Drug dosage calculator

With this handy tool you can calculate drug dosages in 3 steps:

Step 1: Enter the amount of drug you want, or the dose prescribed in the 'Strength Required' (SR) field.

Step 2: Enter the strength you've got, or the available dose in the 'Stock Strength' (SS) field.

Step 3: Enter the volume or quantity, which is the amount the drug is supplied in, in the 'Volume of Stock' (VS) field.

Note: For tablets, the volume of stock is always 1, as tablets are not supplied in a solution.

The tool then uses information to do some number crunching based on the formula: VOLUME REQUIRED = SR x VS / SS. 

The online medical calculators provided on Aidstat.com are intended for informational purposes only. They are not a substitute for clinical reasoning, professional judgement, or expert advice from qualified healthcare practitioners.

While extensive effort has been made to ensure the accuracy and completeness of the information provided by these calculators, Aidstat.com cannot guarantee its accuracy or reliability.

Users are advised to independently verify any results obtained through the use of these tools before making any medical or healthcare decisions.

5-Step Guide to Solve Clinical Drug Calculations.

Step 1: Identify Key Figures
Note down the Strength Required (SR) and the Stock Strength (SS) in the scenario. Then note down the Volume of Stock (VS) which is the amount the drug is supplied in.

Note: For tablets, the volume of stock is always 1, as tablets are not supplied in a solution.

Ensure that the units are the same, so no conversion is needed.

Step 2: Apply the Formula
Use the formula:

VOLUME REQUIRED = SR x VS / SS.

Step 3: Perform the Calculation
Calculate the volume required based on the given strength required and stock strength.

Step 4: Check for Rough Answer
Estimate the answer based on the key figures to ensure the calculated result is reasonable.

Step 5: Finalise the Answer
Based on the calculation, provide the final answer in the appropriate units (e.g., tablets, milliliters).

Consistent Units: Ensure that all quantities used in the calculation have the same units. If different units are involved, convert them to a common unit before performing the calculation.

Double-Check Formulas: When using formulas, ensure that the units of the input values match the units expected by the formula. This helps to ensure that the output will have the correct units.

Final Answer Units: When presenting the final answer, always include the appropriate units. This helps to clearly communicate the quantity being calculated and ensures that the answer is meaningful in a clinical context.

Question: 1000 mg of clarithromycin is prescribed. On hand are 250 mg tablets. How many tablets should be given?

VOLUME REQUIRED = SR x VS / SS
Strength Required - SR = 1000mg
Stock Strength - SS = 250mg
Volume of Stock - VS = 1
Note: For tablets, the volume of stock is always 1, as tablets are not supplied in a solution.

VOLUME REQUIRED = 1000 x 1/250 = 4

Solution: Based on the formula, the answer is 4 tablets.

Question: A patient is prescribed a subcutaneous injection of 20 mg of Hyoscine Butylbromide. Each stock ampoule contains 20 mg per 1 mL. How much should be drawn?

VOLUME REQUIRED = SR x VS / SS
Strength Required - SR = 20mg
Stock Strength - SS = 20mg
Volume of Stock - VS = 1

VOLUME REQUIRED = 20 x 1/20 = 1

Solution: The answer is 1 mL, calculated using the formula and the given stock strength.

Question: A patient requires 2.5 milligrams of Midazolam. If stock ampoules contain 10 milligrams in 2 mL, how much will you draw up?

VOLUME REQUIRED = SR x VS / SS
Strength Required - SR = 2.5mg
Stock Strength - SS = 10mg
Volume of Stock - VS = 2

VOLUME REQUIRED = 2.5 x 2/10 = 0.5

Solution: Using the formula, the answer is 0.5 mL, calculated based on the given stock strength and required dosage.

Question: Prepare a morphine infusion 60 mg to be made up to a final volume of 30 mLs. Stock ampoules of morphine contain 10 mg/mL. A strength of 1mg/mL is required. How much normal saline would need to be added to the syringe?

VOLUME REQUIRED = SR x VS / SS
Strength Required - SR = 60mg
Stock Strength - SS = 10mg
Volume of Stock - VS = 1

VOLUME REQUIRED = 60 x 1/10 = 6mL

3mL of 10mg/mL ampoule contains our required strength of 30mg.

We now need to make it up to a final volume of 30mL, so we need to calculate how much saline we need to add to the syringe so that we have 60mg of morphine in 30mL.

30mL - 6mL = 24mL

Solution: 24 mL of saline should be added to the syringe to achieve 60mg of morphine in 30mL.