<p>Resistance evolution can undermine antiviral treatment. However, targeting antivirals to shared viral proteins could inhibit resistance evolution if susceptible viruses sensitize resistant ones during cellular coinfection. Pocapavir, a poliovirus capsid inhibitor, uses this sociovirological interference strategy. While susceptible viruses substantially suppress pocapavir resistance in cell culture, a pocapavir clinical trial found widespread resistance and limited clearance time improvements in treated participants. Here, to reconcile these findings, we present an intrahost eco-evolutionary model of pocapavir-treated poliovirus, which reproduces both in vitro interference and clinical resistance evolution. In the short term, high densities of susceptible viruses sensitize resistant ones, mirroring cell culture results. However, over multiple replication cycles, pocapavir’s high potency collapses viral density, reducing coinfection and enabling resistance evolution, as observed clinically. Because resistance suppression relies on coinfection, enhancing susceptible virus survival could offer therapeutic advantages. Counterintuitively, we demonstrate that lessening antiviral potency can increase coinfection, limiting resistance while also maintaining low viral load. These findings suggest that antivirals relying on viral intracellular interactions must balance immediate neutralization with preserving future coinfection for sustained inhibition. Explicitly considering the eco-evolutionary feedback encompassing viral density, shared phenotypes and absolute fitness provides new insights for effective therapy design and illuminates viral evolutionary dynamics more broadly.</p>