[Biopharmaceutics of ophthalmic drugs]

The importance of biopharmaceutics in the development of ophthalmic drugs is pointed out. Ophthalmic drugs have to be stable, sterile, well tolerated and effective. The constraints resulting from these requirements limit the number of pharmaceutical presentations. The development of pilocarpine eye drops is taken as an example to illustrate how difficult it is to satisfy Goldmann's criteria of stability, sterility, tolerance, and efficacy simultaneously. A rapid and sensitive ocular tolerance test for the selection of the most favorable formulations is proposed as a means of counteracting the present shortage of screening tests. Additionally, the physiological, physicochemical, and pharmaceutical factors are discussed which can influence the drugs' passage through the cornea and consequently increase or decrease their efficacy. Two examples, taken respectively from the aqueous solutions and lipophilic gels, demonstrate the importance of pharmaceutical and biological availability as well as the present tendency toward optimization in the development of ophthalmic preparations.