PHAR115 - Calculations Week 4

Understanding Drug Dosage

• Strength vs. Dose

  • Strength: Refers to the concentration of the drug, as displayed on packaging (e.g., 200 milligrams per milliliter).

  • Dose: The specific amount the doctor prescribes for a patient to take at a time.

  • Important to distinguish between the two; dosage might differ from the strength indicated on the package.

• Defining Dose

  • The amount prescribed for a single administration (e.g., "What does the patient take in the morning?" is related to dose).

  • Not to be confused with total daily intake.

Calculating Dosage

• Formula for Dosage Calculation

  • Utilize the abbreviation d/h * q = x where:

    • d = Desired dose to be administered.

    • h = Strength (amount available on the shelf).

    • q = Quantity (usually in milliliters or tablets).

    • x = Amount to be given (desired dose).

• Example Calculation

  • For a drug labeled 875 mg per tablet:

    • Strength (h) = 875 mg

    • Quantity (q) = 1 tablet

    • Doctor prescribes a certain dose (d) which will be plugged into the formula.

Labeling and Drug Information

• Reading the Drug Label

  • Identify essential information such as:

    • Drug name: e.g., Amoxicillin

    • Strength per unit: e.g., 875 mg/tablet

    • Quantity available: e.g., 20 tablets

    • Manufacturer and storage conditions.

• Identifying Tablet Characteristics

  • Tablets may vary in shape and whether they can be split (cored).

    • Important when a prescription requires a half tablet.

Practical Application in Pharmacy

• Entering Prescriptions

  • Knowledge of inventory is essential when selecting drugs for prescriptions.

  • If unsure about what is available, checking the physical stock is necessary.

Methodologies for Dosage Calculation

• Formula vs. Proportion Method

  • Both methods can be used to find desired dosage but formula method tends to be clearer for beginners.

  • Example calculation using proportions:

    • For a drug with a desired dose in a different unit (micrograms vs. milligrams), conversion is required.

Conclusion and Preparations for Next Week

• Uniformity of Units

  • Ensure units of measurement are consistent (e.g., mg vs. µg) before performing calculations.

• Looking Ahead

  • Next session will cover oral liquid dosages, including various concentrations and forms (e.g., per 5 ml, per 1 ml).

  • Worksheet with 8 prescriptions to practice upcoming concepts.