metabolism may be reduced in the elderly, possibly a consequence of the reduction in liver mass and blood flow. As a result, drugs that undergo extensive first‐pass metabolism (e.g. labetalol and propranolol) may show considerably increased bioavailability in the elderly, an effect amplified by the presence of chronic liver disease.
Renal excretion
With ageing, there is a fall in both renal blood flow and renal function and dose reduction should be considered if prescribing a renal‐excreted drug in the elderly. Glomerular filtration falls by approximately 30% by the age of 65 years. Digoxin and the aminoglycoside antibiotics are excreted mainly by glomerular filtration and these will tend to accumulate in the elderly if the dose is not reduced.
Renal tubular function also declines and drugs that undergo active tubular secretion (in routine practice mainly penicillin) have a marked reduction in clearance, but this is of limited clinical relevance. Often acutely unwell elderly patients are dehydrated, further compromising renal function. In these circumstances (i.e. acute kidney injury), potentially nephrotoxic drugs should be withheld.
Receptor sensitivity
Although the mechanisms are poorly understood, the elderly seem to be more sensitive to certain drugs. These tend to be drugs where caution should be exercised, e.g. benzodiazepines and warfarin.
Impairment of homeostasis
Cardiovascular postural reflexes are less effective in the elderly. Falls due to presyncope and syncope are exacerbated by the use of drugs that cause postural hypotension, including diuretics, antihypertensive agents and sedatives.
Polypharmacy
The prescription of multiple drugs can lead to a multitude of problems both for the prescriber and the patient, including poor adherence, drug interactions and adverse reactions. The incidence of adverse reactions has been reported as 4% when taking less than five drugs and increases to 54% when taking over five. When prescribing in the elderly it is important to ensure that both you, as prescriber, and the patient understand the indication for the prescription (i.e. symptomatic and/or prognostic benefit) versus potential for side effects.
There is no evidence that an elderly patient whose mental function is normal is more likely to make mistakes with their medication than a younger patient. However, polypharmacy contributes to poor adherence and safety at all ages. The rate of errors when three drugs are prescribed is approximately 20% but it is close to 100% when 10 drugs are prescribed – and the high rate of prescribing for the elderly results in a greater opportunity to make errors. This is, however, potentially made worse by the prevalence of cognitive impairment, which is as high as 25% in those over the age of 85 years.
Physical disability, such as arthritis can contribute to poor adherence as opening ‘child‐proof’ containers or ‘bubble‐pack’ drugs becomes more difficult. Medication aids such as ‘blister packs’ and non‐childproof containers should be considered in this population.
1 The presentation of disease in the elderly is often non‐specific (e.g. confusion). It is important to make an accurate diagnosis to allow appropriate therapy
2 Treat only when benefit outweighs risks. Elderly patients frequently have multiple symptoms and pathologies leading to polypharmacy. This increases the risk of side effects and results in poor adherence
3 It is important to review the need for each prescription on a regular basis. If a drug is considered necessary for symptomatic or prognostic benefit, ensure the minimum dose required is used
4 Understand the change in pharmacology with age (particularly decline in renal function) for each drug used, remembering that dose alterations may be required, particularly in the acute setting
Drugs in pregnant and breastfeeding women
Drugs in pregnancy
A 28‐year‐old woman attends her GP for preconception advice. She has epilepsy and has been on carbamazepine 800 mg bd for several years. She has been seizure free for over 12 months. She has recently got married and wishes to discuss the implications of her epilepsy on planning a pregnancy. She has no other medical or family history of note. What are the risks of the medication on a developing baby and is there anything she can do to minimise this risk?
The greatest risk of teratogenesis occurs at a stage when a women might not know that she is pregnant
Only a few drugs are known definitely to be teratogenic, but many more could be under certain circumstances
When prescribing for a woman of childbearing age, remember that she might be pregnant and ask yourself if the benefits of drug use outweigh the risks of teratogenesis
Introduction
Nearly 40% of women in the UK take at least one drug during pregnancy, excluding iron, vitamins and drugs used during delivery. Once in the maternal circulation, drugs are separated from the foetus by a lipid placental membrane, which any given drug crosses to a greater or lesser extent depending on the physicochemical properties of the molecule.
Drugs in pregnancy can be viewed from two perspectives:
1 Effect of drugs on the foetus
2 Effect of pregnancy on the drug
Effect of drugs on the foetus
Drugs can influence foetal development at three separate stages:
1 Fertilisation and implantation period: conception to about 17 days' gestation
2 Organogenesis: 18–55 days
3 Growth and development: 56th day onwards
The possible consequences of drug exposure are different at each stage. In addition, drugs given at the end of pregnancy can influence structure or function in the neonate.
Fertilisation and implantation period
Interference by a drug with either of these processes leads to failure of the pregnancy at a very early and probably subclinical stage. Therefore, very little is known about drugs that influence this process in humans.
Organogenesis
