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Weight-Based Extended-Interval Gentamicin Dosing Nomogram of Murphy and Roether for a Neonate: Lower Trough Serum Concentration

Description

Murphy and Roether reported 2 nomograms for dosing gentamicin in neonates at extended intervals. One nomogram has a lower target gentamicin trough than the other nomogram. The authors are from the University of Arizona and United Drugs in Tuscon.


 

Dose of gentamin: 4 mg per kg weight at birth

 

Target gentamicin trough: <= 0.5 mg/L at 22 hours

 

Preferred time for blood sample collection: 15 to 21 hours after previous dose (allowed range 13 to 22 hours)

 

Parameters:

(1) birthweight in kilograms

(2) number of hours since previous gentamicin infusion

(3) serum gentamicin concentration in mg/L

 

Line

Formula for Serum Gentamicin Concentration

A

(0.00796 * ((hours)^2)) - (0.4063 * (hours)) + 5.618

B

(0.0072 * ((hours)^2)) - (0.4240 * (hours)) + 7.257

C

(0.004167 * ((hours)^2)) - (0.3343 * (hours)) + 7.550

 

 

Serum Level at Sampling Time

Dosing Instruction

<= A

every 24 hours

> A but <= B

every 36 hours

> B but <= C

every 48 hours

> C

repeat blood level

 

where:

• If the serum level is > C, then a repeat blood level is performed at 48 hours. If trough level exceeds the target concentration at that time then withhold the next dose for a longer interval. Further doses should be administered cautiously.

 


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