16.2  Background

Some chapters in this book consider ways to improve drugs and to identify better candidate targets for different and more efficacious drugs in treating diseases of the posterior segment. Other chapters consider the current state of the art, current standard of care, and the problems associated with current best practices for the treatment of eye diseases in the posterior segment of the eye. Key elements in the success of a new drug include its formulation, the route of delivery, and its targeting to appropriate cells. The latter two points are the focus of this chapter.

16.2.1  Intravitreal Injections

The greatest success in treating diseases of the posterior segment have been through intravitreal injection or intravitreal implantation of slowly eroding materials to release a drug. Most other methods (topical eye drops, systemic oral, subconjunctival, and parenteral) have not been as effective in drug delivery due primarily to dilution. Because of the rapid rate of increase and the already large number of intravitreal injections for treating wet AMD, there are concerns on several fronts that this approach might warrant improvement or change to reduce risks of complications, changes in protocol to reduce health care cost, and modification to reduce burdens on patients and their caregivers. Drugs such as Ranibizumab (Lucentis) and Bevacizumab (Avastin) are remarkable in that they halt neovascularization and improve visual acuity in wet AMD. These two drugs appear to improve the quality of life for the patient, though these drugs handcuff the patient to the doctor and present logistical nightmares for relatives and caregivers because of the high frequency of treatment and continued need for repeat treatments. Ranibizumab is expensive. Treatment with either drug raises costs including physicians’ services and imaging services (cf., OCTs to judge the effectiveness of these treatments). Clearly, these drugs have become the standard of care despite these limitations, because of their apparent superiority over previous treatments such as macugen, PDT, laser photocoagulation, or forms of combination therapy.

Alternatives are needed for the treatment of AMD, especially for the dry form. Similar issues are becoming more obvious with other related retinal diseases that all culminate in Macular Edema.

A major part of the success of Bevacizumab and Ranibizumab is the route of drug delivery, intravitreal injection across the pars plana. Highlighted in other chapters in this book were the initial reticence to undertake intravitreal injections of any agent until the success of clinical trials to treat endophthalmitis and uveitis, and successful implantation of slow release formulations of ganciclovir for CMV retinitis in AIDS patients.