Page 1079 - Basic _ Clinical Pharmacology ( PDFDrive )

CHAPTER 60 Special Aspects of Geriatric Pharmacology 1065

Macular Degeneration unaware of incompatible drugs prescribed by other practitioners
Age-related macular degeneration (AMD) is the most common for the same patient. For example, cimetidine, an H 2 -blocking
drug heavily prescribed (or recommended in its over-the-counter
cause of blindness in the elderly in the developed world. Two form) to the elderly, causes a higher incidence of untoward effects
forms of advanced AMD are recognized: the neovascular “wet” (eg, confusion, slurred speech) in the geriatric population than
form, which is associated with intrusion of new blood vessels in younger patients. It also inhibits the hepatic metabolism of
in the subretinal space, and a more common “dry” form, which many drugs, including phenytoin, warfarin, β blockers, and other
is not associated with abnormal vascularization. Although the agents. A patient who has been taking one of the latter agents
cause of AMD is not known, smoking is a documented risk fac- without untoward effect may develop markedly elevated blood
tor, and oxidative stress has long been thought to play a role. On levels and severe toxicity if cimetidine is added to the regimen
this premise, antioxidants have been used to prevent or delay the without adjustment of dosage of the other drugs. Additional
onset of AMD. Proprietary oral formulations of vitamins C and examples of drugs that inhibit liver microsomal enzymes and lead
E, β-carotene, zinc oxide, and cupric oxide are available. Some to adverse reactions are described in Chapters 4 and 66.
include the carotenoids lutein and zeaxanthin, and omega-3 Patient errors may result from nonadherence for reasons
long-chain polyunsaturated fatty acids. Evidence for the efficacy described below. In addition, they often result from use of non-
of these antioxidants is modest. prescription drugs taken without the knowledge of the physician.
In advanced neovascular AMD, treatment has been moderately As noted in Chapters 63 and 64, many over-the-counter agents
successful. This form of AMD can now be treated with laser photo- and herbal medications contain “hidden ingredients” with potent
therapy or with antibodies against vascular endothelial growth fac- pharmacologic effects. For example, many antihistamines con-
tor (VEGF). Two antibodies are available—bevacizumab (Avastin, tained in over-the-counter drugs have significant sedative effects
used off-label) and ranibizumab (Lucentis)—as well as aflibercept and are inherently more hazardous in patients with impaired
(Eylea, a decoy protein receptor that binds VEGF) and the oligo- cognitive function. Similarly, their antimuscarinic action may pre-
peptide pegaptanib (Macugen). Aflibercept is also approved for cipitate urinary retention in geriatric men or glaucoma in patients
the treatment of diabetic macular degeneration. These agents are with a narrow anterior chamber angle. If the patient is also tak-
injected into the vitreous for local effect. Ranibizumab is extremely ing a metabolism inhibitor such as cimetidine, the probability
expensive. Other agents that bind VEGF are under study.
of an adverse reaction is greatly increased. A patient taking an
herbal medication containing gingko is more likely to experience
■ ADVERSE DRUG REACTIONS IN bleeding while taking low doses of aspirin.
THE ELDERLY
■ PRACTICAL ASPECTS OF
The relation between the number of drugs taken and the incidence GERIATRIC PHARMACOLOGY
of adverse drug reactions (ADRs) has been well documented. In
long-term care facilities, in which a high percentage of the popu- The quality of life in elderly patients can be greatly improved
lation is elderly, the average number of prescriptions per patient and life span can be prolonged by the intelligent use of drugs.
varies between 6 and 8. Studies have shown that the percentage However, the prescriber must recognize several practical obstacles
of patients with adverse reactions increases from about 10% when to compliance.
a single drug is being taken to nearly 100% when 10 drugs are The expense of drugs can be a major disincentive in patients
taken. Thus, it may be expected that about half of patients in receiving marginal retirement incomes who are not covered or
long-term care facilities will have recognized or unrecognized inadequately covered by health insurance. The prescriber must
ADRs at some time. Patients living at home may see several differ- be aware of the cost of the prescription and of cheaper alterna-
ent practitioners for different conditions and accumulate multiple tive therapies. For example, the monthly cost of arthritis therapy
prescriptions for drugs with overlapping actions. It is useful to with newer NSAIDs may exceed $100, whereas that for generic
conduct a “brown bag” analysis in such patients. The brown bag ibuprofen and naproxen, two older but equally effective NSAIDs,
analysis consists of asking the patient to bring to the practitioner about $20.
a bag containing all the medications, supplements, vitamins, etc, Nonadherence may result from forgetfulness or confusion,
that he or she is currently taking. Some prescriptions will be found especially if the patient has several prescriptions and different dos-
to be duplicates, and others unnecessary. The total number of ing intervals. A survey carried out in 1986 showed that the popula-
medications taken can often be reduced by 30–50%. tion over 65 years of age accounted for 32% of drugs prescribed in
The overall incidence of ADRs in geriatric patients is estimated the USA, although these patients represented only 11–12% of the
to be at least twice that in the younger population. Reasons for population at that time. Since the prescriptions are often written
this high incidence include errors in prescribing on the part of the by several different practitioners, there is usually no attempt to
practitioners and errors in drug usage by the patient. Practitioner design “integrated” regimens that use drugs with similar dosing
errors sometimes occur because the physician does not appreci- intervals for the several conditions being treated. Patients may
ate the importance of changes in pharmacokinetics with age and forget instructions regarding the need to complete a fixed dura-
age-related diseases. Some errors occur because the practitioner is tion of therapy when a course of anti-infective drug is being given.