Question

The dose of gentamicin for patients with impaired renal function is adjusted to ensure therapeutically optimal dosage. If the normal daily dose of the drug for adults is 3 mg/kg/day, administered in three divided doses, what would be the single (8-hour) dose for a patient weighing 165 lb. and scheduled to receive only 40% of the usual dose, based on renal impairment?

Answer 1

answer:30mg per dose

Solution with the calculations ,formulae and explanation.

Weight of the patient in lbs = 165 lbs

Normal adult daily dose of gentamicin =3 milligram per kg per day

number of doses per day=3

single dose of gentamicin 40% of the usual dose for renal impairment = ?

The steps:

1.Conversion of the patient weight in lbs to weight in kg

2. Estimation of the usual adult daily drug dose

3. Estimation of the usual adult single drug dose

4. Estimation of renal adjusted single drug dose

Explanation:Since the dose of the patient is in mg per kg per day and the patient weight is in lb pounds,the weight of the patient has to be converted into kilograms to get the daily drug requirement.

conversion factor

1 kg equals to 2.2 lbs.

The patient weight in kilograms = patient weight in lb / 2.2(lbs per kg)

The patient weight in kilograms = 165 lbs/ 2.2lbs per kg =75kg

The patient weight in kilograms =75 kg

Formula:

The dose of gentamicin in mg per day = dose of gentamicin mg per kg per day * weight in kg

The dose of gentamicin in milligrams per day=3 milligrams per kg per day * 75 kg

The dose of gentamicin in milligrams per day= 225 milligrams per day.

The normal adult usual daily dose of gentamicin=225mg/day

Explanation:

The 8 hour single gentamicin dose is required and the total number of doses given in the day that is 24 hours is 3.

The daily total dose of gentamicin has to be converted into the drug amount per dose.

Since the problem requires to measure the amount of gentamicin to be given for the single dose, the daily dose has to be converted into the dosing requirement for a single dose by dividing the total daily dose by the number of doses.

Formula:

drug amount per dose =drug amount per day / number of doses per day

Calculation:

drug amount per dose=225 milligrams per day /3 doses per day

drug amount per dose = 75 milligrams/dose.

The normal adult usual single dose of gentamicin=75 milligrams/dose.

Calculation of the dose of gentamicin for the patient with renal impairment scheduled to receive only 40% of the usual dose:

Formula for adjusted drug dose

adjusted drug dose = usual single dose * percentage adjustment

gentamicin dose adjustment for renal impairment =40% of the usual drug dose

therefore, gentamicin dose to be given to the patient equal to 40% of 75 milligrams per dose

gentamicin dose to be given to the patient = 40 / 100 x 75mg/dose

gentamicin dose to be given to the patient= 30 milligrams/dose

answer: The single 8 hour dose for the patient weighing 165 lb and scheduled to receive only 40% of the usual dose of gentamicin at a rate of 3 milligrams per kg per day based on renal impairment is 30 milligrams per dose or 30mg/dose.

Pleases note : * reads as multiplication sign