Many patients take multiple drugs. The patient and physician may not be aware that starting a new drug or stopping an old one will have an effect on the drugs that continue to be taken.
Parameters:
(1) dose requirement
(2) duration of effect
(3) drug levels in serum or urine
(4) effect on a mood altering drug
Parameter
Increased Metabolism
Decreased Metabolism
dose requirement
needs to be increased (insufficient effect)
needs to be reduced (dose-related toxicity)
duration of effect
short
prolonged
drug levels
very low to undetectable
very high
effect on mood altering drug
symptoms of withdrawal
intoxication
Differential diagnosis for increased metabolism:
(1) noncompliance
(2) habituation (self-induced metabolism)
(3) prozone effect on immunoassay
(4) inability to measure target drug with assay
Differential diagnosis for decreased metabolism:
(1) excessive intake
Change in Drug Use
Change in Metabolism
Type of Drug Effect
start drug
increased metabolism
induction
start drug
decreased metabolism
inhibition
stop drug
increased metabolism
inhibition
stop drug
decreased metabolism
induction
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