Project summary Systemic fungal infections are a primary cause of death for AIDS patients. These infections are difficult to treat due primarily to patients’ immunocompromised state. Moreover, patients receiving treatment are frequently taking multiple medications, creating a high potential for interactions between patients’ routine medication and antifungal therapies. Our goal is to understand how drug-drug interactions can both improve and complicate management of systemic fungal diseases. Drug-drug interactions can be positive (“synergistic” – when the efficacy of the combination is greater than the sum of each drug’s activity alone), negative (“antagonistic” – when the combined efficacy is less than the sum of each drug’s activity alone), or merely additive. We propose to improve treatment by 1) advancing synergistic combination therapies and 2) reliable identification of antagonistic drug interactions that decrease treatment efficacy. We completed a high-throughput screen for small molecules that interact with the azole class antifungal drug fluconazole, identifying 14 synergistic partners and 8 antagonistic partners. We will advance the synergistic pairs as potential treatments against three fungal species (Cryptococcus neoformans, Candida albicans, and C. glabrata) by 1) quantitating improvement outcomes in vertebrate infection model of fungal disease, 2) elucidating the molecular mechanisms underlying synergistic interactions and 3) calculating the potential clinical impact of antagonistic interactions and determining if they are widespread within drug classes. This work will advance potential treatments for systemic, azole-resistant fungal infections. Our analogous studies on antagonism will facilitate prediction of these interactions to prevent harmful interactions and improve treatments for patients with complex conditions.