<prompt> Rifampicin and ritonavir are:Physical antagonistChemical antagonistPharmacokinetic antagonistCompetitive antagonist  <response>: Ans. C. Pharmacokinetic antagonista. Rifampicin is an enzyme inducer of CY3A4 and ritonavir is metabolized by CYP3A4.b. Thus rifampicin can antagonize ritonavir by inducing its metabolism; known as pharmacokinetic antagonism. 