Extrusion of niosomes from capillaries: approaches to a pulsed delivery device

We describe an early prototype of a pulsatile delivery system for drug cont aining vesicles. Nonionic surfactant vesicles (niosomes) of average diamete r 4-30 mu m are extruded from glass capillaries (exit diameter, 5-10 mu m), using air pressures of 0.5-5 p.s.i. The formulation of the vesicles is vit al. Extrusion was affected by the size, shape, and membrane composition of the niosomes used. Spherical or polyhedral niosomes, formed by polyoxyethyl ene alkyl ethers with and without cholesterol, respectively, with diameters larger than the exit diameter of the capillary do not retain their membran e integrity on extrusion and were sheared to form new ultrastructures. The expulsion of single or groups of intact polystyrene microspheres or tetrade cyl-P-D-maltoside niosomes with sizes smaller than the exit diameter can be achieved readily. The stepwise release profile of luteinizing hormone rele asing hormone (LHRH) obtained after pulsatile expulsion of groups of niosom es entrapping LHRH indicates the feasibility of this system for pulsatile d elivery of vesicles, although it requires miniaturization. (C) 1999 Elsevie r Science B.V. All rights reserved.