1-C: Renal and Hepatic Elimination

1-C: Renal and Hepatic Elimination
400 mg of moxifloxacin is administered by IV bolus to Mr BB, a 68 yr old male who weighs 75 kg. Blood samples were drawn following the dose and the plasma concentration determined. It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. A further 20% is excreted unchanged in the bile and the rest is metabolised to either M1 (sulpho) or M2 (acyl-glucuronide) The intent of this slide pack is to evaluate Renal Clearance of a drug … How much moxi is in the urine ? But first, although we have already analyzed plasma data, as a review calculate volume, AUC, K, half-life and clearance. Then: 1. How much unchanged moxi is in the urine at 12 hrs? ..at 36 hrs? Calculate K and ke. from urine data. 2. What is the ClR of moxifloxacin?

1-Compartment IV Dosing Concentration –Time Data
Analysis of Concentration –Time Data This data set provided is identical in many ways to the tobramycin data set analysed in Slide Pak 07. While the solution to volume, AUC, K, half-life and clearance is shown briefly in the following slides, you should complete the calculation of these parameter values independently … for practice. Class time will not be spent reviewing the method of calculation of the initial concentration, AUC, K, half-life or clearance.

1-Compartment IV Dosing Analysis of Concentration –Time Data
You need to calculate the initial concentration, AUC, K, half-life and clearance. You must FIRST determine the log of the concentration and then from any pair of points (or using all data in Excel) determine the slope. K is be determined from inspection of the data, graphical methods or by calculation of the slope.

1-Compartment IV Dosing
Analysis of Concentration –Time Data Estimation of K. K is the slope of the line (t=2 to 12 hr) K = [log(C2) – log(C1)] / (t2 - t1) = [log(1.16) – log(2.32)] / (12 – 2) = [0.064 – 0.365] / (10) = [ ]/10 = hr-1 T½ = 10.0 hr. Excel = hr-1

1-Compartment IV Dosing Analysis of Concentration –Time Data
K hr-1 Volume L Analysis of Concentration –Time Data Using K, we can then estimate the initial concentration by extrapolation. Then calculate the volume & AUC by trapezoidal rule between each time point (or the pharmacokinetic method). A variety of estimates of K are possible given the concentrations. The Excel sheet (posted) provides a range of answers. Those calculated by hand should be very similar.

1-Compart.IV Dosing Volume AUC K T½ Cl 150.12 L 0.0694 hr-1 9.98 hr
38.38 mg*hr/L K hr-1 T½ 9.98 hr Cl 10.42L/hr

400 mg of moxifloxacin is administered by IV bolus to Mr BB, a 68 yr old male who weighs 75 kg. Blood samples were drawn following the dose and the plasma concentration determined. It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. A further 20% is excreted unchanged in the bile and the rest is metabolised to either M1 (sulpho) or M2 (acyl-glucuronide) Parameter Estimates K = hr-1 T½ = 9.98 hr AUCI =38.38 mg*hr/L V = L

describes this profile?
Graph Patient Data What model best describes this profile? Terminal elimination phase is log-linear… 1 Compartment Model with first order elimination (K)

Graph Patient Data What model best describes this profile? It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. A further 20% is excreted unchanged in the bile and the rest is metabolised to either M1 (sulpho) or M2 (acyl-glucuronide)

Graph Patient Data What model best describes this profile? It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. A further 20% is excreted unchanged in the bile and the rest is metabolised to either M1 (sulpho) or M2 (acyl-glucuronide) kH = kM1 + kM2 KNR = 20% excreted into bile as unchanged drug.

Graph Patient Data What model best describes this profile? It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. A further 20% is excreted unchanged in the bile and the rest is metabolised to either M1 (sulpho) or M2 (acyl-glucuronide) K = ke + kH + kNR

400 mg of moxifloxacin is administered by IV bolus to Mr BB, a 68 yr old male who weighs 75 kg. Blood samples were drawn following the dose and the plasma concentration determined. It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. The intent of this slide pack is to evaluate Renal Clearance of a drug … How much moxi is in the urine ? But first, although we have already analyzed plasma data, as a review calculate volume, AUC, K, half-life and clearance. Then: 1. How much unchanged moxi is in the urine at 12 hrs? ..at 36 hrs? Calculate K and ke. from urine data. 2. What is the ClR of moxifloxacin?

400 mg of moxifloxacin is administered by IV bolus to Mr BB, a 68 yr old male who weighs 75 kg. Blood samples were drawn following the dose and the plasma concentration determined. It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. Urine collection following the 400-mg IV dose yields: Plasma Urine Amount Urinary Time Conc Collection Urine Urine Recovered Excretion (hr) (mg/L) Period Volume conc in Urine Rate (hr) (mL) (mg/L) (mg) (mg/hr) 0 no sample –

400 mg of moxifloxacin is administered by IV bolus to Mr BB, a 68 yr old male who weighs 75 kg. Blood samples were drawn following the dose and the plasma concentration determined. It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. Calculate the Urinary excretion Rate (mg/hr): Amount recovered in urine / duration of urine collection. Plasma Urine Amount Urinary Time Conc Collection Urine Urine Recovered Excretion (hr) (mg/L) Period Volume conc in Urine Rate (hr) (mL) (mg/L) (mg) (mg/hr) 0 no sample – mg / 4 hr

400 mg of moxifloxacin is administered by IV bolus to Mr BB, a 68 yr old male who weighs 75 kg. Blood samples were drawn following the dose and the plasma concentration determined. It is known that about 20% of a moxifloxacin dose is excreted in the urine unchanged. Calculate the Urinary excretion Rate (mg/hr): Amount recovered in urine / duration of urine collection. Plasma Urine Amount Urinary Time Conc Collection Urine Urine Recovered Excretion (hr) (mg/L) Period Volume conc in Urine Rate (hr) (mL) (mg/L) (mg) (mg/hr) 0 no sample –

Renal Clearance of moxifloxacin
When evaluating Aminoglycoside Renal Clearance (following IV dose with no metabolism and complete renal excretion) we observed: ClR = ClT and therefore, ClNR = 0 L/hr It would have also been apparent that the amount excreted in the urine after infinite time (Ae0-) would equal the dose. … that an Excretion Rate vs. Time plot had a slope proportional to K …that an Excretion rate vs. mid point plasma concentration had a slope equal to Renal clearance (ClR). But now, moxi has other routes of elimination…?

When evaluating Aminoglycoside Renal Clearance (following IV dose with no metabolism and complete renal excretion) we observed: ClR = ClT and therefore, ClNR = 0 L/hr It would have also been apparent that the amount excreted in the urine after infinite time (Ae0-) would equal the dose. … that an Excretion Rate vs. Time plot had a slope proportional to K …that an Excretion rate vs. mid point plasma concentration had a slope equal to Renal clearance (ClR). But now, moxi has other routes of elimination…? Calculations to complete 1. Plot Excretion rate vs. Time. 2. Calculate K 3. Plot Excretion rate vs. mid-point plasma conc. Calculate Renal clearance Calculate ke Determine Ae0- Establish some principles of Elimination

Plot Excretion Rate vs. Time. Plot at the mid point of the collection period as this is the time which most accurately reflects the rate Plasma Urine Amount Urinary Time Conc Collection Urine Urine Recovered Excretion (hr) (mg/L) Period Volume conc in Urine Rate (hr) (mL) (mg/L) (mg) (mg/hr) 0 no sample –

1-C: Renal and Hepatic Elimination Plot Excretion Rate vs. Time
Slope = -K/2.303

1-C: Renal and Hepatic Elimination Plot Excretion Rate vs. Time
Urine Data Slope = -K/2.303 = K = * = hr-1 T½ = hr

Plot Excretion Rate vs. Time Change in the Rate at which drug appears in the urine ( Ex. Rate) is proportional to concentration in serum and slope is –K/2.303.

When evaluating Aminoglycoside Renal Clearance (following IV dose with no metabolism and complete renal excretion) we observed: ClR = ClT and therefore, ClNR = 0 L/hr It would have also been apparent that the amount excreted in the urine after infinite time (Ae0-) would equal the dose. … that an Excretion Rate vs. Time plot had a slope proportional to K …that an Excretion rate vs. mid point plasma concentration had a slope equal to Renal clearance (ClR). But now, moxi has other routes of elimination…? Calculations to complete 1. Plot Excretion rate vs. Time. 2. Calculate K 3. Plot Excretion rate vs. mid-point plasma conc. Calculate Renal clearance Calculate ke Determine Ae0- Establish some principles of Elimination

Plot Excretion Rate vs. Mid-point Plasma concentration. Plot the excretion rate vs. the concentration at the mid point of the collection period Plasma Urine Amount Urinary Time Conc Collection Urine Urine Recovered Excretion (hr) (mg/L) Period Volume conc in Urine Rate (hr) (mL) (mg/L) (mg) (mg/hr) 0 no sample –

Plot Excretion Rate vs. Mid-point Plasma concentration. Slope = ClR (L/hr)

Renal Clearance & Urinary Excretion Slope = ClR (L/hr) = L/hr

Renal Clearance & Urinary Excretion. Slope = ClR (L/hr) CLR = L/hr Plasma Data; ClT = L/hr What does this tell us?

Renal Clearance & Urinary Excretion. ClR = L/hr ClT = L/hr ClR / ClT =

Renal Clearance & Urinary Excretion If 17.89% of ClT is determined by ClR what is ClNR?

Renal Clearance & Urinary Excretion If 17.89% of ClT is determined by ClR what is ClNR? ClT = ClR + ClNR ClNR = 10.4 – 1.8 ClNR = 8.55 L/hr

When evaluating Aminoglycoside Renal Clearance (following IV dose with no metabolism and complete renal excretion) we observed: ClR = ClT and therefore, ClNR = 0 L/hr It would have also been apparent that the amount excreted in the urine after infinite time (Ae0-) would equal the dose. … that an Excretion Rate vs. Time plot had a slope proportional to K …that an Excretion rate vs. mid point plasma concentration had a slope equal to Renal clearance (ClR). But now, moxi has other routes of elimination…? Calculations to complete Plot Excretion rate vs. Time. Calculate K Plot Excretion rate vs. mid-point plasma conc. Calculate Renal clearance Calculate ke Determine Ae0- Establish some principles of Elimination

1-C: Renal and Hepatic Elimination proportionality constant
Renal Clearance & Urinary Excretion. If 17.89% of ClT is determined by ClR ClT = ClR + ClNR and K = ke + knr and K and ClT are related by the proportionality constant Volume what is ke?

Renal Clearance & Urinary Excretion. If 17.89% of ClT is determined by ClR ClT = ClR + ClNR and K = ke + knr and K and ClT are related by the proportionality constant - Volume what is ke?

Renal Clearance & Urinary Excretion. If 17.89% of ClT is determined by ClR ClT = ClR + ClNR and K = ke + knr and K and ClT are related by the proportionality constant - Volume what is ke? ClR ke ClT K = ----- ClT = L/hr and ClR = L/hr K = hr-1 and ke = hr-1

When evaluating Aminoglycoside Renal Clearance (following IV dose with no metabolism and complete renal excretion) we observed: ClR = ClT and therefore, ClNR = 0 L/hr It would have also been apparent that the amount excreted in the urine after infinite time (Ae0-) would equal the dose. However, now there is at least one other source of elimination (kNR which is likely made up of kH (or kM1 and kM2) and kB and since … If ke is determining how much drug appears in the urine then … ClR ke ClT K = -----

However, now there is at least one other source of elimination (kNR which is likely made up of kH (or kM1 and kM2) and kB and since … If ke is determining how much drug appears in the urine then … Ae0- ke DoseIV K and and all will have a ratio of ~ in this patient. ClR ke ClT K = ----- = ClR ke Ae0- ClT K DoseIV = =

67.55 mg Over the first 40 hours, mg of moxi is collected in the urine. Based proportion of drug being eliminated into the urine (ke/K) the total amount expected in the urine would be 400 mg x = mg. Would 4.01 mg be expected to appear in the urine after 40 hr? (40 hr  )

67.55 mg Would 4.01 mg be expected to appear in the urine after 40 hr? (40 hr  ) At 40 hours, 0.16 mg/L of moxi remains in plasma. The estimated volume is L. Therefore the amount remaining in the body at 40 hours is: 0.16 mg/L x L =

67.55 mg Would 4.01 mg be expected to appear in the urine after 40 hr? (40 hr  ) At 40 hours 0.16 mg/L of moxi remains in plasma. The estimated volume is L. Therefore the amount remaining in the body at 36 hours is: 0.16 mg/L x L = 24.6 mg The amount that should appear in the urine (40 hr  ) would be: x 24.6 =

67.55 mg Would 4.01 mg be expected to appear in the urine after 40 hr? (40 hr  ) At 40 hours 0.16 mg/L of moxi remains in plasma. The estimated volume is L. Therefore the amount remaining in the body at 40 hours is: 0.16 mg/L x L = 24.6 mg The amount that should appear in the urine (40 hr  ) would be: x 24.6 = 4.29 mg

Principals of Elimination
Equations K = ke + kH + kNR TBC = ClT = ClR + ClH + ClNR ClH = ClM1 + ClM2 kH = kM1 + kM2 ClR = keV Change in the Rate at which drug appears in the urine ( Ex. Rate) is proportional to concentration in serum and slope is –K/2.303. Slope of log Excretion Rate vs. Time is proportional to K (-2.303) ClR ke ke Ae0- ClT K k DoseIV = = = the amount excreted in the urine after infinite time (Ae0-) equals ke/K …that an Excretion rate vs. mid point plasma concentration has a slope equal to Renal clearance (ClR).

Summary of Urinary Elimination
Change in the Excretion Rate at which drug appears in the urine [Slope (Log) Ex. Rate) vs.Time] is parallel the slope of the Concentration in serum vs. Time Slope is –K/2.303. This is true regardless of the proportion of the dose excreted into the urine ... as long as Ae0- >0 the amount excreted in the urine after infinite time (Ae0-) equals ke/K

K is the overall rate constant which determines the half-life. ke determines the proportion of the dose excreted into the urine. Ae0- ke DoseIV K = the amount excreted in the urine after infinite time (Ae0-) equals ke/K …that an Excretion rate vs. mid point plasma concentration has a slope equal to Renal clearance (ClR).

Second use of Excretion Rate: If Excretion Rate is plotted (not Log Excretion Rate) vs. mid point plasma concentration …slope is equal to Renal clearance (ClR). Minimum requirement is a single blood sample drawn at the mid point of the urine collection interval.

What do you need to calculate K? At least 2 blood (plasma) concentrations drawn at known times. (ii) At least 2 urine collections of known intervals and time since the dose. Plot Log Excretion Rate vs. Time

What do you need to calculate ke? A complete urine collection and a known dose Ae0- ke DoseIV K (ii) Through relationships with other variables ---- = = ----- = ClR ke Ae0- ClT K DoseIV

What do you need to calculate ClR? Minimum requirement is a single blood sample drawn at the mid point of the urine collection interval. If Urinary Excretion Rate is plotted vs. mid point plasma concentration …slope is equal to Renal clearance (ClR).

Renal Excretion is based on: Creatinine clearance will
Renal Function & Drug Clearance ClR Renal Excretion is based on: Filtration at the glomerulus. This is a function of a number of competing pressures. The hydrostatic pressure of blood is the overall driving force filtering blood. Working against this pressure is the osmotic pressure of the blood to hold on to the fluid and the hydrostatic pressure of the capsule. The result of these completing pressures is a net ~10 mmHg pushing fluid through the capsule and into the proximal tubule. In addition to filtration, there is active secretion, in the proximal renal tubule and reabsorption most likely in the distal tubules. Remaining Slides in this file are for interest only. Creatinine clearance will be covered in the 2nd term.

Renal Function & Drug Clearance ClR
Filtration at the glomerulus Approximately 125 mL of protein free filtrate is removed from the blood every minute as it passes through the glomeruli of the kidneys. However, only drugs that have a low molecular weight and are not protein bound can pass through the glomeruli [since protein is not filtered, drug bound to protein is not filtered]. Since most drugs are small molecules, only a high degree of protein binding will reduce the amount of drug found in the protein free filtrate.

Active secretion Active secretion, In addition to glomerular filtration, some drugs may be actively secreted into the proximal renal tubules. Since secretion is an active process, the secretion rate does not appear to be influenced by protein binding and is therefore, generally felt to be “nonrestrictive”.

Reabsorption Reabsorption is a passive process &may occur at any point in the Tubule but is more likely occur in the distal tubules as the urine and the concentration of the drugs within it, becomes more concentrated. Reabsorption can occur for any drug but it is more likely to occur for unionized, non-polar drugs. As a result, the reabsorption of weakly basic or acidic drugs may be dependant on urine pH, which will determine the degree to which the drug exists in the unionized state.

Renal function is often estimated. There are at least three compounds that have been widely used to estimate kidney function: Inulin (MW ~ 5000); total eliminated by GFR. PAHA [para amino hippuric acid] filtered and secreted. Creatinine, endogenous, filtered and secreted.

Creatinine, easy & most popular. Compoun used to estimate renal function.It is an endogenous end product of muscle metabolism. Calculation of CrCl. To properly estimate creatinine clearance a 24-hour collection of urine is completed and the creatinine measured. The amount of creatinine excreted is determined based on the urine volume.

Calculation of CrCl Creatinine Clearance (CrCl) is then determined based on a single serum creatinine measurement, assuming that the measured serum creatinine is the average concentration of creatinine or that the serum creatinine concentration is constant over the 24-hr collection period.

Calculation of CrCl…Example Consider a patient with a serum creatinine 1.1 mg/dL and following a 24 hr urine collection is found to have a creatinine concentration of 1.4 mg/mL and 1250 mL of urine. CrCl (mL/mIn = (100 x U x V ) / SCr x 1440 Where U is the concentration of creatinine in the urine in mg/dL, V is the urine volume in mL and 100 is the conversion from dL, and SCr is the creatinine concentration in plasma, in mg/dL. 1440 is the conversion to units of mL/min from mL/24 hrs

Calculation of CrCl…Example Consider a patient with a serum creatinine 1.1 mg/dL and following a 24 hr urine collection is found to have a creatinine concentration of 1.4 mg/mL and 1250 mL of urine. CrCl (mL/mI) = (100 x U x V ) / SCr x 1440 = (100 x 1.4 x 1250) / (1.1 x 1440) = / 1584 = mL/min = 110 mL/min

Although creatinine is easy & popular, as endogenous end product of muscle metabolism, creatinine production is directly related to muscle mass. Therefore, it is necessary to correlate serum creatinine with urinary creatinine clearance in males and females of various ages. There are many nomograms that describe a relationship between serum creatinine and renal function. One is the Cockcroft & Gault equation. Cockcroft DW, Gault MH. Prediction of Creatinine clearance from Serum Creatinine. Nephron 1976; 16:

Prediction of Creatinine Clearance from Serum Creatinine DONALD W COCKCROFT & M HENRY GAULT Nephron 1976; 16: Derived Equation (x 0.85 for females) When SCr is reported in mg/100 mL CrCl is calculated in mL/min. When Serum Creatinine is reported in μmol/L the equation is: and CrCl is calculated in mL/sec and must be multiplied by 60 to yield mL/min.

1-C: Renal and Hepatic Elimination

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