Enhancement of Nasal Salmon Calcitonin Absorption by Lauroylcarnitine Chloride in Rats

Purpose. We investigated optimum formulation characteristics in the nasal absorption of salmon calcitonin (sCT) by incorporation of acylcarnitines.Methods. Nasal sCT formulations were administered to anesthetized rats. Plasma calcium level was measured and pharmacological bioavailability (P.bioav) was calculated.Results. Nasal sCT absorption was significantly enhanced by carnitines with acyl groups of 12 or more carbon atoms. Enhancement by lauroylcarnitine chloride (LCC) was observed at its critical micelle concentration and reached a plateau at the concentration of 0.1%. Optimal absorption was achieved at a molar ratio of LCC to sCT of 5:1. Enhancement was not influenced by osmolarity and maximum enhancement was obtained at pHs 3.1 and 4.0.Conclusions. The 12-carbon LCC was the strongest enhancer among acylcarnitines. Micelle formation played a key role in this enhancement effect.