A patient weighing 120 pounds was administered 2.1 g of a drug supposed to be dosed at 30 mg/kg. Was the dose correct, an overdose, or an underdose?
The correct answer and explanation is :
To determine whether the dose was correct, an overdose, or an underdose, let’s start by calculating the correct dose for the patient using the given dosage recommendation.
Step 1: Convert weight from pounds to kilograms
1 kilogram = 2.20462 pounds
Patient’s weight = 120 lb
[ \text{Weight in kg} = \frac{120}{2.20462} \approx 54.43 \, \text{kg} ]
Step 2: Calculate the correct dose using the recommended dosage
Recommended dose = 30 mg/kg
[ \text{Correct dose} = 30 \, \text{mg/kg} \times 54.43 \, \text{kg} \approx 1632.9 \, \text{mg} ]
Convert to grams:
[ 1632.9 \, \text{mg} = 1.6329 \, \text{g} ]
Step 3: Compare with the administered dose
Administered dose = 2.1 g
Correct dose = 1.6329 g
[ \text{Difference} = 2.1 \, \text{g} – 1.6329 \, \text{g} = 0.4671 \, \text{g} ]
Percentage overdose:
[ \left( \frac{0.4671}{1.6329} \right) \times 100 \approx 28.6\% ]
Conclusion: Overdose
The patient received approximately 28.6% more than the recommended dose, which classifies this as an overdose.
Explanation (300 words)
Drug dosing based on body weight is a common practice in clinical settings to ensure efficacy while minimizing toxicity. In this scenario, the patient weighs 120 pounds, which converts to about 54.43 kilograms. The prescribed dose is 30 mg per kilogram, leading to a total correct dose of approximately 1.6329 grams. However, the patient was administered 2.1 grams of the drug.
This administered amount exceeds the correct dosage by around 0.4671 grams, which is roughly 28.6% higher than recommended. Such a deviation is significant and constitutes an overdose. While the impact of this overdose depends on the drug’s therapeutic window—the range between effective and toxic doses—even moderate overdoses can increase the risk of side effects, adverse reactions, or organ stress, particularly with drugs that are metabolized by the liver or kidneys.
Accurate weight-based dosing is especially important in pediatric, geriatric, and underweight or overweight patients, where body composition may influence drug distribution and clearance. Overdosing can lead to complications such as toxicity, allergic reactions, or ineffective therapy due to physiological stress.
This case underscores the importance of double-checking dosage calculations, unit conversions (mg vs. g), and weight measurements. Automated systems, clinical decision support tools, or simple peer reviews can help minimize such errors in a medical setting.
In conclusion, the patient received an overdose of the medication, highlighting the need for vigilance in dosing calculations to ensure patient safety and treatment efficacy.
