8.7 Calculating Medication Quantity and Days’ Supply

Preparing a drug claim for online processing includes entering specific information about each prescription filled, including the medication quantity and days’ supply of medication. Days’ supply is the correct amount of medication to fit the prescription duration until refill or end of use. If the information submitted is incorrect, the claim may be denied, or—if audited—the costs of the medication and services may not be reimbursed. Thus, calculating days’ supply of medication accurately is an important skill.

Certain drug formulations, such as ear (otic) and ophthalmic solutions and suspensions, are challenging to calculate when determining days’ supply. Many are available in both a solution and a suspension formulation. When calculating drops for a solution, the standard measure is equivalent to 20 drops per mL. For example, suppose that a prescription was written for Cortisporin otic solution, 4 drops into affected ear 3 times a day for 7 days, or 12 drops daily for 7 days. That would equal 84 solution drops. The 5 mL package size (providing 100 drops) would be dispensed.

However, suspension drops, because they are thicker in density, have fewer drops per mL than solutions. In the past, the measure was 16 drops of suspension to 1 mL, but since IV drops go in rates of 10, 15, and 20 gtt (drops) per minute, there has been a movement toward standardization to round down the measurement to 15 drops of suspension per mL rather than up to 16. The suspension drop rate now depends on individual pharmacy and insurance reimbursement policies.

You could receive a prescription for loteprednol (Lotemax) suspension with the sig “Place two drops in each (OU) eye four times a day for 10 days with one refill.” So two drops times four is eight drops a day. For 10 days, this prescription would need 80 drops. If you go by 16 gtt/mL, a 10 mL bottle would be estimated to contain 160 drops, and a 5 mL bottle estimated to contain 80 drops.

However, if 15 drops per mL were used for estimation, the 5 mL bottle would be calculated to have 75 drops, which would be insufficient for a 10 days’ supply. The 10 mL bottle would be needed. If the technician provided the 15 mL package size pictured, or entered a 7 days’ supply amount instead of 10 days’ supply, then the claim could be rejected or challenged in an audit.

For some prescriptions, dispensing the exact days’ supply is not practical. A pharmacy may receive a prescription for cefdinir (Omnicef) antibiotic suspension with a sig “Give 1 teaspoonful daily for 10 days.” The total volume is 50 mL (5 mL/day × 10 days), but the smallest bottle of cefdinir suspension is 60 mL. Insurance plans recognize that there will be 10 mL of wastage and will approve the claim. In this circumstance, the technician should add the statement “Discard remainder after 10 days” to the medication container label.

The following examples show how to calculate medication amounts and days’ supply for actual prescriptions.

Technicians find that it can often be tricky to calculate the days’ supply of prescribed suspension drops for eyes and ears. One needs to apply the formulation of the specific pharmacy or PBM for suspension drops per milliliter (gtt/mL).