From the Research
To calculate the dose of a medication prescribed at 0.3 milligrams per kilogram (mg/kg), multiply the patient's weight in kilograms by 0.3 mg/kg. For example, if a patient weighs 70 kg, the dose would be 70 kg × 0.3 mg/kg = 21 mg. This weight-based dosing method ensures appropriate medication administration based on the patient's size, which is important because drug distribution, metabolism, and clearance often correlate with body weight 1. Before calculating, make sure you have an accurate and recent weight measurement for the patient, preferably in kilograms (if the weight is in pounds, divide by 2.2 to convert to kilograms). After calculating the dose, always double-check your math and consider any maximum dose limitations that might apply to the specific medication, as some medications have upper limits regardless of weight. Weight-based dosing is particularly important for medications with narrow therapeutic windows where precise dosing is critical for efficacy and safety. Some studies suggest that doctors and medical students may struggle with drug dose calculations, especially when the strengths of drug solutions are expressed as ratios or percentages 2, highlighting the need for careful attention to calculation methods. However, the basic principle of multiplying the patient's weight by the prescribed dose per kilogram remains the foundation of accurate dose calculation. It is also worth noting that standardizing drug concentrations and labeling can help reduce errors in dose calculation 2. In clinical practice, following a few simple rules and double-checking calculations can help simplify the process and minimize the risk of errors 3.