Drug interactions are said to occur when the pharmacological activity of a drug is altered by the concomitant use of another drug or by the presence of some other substance.
Pharmacokinetic
Drug Interactions
Drug interactions are said to occur when the
pharmacological activity of a drug is altered by the concomitant use of another drug or by the presence of some
other substance. The drug whose activity is affected by such an
interaction is called as the object
drug and the agent which precipitates
such an interaction is referred to as the precipitant.
Drug interactions include –
1. Drug-drug interactions.
2. Food-drug interactions, for
example, inhibition of metabolism of several
drugs by grapefruit juice.
3. Chemical-drug interactions, for
example, interaction of a drug with alcohol,
tobacco or environmental chemicals.
4. Drug-laboratory test interaction, for
example, alteration of diagnostic laboratory
test results by the presence of drug.
5. Drug-disease interactions, for
example, worsening of disease condition by
the drug.
The net effect of a drug interaction is –
·
Generally quantitative i.e.
increased or decreased effect.
·
Seldom qualitative i.e. rapid or
slower effect.
·
Precipitation of newer or
increased adverse-effects.
Most interactions are specific types of adverse reactions with altered efficacy
of the drug, for example an enhanced pharmacological activity (e.g.
haemorrhagic tendency of warfarin when phenylbutazone is given subsequently) or
a decrease in the therapeutic activity resulting in loss of efficacy like that
of tetracycline when concomitantly administered with food, antacids or mineral
supplements containing heavy metal ions. Drug interactions are thus –
·
Mostly undesirable.
·
Rarely desirable (beneficial) –
for e.g., enhancement of activity of penicillins when administered with
probenecid.
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