Steady state q

[shigella123]

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Please, show your calculation. Thanks

Drug X has a t 1/2 of 4 hours and is renally eliminated. After elimination of one kidney, how long (in hours) would it take for Drug X to reach steady state?

A. 10
B. 20
C. 30
D. 40
E. 60

 

[ArmyTiger]

Drugs take apx. 4-5 half-lives to reach steady state equilibrium. Elimination of one kidney does nothing, as the other kidney will compensate for it. Answer is B.

 

[shigella123]

Drugs take apx. 4-5 half-lives to reach steady state equilibrium. Elimination of one kidney does nothing, as the other kidney will compensate for it. Answer is B.

Nope, try again.

 

[CherryRedDracul]

I'm going to assume this question is talking about very recent kidney removal before adequate compensation.

t1/2 = (ln(2) * Vd)/Cl)

t1/2 = half life
Vd = volume of distribution
Cl = clearance

So if the patient loses one kidney, clearance would be 50% of baseline and thus the half-life would double to 8 hours. So, because steady state is often reached at 4-5 half lives, the answer would be 40 hours without compensation.

My answer is then D.

But if we're talking about compensated renal function--if I recall correctly, GFR eventually reaches 80% of baseline after loss of a kidney--then we would divide the half life by 0.8 (because new clearance = 0.8*baseline clearance), so the new half life would be 5. Multiply that by 4-5, and you get a range of 20-25. Answer B would be within that range.

Depending on time elapsed, B, C, or D could be valid answers.

 

[shigella123]

[QUOTE="CherryRedDracul, [/QUOTE]

Wow, great explanation.... You are right..

 

[Miracoli]

@shigella123, your Q was nice.
Here is Q2
A 28 yrs old man decides to donate a kidney to his brother, who is in chronic renal failure, after HLA typing suggests that he would be a suitable donor. He is admitted to the hospital, and his right kidney is removed and transplanted into his brother. Which of the following indices would be expected to be decreased in the donor after full recovery from the operation?
(A) Creatinine clearance
(B) Creatinine production
(C) Daily excretion of sodium
(D) Plasma creatinine concentration
(E) Renal excretion of creatinine

 

[shigella123]

Thanks. Would it be the creatinine clearance? A.

 

[Miracoli]

Yes. This is the given answer:-
The correct answer is A. Because creatinine is freely filtered by the glomerulus, but not secreted or reabsorbed to a significant extent, the renal clearance of creatinine is approximately equal to the glomerular filtration rate (GFR). In fact, creatinine clearance is commonly used to assess renal function in the clinical setting. When a kidney is removed, the total glomerular filtration rate decreases because 50% of the nephrons have been removed, which causes the creatinine clearance to decrease. In turn, the plasma creatinine concentration (choice D) increases until the rate of creatinine excretion by the kidneys (choice E) is equal to the rate of creatinine production by the body. Recall that creatinine excretion = GFR x plasma creatinine concentration. Therefore, creatinine excretion is normal when GFR is decreased following removal of a kidney because the plasma concentration of creatinine is elevated.
Creatinine is a waste product of metabolism. Creatinine production (choice B) is directly related to the muscle mass of an individual, but is independent of renal function.
The daily excretion of sodium (choice C) is unaffected by the removal of a kidney. The amount of sodium excreted each day by the remaining kidney exactly matches the amount of sodium entering the body in the diet.

 

[GadRads]

@shigella123, your Q was nice.
Here is Q2
A 28 yrs old man decides to donate a kidney to his brother, who is in chronic renal failure, after HLA typing suggests that he would be a suitable donor. He is admitted to the hospital, and his right kidney is removed and transplanted into his brother. Which of the following indices would be expected to be decreased in the donor after full recovery from the operation?
(A) Creatinine clearance
(B) Creatinine production
(C) Daily excretion of sodium
(D) Plasma creatinine concentration
(E) Renal excretion of creatinine

I think it is D. Here is my reasoning.

Creatinine clearance approximates GFR. Initially, loss of one kidney represents approximately loss of 50% of nephron units [see graph]. This will predictably cause serum creatinine concentration to increase since filtration (GFR/creatinine clearance) has decreased, but only slightly. Full recovery should add more nephron units to the single functioning kidney and in turn increase creatinine clearance/GFR and renal excretion of creatinine, leading to decreased plasma/serum creatinine concentration.

 

[GadRads]

Yes. This is the given answer:-
The correct answer is A. Because creatinine is freely filtered by the glomerulus, but not secreted or reabsorbed to a significant extent, the renal clearance of creatinine is approximately equal to the glomerular filtration rate (GFR). In fact, creatinine clearance is commonly used to assess renal function in the clinical setting. When a kidney is removed, the total glomerular filtration rate decreases because 50% of the nephrons have been removed, which causes the creatinine clearance to decrease. In turn, the plasma creatinine concentration (choice D) increases until the rate of creatinine excretion by the kidneys (choice E) is equal to the rate of creatinine production by the body. Recall that creatinine excretion = GFR x plasma creatinine concentration. Therefore, creatinine excretion is normal when GFR is decreased following removal of a kidney because the plasma concentration of creatinine is elevated.
Creatinine is a waste product of metabolism. Creatinine production (choice B) is directly related to the muscle mass of an individual, but is independent of renal function.
The daily excretion of sodium (choice C) is unaffected by the removal of a kidney. The amount of sodium excreted each day by the remaining kidney exactly matches the amount of sodium entering the body in the diet.

It is A if the question meant simple recovery from surgery. I interpreted it to be FULL recovery both in surgery and physiology (compensatory hypertrophy). Interpretation is serious business 🙂

 

[Miracoli]

It is A if the question meant simple recovery from surgery. I interpreted it to be FULL recovery both in surgery and physiology (compensatory hypertrophy). Interpretation is serious business 🙂

Yeah it is serious business 🙂 I am understanding it as "soon after surgery" and i think compensatory hypertrophy will take time . Thank you for the graph.