Refer to the text below the tool for more information about estimating daily doses based on weight and for explanations on each type of administration.
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Determining Daily Doses
Dosing medication by weight may at a glance seem like a simple task but with different formulations of drugs and patient prescription requirements, the process can quickly complicate. Often, drug doses can be found expressed in various ways, such as:
- mg/kg or mcg/kg;
- mg/kg/day or mcg/kg/day;
- mg/kg/dose or mcg/kg/dose.
The key formula to remember when determining the daily required dose to administer is:
Medication Daily Dose (mg/day) = Dose in mg/kg x Patient weight in kg
Depending on the selected dose frequency, the correct amount of drug will also pe expressed as amount per dose. The table below summarizes the most commonly used drug administration frequencies:
|qD||Stands for “quaque die” meaning once a day – this dosage is the same as dose per day|
|BID||Stands for “bid in die” meaning twice a day, so a dose of medicine must be administered twice during the waking hours|
|TID||Stands for “ter in die” meaning three times a day, so a dose of medicine must be administered thrice during the waking hours|
|QID||Stands for “quater in die” meaning four times a day, so a dose of medicine must be administered four times during the waking hours|
|q8 hr||The q stands for “quaque” which means every, and the h indicates the number of hours, where a dose of medicine must be administered every 8, 6, 4, 3, 2 hours, respectively every hour.|
Some drugs are available in multiple concentrations, for example a solution of 5mg/10mL. When the daily dose is known, the amount of required solution may be derived.
If you wish to calculate dosage for an infant or child, you may wish to use the Pediatric Dosage Calculator, as it provides different estimation methods, not only the weight one which is used for adults.
Some drugs may also require more sensible estimation of the dose, for example based on body surface area, so this Dose Adjustment Calculator by BSA may prove useful.
Other dose adjustment factors one might be required to take into account when prescribing drugs include:
- Acute or chronic character of the condition;
- Other comorbidities;
- Pharmacological interactions;
- Medicine half time;
- Metabolism and elimination.
Gerald MC, O’Bannon FV. Nursing pharmacology and therapeutics. (2nd ed.). Englewood Cliffs, NJ: Prentice Hall Incorporated, 1988.
Hammett-Stabler CA, Dasgupta A, eds. (2007) Therapeutic Drug Monitoring Data: A Concise Guide. 3rd ed. Washington, DC: AACC Press.
Pai MP. Drug dosing based on weight and body surface area: mathematical assumptions and limitations in obese adults. Pharmacotherapy. 2012; 32(9):856-68.
Published On: November 4, 2020 · 12:00 AM
Last Checked: November 4, 2020
Next Review: November 4, 2025