drug use

Drug tolerance

Diminished response to a drug after repeated exposure

Cross tolerance

Tolerance to one drug can diminish effectiveness of a similar second drug

Ex: alcohol & phenobarbital

Tolerance characteristics

• reversible when drug use stops

• dependent on dose & frequency of drug use & drug taking environment

• may occur rapidly after long periods of chronic use, or never

• not all effects of drug show some degree of tolerance

• there are several different mechanisms explain tolerance

Acute tolerance

Develops during a single administration of a drug Ex: when using alcohol as you first drink & BAC is climbing you feel drunk & when BAC is falling and you hit the same BAC you feel less drunk

Metabolic tolerance

Repeated use reduces the amount of the drug available at the target tissue

Ex: when drugs increase their own metabolic rate, more enzymes available to metabolize the drug so less drug to bind to target sites

Pharmacodynamic tolerance

Changes in nerve cell function to compensate for continued presence of the drug

Ex: receptor changes like down drop regulation

Behavioral tolerance

(Context-specific) tolerance is not apparent or reduced in a novel environment

Ex: some types of learning withdrawal symptom

Pavlovian or classical conditioning

Environment/procedures can elicit conditioned euphoria before taking the drug

When does tolerance occur in Pavlovian terms

Occurs when conditioned response is opposite (compensatory) of the unconditioned response (this is a condition compensatory response)

Conditioned compensatory response example

Inject adrenaline (unconditioned stimulus) into a rat causing increased heart rate (unconditioned response) eventually conditioned stimulus (environmental cues) leading to a conditioned response (decrease heart rate) to try and stay in homeostasis

Context is the conditioned stimulus, a testing chamber

this is tolerance

Sensitization

Reverse tolerance, can see enhancement of drug effects after repeated administration of the same dose

• can persist over longer periods of abstinence

• some drugs induce tolerance & some sensitization for other