When one drug interacts with another at the level of metabolism, absorption or excretion then such interaction is known as Pharmacokinetic interaction.
Due to these Pharmacokinetic interactions, the effect of the drugs administered together is different than when the drugs are administered individually.
Concomitant use of allopurinol with azathioprine results in significantly increased azathioprine-induced toxicity as it shows significant pharmacokinetic interaction when administered with azathioprine.
