- Witamy!! Forum ruszyło na nowo. Przy rejestracji proszę o wysłanie wiadomosci email (usmle.fora@gmail.com) z krótkim opisem siebie/ planów związanych z USMLE. Jest to niezbędne do weryfikacji i aktywowania konta :)

anka

Your 74-year-old patient with MI has a severe cardiac arrhythmia. U have decided to give lidocaine to correct the arrhythmia.

1. A continuous IV infusion of lidocaine, 1.92 mg/min, is started at 8 AM. The average pharmacokinetic parameters of lidocaine are:
Vd=77L
CL=640 mL/min
half-life= 1.8h.
The expected steady-state plasma concentration is approximately:

A. 40mg/L
B. 3 mg/L
C. 0.025mg/L
D. 7.2mg/L
E. 3.46mg/L

2.Your patient has been receiving lidocaine for 8 h and u decide to obtain a plasma concentration measurement. When the results come back, the plasma level is exactly half of what u expected. The most probable explanation is:

A. the patient's lidocaine Vd is half the average value
B. the patient's lidocaine CL is twice the average value
C. the patient's lidocaine half-life is 4 times the average value
D. the patient's infusion rate was accidentally decreased by half
E. the laboratory made a mistake in the assay for lidocaine

Gość

Ad1. B
Ad2. D

anka

No więc pierwsze faktycznie B Very Happy

ale drugie też Confused

If the half life is 1.8, the plasma concentration should approach steady-state after 8h ( more than 4 half-lifes ). As indicated by the equation (dosage = plasma level x clearance), the steady-state concentration is a function of dosage and clearance, not volume of distribution. If the plasma level is less than predicted, the clearance in this patient must be greater than average. In questions of this type, do not assume errors of analysis or administration as answers, unless all other possible answers can be ruled out.