LECITHIN-ORGANOGELS FOR TOPICAL DELIVERY OF DRUGS
Objective: This laboratory provides an opportunity for the student to prepare a new topical drug delivery vehicle, lecithin-organogel emulsion.
Recent developments in topical vehicles for the delivery of drugs for systemic effect has produced new formulations that may be easily prepared by the pharmacist. Physicians are becoming aware of the advantages of these vehicles, and are calling upon pharmacists to prepare drug products utilizing the formulation described here, as well as many others.
Lecithin has become recognized as a possible permeation enhancer in the transdermal delivery of drugs. Studies have also revealed that, when mixed with water, lecithin solutions in organic solvents, produce gels which make vehicles of suitable viscosity for topical delivery. Thus, it would seem that this emulsion base would be ideal for certain types of topical products. And, indeed, research has shown that systemic absorption does occur with this base. Unfortunately, only lecithin of very high purity forms gels with water. The compounding pharmacist may not be able to obtain materials of the quality necessary to produce the proper viscosity. But, with the addition of a synthetic polymer such as Carbopol or Pluronic, a semi-solid product can be produced.
This base was used for the topical administration of scopolamine when the commercially available product unavailable. It has also been used with non-steroidal anti-inflammatory drugs such as ketoprofen. One formulation can be found at the Pharmacy Times compounding link (www.pharmacytimes.com) under "ibuprofen".
The following is a proposed formulation for which the oil and water phases can be prepared in advance. The prescribed drug can then be added to the oleaginous phase if it is lipophilic or into the gel phase if the drug is water soluble. The two phases emulsified at the time of dispensing.
Topical Emulsion, Semi-solid
Oil Phase: The oil phase for this topical emulsion may be inexpensively and easily prepared using the formulation below, or a prepared solution may be purchased from wholesalers who specialize in materials for compounders. This solution will be prepared in lab, covered, and left until use the next week. It will usually dissolve in approximately 24 hours. Stirring of the ingredients IS NOT NECESSARY.
Lecithin, soya granular 6 g
Isopropyl Palmitate, NF 6 g
Sorbic Acid, NF 0.12g
1. Weigh solids.
2. Weigh or measure Isopropyl Palmitate and place in beaker. Disperse solids in beaker. Do not shake. The lecithin will dissolve over night.
Water and Gel Phase: This product is available as a 20% product, also from compounding suppliers. Pluronic is an interesting substance in that when mixed with water, it forms a gel that is very viscous (like jello) at room temperature. Under refrigeration, however, it becomes a liquid, and is easy to work with for this preparation.
Pluronic F127 10 gm
Potassium Sorbate 0.12gm
Purified Water qs 50 mL
1. Calibrate a vessel for 50 mL using water. Mark 50 mL level. Remove water.
2. Weigh out powders and place in calibrated vessel.
3. Add COLD water to the mark. Shake well.
4. Store in refrigerator for dissolution to take place. The Pluronic will dissolve overnight.
***Note: The Oil Phase and Water and Gel phases have been prepared before lab.***
To prepare lecithin/Pluronic Gel for topical use:
Into separate syringes, withdraw 20% of total amount to be prepared lecithin and 80% of pluronic gel. The active ingredient(s) are dissolve in the oil or water phase depending on it's properties of solubility before mixing..Transfer the two mixtures from one syringe to another by using a luer lock to luer lock connector. Continue mixing until uniform. See handoutfor product preparation.