ClinRx

Renal Dosing & Kinetics

Palm OS v. 5.1f      Pocket PC v. 1.0

ClinRx Palm for Pocket PC

By S.W. Turski, D.Ph

updated 3/14/2005

ClinRx is a creatinine clearance and kinetics calculator for vancomycin and aminoglycoside dosing for adult and pediatric patients. It includes "eDrugsRenal", with renal dosing information for over 500 drugs, a phenytoin levels calculator and a carboplatin/AUC dosing calculator.  ClinRx includes a graphical "Hartford Nomogram" and "Urban-Craig Nomogram" to assist in extended interval aminoglycoside dosing.
 

The calculations in ClinRx are based on the following equations:

Cockcroft-Gault equation: 

CLcr (male) = IBW x (140 - Age) / 72Scr)

CLcr (female)= as above multiplied by 0.85

Where: A = age in yrs; IBW = Ideal Body Weight in Kg

IBW For males = 50 kg + 2.3 kg For each inch of height over 5 feet.

IBW For females = 45.5 kg + 2.3 kg For each inch of height over 5 feet.

Colkcroft-Gault Adjusted Wt:  ClCr as in Colkcroft-Gault above but If the patient wt is 20% greater than IBW Then Adjusted Wt is used in the calculation.

            Adj.Wt.=((Actual Wt - IBW) x 0.4) + IBW

MDRD (Levey Equation) From Modification of Diet in Renal Disease Study:

CL = 170 x (Scr)^-0.999 x (age, yr)^-0.176 x 0.762 (if  female)

x 1.18 (if patient is black) x (BUN)^-0.17 * (S. alb)^0.318

 per 1.73 m²

If BUN and S.alb. are not available, then:
CL = 186.3 x (Scr)^-1.154 x (age, yr)^-0.203 x 1.212 (if patient is black) x 0.742 (if  female)

Jelliffe equation: 

ClCr (male) = (114 - 0.8 Age) / Scr  per 1.73m²           female= as above multiplied by 0.9

Schwartz equation:

CrCl = K x Ht/Scr / 1.73m²

Traub-Johnson equation:

CrCl=0.28 x Ht x BSA/Scr adjusted to 1.73m²

The formulas used for the Vanco and Gent/Tobra kinetics calculations are derived from the Sarubbi/Hull method; Clinical Pharmacokinetics, Murphy, 2000, P37; Therapeutic Drug Monitoring, Schumacher, 1995 pp 274-277, and the Sawchuk-Zaske method.

Elimination Rate Constant

(KE) gent/tobra = 0.2467(Clcr/100)+0.01

KE vanco = 0.001131 x CrCl+0.0029 (default)    or

 KE vanco = 0.00083 x CrCl + 0.0044 (Matzke Formula)

Half Life (T 1/2) = 0.693/KE

Volume Distribution

(VD) gent/tobra = 0.27L/DW (dosing wt = IBW or Adjusted Wt if obese) for pts < 65 and 0.3L/DW if 65 and over

VD vanco = 0.65L/DW (dosing wt = actual wt)

% left (PL) = e^-(KE*T) where T = dosing interval

Accumulation factor (AF) = 1/(1-PL)

Peak (Pk) = AF x  Dose/VD

Trough (Tr) = Peak x PL

Actual KE (KEa) = (ln(Pk/Tr)) / TA) (TA = Dosing Interval - time between levels)

True Pk (Pka) = (reported Pk) / (e^{-(KEa x TB)}) (TB = Time from End of infusion till blood drawn For level)

True Tr (Tra) = (reported Tr) x (e-^{(KEa x TC)}) (TC = Time from blood drawn till start of Next infusion)

Actual VD (VDa) = (AF x Dose)/Pka

For calculations with the kinetics equations, I use a maximum value for estimated ClCr of 130. If no weight is entered, I use a weight of 75kg For males And 60kg For females.  The default CrCl carried forward into the kinetics equations is the Colcroft-Gault.  The user may change this default to the Levey formula via the preferences screen. 

References:

Cockcroft-Gault equation; Cockcroft D, Gault MD. Nephron, 16:31-41, 1976

Jelliffe equation; Jelliffe RW. Creatinine clearance: Bedside estimate. Ann Inter Med. 1973; 79:604

Jelliffe RW,  Estimation of creatinine clearance in patients with unstable renal function, without a urine specimen.
Am J Nephrol. 2002 Jul-Aug; 22(4): 320-4.

Levey Equation (MDRD); Levey AS, Bosch JP, Lewis JB, et al.; Ann Intern Med 1999;130(6):461-70

Schwartz equation; Ped Clin N. Amer, 1987, 34:571-90

Traub-Johnson equation; Am J Hosp Pharm 1980, 37:195-201

Sarubbi/Hull method; Clinical Pharmacokinetics, Murphy, 2000, P37

Sawchuk-Zaske method and the Matzke method; Therapeutic Drug Monitoring, Schumacher, 1995 pp 274-277

Hartford Nomogram; Nicolau DP,  Antimicrob Agents Chemother. 1995 Mar; 39(3): 650-5

Urban-Craig Nomogram; Urban AW, Craig WA.; Curr Clin Top Infect Dis. 1997; 17: 236-55

Mosteller formula (Mosteller RD: Simplified Calculation of Body Surface Area. N Engl J Med 1987 Oct 22;317(17):1098

Pocket PC v.1

ClinRx is now available for the Pocket PC / Windows CE platform.  Version one is a freeware program that includes the ClinRx Creatinine Clearance Screen.

It is possible to run the full Palm version of ClinRx on the Pocket PC

For information on this and to download go HERE.

 

ClinRx is intended to be used by a competent healthcare professional as a dosing aid and is not intended to be used For medical diagnosis. The author does not directly or indirectly practice medicine or provide medical services and therefore assumes no liability whatsoever of any kind for the information and data accessed through the program or for any diagnosis Or treatment made in reliance thereon.

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aminoglycoside dosing obese