The formulated ointments should be subjected to the following evaluation tests before being considered for the batch process,

1. Penetration test: This test is carried out by the following methods:
   • A weighed quantity of ointment under test is rubbed on a particular area of skin. After a particulate time period, the ointment is scrapped and weighed. The difference between the initial and final weights will give the rate of penetration of ointment. However, this is a crude method and the results obtained may not be reproducible.
   • It can be tested by using a semipermeable cellulose membrane as diffusion membrane.
   • The Keshery–Chien cell or Franz diffusion cell method is a widely used in vitro instrument for the study of drug penetration. The diffusion membrane used can be a synthetic semipermeable membrane, animal skin membrane or cadaver skin. The study simulates the physiological conditions of human and the results obtained are reproducible.
   • The cup plate method is also used. If the ointment contains any antimicrobial substance, then 2% w/v agar culture media with susceptible microorganism is taken in a petri dish. Bores are made and a preweighed sample of the ointment is introduced aseptically and incubated at 37°C. At frequent intervals of time, the petri dish is taken out and the zone of inhibition is measured, using which the rate of penetration can be calculated.
2. Absorption of a drug: This test is performed for diadermic ointments (systemic circulation). A weighed quantity of ointment is applied to the skin (or mucous membrane). At frequent intervals of times, either the blood or the urine samples are collected and analyzed for drug content, from which the rate of absorption of drug is estimated.
3. Test for sensitivity or irritability: A known amount of ointment is applied to the skin of a rabbit or human and checked for any lesions, patches, redness or any other allergic manifestations for a period of 2-3 weeks. The ointment passes the test if it does not produce any allergy or sensitivity.