Prescribing medicine for older people -technical
Two-thirds of people over the age of 65 take medication regularly. Although they account for about 15% of the population they are responsible for about 40% of the costs of drug prescribing. One-third of people aged 75 and over take at least three medications, and for those living in institutional care this number is on average doubled. There is a tendency to prescribe drugs for older people and then fail to review them. It is therefore not surprising that estimates suggest that about 1 in 10 hospital admissions of older people are caused by, or contributed to by, unwanted effects of drugs. The overall incidents and adverse reactions to drugs must be higher than this as in many incidences the problem will be dealt with in a primary care setting.
Preventing unwanted drug effects
The two most important questions to bear in mind when initiating a prescription are first: ‘Is this treatment really necessary?’, and secondly: ‘If so, for how long should it be prescribed before review?’ It can be surprisingly difficult to know what is necessary, as the evidence on which requirements are based must often be generalized from younger patients, or patients who are typically not as frail as those seen by geriatricians. For instance, while starting a patient on aspirin, a β-blocker, an angiotensin converting enzyme inhibitor, and a statin after a myocardial infarction may be good cardiology, it is often poor geriatrics. At present, there is no evidence to support the necessity for immediate polypharmacy. It is good practice to consider all the existing prescribed medication at the time of initiating a new treatment. It may well be possible to stop some of the existing medication, even if only on a trial basis. This will ensure that the prescriber does not forget to check for the presence of possible drug interactions.
Wherever possible, prescribe drugs that are part of the hospital’s approved formulary, but be prepared to prescribe other medications if there is a genuine reason that can be objectively justified.
The well-known adage ‘start low and go slow’ is very important. The dose of each drug should be increased cautiously, depending upon the balance of benefit on the one hand, and unwanted effects on the other. Remember too the need to ‘go slow, but go’, i.e. to titrate upwards until the desired effect is achieved, lest the result is to expose the patient to the side effects of a drug without maximizing the potential for benefit.
Factors affecting drug efficacy
If the patient’s condition does not respond to treatment as anticipated, there may be a number of reasons. First, ensure that the patient is actually taking the medication as prescribed. Poor vision, cognitive impairment, and sometimes difficulty in hearing are reasons why treatment is not taken properly. Some people will also be reluctant to take medication that tastes unpleasant, or if the individual capsules or tablets are large and difficult to swallow. It is also important to think about the total number of medications a person is taking, as polypharmacy easily contributes to confusion about the drug regime, e.g. where some medication is taken once a day, others more frequently, and if the individual dose consists of more than one tablet and/or capsule.
Absorption of drugs is largely unchanged with ageing, and this is less likely to contribute to lack of efficacy. This is certainly true for those drugs that diffuse passively across the intestinal mucosa, but even though there maybe some reduction in the transport mechanisms for those medications that are actively transported from the bowel lumen, this is usually not sufficient to make a major impact.
Other factors that affect the way drugs are metabolized include the ratio of lean body mass to fat, which has implications for the distribution of some drugs, especially those that are water soluble, and the binding of drugs to plasma proteins, which is often reduced in older people.
Hepatic metabolism and renal excretion of drugs are important considerations. Those that are absorbed from the gastrointestinal tract pass through the liver, whose mass and blood supply decrease with increasing age. Thus, there may be increased levels of some drugs in the systemic circulation because of reduced first-pass metabolism. This can be important, e.g. with some opiates. However, the individual metabolic pathways within hepatocytes for most drugs are probably affected little, if at all, by the ageing process.
Changes in renal function with age have a greater impact on prescribing than hepatic changes. Most older people experience a decline in glomerular filtration rate, which can be exacerbated by medication and illness. Hence, it is necessary to be aware of the patient’s renal function and which drugs this may affect. Good examples are digoxin, gentamicin, and furosemide, which are cleared mainly through the kidneys. As already mentioned, comorbidity can affect renal function. This includes common conditions such as dehydration and renal infection.
Other factors that are important in the way drugs behave in older people include changes in sensitivity at a tissue and cellular level. This can be either a decrease in sensitivity, e.g. of the β-adrenoceptor, which has implications for the bradycardia produced by β-blockers or increased sensitivity such as often seen in the central nervous system to many centrally acting drugs including antidepressants, antiparkinsonian drugs, hypnotics, analgesics, and antipsychotics.
In general terms, the simpler the regime the better the compliance. This obviously relates to the number of drugs and the frequency of their administration. As already mentioned, cognitive ability, sight, and vision are also important.
Sometimes, patients do not take their medication because they or their families do not really understand its importance. A careful explanation, ensuring that they understand the reasons for taking their medicine and also how it works, will often help. Sometimes, a written summary is also of value.
Where compliance appears to be erratic, family and friends can sometimes help, especially if a monitored dosing system is used, e.g. Nomad, or a dosette box i.e. a pill container with individual segments for different days and different times of day.
Finally, pragmatic issues are sometimes of importance, e.g. the patient may omit to take a powerful diuretic before going out to a social occasion where they are aware they may be not be able to find a lavatory in time. This situation can easily be avoided with a little common sense.
Where it proves necessary to investigate compliance, it is possible to check the number of tablets left in the bottle or a dosette box or similar. Blood or urinary levels of some medications are also relatively easily assayed, and in some situations measures of clinical efficacy may help, e.g. if bradycardia is induced by a β-blocker.