Age-related macular degeneration (AMD) is the most common cause of blindness in the elderly in the developed world. Two forms of advanced AMD are recognized: the neovascular “wet” form, which is associated with intrusion of new blood vessels in the subretinal space, and a more common “dry” form, which is not associated with abnormal vascularization. Although the cause of AMD is not known, smoking is a documented risk factor, and oxidative stress has long been thought to play a role. On this premise, antioxidants have been used to prevent or delay the onset of AMD. Proprietary oral formulations of vitamins C and E, β-carotene, zinc oxide, and cupric oxide are available. Some include the carotenoids lutein and zeaxanthin, and omega-3 long-chain polyunsaturated fatty acids. Evidence for the efficacy of these antioxidants is modest.
In advanced neovascular AMD, treatment has been moderately successful. This form of AMD can now be treated with laser photo-therapy or with antibodies against vascular endothelial growth factor (VEGF). Two antibodies are available—bevacizumab (Avastin, used off-label) and ranibizumab (Lucentis)—as well as aflibercept (Eylea, a decoy protein receptor that binds VEGF) and the oligopeptide pegaptanib (Macugen). Aflibercept is also approved for the treatment of diabetic macular degeneration. These agents are injected into the vitreous for local effect. Ranibizumab is extremely expensive. Other agents that bind VEGF are under study.
The relation between the number of drugs taken and the incidence of adverse drug reactions (ADRs) has been well documented. In long-term care facilities, in which a high percentage of the population is elderly, the average number of prescriptions per patient varies between 6 and 8. Studies have shown that the percentage of patients with adverse reactions increases from about 10% when a single drug is being taken to nearly 100% when 10 drugs are taken. Thus, it may be expected that about half of patients in long-term care facilities will have recognized or unrecognized ADRs at some time. Patients living at home may see several different practitioners for different conditions and accumulate multiple prescriptions for drugs with overlapping actions. It is useful to conduct a “brown bag” analysis in such patients. The brown bag analysis consists of asking the patient to bring to the practitioner a bag containing all the medications, supplements, vitamins, etc, that he or she is currently taking. Some prescriptions will be found to be duplicates, and others unnecessary. The total number of medications taken can often be reduced by 30–50%.
The overall incidence of ADRs in geriatric patients is estimated to be at least twice that in the younger population. Reasons for this high incidence include errors in prescribing on the part of the practitioners and errors in drug usage by the patient. Practitioner errors sometimes occur because the physician does not appreciate the importance of changes in pharmacokinetics with age and age-related diseases. Some errors occur because the practitioner is unaware of incompatible drugs prescribed by other practitioners for the same patient. For example, cimetidine, an H2-blocking drug heavily prescribed (or recommended in its over-the-counter form) to the elderly, causes a higher incidence of untoward effects (eg, confusion, slurred speech) in the geriatric population than in younger patients. It also inhibits the hepatic metabolism of many drugs, including phenytoin, warfarin, β blockers, and other agents. A patient who has been taking one of the latter agents without untoward effect may develop markedly elevated blood levels and severe toxicity if cimetidine is added to the regimen without adjustment of dosage of the other drugs. Additional examples of drugs that inhibit liver microsomal enzymes and lead to adverse reactions are described in Chapters 4 and 66.