Complex high axial ratio microstructures (CHARMs) were evaluated for delivery of testosterone in vivo. Methods to incorporate testosterone included noncovalent mixing and covalent attachment of testosterone to the lipid to form a prodrug monomer. When prepared by covalent attachment, testosterone-loaded CHARMs were resistant to in vitro spontaneous hydrolysis; when injected into rats, testosterone was released with biphasic kinetics consisting of a burst followed by a much slower phase. Some CHARM material associated with testosterone persisted at the site of injection for at least 9 days.
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