By Laura Wilson, RPS Director for Scotland
When it comes to prescribing medicines, there’s a lot more to it than meets the eye. It’s not just about picking a medicine and a dose from a book; it’s a precise process that considers various factors to ensure the best possible outcome for patients. Let’s take a look at the complex world of medicine selection and dosing and why it matters.
Tailoring treatment to you
Gone are the days of one-size-fits-all prescriptions. Thanks to advancements in medical research, we’re now witnessing a shift towards personalised medicine. This means that treatments are tailored to individual patients based on a range of factors, including genetic makeup, body composition (percentage of fat, bone and muscle), and overall health.
Role of blood and body fat in medicine dosing
When determining medicine dosages, we need to consider where the medicines go once it is in your body. If a medicine dissolves in body fat e.g. ciclosporin, and exerts its effect from there, we will often need to consider how much a person weighs and use a measure of body fat to determine the appropriate dose for that person. We also need to replicate the calculation of weight that has been used by the manufacturers to determine their dosing regimen. There are various weight calculations, including BMI (body mass index), ideal body weight, actual body weight, adjusted body weight, body surface area and predicted normal weight.
A medicine which dissolves in water, e.g. atenolol, and which then tends to stay in the blood, is slightly more straightforward. Most people have roughly the same amount of blood so we can predict more accurately what the medicine will do once taken and can use more standardised doses.
However, even considering whether a medicine is fat or water-soluble is still not the end of the matter. We need to think about whether we adjust a medicine choice or a dose based on liver and kidney function, the formulation of the medication, or even a patient's genetic predispositions.
We also need to know whether a medicine has an affinity for one body part or not to know how to work out the dosing e.g. iodine, which concentrates mainly in the thyroid gland.
During medicine development and clinical trials, researchers carefully assess how medicines interact with different body compositions to determine the most effective dosing strategies. For example, digoxin (a medicine that helps the heart pump blood more effectively) may require a dose adjustment and monitoring in patients with a higher BMI to ensure the best clinical response with the least side effects for each individual patient. However, creams, which only work where they are applied, would be applied in the same amount for everyone.
Children and medicine dosing
When it comes to children, dosing becomes even more detailed. Children's bodies, including their organs where medicines are metabolised, are still developing, which means that dosages must be carefully decided based on factors such as weight, body surface area, and age. However, the specific dosing method depends on the medication and its unique characteristics.
Medicines and therapeutic windows
Additionally, the therapeutic window of a drug is important to consider. The therapeutic window is the range of doses where the medicine works well to treat a condition without causing harmful side effects. Healthcare providers aim to give patients doses within this window to get the best results with the least risk of problems. Too little medicine might not work, but too much could be harmful. The wider the therapeutic window, the less adjustment to the dose as we will likely get the therapeutic result we want with a lower dose with less risk of harmful or intolerable side effects.
Tailored treatments: The future of medicine
As scientific research continues, personalised medicine will become increasingly common. By using the power of genetic testing and thorough dosing guidelines, healthcare providers will be able to deliver treatments tailored to a patient's unique healthcare needs that we know will work based on their genetic makeup. We will be able to avoid situations where we get low therapeutic results with high adverse effects. By tailoring medicines, we will be able to put the patient and their individual needs at the centre of our prescribing process. This will improve medicines adherence and health outcomes and ultimately, allow our patients to live well while being treated for their long-term conditions.
Read more RPS blogs.