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GENTAMICIN AND TOBRAMYCIN DOSING FOR ADULTS |
I. Introduction
The following guidelines apply to the dosing and monitoring of gentamicin and tobramycin therapy in most adult patients. For Tobramycin, must write "DO NOT EXCHANGE".
II. Therapeutic Levels
| Gram Negative | Peak: 5-8 mcg/ml |
| Infections | Trough: <2 mcg/ml |
| Uncomplicated UTI | Peak: approx. 4 mcg/ml |
| Trough: <1 mcg/ml | |
| Gram Negative | Peak: >= 8 mcg/ml |
| Pneumonia | Trough: <2 mcg/ml |
III. Calculations
Calculations of Loading Dose (LD) and Maintenance Dose (MD) are based on the following parameters: Ideal Body Weight (IBW), True Body Weight (TBW), Dosing Weight (DW), and Creatinine Clearance (CICr)
A. Ideal Body Weight (IBW)
IBW (male) = 50 Kg + (2.3 x no. inches over 60")
IBW (female) = 45 Kg + (2.3 x no. inches over 60")
B. Dosing Weight (DW)
TWB = True Body Weight in Kg
DW = IBW + 0.40 x (TBW-IBW)
Note: If True Body Weight is less than Ideal Body Weight, then True Body Weight must be used in all calculations and the True Body Weight will also be the Dosing Weight. Determination of Dosing Weight is essential in treating the massively obese patient.
C. Loading Dose (LD)
LD = 2 mg/Kg x DW
D. Creatinine Clearance in ml/min (CICr)
Male CICr = {IBW * (140-age)} / {72 * Serum Creatinine}
Female CICr = 85% of Male CICr
IV. Maintenance Dose (MD)
The MD and dosing interval are functions of the calculated LD and Creatinine Clearance as shown in the following chart:
Percentage of Loading Dose Required for Dosage Interval
| CICr, ml/min | half-life hours | Q8H | Q12H | Q24H |
| >90 | 2.7 | 100% | ----- | ----- |
| 90 | 3.1 | 88% | ----- | ----- |
| 85 | 3.2 | 86% | ----- | ----- |
| 80 | 3.4 | 84% | 94% | ----- |
| 75 | 3.7 | 81% | 93% | ----- |
| 70 | 3.9 | 79% | 91% | ----- |
| 65 | 4.2 | 76% | 89% | ----- |
| 60 | 4.5 | 73% | 87% | ----- |
| 55 | 4.9 | 70% | 84% | ----- |
| 50 | 5.3 | 67% | 81% | ----- |
| 45 | 5.9 | ----- | 77% | ----- |
| 40 | 6.5 | ----- | 73% | 93% |
| 35 | 7.4 | ----- | 69% | 90% |
| 30 | 8.4 | ----- | 64% | 87% |
| 25 | 9.9 | ----- | 58% | 82% |
| 22.5 | 10.9 | ----- | 54% | 79% |
| 20 | 11.9 | ----- | 51% | 76% |
| 17.5 | 13.5 | ----- | 47% | 72% |
| 15 | 15.1 | ----- | 43% | 67% |
| 12.5 | 17.7 | ----- | ----- | 63% |
| 10 | 20.4 | ----- | ----- | 56% |
| 7.5 | 25.9 | ----- | ----- | 50% |
| 5 | 31.5 | ----- | ----- | 41% |
| 2.5 | 50.4 | ----- | ----- | 32% |
| 0 | 69.3 | ----- | ----- | 21% |
- This table will provide serum levels within the therapeutic range about 80% of the time. This chart should not be used for children, burn patients, cystic fibrosis patients, or patients undergoing peritoneal or hemo-dialysis.
- When creatinine clearance is less than or equal to 10 ml/min, it is preferable to administer 50% of the loading dose at the estimated half-life interval.
- In the presence of declining renal function, a wide dosing interval will allow time for incorporation of updated information into the dosing adjustment decision.
- Elderly male (usually <>= 70 yr.) and female (usually >= 60 yr.) patients with an estimated CICr of 40-60 ml/min best tolerate a minimum of 12 hour intervals. Those with a CICr of less than 40 ml/min best tolerate a minimum of 24 hour dosing intervals.