Pharmacology Questions

[adi11]

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Pharmacology questions:

1) A drug achieves a plasma level of 16mg / L shortly after the administration of the first oral dose. If the half - life and the dosing interval are both 6 hours, what is the approximate plasma level shortly before the the administration of the 5th dose?
A. 15mg /L
B. 24mg /L
C. 28mg /L
D. 30mg /L
E. 31mg /L

2)At 6 h after IV administration of bolus dose, the plasma level of a drug is 5 mg/L. If the Vd = 10L and the elimination half - life = 3 h , what was the dose administered?
A. 100mg
B. 150mg
C. 180mg
D. 200mg
E. 540mg

please can someone help me with these questions with explanation ?

 

[shan564]

Pharmacology questions:

1) A drug achieves a plasma level of 16mg / L shortly after the administration of the first oral dose. If the half - life and the dosing interval are both 6 hours, what is the approximate plasma level shortly before the the administration of the 5th dose?
A. 15mg /L
B. 24mg /L
C. 28mg /L
D. 30mg /L
E. 31mg /L

This is a question about steady state.

After 1 half-life, the plasma level is 8 mg/L. Then you add another 16 mg dose, so the plasma level is 24 mg/L.
After another half-life, the plasma level is 12 mg/L. Then you add another dose and the level becomes 28 mg/L.
After another half-life, the plasma level is 14 mg/L, and when you add another dose, it becomes 30 mg/L.
After another half-life, the plasma level is 15 mg/L, and when you add the fifth dose, it becomes 31 mg/L (and you're reaching a steady state).
But because the question asks for the plasma level before the fifth dose, the answer should be (A) 15 mg/L.

2)At 6 h after IV administration of bolus dose, the plasma level of a drug is 5 mg/L. If the Vd = 10L and the elimination half - life = 3 h , what was the dose administered?
A. 100mg
B. 150mg
C. 180mg
D. 200mg
E. 540mg

Vd = (amount of drug in the body) / (plasma concentration)
10 L = (amount of drug in the body) / (5 mg/L)
Amount of drug in the body = 50 mg.

If the half-life is 3 hrs, then two half-lives have passed at 6 hours, so the current concentration of the drug is (1/2) * (1/2) = 1/4 of the original delivered dose.

So, the original dose should have been 50mg x 4 = 200 mg. Is that right?

 

[adi11]

yes both the answers are right THANK YOU SO MUCH for the explanation🙂

 

[shan564]

No problem, happy studying!