Absorption enhancement of growth hormone from the gastrointestinal tract of rats

An increased interest in non-injectable dosage forms for polypeptides has led to identification of some compounds which can increase absorption of these drugs. Sodium salicylate administered in rectal suppositories with recombinant methionyl human growth hormone (met-hGH) lead to measurable serum concentrations and demonstratable biological activity of the polypeptide. Sodium salicylate and mineral oil were tested in the ligated stomach, duodenum, ileum and colon of rats for their ability to enhance absorption of met-hGH. Rats were injected in one of the segments of the gastrointestinal tract with 3 mg kg of met-hGH with or without sodium salicylate in aqueous buffer or mineral oil vehicle. Blood samples were collected at various time points and assayed for hGH. Absolute bioavailabilities calculated for each formulation in each intestinal segment indicated that the only treatment with greater than 3% bioavailability was injection of sodium salicylate in mineral oil into the ileum (7%) and colon (9.5%). Statistical analysis proved the surprising interaction of salicylate and mineral oil to be synergistic in absorption enhancement. This is a promising finding but several issues must be addressed and pharmaceutical formulations must be optimized before it can be developed into an oral dosage form for polypeptide drugs.