Several famous ointments of the past were prepared by chemical reactions. An example is the strong iodine ointment B. Vet. C. (British Veterinary Pharmacopoeia), which is used to treat ringworm in cattle. It contains free iodine. Earlier, these types of ointments were used as counterirritants in the treatment of human rheumatic diseases. A limitation is that these ointments stain the skin with a deep red color. The water dries up due to improper storage and the iodine crystals irritate the skin. Hence, instead of water, glycerol is sometimes added to dissolve the iodine–potassium iodide complex.

Example:

Strong iodine ointment B. Vet. C.

 

     Iodine

     Wool fat

     Yellow soft paraffin

     Potassium iodide

     Water

 

Dissolve iodine in aqueous potassium iodide solution. Melt the wool fat and yellow soft paraffin together and maintain the temperature to about 40°C. Slowly add iodine solution with stirring and continue until room temperature attained. The product is stored in a wide-mouthed amber-colored glass jar. It is used to treat ringworm in cattle.

 

Alternative method of preparation: Iodine is effectively reacted with unsaturated jelly acids of the fixed oils. The free iodine gets complexed with the double bonds of the unsaturated constituents.

Example:

Nonstaining iodine ointment B.P.C. 1968

 

     Iodine

     Arachis oil

     Yellow soft paraffin

 

Iodine is finely powdered in a glass mortar and the required amount is added to a glass-stoppered conical flask containing arachis oil and stirred well. The mixture is cautiously heated at 50°C in a water bath in a closed condition, preventing the sublimation of iodine. Heating is continued until the initial brown color is changed to greenish-black, which concludes the chemical reaction process. From this preparation, 0.1 g of the substance is weighed and the amount of iodine is determined by B.P.C. method. The amount of soft paraffin base is calculated suitably to give the product the required strength. Soft paraffin is warmed to 40°C. The iodized oil is added and mixed well. The final preparation is packed in a warm, wide-mouthed, and amber-colored glass bottle. It should be allowed to cool without further stirring.