NEW DRUG DELIVERY SYSTEMS
A. Liposomes: Liposomes are small vesicles with phospholipid bilayers surrounding an aqueous core. Multi lamellar vesicles (MLVs) have diameters in the range of 0.5-100 μm. Small unilamellar vesicles (SUVs) have diameters in the range of 0.02 to 0.05 μm. SUVs are composed of a single lipid outer layer with an aqueous inner core. Liposomes release of deliver the drug either by simple diffusion or by interacting with the cell membrane. Liposomes interact with the cell membrane by –
(a) Fusion: The lipid portion of the vesicle fuses with cell membrane and the contents of the vesicles are released
into the cell.
(b) Endocytosis: Cell engulfs the vesicles and lyses it, releasing the contents.
(c) Adsorption: Vesicle is adsorbed on the surface of the cell membrane and its contents diffuses into the cell.Liposomes drug delivery system offers certain advantages:
1. Protection of a drug compound against degradation and from rapid metabolism.
2. Enhances the cellular uptake of drugs.
3. Sustained in-vivo drug levels.
4. Targeting of drugs to specific cells or organs.
B. NIOSOMES: Niosomes are non-ionic surfactant vesicles and they may have cholesterol also.C. Nanoparticles: Nanoparticles are colloidal drug delivery systems. Nanoparticles can be used to target
drugs to liver, spleen and tumor cells. These are the small particles containing dispersed drug and having a diameter of approximately 200 nm to 500 nm. Because of their small size they can be injected by intravenous route. Nanoparticles are prepared using non-toxic, biodegradable polymers. Nanoparticles release the drug by diffusion, dissolution or by combination of both.
D. Released Erythrocytes: These are prepared by placing RBC‟s in hypotonic media which leads to rupturing of cell membrane and formation of small pores (diameter 200-500 A0) through which intracellular and extracellular exchange takes place. In this way a drug compound in extra cellular media enters the RBC‟s. when these RBCs are again placed in an isotonic media at 37 C, resealing of the membrane takes place. Up to 40% of the drug can be loaded into RBC‟s. Resealed erythrocytes are biodegradable, non-immunogenic. Resealed erythrocytes can be used to target drugs to liver and spleen.
E. Antibody-Targeted Systems: Antibody or Immunoglobulin tagged drug molecule delivers the drug at specific antigen site. Antibody targeted systems consist of either a drug molecule linked covalently to the antibody or vesicles (liposomes) containing drugs attached to antibody. Monoclonal antibodies specific for antigens on tumor cells can be used for targeting of cytotoxic drugs.
F. Zidis System: Modified release tablets that disperse rapidly when placed in mouth (melt in the mouth tablets). Drug dissolved or suspended in an aqueous matrix is filled into performed cavities in the blister pack. The solution or suspension is then frozen and water removed by Lyophilization.
G. OROS Osmotic pump: Consist of tablet core of a drug plus osmotically active agent coated or surrounded by a non-swelling semi-permeable membrane polymer and having a laser drilled hole in the polymeric coating. When OROS comes in contact with the aqueous content of G.I.T. the osmotically active agent dissolves creating a pressure inside the system and forcing the drug out of laser hole at constant rate.
H. Mucoadhesive Drug Delivery System: Employ mucoadhesive polymers which are capable of adhering to the gastrointestinal tract at specific sites. Used for improvement of bioavailability of drugs with narrow absorption window. Mucoadhesives (eg polycarbophil and carbomer, acacia) adhere directly to surfaces either by binding to specific tissues or by complexing with the nucleus coat of the tissue surface.
I. Hydrodynamically balanced systems or Floating drug delivery systems: Low density systems, contain one or more hydrocolloids which swell on contact with water to form a gel layer. This layer presents a low density system that floats on the gastro intestinal contents, thereby prolonging the gastric residence time.Transdermal drug delivery systems: Deliver the drug through intact skin into the systemic circulation. Transdermal drug delivery systems usually employ polymeric multi-layered devices having a drug reservoir or a drug polymer matrix fixed between two laminated layers of polymers. One of the layer serves as backing which is impermeable and prevents the loss of drug from matrix or reservoir. The other layers serves as the rate controlling membrane for the drug.
Transdermal delivery system can be categorized as:
1). Reservoir system
2). Matrix system.Reservoir System: Thee release rate of the drug is controlled by diffusionaal resistance a cross a polyymeric membrane.Matrix system: The releease rate of druug is controlledd by the diffusioon of the drug from polymer matrix.• If ratee of drug trannsport across tthe skin is greeater than the required to produce a steaady state theraapeutic concenntration, then reservoir deliveery system is used.
• If permmeation throug stratum cornneum controls the rate of deliivery to the boddy then a matrix delivery sysstem is used.
Iontophorretic Drug Dellivery Systems:
Iontophereetic drug deliveery systems mploy electric current to activate and conttrol the movemment of ionized drug
molecules across variouss biological membranes.
Skin consiists of 15-20% lipids, 40% proteins and 0% water wheen electric poteential is applieed across the skin, it alters the molecular arranngement of skin components and hence permmeability.