Reflections
Reflection 01: Pharmacokinetics, pharmacodynamics and why they matter in frailty
@Mar 10, 2026
Setting: University teaching session (Independent Prescribing module)
Theme: Pharmacokinetics, pharmacodynamics and why they matter in frailty
What I learned today
Today’s university session focused on pharmacokinetics and pharmacodynamics, delivered by a pharmacist as part of the independent prescribing module.
At first glance, these concepts can feel very theoretical.
They involve molecules, receptors, absorption curves, and elimination constants.
But the deeper we explored them, the clearer it became that this science underpins almost every prescribing decision we make.
Why it matters for safe prescribing
Understanding these mechanisms is essential when we think about:
- Dosing intervals and drug half-life
- Accumulation and toxicity
- Interactions between medications
- Variation in patient response
The frailty lens
What stood out most to me today was how relevant this becomes when working with older adults and frailty.
In frail patients, physiology rarely behaves like the textbook.
Age-related changes in renal function, hepatic metabolism, body composition, and receptor sensitivity mean that drugs often behave differently.
Sometimes they behave differently in ways that are unpredictable.
The same dose that is appropriate for one patient may lead to accumulation, adverse effects, or functional decline in another.
This is where prescribing becomes less about selecting a drug and more about understanding the person in front of you.
It is about physiology, comorbidities, and priorities of care.
Takeaway
Good prescribing begins long before the prescription is written.
It begins with understanding the science that explains why medicines work, and why sometimes they don’t.
Next step for me
- Revisit renal and hepatic function changes in frailty and how they influence dosing.
- Practise applying “start low, go slow” thinking to real prescribing scenarios.