As we age, the way our bodies handle and react to medicines changes. It's not that things change suddenly when we turn 65. Rather, the gradual process of ageing means that the way our bodies handle medicines when we are older differs slightly from the way they handled them when we were younger.

Age-related changes

Age-related changes can affect

• how much medicine is absorbed into the body
• how the body processes medicines
• how the body reacts to medicines
• how the body eliminates medicines.

Kidneys

The kidneys have an important role in eliminating medicines and their metabolites (waste products of medicines) from the body. From the age of 40, we lose approximately 1% of kidney function each year. As a result, older people's kidneys eliminate some medicines less effectively, so they remain in the body for a longer time. Examples include the heart medicine digoxin (Lanoxin or Sigmaxin) and the gout medicine allopurinol (Zyloprim, Progout and other brands).

Changing body composition

Older bodies tend to contain more fat, less muscle and less water than younger bodies. As a result, the dosages of some medicines, including diazepam (Valium, Ducene and Antenex), may need to be adjusted.

More sensitive to some medicines

Older bodies are more sensitive to some medicines, so the intended effects of the medicine are stronger. Examples include sleeping tablets, such as temazepam (Normison, Temaze and Temtabs). Greater sensitivity to sleeping tablets means that a dose that would make a younger person drowsy may make an older person very drowsy, confused or prone to falling.

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More susceptible to some effects

Older people may be more susceptible to the specific effects of some medicines. For example, your blood pressure normally drops when you get out of bed or stand up quickly. The body deals with this problem by having a mechanism that counteracts the drop in blood pressure, so you do not experience the symptoms of low blood pressure (dizziness or fainting) every time you get out of bed or stand up. However, in older people, this mechanism does not work as effectively. As a result, if you take a medicine that lowers your blood pressure, you may feel dizzy or even faint when you get out of bed or stand up too quickly.

Multiple medicines

Chronic health problems are more common in older people. As a result, most older people take medicines regularly. On average, older people take 2–5 medicines regularly, and about a third take 5 or more regularly. Taking multiple medicines increases the possibility of interactions between different medicines, and older people tend to be more sensitive to the effects of such interactions.

Implications

Over the years, these age-related changes mean that you are more likely to experience problems with medicines. You may become

• more sensitive to the intended effects of some medicines
• more susceptible to the side effects of medicines
• more susceptible to experiencing interactions between medicines.

As a result, you may need to take smaller doses of some medicines than a younger person would, especially when taking a medicine for the first time.

The need to take smaller doses may also extend to medicines you have been taking without problems for many years or even decades.

In some cases, you may have to stop taking a medicine altogether, or change to another medicine that does the same job with less likelihood of side effects.

In addition, your doctor may change one or more of your medicines if they feel you are at risk of developing interactions between your medicines.

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Preventing problems

If you are an older person, your doctor will consider all the factors discussed above when deciding what medicine and what dose to prescribe for you.

Older people are more sensitive
to the effects of some medicines.

You can work with your doctor to minimise the potential problems caused by ageing by

• reading the Consumer Medicine Information (CMI) leaflets for your medicines and noting the effects and common side effects
• keeping track of the effects and side effects of your medicines, especially new medicines, and reporting them to your doctor
• reporting to your doctor any changes in how you feel
• periodically discussing with your GP whether your medicines need adjusting, or whether you would benefit from having a Home Medicines Review
• asking your doctor or pharmacist about the suitability of any non-prescription medicines or supplements before you take them to avoid interactions with your existing medicines.

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