Small patients drugs dosage calculator
Introduction
Adequate dosage respecting posology (weight of the patient) is crucial for drug efficacy (avoid underdosing) and safety (avoid overdosing). One of the top causes of medication iatrogeny is when clinicans prescribe or administer an inadequate dosage (Refs: 1), representing up to 43% of medication incidents in pediatrics (Refs: 1), and is the top cause for general iatrogeny in children (Refs: 1 summarized in here and here, 2, 3, 4, for future works, follow UK's NRLS initiative) and elders (Refs: 1). Furthermore, this affects both small non-human creatures such as birds, but also human newborns and babies. Automedication is not the culprit, as a french study found it only accounts for 1.7% of medication incidents, whereas two-thirds of them were due to prescriptions by physicians (Refs: 1). Several authors proposed various solutions at various levels (Refs: 1, 2), one type of these solutions being to train clinicians in safe processes and help them with tools to double-check calculations (Refs: 1)
Below you can find a calculator that implements recommendations on how to avoid dosage calculations errors found in this document for nurses (in French) and this one. A few additional parameters were also implemented that ease common calculations for non-collaborative patients such as small animals, such as the percentage of intake relative to the animal's weight. Although it is primarily intended for small patients, it can likely also be used for adults.
This calculator should be filled with values that can be found either in the drug's documentation, or in clinicians formulary books (either for humans or veterinary depending on who your patients are ) to get the adequate dosages (ie, make sure to target the dosage for the adequate target population, eg, ensure it's the dosage for babies, or for newborns, not just children of several years old ; likewise for animals, even under one order, there can be wide differences, eg, a different dosage for parrots that are big and for much smaller finches).
Although we tried to ensure the calculations here are correct and this tool is intended as a way for clinicians to quickly double-check their calculations, it should not be used by anyone else but trained clinical staff, and it should always be used after you do your calculations first on your own, please only use this calculator to double-check as a safety measure.
Tip: all inputs should be standardized to mg, ml and kg. If you need to do conversion, such as the dosage per volume, try to convert using the awesome open-source scientific calculator Qalculate desktop software, also available online here or here. Indeed, Qalculate is the only calculator that can transparently mix units of different magnitudes with a free-form syntax (eg, 1mg / 10g). Qalculate can also be used to check the calculations such as the sanity checks (just replace some of the terms, eg, unit -> x, day -> d).
Tip2: the posology often changes depending on the weight range and the animal specie, since some animals have a faster metabolism than others or are more sensitive to some molecules. Hence, make sure to always check your formulary for your target specie and weight range of the patient and update the values in this calculator accordingly.
Important: make sure you work in mg (milligrams) and ml (milliliters), not mcg (nonstandard notation for micrograms, standard notation: ug). Convert mcg beforehand to mg by dividing by 1000.
Important2: the app recopies all the inputs (sometimes in a reformulated way such as scientific notation) before giving the resulting outputs, please read carefully to check if the inputs are what you expected.
Limitations: numbers are sometimes rounded off starting from the 4th most significant digit. So this should not be a big issue since 3 significant digits are usually more than sufficient for most clinical purposes, but just be aware of this if you see some numbers not totally fitting together. I need to learn more about javascript strings templating to try to avoid this issue. Also see alternative ways to mitigate dosage calculations issues such as Body Surface Area Based Dosing.
DISCLAIMER: NO WARRANTY OF ANY SORT IS PROVIDED, NOT EVEN OF CORRECTNESS. IT IS YOUR RESPONSIBILITY TO ENSURE THE RESULTS ARE CORRECT.
Model's inputs
Drug name (optional, just to ease sharing results with colleagues):Target drug dosage (in mg/kg of patient's weight):
Patient's weight (in kg):
Type of calculation:
Is the patient an animal?
Drink percentage per day (in animal's weight):
Note: Animals of smaller weight tend to drink a lot more than bigger animals in proportion to their weight. Ref: "Water consumption in birds is influenced by species, age, size, environmental temperatures, and both the type and amount of food that is consumed. Water intake often relates inversely to body size and ranges between 5% and 50% of body weight per day.19 Young birds tend to consume more water than adults. Carnivorous birds as well as those that have evolved in arid environments normally drink little water." Veterinary Hematology and Clinical Chemistry by Mary Anna Thrall et al, 2nd edition, 2012, chapter Electrolytes and acid/base balance
Results
The following results pertain to the drug:
Given a target drug dosage of
The patient must be administered with a volume of
(Sanity check:
For animals, if diluted to get 1L of drinking water with the drug,
However, if we take into account that the patient drinks on average
(Sanity check:
In case dosage is too small to be administered, it can be diluted in a volume to allow to administer drops with a syringe. If we want to administer a volume of the size of a droplet of 0.02ml (the smallest droplet possible with the smallest clinical syringes available: 1mL syringes), we need to target a concentration of
(Sanity checks:
(Sanity check:
In case dosage is too small to be administered, it can be diluted in a volume to allow to administer drops with a syringe. If we assume the droplet to be 0.02ml (the smallest droplet possible with the smallest clinical syringes available: 1mL syringes), then dilute one unit into
(Sanity checks:
Free-form calculator
Use the free-form calculator to do your own calculations (eg, sanity checks) and unit conversions. Unit conversions are done transparently. Example: 12mg/6g.
Kindly provided by qalculator.xyz based on the powerful open-source calculator Qalculate!.
Alternatively, a beta v2 form is available, with support for more functions and plotting: https://v2.qalculator.pages.dev/
Alternatively, yet another implementation with support for plotting is available at: https://flaviutamas.com/qalculate-wasm/
License
This calculator was implemented by Stephen Karl Larroque.
Licensed under MIT. Source code.
TODO
Maybe implement calculations in:
- https://cerebromedico.com/en/pediatric-dosage-calculations/
- https://www.lmunet.edu/caylor-school-of-nursing/documents/Dosage_Calculations_Packet.pdf