Distribution of radiolabeled multilamellar liposomes injected intralymphatically and subcutaneously

The distribution of negatively charged multilamellar vesicles (MLV) composed of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol administered subcutaneously (s.c.) and intralymphatically (i.l.) was studied in rats and dogs. In rats, the drainage of 99mTc-MLV from the s.c. space was slow, with 35% of the activity still remaining at the site of injection after 48 h and minimal systemic distribution (less than 5% at any time point). In the dog, 99mTc-MLV and 111In-MLV injected s.c. on the dorsal surface of a hindpaw were drained both by the lymphatic system and the systemic circulation; at 24 and 72 h, significant activity still remained at the site of injection. Lymphatic uptake was almost limited to the popliteal nodes and was enhanced by dividing the dose in several s.c. injections. Liver and kidney uptake was also observed, most likely as a result of direct liposome absorption into the systemic circulation. The i.l. administration (via left hindpaw) of 99mTc-MLV to a dog resulted in an immediate uptake in the abdominal and mediastinal lymph nodes, and in the liver and spleen. Compared with small unilamellar vesicles, MLV injected s.c. can provide a slower and more prolonged delivery of drugs to the regional lymph nodes.