Medical dose calculations are essential in healthcare to ensure that patients receive the correct amount of medication. These calculations consider various factors such as the patient's weight, age, and specific health conditions. Below are some common medical dose formulas used in different contexts:

1. Basic Dose Calculation Formula
The most fundamental formula for calculating medication dosage is:
Dose=Desired Dose (mg)Available Dose (mg/ml)\text{Dose} = \frac{\text{Desired Dose (mg)}}{\text{Available Dose (mg/ml)}}Dose=Available Dose (mg/ml)Desired Dose (mg)

2. Body Weight Dose Calculation
For medications dosed based on a patient's body weight:
Dose (mg)=Dose per kg (mg/kg)×Body Weight (kg)\text{Dose (mg)} = \text{Dose per kg (mg/kg)} \times \text{Body Weight (kg)}Dose (mg)=Dose per kg (mg/kg)×Body Weight (kg)
3. Body Surface Area (BSA) Dose Calculation
Some medications, especially in oncology, are dosed based on body surface area:
BSA (m2)=(Height (cm)×Weight (kg)3600)\text{BSA (m}^2\text{)} = \sqrt{\left(\frac{\text{Height (cm)} \times \text{Weight (kg)}}{3600}\right)}BSA (m2)=(3600Height (cm)×Weight (kg))
Dose (mg)=BSA (m2)×Dose per m2\text{Dose (mg)} = \text{BSA (m}^2\text{)} \times \text{Dose per m}^2Dose (mg)=BSA (m2)×Dose per m2
4. Pediatric Dose Calculation
Using Clark's rule (for children):
Child’s Dose=(Weight of Child (lb)150)×Adult Dose\text{Child's Dose} = \left(\frac{\text{Weight of Child (lb)}}{150}\right) \times \text{Adult Dose}Child’s Dose=(150Weight of Child (lb))×Adult Dose
Using Young's rule (based on age):
Child’s Dose=(Age of ChildAge of Child + 12)×Adult Dose\text{Child's Dose} = \left(\frac{\text{Age of Child}}{\text{Age of Child + 12}}\right) \times \text{Adult Dose}Child’s Dose=(Age of Child + 12Age of Child)×Adult Dose
Using Fried’s rule (for infants):
Infant’s Dose=(Age of Infant (months)150)×Adult Dose\text{Infant's Dose} = \left(\frac{\text{Age of Infant (months)}}{150}\right) \times \text{Adult Dose}Infant’s Dose=(150Age of Infant (months))×Adult Dose
5. Intravenous (IV) Infusion Calculations
Calculating the flow rate:
Flow Rate (ml/hr)=Total Volume (ml)Time (hr)\text{Flow Rate (ml/hr)} = \frac{\text{Total Volume (ml)}}{\text{Time (hr)}}Flow Rate (ml/hr)=Time (hr)Total Volume (ml)
Calculating drops per minute (using drip factor):
Flow Rate (gtt/min)=Volume (ml) to be infused×Drop Factor (gtt/ml)Time (min)\text{Flow Rate (gtt/min)} = \frac{\text{Volume (ml) to be infused} \times \text{Drop Factor (gtt/ml)}}{\text{Time (min)}}Flow Rate (gtt/min)=Time (min)Volume (ml) to be infused×Drop Factor (gtt/ml)
6. Dilution Calculations
Calculating the concentration after dilution:
C1V1=C2V2\text{C}_1\text{V}_1 = \text{C}_2\text{V}_2C1V1=C2V2
Where:
C1\text{C}_1C1 = initial concentration
V1\text{V}_1V1 = initial volume
C2\text{C}_2C2 = final concentration
V2\text{V}_2V2 = final volume
7. Insulin Dose Calculations
For calculating insulin doses in diabetic patients:
Total Daily Dose (TDD):
TDD=0.5×Weight (kg)\text{TDD} = 0.5 \times \text{Weight (kg)}TDD=0.5×Weight (kg)
Basal and Bolus Insulin: Typically, 50% of TDD is basal insulin, and 50% is bolus insulin divided into three doses for meals.
8. Creatinine Clearance (CrCl)
To estimate renal function:
Cockcroft-Gault formula:
CrCl (ml/min)=(140−age)×weight (kg)×1.23Serum Creatinine (ยตmol/L)\text{CrCl (ml/min)} = \frac{(140 - \text{age}) \times \text{weight (kg)} \times 1.23}{\text{Serum Creatinine (ยตmol/L)}}CrCl (ml/min)=Serum Creatinine (ยตmol/L)(140−age)×weight (kg)×1.23
For women, multiply the result by 0.85.
9. Calculating Adjusted Body Weight (AdjBW) for Obese Patients
AdjBW=IBW+0.4×(Actual Body Weight−IBW)\text{AdjBW} = \text{IBW} + 0.4 \times (\text{Actual Body Weight} - \text{IBW})AdjBW=IBW+0.4×(Actual Body Weight−IBW)
Where:
IBW\text{IBW}IBW (Ideal Body Weight) is calculated as:
Males: 50+2.3×(height in inches−60)50 + 2.3 \times (\text{height in inches} - 60)50+2.3×(height in inches−60)
Females: 45.5+2.3×(height in inches−60)45.5 + 2.3 \times (\text{height in inches} - 60)45.5+2.3×(height in inches−60)
10. Parenteral Nutrition Calculations
For determining the macronutrient content in total parenteral nutrition (TPN):
Calories from Dextrose:
Calories=Volume (L)×Dextrose concentration (g/L)×3.4\text{Calories} = \text{Volume (L)} \times \text{Dextrose concentration (g/L)} \times 3.4Calories=Volume (L)×Dextrose concentration (g/L)×3.4
Calories from Amino Acids:
Calories=Volume (L)×Amino Acid concentration (g/L)×4\text{Calories} = \text{Volume (L)} \times \text{Amino Acid concentration (g/L)} \times 4Calories=Volume (L)×Amino Acid concentration (g/L)×4
Calories from Lipids:
Calories=Volume (L)×Lipid concentration (g/L)×9\text{Calories} = \text{Volume (L)} \times \text{Lipid concentration (g/L)} \times 9Calories=Volume (L)×Lipid concentration (g/L)×9
11. Maintenance Fluid Requirements for Pediatrics
Using the Holliday-Segar method:
100 ml/kg100 \, \text{ml/kg}100ml/kg for the first 10 kg10 \, \text{kg}10kg
50 ml/kg50 \, \text{ml/kg}50ml/kg for the next 10 kg10 \, \text{kg}10kg
20 ml/kg20 \, \text{ml/kg}20ml/kg for each additional 1 kg1 \, \text{kg}1kg
Conclusion
These are some of the most commonly used medical dose formulas across various medical settings. Proper calculation and administration of medication are critical for patient safety and treatment efficacy. Always double-check calculations and consider individual patient factors when determining doses.