9.2 Pharmacy Law Calculations: DEA Verification, Days Supply, Limits & Ratios

Legal Calculations and Numerical Rules

Many jurisprudence errors are arithmetic performed with an obsolete rule. Write the governing number and units before calculating.

DEA registration checksum

For a standard DEA number, first verify the prefix and that the registrant name convention is plausible. Then use the six serial digits:

1. add digits in positions 1, 3, and 5;
2. add digits in positions 2, 4, and 6 and multiply that sum by 2;
3. add the two results; and
4. compare the last digit of the total with the final DEA check digit.

Example: AB1234563. Odd positions: 1 + 3 + 5 = 9. Even positions: 2 + 4 + 6 = 12; doubled = 24. Total = 33, so check digit 3 is consistent. A checksum match does not prove active registration or scope; verify through an authorized source when needed.

Morphine milligram equivalents

For an oral opioid:

daily dose in mg × current conversion factor = estimated MME/day.

Examples using current CDC implementation factors:

• Hydromorphone 4 mg every six hours: 16 mg/day × 5 = 80 MME/day.
• Tramadol 50 mg every six hours: 200 mg/day × 0.2 = 40 MME/day.
• Oxycodone 10 mg every six hours: 40 mg/day × 1.5 = 60 MME/day.

For fentanyl patches, multiply mcg/hour by 2.4. Methadone’s current CDC implementation factor is 4.7, but conversion is clinically complex and should not be used mechanically for rotation. MME is a risk estimate, not a dispensing authorization. Mississippi chronic guidance uses strive ≤50, avoid or significantly justify ≥90, and refer above 100.

Pseudoephedrine cumulative quantity

The sale must fit 3.6 g/day and 7.2 g/30 days. If NPLEx shows 5.4 g during the preceding 30 days and the requested package contains 2.4 g, total would be 7.8 g. Refuse even though 2.4 g alone is below the daily cap.

PIC presence

Compute 50% of weekly pharmacy operating hours and compare with 20; use the smaller. Open 30 hours: half is 15, so PIC minimum is 15. Open 80: half is 40, so minimum is 20.

Technician ratio

Maximum technicians = on-duty pharmacists × 3. Two pharmacists permit up to six technicians. Do not count a purely clerical cashier or automatically count an intern as a technician, but ensure each person actually performs only the role claimed.

Inventory reconciliation

Expected ending inventory equals:

beginning physical inventory + acquisitions − documented dispositions.

If beginning oxycodone is 500 tablets, purchases are 1,000, and documented dispensing/returns/destruction total 1,275, expected stock is 225. A physical count of 215 creates a 10-tablet shortage to investigate. Do not edit the beginning inventory or enter a false disposition to force balance.

Schedule V and emergency quantities

Mississippi eligible nonprescription Schedule V sales use 120 cc or 4 fluid ounces in 72 hours, no more than two sales in seven days and three in 30 days. Emergency oral Schedule II quantity is no more than a 48-hour supply; the signed follow-up is due in seven days. Keep amount and document deadlines separate.

Exam method

Underline units: mg/day, mcg/hour, grams/30 days, hours/week, technicians/pharmacist, or days after discovery. State the rule first, calculate second, and then test every other limit.

Multi-limit practice

A pharmacy open 48 hours weekly has a PIC minimum of 20 hours because half is 24 and the lesser value is 20. If two pharmacists overlap for four hours, the pharmacy can schedule up to six technicians during the overlap but only three after one pharmacist leaves. Recompute as staffing changes; the daily schedule cannot use the number of pharmacists employed by the store.

For an oxycodone prescription of 15 mg every six hours, maximum labeled daily dose is 60 mg. At factor 1.5, exposure is 90 MME/day. That value triggers the current avoid-or-significantly-justify concern; it does not prove illegality or authorize the pharmacist to reduce quantity. Resolve diagnosis, tolerance, concurrent drugs, PMP data, and prescriber plan.

For inventory, suppose expected ending stock is 225 but physical count is 235. An overage also requires investigation: an unrecorded receipt, reversed disposition, counting error, or wrong package multiplier may explain it. Reconciliation detects both shortage and overage.

For PSE, calculate base grams across all requested packages and both time windows. A package that fits today can still fail the rolling 30-day total.

Always distinguish an inclusive ceiling from an exceeded threshold: 7.2 grams is within the PSE 30-day limit, while 7.21 exceeds it; more than 100 MME triggers the referral rule, while exactly 100 is not “above 100.”