Question

The physictan orders gentamicin (Garamycin) for a child weighing \(88 \mathrm{lb}\). If the dose range is \(6-7.5 \mathrm{mg} / \mathrm{kg} / \mathrm{d}\), and the child is to receive the medication tid, what is the therapeturic range for a single dose for this child? a. \(20-40 \mathrm{mg}\) b. \(50-70 \mathrm{mg}\) c. \(80-100 \mathrm{mg}\) d. 110-130 mg

Short answer

The correct therapeutic range for a single dose for this child is 80-100 mg, which corresponds to option c.

Step-by-step solution

Convert weight from pounds to kilograms

Since the dose range is given in mg/kg, you first need to convert the child's weight from pounds to kilograms. Use the conversion factor 1 kg = 2.2 lb. Divide the child's weight by 2.2 to get their weight in kilograms.

Calculate the therapeutic range in mg/kg per day

Using the dose range of 6-7.5 mg/kg/d, multiply the child's weight in kilograms by each end of the range separately to calculate the total daily dose in milligrams.

Determine the single dose by dividing the total daily dose by the number of doses per day

The medication is to be given tid (three times a day). Divide the total daily dose in milligrams by 3 to find the therapeutic range for a single dose.

Select the correct therapeutic range

Compare the calculated range for a single dose with the options given to choose the correct answer.

Key concepts

Gentamicin Dosage Calculation

Understanding how to calculate the correct dosage for medications like gentamicin is crucial in ensuring patient safety and efficacy of treatment, especially in pediatric patients where dosages must be carefully adjusted for weight. When calculating the gentamicin dosage, the first step is always converting the patient's weight into kilograms (kg), as medication dosages are typically prescribed in milligrams (mg) per kilogram.

For gentamicin and other antibiotics, the therapeutic dose range is considered when determining the total daily dose. The range for gentamicin is typically between 6 and 7.5 mg/kg/day. Calculating this involves multiplying the child's weight in kilograms by both the low and the high end of the therapeutic dose range to find the total dose range in milligrams for the entire day. It is worth highlighting the importance of precision in this step, as small errors can lead to incorrect dosing.

To derive the single dose from the daily range, since the medication is to be administered three times a day (tid), the total daily dose is divided by three. The result of this division gives the amount in milligrams that should be administered in each individual dose.

Medication Dosage Conversion

When working with medication dosages, conversion is often necessary to align the units of measure with the prescribed dosage. Nurses and healthcare professionals must be adept at converting weights and dosages using standard conversion factors. One key conversion is pounds (lb) to kilograms (kg), with the knowledge that 1 kg equals 2.2 lb.

To facilitate understanding for all students, here is a simple method for converting pounds to kilograms: divide the weight in pounds by 2.2 to get the weight in kilograms. Converting dosages may also involve calculating the appropriate volume to administer when the medication is available in a certain concentration. For example, to convert a prescribed dose in milligrams to a volume in milliliters, divide the dose by the medication's concentration in mg/ml.

Using bullet points for clarity:

• Always confirm the units of measure before beginning calculations.
• Use the conversion factor 2.2 to convert pounds to kilograms.
• For volume conversions, divide the dose by the medication's concentration.

Correct conversion ensures accurate medication administration which is vital for achieving therapeutic effects and avoiding potential overdoses.

Therapeutic Dose Range

The therapeutic dose range of a medication is the range of dosages which produces the desired effect without causing toxicity. It is critical for healthcare providers to be familiar with these ranges as they indicate the safety margin and ensure effective treatment. When calculating doses, providers should be careful to keep the dosage within the therapeutic range for that specific medication, considering factors such as patient's weight, age, kidney function, and the severity of the condition being treated.

For pediatric patients, like in our gentamicin example, the therapeutic dose range must be strictly followed because children's metabolisms and body compositions are different from those of adults, and they are more sensitive to medications. The ranges are often narrower and more precise. Educators can emphasize this importance by showing how small deviations from the therapeutic range can lead to subtherapeutic dosing or toxicity.

Using real-life scenarios and practice problems where students calculate both the total daily dose and subsequent individual doses helps to reinforce the concept of maintaining doses within the therapeutic range. Always consult the latest drug resources or pharmacology guidelines when determining the therapeutic dose range, as these can change based on new research findings or revised standards of care.