Therapeutic efficacy of liposome-entrapped rifampin against Mycobacterium avium complex infection induced in mice.

Liposome-entrapped rifampin (RFP) was examined for therapeutic efficacy against experimental infection induced in mice by the Mycobacterium avium complex. Intraperitoneal injections (once daily, six times weekly) of liposome-entrapped RFP led to a greater reduction in bacterial growth in the lungs and spleen of infected mice than did free RFP alone. Liposome-entrapped RFP given to mice via the intramuscular or subcutaneous route failed to show such an increased therapeutic efficacy. RFP entrapped in the lipid layer of liposomal vesicles exhibited a level of therapeutic activity similar to that seen with RFP encapsulated in the inner solute of the vesicles. Entrapment of RFP in liposomal vesicles increased incorporation of the drug into host peritoneal macrophages and increased the activity of the agent against M. avium complex phagocytosed into the macrophages.