Skip to main content

TL;DR

Pharmacy Calculations: Dilution/concentration, ratio/proportion, percent solutions, IV flow rates, days supply, and business math.

By Valenke Exam Prep Team·Last updated 2026-06-02

Pharmacy Calculations

PTCB

Definition

Dilution/concentration, ratio/proportion, percent solutions, IV flow rates, days supply, and business math.

Differential Diagnosis

Distinguishing between related concepts for pharmacy calculations:

Fluoroquinolones: Examples: ciprofloxacin, levofloxacin, moxifloxacin. Mechanism: Inhibit bacterial DNA gyrase and topoisomerase IV, bactericidal. Key side effects: Tendon rupture (Achilles); QT prolongation.

Insulins: Examples: lispro (rapid), regular (short), NPH (intermediate), glargine (long). Mechanism: Replaces endogenous insulin, facilitates glucose uptake into cells. Key side effects: Hypoglycemia; Weight gain.

Key Values & Ranges

Dilution/concentration, ratio/proportion, percent solutions, IV flow rates, days supply, and business math. Heavily tested on PTCB exam.

Related drug class: Benzodiazepines includes lorazepam, diazepam, alprazolam, midazolam. Mechanism: Enhance GABA-A receptor, increased chloride conductance, CNS depression.

Practical Example

Pharmacy Calculation Example: percentage strength

Formula: w/v: g/100mL, w/w: g/100g, v/v: mL/100mL

Worked example: 2% hydrocortisone cream = 2g HC per 100g cream

Patient Communication

Clear communication about pharmacy calculations with patients, families, and the healthcare team is essential. Use standardized handoff tools (SBAR) for shift changes and transfers. Verify understanding by asking the patient to repeat key information back to you.

Clinical Significance

Pharmacy technicians must understand how pharmacy calculations connects to medication therapy. For example, Insulins (lispro (rapid), regular (short), NPH (intermediate), glargine (long)): Replaces endogenous insulin, facilitates glucose uptake into cells.

Why It Matters

Heavily tested on PTCB exam.

Related Terms

Dosage CalculationsSig Codes (Prescription Abbreviations)

Practice This Topic

Practice ptcb oe calculations → PTCB

Ready to practice for the PTCB?

Adaptive practice powered by Item Response Theory targets your weak areas. Start with 3 free sessions.

Start free practice →

Frequently Asked Questions

What calculations are involved in pharmacy calculations?▼
For pharmacy calculations: body weight dosing: dose (mg/kg) * weight (kg) = total dose. Example: Vancomycin 15mg/kg * 80kg = 1200mg.
What sig codes are commonly seen with pharmacy calculations prescriptions?▼
For pharmacy calculations: QID = four times daily, OS = left eye, BID = twice daily, QHS = at bedtime, AU = both ears.
What DEA schedule considerations apply to pharmacy calculations?▼
For pharmacy calculations: Schedule III: Moderate abuse potential (testosterone, ketamine, Tylenol with codeine). Schedule I: No accepted medical use, high abuse potential (heroin, LSD, peyote, ecstasy, marijuana (federal)).