Gastrointestinal uptake of liposomes. II. In vivo studies

The effect of liposomal entrapment on oral absorption of drugs was deter~ned from the excretion profiles of entrapped markers after oral administration to rats. Liposomal entrapment does not facilitate the uptake of PEG-4000, a non-absorbable, water-soluble marker. The excretion patterns of hydrocortisone and salicylic acid, when entrapped in L-a-phosphatidylcholine distearoyl/cholesterol or egg lecithin/cholesterol multilamellar or unilamellar liposomes, were not significantly different from the excretion patterns of the unencapsulated drugs. These results are in agreement with in vitro and in situ studies which suggest that liposomal entrapment does not influence the intestinal absorption of drugs and, moreover. does not even protect entrapped drugs from the environment of the gastrointestinal tract, The combined in vitro, in situ and in vivo results strongly indicate that liposomes show littk promise as a drug delivery system for oral ad~~stration. The increased oral b~oavailabi~ity of liposomally inco~orated drugs occasionally reported in the literature may be due to factors other than liposomal uptake.