This disclosure features compounds and compositions that are useful in methods of treating coronavirus infections (e.g., useful in methods of treating COVID-19) in a subject in need thereof. The methods include administering to the subject niclosamide compounds (or pharmaceutically acceptable salts and/or co-crystals thereof, e.g., niclosamide). In some embodiments, the niclosamide compounds have one or more properties that include, but are not limited to: a particular purity (e.g., a chemical purity of greater than about 99.0%) or a particular particle size (e.g., a particular particle size distribution and/or a particular particle size range and/or a specific surface area range). In an aspect, the niclosamide compounds described herein (e.g., niclosamide) can form part of compositions, dosage forms (e.g., unit dosage forms), and the like, which are suitable for respiratory administration (e.g., via inhalation and/or intranasally). In another aspect, the niclosamide compounds described herein (e.g., niclosamide) can form part of compositions, dosage forms (e.g., unit dosage forms), and the like, which are suitable for administration to the GI tract (e.g., orally or rectally such as via enema)).