Pharmacokinetics+-+Exam+3+spr+2012+answer+key

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Clinical PharmacokineticsDr. Scott

4/12/2012 Exam #3

K.J. is a 65 year-old white male admitted to the hospital two days ago.

CC: Fever, dyspnea, fatigue, productive cough, swelling in hands and feet as well as nasal and

chest congestion.

HPI: K.J. was fine until about five days ago when he began to feel excessively fatigued, and

weak. He contributed these symptoms to a cold or allergiesPMH: Hypertension, Diabetes, Hyperlipidemia, Asthma, Cystic Fibrosis and newly diagnosed

CHF

Home Meds: Lasix 40mg poqd, Vasotec5mg poqd, ADVAIR 500/50 -1 puff bid, Aspirin

325mg qd, Pepto-bismol 30ml q6h prn, and Ventolin MDI 2 puffs qidprnPE: BP 189/106, HR 102, Temp 102, RR 12, ht. 59; wt205 lbs. Patient appears wellhydrated and in good spirit. Stools are dark, tarry and heme positive. Also CXR revealed

LLL infiltrate.

Admitting Labs: SrCr 1.3mg/dL, BUN 40mg/dl, Na 140meq/L, K 5.4meq/L, glucose 107mg/dl, Phenytoin

3mg/L, Ca++ 7.9meq/L, WBC 13,000, and albumin 2.0gm/dL.

Assessment/plan

1. Possible Pneumonia2. Possible Dehydration3. Start Tobramycin 140mg q8hQuestions: Must show all work/calculations when necessary in order to receive credit 1. Which of the following is true?

a. Patient is experiencing GI bleedb. Patient is experiencing Dehydrationc. Patient is experiencing Stroked. A and B onlye. All of the above

2. Which of the following factors can affect the disposition of drugs used in this case?a. Cystic Fibrosisb. Renal functionc. CHFd. All of the abovee. A and C only

3. Patients on dialysis will require a vancomycin dose approximately 3 times normal dose becauseaminoglycosides will be lost (concentration drastically reduced) during the process.

a. Trueb. False

4. Which of the following factors associated with this case could result in an increase pharmacodynamicresponse to Coumadin, due to an alteration in the pharmacokinetics of Coumadin.

a. Aspirinb. Pepto-bismalc. Albumin leveld. A and C onlye. All of the above


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5. Do you agree or disagree with the dose of Tobramycin ordered by the physician? Very briefly explain yourreasoning.

70.7kg Cmax = 140mg * (1-e-0.1923) = 9.18mg/L Vd=17.675 L 3.399 L/h * (1-e-0.1923 *8) CL=3.399 k = 0.1923 Cmin = 9.18 * e-0.1923(7) = 2.389mg/L Tau = 8 hr

I disagree because trough (2.389mg/L) is too high

6. If you disagree calculate a Tobramycin dose that will maintain a peak of 8mg/L and a trough of


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9. Gentamicin and Tobramycin have the ability to kill gram + organisms such as Staphylococci(MRSA) whengiven with vancomycin.

a. Trueb. False

10.When an aminoglycoside (i.e. tobramycin) is given with vancomycin, the pharmacodynamics response ofvancomycin increases against MRSA because

a. Aminoglycosides displace vancomycin from protein binding sites.b. Aminoglycosides decrease the clearance of vancomycin, thus causing the concentration to increase.c. Aminoglycosides and vancomycinis said to have a synergistic effect; however, they do not have an

effect on the same organisms and have different spectrum of antibiotic activityd. B and C onlye. None of the aboave

11.The physician wants to start vacomycin at a dose 500mg q6h, do you agree or disagree with the physiciansdose?

70.7kg Cmax = 500mg * (1-e-0.044642851) = 42.049mg/L Vd = 49.49 L 2.2093747 L/h * (1-e-0.044642851*6) CL = 2.2093747 k = 0.044642851 Cmin = 42.049 * e-0.044642851(5)= 33.64mg/L Tau = 6hr

I disagree because peak (42.049mg/L) and trough (33.64mg/L) are both too high

12.If you disagree calculate a vancomycin dose that will maintain a Peak of 30mg/L and a trough of 6.3mg/L.

new T = [ ln (6.3/30) * -1 ] + 1= 35.9 36hr0.044642851

D= Cmax desired (30mg/L) * 2.2093747L/h * (1-e-0.044642851*36) =(1-e-

0.044642851)

D = 1213.77mg q36hr


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13.The physician wants to start a continuous infusion of aminophylline that will maintain a theophyllineconcentration of 15mg/L. Calculate the continuous infusion dose.

CL = 70.7 * 0.04 = 2.828 L/h D = 2.828 L/h*15mg/L*1h= 53.025 mg/hr

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14.The physician decided to use a continuous infusion dose of 75mg/hr. Based on this continuous infusiondose of aminophylline, what will the concentration be 15 hours after the start of the continuous infusion?

Cp = 75mg*0.8*1* 1-e-0.08 (15) = 14.826 mg/L2.828 L/hr *1hr

15.Because the steady state concentration of Theophylline was 25mg/L at the current dose of aminophylline,the physician decided to stop the infusion. How long will it take for the concentration to drop 15mg/L?

CL = 75mg*0.8*1= 2.4 L/hK = 2.4 L/h = 0.067892525mg/L 35.35

t = ln (15/25) *

-

1 = 7.52 hr0.0678925 note: if you continued using 0.08 as your k credit was given this time; however

for future reference calculate individualized CL. t= 6.385h

16.The steady state concentration of Theophylline was 25mg/L at 8pm using the current dosing information,thus the physician decided to stop the infusion. If the physician decided to recheck the concentration at 8am

what would the concentration be at that time?

C = 75mg*0.8*1* e-0.0678925 (12)= 11.07mg/L2.4 L/h

note: if you continued using 0.08 as your k credit was given this time; howeverfor future reference calculate individualized CL. C =9.57h

17.If the concentration from question is less than 10mg/L, calculate an aminophylline LD that achieve aconcentration of 15mg/L.

note: if you continued using 0.08 as your k credit was given this time; howeverfor future reference calculate individualized CL. LD= 239.84mg

Concentration > than 10mg/L no Calculations required

K.J. has a theophylline concentration of 25mg/L at 8pm and at 8 hours later he had a serum concentration of

14.52mg/L. K = ln(14.52/25) = 0.067919-h

818.From the information given calculate the half-life of theophylline for this patient.

t1/2= 0.693/0.067919

h = 10.2 hr

19.From the information given calculate at what time was the second concentration taken.4am

20.Also determine, what is the minimum amount of time needed for the drug to reach steady state in thispatient?

10.2 * 5 =51hr


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21.If Drug X has a distribution half-life of 0.2 hours and an elimination half-life of 23 hours. If A = 40 and B =30mg/L. What will the Drug X plasma concentration be 12 hour after the infusion?

20.898mg/LCp = 40mg* e-3.465 (12)

+50mg*e-0.03013 (12)

22.Using the information in question #21, how much Drug X will accumulate if 750mg was given q48 hours.ACC = 750mg

980mg1-e-0.03013 (48) =

23.Which of the following factors will decrease bioavailabilty?a. first pass effectb. GI motilityc. Salt Form of the drugd. B and C onlye. None of the abovef. All of the above

24.Nephrons excretes drugs from by the body which of the following processes?I. glomerular filtrationII. tubular secretion

III. tubular reabsorption

a. I onlyb. I and II onlyc. I and III onlyd. I, II, and IIIe. none of the above

Assuming a patient has received IV loading dose of Drug X 1000mg. Immediatelyafter the dose was given the

concentration was 25mg/L and 22 hours after the dose was given the concentration was 2mg/L. When given

orally drug X is 95% metabolized via first past effect. (Use this information for questions 25-27)

25.Base on the information directly above, what is the elimination rate constant of Drug X? k = ln (2/25)* -1 = 0.114806 -h

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26.Base on the information directly above, what is the half life of Drug X?t1/2= 0.693/0.067919

h = 6.036585 -h

27.Base on the information directly above, what is the clearance of Drug X? VD = 1000mg = 40 L CL = 40 L * 0.114806 =4.592L/h

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28.Write out the equation for adjusted dosing weight and give the range for the correction factors ADW = IBW + CF (ABW IBW) CF = 0.1 0.4


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29.Which of the following is true in Zero Order Kineticsa. Amount of drug eliminated at a set time is constant, regardless of the amount of drug in the body.b. Fraction or percent eliminated does not vary.c. Non-lineard. All of the above are truee. A and C only are true

30.Ionized drugs are completely inhibited from crossing the cell or plasma membrane and will never cross?a. Trueb. False

Pharmacokinetics+-+Exam+3+spr+2012+answer+key

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