Vancomycin

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Vancomycin

• Problem sets answers

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Problem 1

• 1. Calculate an initial dose for a 57, 39 y/o,
  65kg female with a SrCr 1.3 mg/dL to get
  steady-state Cmax and Cmin of 30 and 7 mg/L.
• IBW 61 kg
• CrCl 56 mL/min
• Vanc Cl 42 mL/min or 2.5 L/hr
• Estim Vd 45.5L
• Kel 0.055hr-1
• Estim t1/2 12.6hr
• Estim Tau 27.4hr (use 24hr)
• Initial dose 1028mg (use 1GM)
• Verifying Cmax and Cmin at steady-state 29.2
  8.2 mg/L

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Problem 2

• An 88 y/o, 54kg female patient receiving therapy
  for neutropenic fever secondary to a bone marrow
  transplant is currently on vancomycin 1500mg
  Q12hr. The last dose was given at 1400hrs and
  administered over 2 hours. Levels at 1345 and
  1755 were 11.6 mg/L and 29.4 mg/L, respectively.
• Calculate a new dosage regimen for this patient
  to obtain troughs of 5-10mg/L and peaks of
  lt40mg/L.
• Kel 0.119 hr-1
• T 1/2 5.8hr
• Cpmax 37 mg/L (back extrapolated from level at
  1755hrs using 1.92 hrs from end of infusion)
• Cpmin 11.2 mg/L (degraded from level at 1345hrs
  to 1400hrs)
• Vd 0.53 L/kg or 46.9 L (using 37 and 11.3)
• New dose
• 1500mg Q12hrs gives 37.2 11.2
• 1250mg Q12hrs gives 31.1 9.3
• 1000mg Q12hrs gives 24.4 7.4
• Using 1500mg Q12hrs gives less than
  ideal/textbook troughs, so it would be better
  to use a lower dose. The 1250mg Q12hrs gives
  levels gt30, which in and of themselves are not
  toxic, but may be more drug than is necessary
  as this is not a CNS infection.
• The 1000mg Q12hr would be the most appropriate
  dose to use in this patient.

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Problem 3

• A 93kg, 51 y/o male is being treated with 1500mg
  Q24hr vancomycin for MRSA bacteremia with a SrCr
  1.7 mg/dL since July 8th. For July 10th, the
  following information is available
• Level at 1200hrs of 19.8 mg/L
• Dose at 1215-1315 of 1500mg
• Level at 1435 hrs of 39.6 mg/L
• Level at 2200 hrs of 18.2 mg/L
• Calculate a new dosage regimen for this patient
  to obtain troughs of 5-10 mg/L and peaks of 30-40
  mg/L.
• The best way to approach this is to graph it out
  get some graphing paper to keep it to scale.
  It will make a difference to see this visually.
  Look at what has happened to the level in
  response to dosing.
• This patient is NOT likely at steady-state given
  the elevated trough level after 2 doses (on 7/8
  7/9). Also, trough level on 7/10 does not
  correlate with the same level 23 hours after the
  dose on 7/10. To solve for this patient, you
  would have to use non-steady-state kinetics by
  using the peak and random to calculate your data.
• Kel 0.025hr-1 (using 39.6 and 18.2)
• T ½ 28hr
• Cpmax 40.9 mg/L (back extrapolating from 39.6
  using 1.33 hrs)
• Cpmin 19.7 mg/L (degrading down from 19.8 using
  0.25 hrs)
• Vd 0.73 L/kg or 68.3L (using 40.9 19.7)
• Select Tau not a real pretty choice here. The
  optimal one would be about 56 hrs, but that is
  unrealistic in a clinical setting. The closest
  to this is 48hrs, so go with this one. The
  levels wont be optimal, but not all patients
  are.
• Dose 1500mg
• Predicting trough on this regimen 9.6 mg/L