Pharmaceutical Calculations for Dosage Forms PDF

# Pharmaceutical Calculations for Dosage Forms ## 1. Basic Formula To calculate drug dosage: Dose = Strength of Drug (mg or g) × Volume or Number of Units ## 2. Dosage Based on Patient Weight (Body Weight Dosing) For medications calculated per kilogram (kg) of body weight: Dose = Dose per kg × B...

# Pharmaceutical Calculations for Dosage Forms ## 1. Basic Formula To calculate drug dosage: Dose = Strength of Drug (mg or g) × Volume or Number of Units ## 2. Dosage Based on Patient Weight (Body Weight Dosing) For medications calculated per kilogram (kg) of body weight: Dose = Dose per kg × Body Weight (kg) ### Example: A drug is prescribed at 5 mg/kg. Patient weighs 50 kg. Total dose = 5 mg/kg × 50 kg = 250 mg ## 3. Dosage Based on Body Surface Area (BSA) For drugs that depend on a patient's body surface area (used in oncology or pediatrics): Dose = Dose per m2 × BSA (m2) ### BSA Calculation (Mosteller Formula): BSA (m²) = √ (Height (cm) × Weight (kg)) / 3600 ### Example: BSA = 1.5 m², Drug dose = 100 mg/m². Total dose = 100 mg/m² × 1.5 m² = 150 mg ## 4. Pediatric Dosage Calculations For children, common rules are: ### a. Clark's Rule (Weight-Based): Child's Dose = (Weight (lbs) / 150) × Adult Dose ### b. Young's Rule (Age-Based): Child's Dose = [Age (years) / (Age + 12)] × Adult Dose ## 5. Dosage for Oral Liquids For syrups or suspensions: Volume of Dose (mL) = Prescribed Dose (mg) / Concentration (mg/mL) ### Example: Drug concentration = 125 mg/5 mL. Prescribed dose = 250 mg. Volume = 250 / 125 × 5 = 10 mL ## 6. Intravenous (IV) Dosage For IV infusions, calculate the flow rate: ### Flow Rate (mL/hour): Flow Rate = Volume (mL) / Time (hours) ### Drop Rate (gtt/min): Drop Rate = Volume (mL) × Drop Factor (gtt/mL) / Time (minutes) ## 7. Conversion Factors to Remember: 1 g = 1000 mg 1 mL = 1 cc 1 kg = 1000 g 1 pound = 454 g 1 teaspoon = 5 mL 1 tablespoon = 15 mL ## 8. Solid Dosage Forms (Tablets and Capsules) For dividing doses: Number of Tablets = Total Dose (mg) / Strength per Tablet ### Example: Strength = 500 mg/tablet, Dose = 1000 mg. Number of tablets = 1000 / 500 = 2 tablets