Lopinavir (ABT-378), designed in response to Val82 mutant strains of HIV [1], is a potent inhibitor of HIV protease with Ki of 1.3-3.6 pM. Lopinavir inhibits replication of HIV-1 with an EC50 of 6-17 nM. [2]

Ritonavir was found to inhibit the metabolism of lopinavir with no other antagonistic effects; therefore lopinavir's drug exposure can be enhanced by co-formulation with ritonavir. In the presence of 50% human serum, the mean EC50 of lopinavir for five laboratory HIV-1 isolates ranged from 65 to 289 nM. [3]