Ointments Lecture 2

2. Absorption bases: Examples Anhydrous ▹ Hydrophilic Petrolatum ▹ Anhydrous Lanolin Hydrous ▹ Lanolin 2. Absorption bases: Examples Anhydrous ▹ Hydrophilic Petrolatum Emulsifying agents Cholesterol Stearyl alcohol White wax White petrolatum ▹ Can absorb up to 3X its weight of water ▹ Used to incorporate water soluble drugs such as tobramycin sulfate into oleaginous bases In general, High molecular weight fatty alcohols such as cetyl alcohol and stearyl alcohol: ▹ ▹ Enhance the water-holding ability of the base Increase its consistency and smoothness 30 g 30 g 80 g 860 g 2. Absorption bases: Examples Anhydrous ▹ Anhydrous Lanolin ▹ AKA: wool fat ▹ Too sticky to be used on its own, but it mixes well with oleaginous bases to increase their hydrophilic properties ▹ Can absorb 2X its weight of water Wool alcohols Ex: Sheep wool Purification Wax-like substance (Wool fat) Cholesterol Lanosterol Agnosterol ▹ Emulsifying ▹ Emollient 2. Absorption bases: Examples Hydrous ▹ ▹ Hydrous wool fat (hydrous lanolin) ▹ Prepared by adding 25-30% of water to form a W/O emulsion ▹ Thinner in consistency than anhydrous lanolin Lanolin Lanolin is considered a skin sensitizer People susceptible to wool allergies should avoid it 3. Water-removable bases ▹ AKA: Emulsion bases ▹ O/W emulsions, water miscible ▹ Resemble creams in appearance Absorption of serous discharges in dermatological conditions Absorb up to 30-50% of their weight as water Suitable for cosmetic purposes Water washable Water absorbing 3. Water-removable bases ▹ Emulsifying agents that form O/W emulsions Anionic Cationic Non-ionic • Ex: Sodium lauryl sulfate • Ex: Cetrimide • Ex: Cetomacrogol • Might be ineffective in presence of cationic agents • Effective at high pH levels • Might be ineffective in presence of anionic agents • Effective at low pH levels • Compatible with electrolytes and ionic molecules • Less irritating than ionic ones ▹ Ionic emulsifiers are sensitive to the presence of ions and to pH changes ▹ The choice is based on compatibility with the added drug ▹ Ex: Cationic drug...? 3. Water-removable bases: Example Antimicrobial preservatives ▹ The Hydrophilic Ointment Humectant Oleaginous phase Methylparaben Propylparaben Sodium lauryl sulfate Propylene glycol Stearyl alcohol White petrolatum Purified water 0.25 g 0.15 g 10 g 120 g 250 g 250 g 370 g Prone to microbial growth High water content External phase  can dry out Stearyl alcohol + SLS  anionic emulsifying wax  O/W emulsion 4. Water-soluble bases ▹ AKA: Water-miscible bases, Greaseless bases Water-miscible Do NOT contain any fatty components Non-occlusive Greaseless Non-emollient Prepared from a mixture of watersoluble polyethylene glycols Miscible with aqueous skin secretions Easily washed of the skin Easily spread on skin surface 4. Water-soluble bases: Uses ▹ They cannot hold large volumes of aqueous solutions (up to 5% of the total weight) and are rather used to incorporate non-aqueous or solid substances. ▹ Not suitable for water-soluble drugs if percutaneous absorption is desired...Why? ▹ They allow evaporation of moisture and dryness of the skin, so are desirable for the treatment of moist lesions. 4. Water-soluble bases MWt Viscosity ▹ Polyethylene glycol (PEG) ▹ A polyether consisting of an oxyethylene (-O-CH2-CH2-) backbone ▹ The molecular weight varies based on the number of oxyethylene groups (ex: PEG 200, PEG 400, PEG 1000,.....etc) ▹ < PEG 600  Viscous liquids ▹ > PEG 800  Soft semisolids to waxy solids Some medicaments (ex: salicylic acid, benzoic acid, phenol and tannic acid) are incompatible with PEG-based bases Interact with high MWT PEGs  solubilize them  base softening Liquid PEG Solid PEG Soft pliable semisolid ointment 4. Water-soluble bases: Example ▹ Polyethylene Glycol Ointment PEG 3350 PEG 400 400 g 600 g ▹ The ratios can be varied up to equal parts of each (1:1)  enhance consistency. ▹ Substituting part of PEG 3350 with 5% stearyl or cetyl alcohol will yield: ▸ Firmer base ▸ Higher water-absorption potential allowing inclusion of up to 20% of water.