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Pharmacy Calculation Guides

Practical, pharmacist-written explainers for the calculations you run every shift — plus PTCB exam prep. New guides are released regularly.

  • Renal Dosing

    Cockcroft–Gault CrCl: A Practical Guide for Pharmacists

    When to use Actual vs Ideal vs Adjusted Body Weight in the Cockcroft–Gault equation, and how renal dose adjustments work in practice.

    Read outline
    1. The Cockcroft–Gault formula and what it actually estimates
    2. ABW vs IBW vs AdjBW: choosing the right body weight
    3. Common renally-adjusted drugs (DOACs, vancomycin, gabapentin)
    4. Edge cases: obesity, low muscle mass, AKI
    5. Worked example using the PharmaCalc Pro CrCl calculator
    Full article coming soon. In the meantime, try the related calculator
  • Opioid Safety

    MME Explained: Safer Opioid Conversions with CDC Factors

    Step-by-step morphine milligram equivalent (MME) conversion using current CDC factors, plus the 50 and 90 MME/day thresholds.

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    1. What MME is and why it matters for opioid safety
    2. CDC conversion factors table (oxycodone, hydrocodone, fentanyl patch, methadone)
    3. Methadone's non-linear conversion and why it deserves caution
    4. Reading the 50 / 90 MME/day risk thresholds
    5. Documenting MME on a patient chart
    Full article coming soon. In the meantime, try the related calculator
  • Compounding

    Reconstitution Math: Final Concentration, Diluent & Displacement

    How to reconstitute powdered drugs accurately, account for powder displacement volume, and verify final concentration.

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    1. Why powder displacement volume matters
    2. Diluent volume vs final volume — the difference that trips technicians up
    3. Worked example: ceftriaxone reconstitution
    4. Stability and beyond-use dating after reconstitution
    5. Common reconstitution errors and how to catch them
    Full article coming soon. In the meantime, try the related calculator
  • Pediatrics

    Pediatric Dosing: mg/kg, BSA, Young's Rule & Clark's Rule

    Four pediatric dosing methods compared, with guidance on when each is appropriate and how to verify against published max doses.

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    1. Weight-based (mg/kg) dosing as the default
    2. BSA-based dosing for oncology and other high-risk drugs
    3. Young's Rule and Clark's Rule as estimators
    4. Always check the adult max dose ceiling
    5. Documenting the dose calculation for verification
    Full article coming soon. In the meantime, try the related calculator
  • Compounding

    Alligation Made Simple: The Tic-Tac-Toe Method for Compounding

    A walkthrough of the alligation method for mixing two strengths to get a target concentration, with PTCB-style practice problems.

    Read outline
    1. When alligation applies (and when it doesn't)
    2. Setting up the tic-tac-toe grid
    3. Worked example: mixing 70% and 20% to get 40%
    4. Converting parts to actual volumes
    5. PTCB-style practice problems
    Full article coming soon. In the meantime, try the related calculator

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