The
answers to this problem set will need to be handed
in at the start of the class on
January 31, 2008.
Aminoglycoside Problem
Set 2
HP is a 58 y/o male who presents to the ER
with mental status changes, lethargy, fever
and diaphoresis. His wife says “he just
hasn’t been himself”. She found
him on the sofa somewhat unresponsive and decided
to get help. Looking at his chart you see he
was treated for prostate cancer in 2006 and
was seen in the outpatient clinic for a UTI
6 days ago. Blood and urine cultures are obtained
and IV fluids are started.
Physical Exam: Tmax 39.8°C, BP 114/65 mmHg,
P 80 BPM, R 18 /min, Ht 67 in, Wt 58.2 kg
Labs: WBC 17.8 (84% segs), BUN 48 mg/dL, Scr
2.0 mg/dL
Gram stains of the blood culture reveals GNR
(Gram-negative rods) 2 of 2
The ER attending makes the diagnosis of Gram-negative
sepsis likely secondary to UTI. As the pharmacist
on the ER team you are consulted for recommendations.
You recommend starting tobramycin ASAP and the
team agrees. The plan is to give HP one dose
of tobramycin in the ER and get him transferred
up to the MICU for further care.
1. What is HP’s ideal body weight?
2. What is HP’s CrCl?
3. What is the anticipated half-life of tobramycin
in HP?
4. What dose of tobramycin do you recommend based
on 2mg/kg/dose?
Three days later you are in the MICU monitoring HP
(now admitted for continued IV antibiotics). Looking
in the chart you see that after your initial dose
in the ER, HP was started on a tobramycin regimen
of 80 mg Q8h. You also notice that his cardiac output
has improved, his Scr is trending down and his urine
output has increased. You request tobramycin levels
with the next dose to ensure you are within therapeutic
range. The lab reports the following:
Tobramycin 0.8 mg/L @ 1430
Tobramycin 3.9 mg/L @ 1630
You talk to the nurse and she says HP gets his tobramycin
at 0700, 1500 and 2300. As per hospital policy, all
aminoglycosides are infused over 30 minutes.
5. Calculate the half-life based on HP’s actual
renal function
6. Determine the actual (back-extrapolated) tobramycin
peak
7. Calculate the volume of distribution
You speak with the physician about HP’s tobramycin
therapy and you both agree to target a peak of 8 mg/L
and trough of 1 mg/L. Based on your calculations above:
8. What dosing interval will you use to achieve this
target?
9. What tobramycin dose will achieve this target
with your selected interval?
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