Calculating Days Supply

The days supply calculation is one you will be making for each and every prescription you fill as a pharmacy technician.

In most cases, “Days Supply” is calculated by dividing the maximum amount of the medication used in 1 day by the dispensed amount.

“Days Supply” means just what it sounds like: it is how many days the supply of dispensed medication will last.

Here are a couple of examples:

Example #1

Motrin (ibuprofen) 800mg, 1 tablet 3 times daily as needed, #30. Days supply takes the maximum amount the patient could take in 1 day, in this case 3 tablets, divided into the amount dispensed of 30 pills-

30/3=10 days supply.

Example #2

Toradol (ketorolac) 10mg, 1 tablet every 4-6 hours as needed, not more than 4 per day. #80.

Quantity of pills: 80 divided by 4 (maximum amount per day) = 20 days supply.

Celexa (citalopram) 40mg, 1 tablet daily, #30.

30/1=30 days supply.

These previous examples seem straightforward, but it gets a bit more complicated when you are dealing with other types of prescriptions.

Calculating Ear Drop and Eye Drop Days Supply are different than the example problems above.

Usually with ear and eye drops, 1ml (1 milliliter) will have 15 drops of medication.

Example #4

Tobramycin Eye Suspension, 1 drop into each eye 3 times daily, 5ml bottle.

1 drop into each eye=2 drops X 3 times daily = 6 drops per day.

5ml X 15 drops per mL = 75 drops total.

75 drops / 6 drops per day = 12.5

Note: In this case the days supply is not a round number. Most pharmacy computer systems are unable to take a decimal number like 12.5. In this case you should round the number down to the nearest round number. So the answer to this example would be 12 days supply.

Topical Agents: Creams, Ointments, Gels, Pledgets, Topical Solutions, and Powders, are also different from our previous examples. Usually as a rule, the days supply on these are between 7-10 days. This is not an exact calculation. Or, if the physician indicates the days supply on the prescription, then your are all set, you have been given your days supply.

Example #5

Triamcinolone Cream .01%, Apply to Affected Area on Hand As Needed, 30 gram tube.

Days supply=7-10 days

Liquids: Solutions, Suspensions, Syrups

Example #6

Robutussin AC Syrup:

Take 1 Teaspoonful Every 6 Hours As Needed for Cough, 4oz.

With Liquids, we are back to calculating days supply mathematically using our formula as in examples #1-4. In this example, you need to be able to convert Ounces (the American Standard System of Measurement) to Milliliters (the Metric System of Measurement.)

There are 30 ML in 1 Oz., so 4 Oz = 120 ML. There are 5ML’s in 1 Teaspoonful.

The maximum the patient could take in one day is 5ML times 4 (24 hours in 1 day, divided by 6 = 4) = 20ml used in one day. 120ML divided by 20ML = 6 Days Supply

Hopefully these examples have helped you to understand how to calculate days supply.

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