Review: Implants

An implantable sustained release device has been developed to treat chronic disorders of the eye. The device, consisting of a central core of drug encased in layers of permeable and impermeable polymers, can be implanted subconjunctivally or intravitreally. This technique was used to develop a ganciclovir device which, when implanted into the vitreous, maintains therapeutic vitreous levels of drug for 8 months. Initial studies in patients with cytomegalovirus (CMV) retinitis indicate that this treatment may offer better control of the disease and fewer side effects than existing therapies. Cyclosporine A devices were prepared for the treatment of uveitis. Early data suggests that these devices maintain therapeutic levels in the vitreous for approximately 3 years. Work on efficacy and toxicity is continuing. Although clinical applications of these devices are likely to be restricted to diseases requiring chronic drug therapy, they can be used to investigate optimal delivery rates. Subconjunctivally implanted devices releasing 5-FU for 12 days maintained filters in cynomolgus monkeys for 3 months. Similar devices maintained low intraocular pressure in 75% of high risk filter patients.