The disclosure features compositions and methods for increasing the half-life of a therapeutic agent (e.g., a C5 antagonist) in the serum of a subject (e.g. a human). Also featured are compositions and methods for. (i) decreasing the frequency by which a therapeutically effective amount of a therapeutic agent must be administered to a human having, suspected of having, or at risk for developing, a medical condition for which the therapeutic agent is effective and (ii) decreasing the dosage of the therapeutic agent required for therapeutic efficacy in a human having, suspected of having, or at risk for developing, a medical condition for which the therapeutic agent is effective. The methods include reducing the serum concentration of the antigen to which the therapeutic agent binds.