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i. Vegetable oils: may be used to replace mineral oils to increase the emollient properties of
the formulated product. Examples of oils that are used for this purpose are coconut oil and
arachis oil.

ii. Organic esters: may be used partly to replace a mineral oil to enhance the spreadability and
to enhance drug dissolution within the ointment base. One of the most commonly used
examples is isopropyl myristate.

Selection of the appropriate base:

1. Desired release rate of the drug substance from the semisolid base
▪ Substances with both aqueous and lipid solubility are good candidates to be released
from the base and diffuse through the skin
▪ Ointments persist at the site of application, enabling the duration of drug release to
be greater than for other topical dosage forms

2. Desirability of topical or percutaneous drug absorption
▪ Product for systemic use or subcutaneous diseases need a penetrating base while
products for topical treatment of keratolytic effect need a non penetrating base
▪ Penetration enhancer could be used to enhance drug permeation

3. Desirability of occlusion of moisture from the skin
▪ Do not use a dehydrating base like PEG or gel base for dry skin and use an occlusive
fatty base
▪ Use a dehydrating base (PEG or gels) for wet skin and weeping lesions and never
use occlusive fatty base

4. Stability of the drug in the semisolid base

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