Desired Over Have Method for Dosage Calculations

Overview

• Desired Over Have Method: A formula for solving dosage calculations
  • Other methods: ratio proportion, dimensional analysis
  • Method choice depends on personal preference and program requirements

Formula

• Formula: Desired (D) / Have (H) * Quantity (Q) = x (Dose to be given)
  • Desired (D): The ordered dose from the prescribing provider
  • Have (H): What you have on hand (from the medication label)
  • Quantity (Q): Volume/amount of the dosage strength on hand
  • x: The dose to be given (the answer)*

Units

• Ensure units match between Desired and Have
  • If not, conversions are necessary

Metric Table

• Important for conversions
  • Example: 1 gram = 1000 milligrams

Practice Problems

1. Example 1: Physician orders 500 mg PO daily, supplied with 250 mg capsules

• D = 500 mg
  • H = 250 mg
  • Q = 1 capsule
  • Solve: (500 mg / 250 mg) * 1 capsule = 2 capsules*

2. Example 2: Physician orders 3.6 g IV daily, supplied with 1200 mg per 2 mL vial

• D = 3.6 g
  • H = 1200 mg
  • Q = 2 mL
  • Conversion needed: 3.6 g = 3600 mg
    • D = 3600 mg
    • Solve: (3600 mg / 1200 mg) * 2 mL = 6 mL*

3. Example 3: Physician orders 750 mcg PO daily, supplied with 0.25 mg per tablet

• D = 750 mcg
  • H = 0.25 mg
  • Q = 1 tablet
  • Conversion needed: 750 mcg = 0.75 mg
    • Solve: (0.75 mg / 0.25 mg) * 1 tablet = 3 tablets*

Key Tips

• Always check and convert units if necessary
• Memorize common metric conversions
• Practice multiple problems to become proficient

Interested in more dosage calculation videos? Check the link in the YouTube description below.