Steady State (IV Infusion & Multiple Administration & Renal Dysfunction)
Dr/ Mohamed Shahen
Questions and Answers
- 1.
A patient was admitted to the hospital because of an acute episode of bronchial asthma. Theophylline was administered to the patient as an iv loading dose of 300 mg followed immediately by a constant rate iv infusion of 45 mg/hr. The theophylline steady state concentration achieved is 15 mg/L ( k is 0.1 hr-1) the volume of distribution???
- A.
20 L
- B.
30 L
- C.
40 L
- D.
50 L
Correct Answer
B. 30 LExplanation
don't calculate the steady state concentration and volume of distribution from the law of loading dose law of loading dose is used only to calculate loading doseRate this question:
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- 2.
The first-order elimination rate constant for penicillin G is 1.2 hr-1, for gentamicin is 0.35 hr-1, for flucytosine is 0.1 hr-1, and for rifampin is 0.2 hr-1. Which of these drugs will reach steady state faster during repeated administration?
- A.
Penicillin G
- B.
Gentamicin
- C.
Flucytosine
- D.
Rifampin
Correct Answer
A. Penicillin GExplanation
the correct answer is A. It takes 5-6 half lives for the drug to reach steady state during repeated administration. Drugs that have shorter half lives will reach steady state faster than drugs that have longer half lives. In this group of drugs, penicillin G has the shortest half life (largest K)Rate this question:
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- 3.
Digoxin is a drug used in the treatment of congestive heart failure. Its elimination rate constant is 0.4 day-1, and its volume of distribution is 7 L/kg. How long it will take to reach steady state if a patient started taking 0.25 mg digoxin every day ?
- A.
2 days
- B.
5 days
- C.
9 days
- D.
2 weeks
Correct Answer
C. 9 daysExplanation
the correct answer is (9 days). It takes 5-6 half lives to achieve steady state. Since digoxin half life is 1.7 days (0.693/0.4 day-1), so it will take about 9 days to reach steady state.Rate this question:
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- 4.
A patient was admitted to the hospital because of acute myocardial infarction. After stabilizing his condition, he was given an iv loading dose of 150 mg propranolol followed immediately by a constant rate iv infusion of 3 mg/hr. What is the rate of propranolol elimination at steady state?
- A.
3 mg
- B.
50 mg/hr
- C.
3 mg/hr
- D.
150 mg/hr
Correct Answer
C. 3 mg/hrExplanation
the correct answer is c. At steady state the rate of drug administration is equal to the rate of drug elimination. So, at steady state the rate of propranolol elimination will be equal to the infusion rate or 3 mg/hrRate this question:
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- 5.
Procainamide is a class Ia antiarrhythmic drug that alters conduction in normal and ischemic cardiac tissues by sodium-channel blockade. What is the steady state procainamide concentration achieved during constant rate iv infusion of 2 mg/min if procainamide volume of distribution is 120 liters and elimination rate constant is 0.2 hr-1 ?
- A.
10 mg/L
- B.
5 mg/L
- C.
60 mg/L
- D.
1 mg/L
Correct Answer
B. 5 mg/LExplanation
The infusion rate is 2 mg/min which is equivalent to 120 mg/hr. The steady state procainamide concentration = Ko/kVd= (120mg/hr)/(0.2hr-1)(120L) =5 mg/L.Rate this question:
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- 6.
Procainamide was administered to a patient as a constant rate iv infusion of 2 mg/min to control his ventricular arrhythmia. The steady state procainamide concentration was found to be 4 mg/L. Because the patient condition was not controlled, the physician asked you to recommend an infusion rate that will increase the steady state plasma procainamide concentration in this patient to 6 mg/L. What will be your recommendation?
- A.
2 mg/min
- B.
3 mg/min
- C.
4 mg/min
- D.
6 mg/min
Correct Answer
B. 3 mg/minExplanation
The steady state drug concentration is proportional to the infusion rate as long as the elimination process follows first-order kinetics. Fifty percent increase in procainamide plasma concentration will require 50% increase in the infusion rate. The infusion rate has to increase to 3 mg/min.Rate this question:
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- 7.
Bretylium is an antiarrhythmic drug used in the treatment of ventricular arrhythmia. Its elimination rate constant in patients with renal insufficiency is 0.5 day-1, and its volume of distribution is 6 L/kg. How long it will take to reach steady state if a patient with renal insufficiency was started on a constant rate iv infusion of 90 mg/hr ?
- A.
1 week
- B.
2 weeks
- C.
2.5 days
- D.
5 days
Correct Answer
A. 1 weekExplanation
It takes 5 half lives to achieve steady state. Since bretylium half life is 1.4 days (0.693/0.5 day-1), so it will take about 7-8 days to reach steady state.Rate this question:
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- 8.
A patient is receiving a constant rate iv infusion of 60 mg/hr theophylline to control an acute episode of bronchial asthma. Theophylline steady state concentration during this infusion was 15 mg/L. Calculate the total body clearance of theophylline in this patient.
- A.
12 L/hr
- B.
0.25 L/hr
- C.
1 L/hr
- D.
4 L/hr
Correct Answer
D. 4 L/hrExplanation
The total body clearance can be calculated from the iv infusion rate and the steady state concentration (TBC=Ko/Cpss). TBC=(60 mg/hr)/(15 mg/L)= 4 L/hr.Rate this question:
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- 9.
Theophylline therapeutic range is between 10-20 mg/L. calculate theophylline steady state concentration during a constant rate IV infusion of 25 mg/hr? (Vd = 30 L, and K = 0.1155 hr-1) please note will the concentration achieved reach the therapeutic range ???
- A.
1.5 mg/L
- B.
7.2 mg/L
- C.
10 mg/L
- D.
14 mg/L
Correct Answer
B. 7.2 mg/LExplanation
During a constant rate IV infusion, the steady state concentration of a drug can be calculated using the formula: Css = (Dose/CL) * (1 - e^(-K*t)), where Css is the steady state concentration, Dose is the infusion rate, CL is the clearance, K is the elimination rate constant, and t is the duration of infusion. In this case, the infusion rate is 25 mg/hr, the clearance is Vd * K (30 L * 0.1155 hr-1 = 3.465 L/hr), and the duration of infusion is not given. Therefore, it is not possible to calculate the steady state concentration and determine if it reaches the therapeutic range.Rate this question:
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- 10.
Theophylline therapeutic range is between 10-20 mg/L. what is the infusion rate required to achieve steady state concentration of 15 mg/L (Vd = 30 L, and K = 0.1155 hr-1)
- A.
40 mg/hr
- B.
4.3 mg/hr
- C.
51.9 mg/hr
- D.
None of the above
Correct Answer
C. 51.9 mg/hrExplanation
من السؤال دا واللى قبله تستفيد ان عشان اتحكم وازود فى التركيز بزود فى infusion rate infusion rate controls steady state concentrationRate this question:
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- 11.
A patient is taking 200 mg quinidine sulfate tablet every 8 hours for the treatment of cardiac arrhythmia. His average plasma quinidine concentration at steady state was 2 mg/L. Because the patient condition was not controlled, the physician asked you to recommend a dosing regimen that will increase the average steady state plasma quinidine concentration in this patient to 6 mg/L. What will be your recommendation?
- A.
200 mg every 12 hours
- B.
300 mg every 8 hours
- C.
600 mg every 8 hours
- D.
400 mg every 12 hours
Correct Answer
C. 600 mg every 8 hoursExplanation
The average steady state drug concentration is proportional to the administered dose as long as the elimination process follows first-order kinetics. Three fold increase in the plasma concentration will require three fold increase in the dose. The new dosing regimen should be 600 mg every 8 hours.Rate this question:
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- 12.
A patient is taking 450 mg of an antibiotic every 12 h as IV bolus doses. At steady state, the maximum and minimum plasma antibiotic concentrations were 40 and 10 mg/L, respectively. the half life of this drug is
- A.
3 hrs.
- B.
6 hrs.
- C.
9 hrs.
- D.
12 hrs
Correct Answer
B. 6 hrs.Explanation
The half-life of a drug is the time it takes for the concentration of the drug in the body to decrease by half. In this case, the maximum plasma concentration is 40 mg/L and the minimum plasma concentration is 10 mg/L. Since the drug is being administered every 12 hours, it means that the concentration is being reduced by half every 12 hours. Therefore, it would take 6 hours for the concentration to decrease from 40 mg/L to 20 mg/L, and another 6 hours for it to decrease from 20 mg/L to 10 mg/L. Therefore, the half-life of the drug is 6 hours.Rate this question:
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- 13.
A patient is taking a daily 25 mg prednisone tablet which is 100% bioavailable for the treatment of ulcerative colitis, and his condition is well under control. The patient is to start taking a new prednisone formulation which is known to have bioavailability of 80%. What will be the required dose from this new formulation to control the patient's condition ?
- A.
25 mg daily
- B.
20 mg daily
- C.
5 mg daily
- D.
30 mg daily
Correct Answer
D. 30 mg dailyExplanation
The patient is currently taking a 25 mg prednisone tablet with 100% bioavailability, and his condition is well under control. The bioavailability refers to the proportion of the drug that enters the systemic circulation and is available to produce a therapeutic effect. The patient is now switching to a new prednisone formulation with a bioavailability of 80%. To maintain the same therapeutic effect, the required dose from the new formulation would need to be higher. Therefore, the patient would need to take 30 mg daily from the new formulation to control his condition.Rate this question:
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- 14.
During repeated administration of 40 mg ibuprufen tablet every 8 hours (F=1) for the treatment of rheumatoid arthritis the AUC during one dosing interval was 16 mg-hr/L. What is the average ibuprufen steady state plasma concentration during this dosing regimen (40 mg every 8 hours) ?
- A.
2 mg/L
- B.
7.5 mg/L
- C.
5 mg/L
- D.
1.5 mg/L
Correct Answer
A. 2 mg/LExplanation
The average steady state plasma concentration can be determined from the AUC and the dosing interval (Average Cp = AUC/dosing interval). Average concentration = (16 mg-hr/L)/8 hours= 2 mg/L).Rate this question:
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- 15.
A patient is taking procainamide 600 mg/ 6hrs to control cardiac arrhythemia. the average procainamide conc. at s.s was 4 mg/L. what will be the dose requiredto increase the average s.s. conc to 5 mg/L. F= 1 K=0.231 hr-1 Vd=110 L
- A.
1200 mg/6hrs
- B.
750 mg/6hrs
- C.
900 mg/6hrs
- D.
Can't be determined
Correct Answer
B. 750 mg/6hrsExplanation
The correct answer is 750 mg/6hrs. This can be determined by using the formula for calculating the new dose required to achieve a desired steady-state concentration:
New dose = (desired concentration - current concentration) × (Vd / F) / K
Plugging in the values given:
New dose = (5 mg/L - 4 mg/L) × (110 L / 1) / 0.231 hr-1
New dose = 1 mg/L × 110 L / 0.231 hr-1
New dose = 110 / 0.231
New dose ≈ 476.19 mg/6hrs
Since the available answer options are in multiples of 150 mg, the closest option is 750 mg/6hrs.Rate this question:
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- 16.
After administration of a single 400 mg iv dose of ciprofloxacin 240 mg excreted unchanged in urine. If the TBC of ciprofloxacin is 0.45 L/hr/kg, what is the renal clearance of this drug ?
- A.
0.45 L/hr/kg
- B.
0.27 L/hr/kg
- C.
0.33 L/hr/kg
- D.
0.225 L/hr/kg
Correct Answer
B. 0.27 L/hr/kgExplanation
the correct answer is B. The renal clearance of ciprofloxacin can be calculated from the fraction of the iv dose excreted unchanged in urine and the TBC (Renal clearance = Fraction x TBC). Since the fraction of the iv dose excreted unchanged in urine is 0.6, the renal clearance is 0.27 L/hr/kg. Fraction (f) = (𝐂𝐋𝐫𝐞𝐧𝐚𝐥 )/𝐓𝐁𝐂=(𝐝𝐨𝐬𝐞 𝐞𝐱𝐜𝐫𝐞𝐭𝐞𝐝 𝐮𝐧𝐜𝐡𝐚𝐧𝐠𝐞𝐝 𝐢𝐧 𝐮𝐫𝐢𝐧𝐞)/(𝐭𝐨𝐭𝐚𝐥 𝐝𝐨𝐬𝐞 )Rate this question:
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- 17.
A patient is taking 500 mg tetracycline tablet every 12 hours. Tetracycline is rapidly and completely absorbed after oral administration and its renal clearance represent 20% of its total body clearance. What is the amount of tetracycline eliminated unchanged in urine during one dosing interval at steady state ?
- A.
50 mg /12 hrs.
- B.
100 mg/12 hrs.
- C.
250 mg/ 12 hrs
- D.
500 mg/ 12 hrs
Correct Answer
B. 100 mg/12 hrs.Explanation
Tetracycline is rapidly and completely absorbed after oral administration, meaning that the entire 500 mg dose is absorbed into the body. The renal clearance of tetracycline represents 20% of its total body clearance, indicating that 20% of the drug is eliminated through the urine. Therefore, during one dosing interval at steady state (12 hours), 20% of the 500 mg dose (100 mg) will be eliminated unchanged in the urine. Therefore, the correct answer is 100 mg/12 hrs.Rate this question:
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- 18.
A patient is receiving a constant rate IV infusion of 30 mg/hr propranolol to control an acute episode of arrythemia. propranolol steady state concentration during this infusion was 10 mg/L. You were asked to recommend an oral dosing regimen to achieve the same average steady state concentration. What will be your recommendation if the bioavailability of the oral preparation is 100%?
- A.
120 mg/12 hrs.
- B.
150 mg/12 hrs
- C.
720 mg daily
- D.
300 mg/12 hrs
Correct Answer
C. 720 mg dailyExplanation
the same administration rate gives the same concentration in the same patient. so you will look for the dosing regimen that gives the same administration rate (30 mg/hr)which is 720/24= 30Rate this question:
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- 19.
A patient was taking his antihypertensive medication as 500 mg every 12 h. He was taking his medication in the form of an oral tablet that is rapidly and completely absorbed. After administration of a single oral 500 mg dose, 375 mg is excreted unchanged in urine and the drug half-life is 8 h. The average plasma concentration of this antihypertensive drug in this patient while taking 500 mg every 12 h was 20 mg/L. Calculate the volume of distribution of this drug in this patient اكتب القيم عشان القيم مكملة معانا للسؤال الجايين
- A.
0.26 L
- B.
24 L
- C.
30 L
- D.
35 L
Correct Answer
B. 24 LExplanation
The volume of distribution (Vd) is a pharmacokinetic parameter that represents the theoretical volume in which a drug is distributed throughout the body. It is calculated by dividing the amount of drug in the body by the plasma concentration of the drug. In this case, the patient is taking a 500 mg dose of the antihypertensive drug, and the average plasma concentration is 20 mg/L. By rearranging the equation Vd = amount of drug / plasma concentration, we can calculate the Vd as 500 mg / 20 mg/L = 25 L. Therefore, the closest answer option is 24 L.Rate this question:
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- 20.
This patient developed acute renal failure and his creatinine clearance decreased from the normal value of 120 to 30 mL/min. Calculate the new total body clearance for this drug in this patient after developing the renal failure assuming that the deterioration in the kidney function does not affect the drug distribution characteristics.
- A.
Remain constant
- B.
0.85 L/hr
- C.
0.91 L/hr
- D.
1.5 L/hr
Correct Answer
C. 0.91 L/hrExplanation
The new total body clearance for the drug in this patient after developing renal failure is 0.91 L/hr. This is because the question states that the deterioration in kidney function does not affect the drug distribution characteristics. Therefore, the drug's clearance is not affected by the decrease in creatinine clearance.Rate this question:
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