Development of an ocular drug release system for cattle
An erodible ring-shaped ocular insert containing an antibiotic (tylosin tartrate) has been developed for treatment of infectious bovine keratoconjunctivitis (IBK). Four additional tasks have been completed: (1) a test to determine the retention time of the ocular device in the eyes of the calves, (2) an in vitro test to determine the degradation characteristics of the device, (3) an in vitro study to obtain the drug release profiles of the insert, and (4) a study to compare the use of rings and a field treatment method using infected cattle;The device remained in the eyes an average of 3.92 days, with the retention time ranging from 1 day to 6 days;The device completely dissolved in saline in 80 days. The device seemed to erode faster in the eyes of the calves than when used in in vitro tests;The drug release rate from the device after 5 days was still above the minimum release rate of 1.3 [mu]g/hr required to treat IBK infections;Two groups of Holstein calves were infected with Moraxella bovis, the agent that causes IBK. A comparison of the ocular ring treatment with that of a field method of treatment using subconjunctival injections of Azimycin°ler demonstrated that the treatment using the ring device was significantly more effective than the subconjunctival injection method. Clinical observations showed that the eyes receiving the medicated ocular devices improved while the eyes which were treated with subconjunctival injections of Azimycin°ler remained the same or worsened (p < 0.008). Also, bacterial evaluations performed by quantatively monitoring the number of bacteria in treated and control eyes for both treatment methods over a test period in excess of 5 days showed that the medicated ocular devices suppressed or kept the bacteria counts low (or nil) as compared to relatively high counts seen in those eyes that were treated with subconjunctival injections of Azimycin°ler (p < 0.03);The bioerodible ocular device has several advantages over conventional methods, including the subconjunctival injection method, in that it is more effective in treating IBK, is easy to insert, and can provide extended treatment therapy.