Math: Basic Tutorials : Oral Dosages

Oral Dosages

Oral medication administration is one of the most common and convenient methods for delivering drugs, but accurate dosage calculations are essential to ensure client safety and effectiveness. Medications taken by mouth can come in various forms, including tablets, capsules, liquids, and suspensions, each requiring proper measurement and administration.

This section covers how to calculate oral dosages based on prescribed amounts, available drug concentrations, and unit conversions. Step-by-step examples will help reinforce these concepts for accurate medication administration.

Calculating Dosages

Single Dosage Amount

$X = D \times \frac{Q}{H}$

$X$ : Single Dose	$D$ : Dosage Ordered	$H$ : Strength on Hand	$Q$ : Quantity
The single individual dose amount of medication given (usually in tablets or mL).	The amount of drug prescribed or ordered by the physician to be administered to the patient.	The available strength of one dose of the drug to be administered to the patient.	The available form of one dose of the drug.

Examples

Click on the titles below to view each example.

Example 1

Example 1:
The prescriber orders Ibuprofen 500mg PO q8h x 14 days for a client. The medication Ibuprofen is supplied as 250mg per tablet.
a. What single dose should you administer?
$D = 500$ mg of ibuprofen $H = 250$ mg $Q = 1$ tablet of ibuprofen	$X = 500 mg \times \frac{1 tablet}{250 mg} = 2 tablets$
Solution:	You would administer 2 tablets of Ibuprofen in a single dose orally.
b. What is the daily dose?
The order is q8h represents every 8 hours. Since there are 24 hours each day. Every 8 hours represents three times a day.	$3 \times 2 = 6$
Solution:	The client will receive 6 tablets each day.
c. What is the total dose for 14 days?
$14 \times 6 = 84$
Solution:	In 14 days, the client will recieve 84 tablets.

Example 2

Example 2:
The prescriber orders Zoloft (sertraline hydrochloride) 25mg PO oral solution BID for 7 days. The drug label can be seen below.
a. What single dose should you administer?
$D = 25$ mg of sertraline oral solution $H = 20$ mg $Q = 1$ mL	$X = 25 mg \times \frac{1 mL}{20 mg} = 1.25 mL$
Solution:	You would administer 1.25 mL of Zoloft oral solution in a single dose orally.
b. What is the daily dose?
The order is BID or twice a day.	$2 \times 1.5 = 2.5 mL$
Solution:	The client will recieve 2.5 mL each day.
c. What is the total dose for 7 days?
$7 \times 2.5 = 17.5$
Solution:	In 7 days, the client will recieve 17.5 mL.

Example 3

Example 3:
Order: Ziagen (abacavir sulfate) 0.9 g PO once per day. Available: Ziagen 300 mg tablets. Question: How many tablets should be administered to the client to provide the daily ordered dose? Notice that there are mg and g listed as the unit of the tablets. Thus, you need to convert into the same unit of measurement before finding the number of tablets.
We can start by converting 0.9g into mg, knowing that $1 g = 1000 mg$	$0.9 g \times \frac{1000 mg}{1 g} = 900 mg$
Now we convert 900mg into tablets	$900 mg \times \frac{1 tablet}{300 mg} = 3 tablets$
Solution:	The client will receive 3 tablets (300 mg each) for a total daily dose of 0.9g of Ziagen.

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Last Updated: Jun 25, 2025 4:00 PM
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