The Pharmaceutics and Compounding Laboratory
Ointments: Preparation and
Evaluation of Drug Release

Preparation of Ointment Bases

Prepare 120 g of each of the following five ointments on a w/w basis. One partner should prepare bases #1, 3 and 5 while the other prepares #2 and 4. Make sure that you follow closely the procedures for preparation.

General Comments About Compounding Ointment Bases

  • Between 2 and 4 grams of an ointment may be lost in the compounding process. The ointment is lost as it adheres to beakers, ointment tiles, or ointment pads. To compensate for this loss, make an excess of the ointment. Some general rules might be to add 10% or 3 grams excess to the prescribed amount.

  • When heat is used to melt ingredients, use a water bath or special low temperature hotplate. Most ingredients used in ointment bases will liquefy around 70°C These two heating devices provide adequate control over the heating and will ensure that the ingredients are not over heated. A water bath will only heat to the boiling point of water which is 100°C. Special "low temperature" hotplates (full range is 25°C to 120°C) are not a standard laboratory type hotplate; those hotplates heat at 125°C to 150°C at their lowest setting.

  • When both an oil and aqueous phase are being mixed together to make an ointment, it is helpful to heat the aqueous phase a few degrees higher than the oil phase prior to mixing. The aqueous phase tends to cool faster than the oil phase and may cause premature solidification of some ingredients. However, use the lowest temperature possible and keep the time of heating as short as possible. This will minimize the quantity of water lost through evaporation.

  • When melting a number of ingredients, melt the ingredient with the highest melting point first. Then gradually reduce the heat to melt the ingredient with the next lowest melting point. Continue this process until all ingredients have been added. This will ensure that the ingredients were exposed to the lowest possible temperature and thus enhance the stability of the final product.

  • The cooling step in an ointment's preparation is an important part of the compounding process.
    • Do not accelerate the cooling process by putting the melt in water or ice. This will change the consistency of the final product making it more stiff than desired.

    • If adding volatile ingredients such as oils, flavors, or drugs, add them when the product is "cool to the back of the hand." The melt will still be fluid enough for adequate mixing but not hot enough to evaporate the ingredient.

    • Ointments should be cooled until just a few degrees above solidification before they are poured into tubes or jars. They should be thick, viscous fluids. This will minimize "layering" of the ointment in the packaging container. However, this is not the preferred method of packing an ointment tube or jar.

    • Most bases achieve their final consistency and texture several hours after they are compounded.

 

BASE NO. I: Oleaginous Base (White Ointment)

White Wax 5% ________ g
White Petrolatum 95% ________ g

Procedure for Preparation:

  1. Melt the white wax on a hot plate. No need to heat beyond 70 - 75°C
  2. When the wax has completely melted, add the petrolatum and allow the entire mixture to remain on the hot plate until liquefied.
  3. Following liquefication, remove from heat and allow the mixture to congeal. Stir the mixture until it begins to congeal.

 

BASE NO. II: Absorption Base

Cholesterol 3% ________ g
Stearyl Alcohol 3% ________ g
White Wax 8% ________ g
White Petrolatum 86% ________ g

Procedure for Preparation:

  1. Melt the stearyl alcohol, white wax, and petrolatum together on a hot plate.
  2. Add the cholesterol to the mixture; stir until completely dissolved.
  3. Remove the mixture from the hot plate and stir until congealed.

 

BASE NO. III: W/O Emulsion Base (Cold Cream type base)

White wax 12.0% ________ g  
Cetyl Esters Wax (or Spermaceti) 12.5% ________ g  
Mineral Oil (Sp Gr = 0.9) 56.0% ________ g ________ ml
Sodium Borate 0.5% ________ g  
Water 19.0% ________ g ________ ml

Procedure for Preparation:

  1. Melt the white wax and spermaceti on a hot plate.
  2. Add the mineral oil to this mixture and bring the temperature to 70°C.
  3. Dissolve the sodium borate in water.
  4. Heat the sodium borate solution to 70°C.
  5. When both phases have reached the desired temperature, remove both phases from the hot plate and add the aqueous phase slowly and with constant stirring to the oil phase.
  6. Stir briskly and continuously until congealed.

 

BASE NO. IV: O/W Emulsion Base (Hydrophilic Ointment)

Sodium Lauryl Sulfate 1.0% ________ g  
Propylene Glycol (SP Gr = 1.035) 12.0% ________ g ________ ml
Stearyl Alcohol 25.0% ________ g  
White Petrolatum 25.0% ________ g  
Purified Water 37.0% ________ g ________ ml

Procedure for Preparation:

  1. Melt the stearyl alcohol and white petrolatum on a hot plate.
  2. Heat this mixture to 70°C.
  3. Dissolve remaining ingredients in water and heat the solution to 70° C.
  4. Add the oleaginous phase slowly to the aqueous phase, stirring constantly.
  5. Remove from heat and stir the mixture until it congeals.

 

BASE NO. V: Water Soluble Base

Polyethylene Glycol 400 (SP Gr = 1.12) 60% ________ g ________ ml
Polyethylene Glycol 3350 40% ________ g  

Procedure for Preparation:

  1. Melt the PEG 400 and Carbowax 3350 on a hot plate.
  2. Warm the mixture to about 65°C.
  3. Remove from the hot plate and stir until congealed.