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(1) Obtain baseline data:
Patient age, sex, height, weight, allergies, diagnosis, infection site, current
drug therapy, I/O's for past 24 hours, Tmax, WBC with diff, albumin,
Past medical history, Lab work-up: Scr, Bun, cultures etc. (2) Estimate Ideal body weight in (kg)
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.
(3) If the actual body weight is greater than 25 - 30% of the calculated
IBW, calculate the adjusted body weight (ABW):
ABW = IBW + 0.4(Total body weight - IBW)
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(4) Estimate Creatinine Clearance: (ml/min)
Cockcroft and Gault equation:
CrCl: (140 - age) x IBW / (Scr x 72) (x 0.85 for females)
Note: if the ABW (actual body weight) is less than the IBW use the
actual body weight for calculating the CRCL. If the patient is >65yo and
creatinine<1, use 1 to calculate the creatinine clearance.
<Top> (5) Estimate kel (Elimination rate constant):
Amikacin /Gentamicin/Tobramycin: Kel = (0.00285 x CrCl) + 0.015
May also use: (0.003 x CrCl) + 0.01
Vancomycin: kel = 0.0016 x Crcl
The above equations provide an estimate of the elimination rate
constant based on population kinetics. The following may decrease
the usefulness of these equations:
*Renal failure, CHF, Burn patients, cystic fibrosis, severe
hypotension, rapidly changing renal function. (Burn victims
and patients with cystic fibrosis usually have increased
rates of elimination. Patients with CHF or severe hypotension
will have decreased rates of elimination due to decreased
renal perfusion).
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Kel determination from reported levels:
kel = (Ln C1 / C2) / (t2 - t1)
C1= actual or extrapolated Peak; or post peak level
C2= actual or extrapolated trough; or random level
Drawn at least 1.5 x estimated half-life after first level.
(t2 - t1) = Time difference between levels.
(6) Estimate half-life (T1/2) in hours:
T1/2 = 0.693 / Kel
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(7) Estimate Volume of Distribution (Vd): (Liters)
Aminoglycosides:
Use IBW unless obese, then use ABW= 0.4 x (TBW-IBW) + IBW
Vd (Normal) = 0.25 to 0.3 L/kg
Bun/Cr ratio 10 to 15:1 (nml). Patient normally hydrated or a
patient that will return rapidly to normal status.
Vd (dehydrated) = 0.2 to 0.25 L/kg
Bun/Cr ratio > 20:1; acute weight loss; decreased skin turgor; dry
mucous membranes, thirst, massive hemorrhage, acute diuresis.
Vd (overhydrated) = 0.35 to 0.4 L/kg.
Bun/Cr ratio < 10:1 , patients with ascites; edema, chronic renal
failure, severe hypalbuminemia (less than 2.5 gm/dl)-promotes
edema.
Vancomycin:
[Use actual body wt unless obese (> 30% over IBW)-then use adjusted
body weight = 0.4(TBW- IBW) + IBW.]
Vd (Normal): 0.6 to 0.7 L/kg (usually 0.65)
(dehydrated): 0.5 to 0.6 L/kg
(overhydrated): 0.7 to 0.85 L/kg
<Top> Volume of distribution calculation based on actual or
extrapolated peak and trough concentrations:
Vd = MD x (1-e-kti) / (k) (ti) [Cmax - (Cmin e-kti)]
(8) Desired Peak___ (mcg/ml) Desired trough___.
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| (Review levels) |
Gentamicin /Tobramycin |
Amikacin |
| Infection Site |
Peak |
Trough |
Peak |
Trough |
| Abdominal |
6-7 |
<1 |
25-30 |
4-6 |
| Cystitis |
4-5 |
<1 |
20-25 |
4-6 |
| Endocarditis |
4-12 |
<1.5 |
25-30 |
<8 |
| Osteomyelitis |
6-7 |
<1 |
25-30 |
4-6 |
| Pneumonia |
8-10 |
<1.5 |
25-30 |
<8 |
| Pyelonephritis |
6-7 |
<1 |
25-30 |
4-6 |
| Sepsis |
7-8 |
<1 |
25-30 |
4-6 |
| Soft tissue |
6-7 |
<1 |
20-25 |
<6 |
| Synergy |
5-6 |
<1 |
20-25 |
4-6 |
| Wound Infections |
6-7 |
<1 |
25-30 |
<6 |
Vancomycin - Target trough levels
Rybak M, Lomaestro B, Rotschafer JC, et al. (2009). "Therapeutic monitoring of vancomycin in adult patients: A consensus review of the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists". American Journal of Health-System Pharmacy 66 (1): 82–98.
Direct quotes from this reference (Rybak et al.):
"Further, data derived from more recent studies appear to suggest that vancomycin has little potential for nephrotoxicity or ototoxicity when used at conventional dosages (e.g., 1 g every 12 hours [15 mg/kg every 12 hours]), unless it is used concomitantly with known nephrotoxic drugs or at very high dosages."
Recommended TDM Parameters- Optimal monitoring parameter: "Trough serum vancomycin concentrations are the most accurate and practical method"
Timing of monitoring: "Troughs should be obtained just prior to the next dose at steady-state conditions (approximately after the fourth dose)."
Optimal trough concentration (see also Optimal trough concentration—complicated infections) : "Minimum serum vancomycin trough concentrations should always be maintained above 10 mg/L to avoid development of resistance. For a pathogen with an MIC of 1 mg/L, the minimum trough concentration would have to be at least 15 mg/L to generate the target AUC:MIC of 400."
Criteria for monitoring: "Data do not support using peak serum vancomycin concentrations to monitor for nephrotoxicity."
"Trough monitoring is recommended for patients receiving aggressive dosing (i.e., to achieve sustained trough levels of 15–20 mg/L) and all patients at high risk of nephrotoxicity (e.g., patients receiving concurrent nephrotoxins). Monitoring is also recommended for patients with unstable (i.e., deteriorating or significantly improving) renal function and those receiving prolonged courses of therapy (more than three to five days)."
Summary and recommendations:
"Vancomycin dosages should be calculated on ABW. For obese patients, initial dosing can be based on ABW and then adjusted based on serum vancomycin concentrations to achieve therapeutic levels. Continuous infusion regimens are unlikely to substantially improve patient outcome when compared with intermittent dosing. (Level of evidence = II, grade of recommendation = A.)"
"Trough serum vancomycin concentrations are the most accurate and practical method for monitoring vancomycin effectiveness. Trough concentrations should be obtained just before the next dose at steadystate conditions. (Level of evidence = II, grade of recommendation = B.) (Note: Steady-state achievement is variable but occurs approximately after the fourth dose.)"
"Based on evidence suggesting that S. aureus exposure to trough serum vancomycin concentrations of <10 mg/L can produce strains with VISAlike characteristics, it is recommended that trough serum vancomycin concentrations always be maintained above 10 mg/L to avoid development of resistance. (Level of evidence = III, grade of recommendation = B.)"
"Based on the potential to improve penetration, increase the probability of optimal target serum vancomycin concentrations, and improve clinical outcomes for complicated infections such as bacteremia, endocarditis, osteomyelitis, meningitis, and hospital acquired pneumonia caused by S. aureus, total trough serum vancomycin concentrations of 15–20 mg/L are recommended. Trough serum vancomycin concentrations in that range should achieve an AUC/MIC of  400 in most patients if the MIC is 1 mg/L. (Level of evidence = III, grade of recommendation = B.) In order to achieve rapid attainment of this target concentration for seriously ill patients, a loading dose of 25–30 mg/kg (based on ABW) can be considered. (Level of evidence = III, grade of recommendation = B.) A targeted AUC/MIC of 400 is not achievable with conventional dosing methods if the vancomycin MIC is 2 mg/L in a patient with normal renal function (i.e., CLcr of 70–100 mL/min). Therefore, alternative therapies should be considered. Vancomycin dosages of 15–20 mg/kg (based on ABW) given every 8–12 hours are required for most patients with normal renal function to achieve the suggested serum concentrations when the MIC is 1 mg/L. It should be noted that currently available nomograms were not developed to achieve these targeted endpoints. Individual pharmacokinetic adjustments and verification of serum target achievement are recommended. When individual doses exceed 1 g (i.e., 1.5 and 2 g), the infusion period should be extended to 1.5–2 hours. (Level of evidence = III, grade of recommendation = B.)"
"Available evidence does not support monitoring peak serum vancomycin concentrations to decrease the frequency of nephrotoxicity. (Level of evidence = I, grade of recommendation = A.) Monitoring of trough serum vancomycin concentrations to reduce nephrotoxicity is best suited to patients receiving aggressive dosing targeted to produce sustained trough drug concentrations of 15–20 mg/L or who are at high risk of toxicity, such as patients receiving concurrent nephrotoxins. (Level of evidence = III, grade of recommendation = B.) Monitoring is also recommended for patients with unstable renal function (either deteriorating or significantly improving) and those receiving prolonged courses of therapy (over three to five days). (Level of evidence = II, grade of recommendation = B.) All patients receiving prolonged courses of vancomycin should have at least one steady-state trough concentration obtained (approximately after the fourth dose). Frequent monitoring (more than a single trough concentration before the fourth dose) for short-course therapy (less than five days) or for lower-intensity dosing (targeted to attain trough serum vancomycin concentrations below 15 mg/L) is not recommended. (Level of evidence = II, grade of recommendation = B.)"
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(9). Select Time of Infusion (ti):
(a) Aminoglycosides: 30 minutes (0.5 hrs)
(b) Vancomycin: 0-500 mg/ 0.5 hrs ; 501 to 1250 mg/ 1 hour ;
1251 to 1750/ 1.5 hrs ; >1750/ 2 hours.
(10) Calculate Loading Dose:___________(mg).
Gentamicin/Tobra: 1.5-2.5 mg/kg x ABW (usually 2 mg/kg)
Amikacin: 6-7.5 mg/kg x ABW
Vancomycin: Loading doses may be administered to moderately to severely ill patients requiring rapid attainment of therapeutic levels.
<Top> (11) Calculate Dosing Interval (T) hrs.
T = Ln (Cmax/Cmin) / kel + ti or estimated T = 3 x T1/2
(12) Calculate Maintenance dose (MD):_____mg.
MD = [(kel) x (Vd) x (ti) x (Cpeak desired) x (1 - e-kT)] / (1 - e-kti)
or MD = (Cpeak desired) x Vd (eg: C = D/V, therefore D=C*V)
(13). Calculate Predicted Peak and Trough at Steady State.
Cmax = [Dose * 1-e-kti] / (kel)(Vd)(ti) 1-e-kT
Cmin = Cmax * e-k(T-ti)
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400 in most patients if the MIC is 
1 mg/L. (Level of evidence = III, grade of recommendation = B.) In order to achieve rapid attainment of this target concentration for seriously ill patients, a loading dose of 25–30 mg/kg (based on ABW) can be considered. (Level of evidence = III, grade of recommendation = B.) A targeted AUC/MIC of 
