<p>Drug resistance has led to an increasing number of deaths and illnesses in humans. Therefore, slowing the evolution of drug resistance to antimicrobial chemotherapy is of utmost importance. Experimental studies have shown that competitive interaction could be a crucial factor in preventing the spread of drug resistance, and drug treatment can greatly affect the fitness of drug resistance. In our paper, we created two intra-host epidemiological models to describe and predict the dynamics of mixed malaria parasite infections during drug treatment, incorporating the effects of competition between drug-sensitive and drug-resistant parasites. The model with competition was fitted to experimental data to obtain parameter estimations. Detailed theoretical analyses, including the existence and stability of the equilibrium, were performed and verified through numerical simulations. Our results show that developing drug treatment policies that consider intra-host competition could slow the evolution of drug resistance. The model also exhibits bistable dynamics, with two different boundary equilibria, which have significant implications for controlling drug resistance.</p>