Case Study 1 PHA 5127 Fall 2006 Revised 9/19/06

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Georgiana Boone
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1 Cas Study Qustion. A 3 yar old, 5 kg patint was brougt in for surgry and was givn a /kg iv bolus injction of a muscl rlaxant. T plasma concntrations wr masurd post injction and notd in t tabl blow: Tim () Plasma Conc. (/) Dtrmin t following parmacokintic paramtrs of t drug for tis patint: Bfor w bgin to dtrmin t parmacokintic paramtrs, w nd to know wat limination procss t drug is following. If w plot t data points from t tabl abov, w would gt t following: Plasma Concntration (/m) Tim (rs) Notic, w do not gt a straigt curv, so w cannot assum tat t drug is following a zro ordr limination procss.

2 Cas Study t s plot t data on a smi-log scal: Plasma Concntration (/m) Tim (rs) Notic w do gt a fairly straigt lin, so w can assum tat tis drug follows a firstordr limination procss. a) T limination rat constant (k ). Tr ar svral ways to gt k. T following just gos ovr two mtods: I. Plot t abov data points on a smi-log papr (wit tim on t x-axis and plasma conc. on t y-axis) and draw a straigt lin tru t data points. Slct two data sts on t lin and plug into quation as sown blow. Say from t straigt lin, w gt t concntration at 4 rs wic is 5 / and at 6 rs wic is 5 /. ln 5 ln 5 ln ln C C k.r t t 6r 4r II. You can also us xcl. Plot t tim on t x-axis and t ln(plasma Conc.) on t y-axis and put a trndlin tru t data points. Wn you slct t trndlin option, you sould also b abl to gt t quation of t trndlin wic in tis cas is ln( C) k t + ln( Co ). t From tis quation you gt k. r -

3 Cas Study Plas not, it usually is bttr to slct data points from t trndlin/lin drawn to us for your calculations sinc t data may not always b prfct and fall on t trndlin/bst-fit-curv prfctly. Tis is wy som popl gt two diffrnt k wn slcting two diffrnt data sts straigt from t tabl. b) T alf lif (t / ). ln() t 3.4r k k.r c) T initial plasma drug concntration (C o ). Plas not tat t rout of administration is i.v. bolus! Again, tr ar svral ways to gt C o. T following just gos ovr two mtods: I. Using t smi-log plottd mtod, xtnd t straigt lin tru t y-axis and t concntration at t y-axis, wn t rs, is C wic in tis cas is /. II. Using t trndlin xcl quation, you gt ln( C ) 4. 7, so C o /. o d) T volum of distribution (V d ). 5kg Dos kg 5 V d 3. 6 C ) T ara undr t curv ( ) using t trapzoidal rul. First start by gtting t concntration at constant tim intrvals say, 4, 8,, 6, and rs. You can t data points by i) rading tm off t straigt lin plottd on t smi-log papr or ii) by using t trndlin quation. T data points ar as follows: Tim (rs) Concntration (/) T calculations for ar as follows:

4 t t Cas Study Ct + C t ( t t) 5 + (4r r) 3 r 44 r r 64 r 3 r 4 C r k.r r r ( ) 58 + f) At ours aftr injction, wat is t plasma drug concntration? r k t C C. r 74 Qustion. Following ar t pysicocmical proprtis of tr drugs: Proprty Drug A Drug B Drug C Molcular Wigt , pka Nutral Bas - Polarity of unionizd form Non-polar Polar Protin T muscl would most likly tak up wic of t abov mntiond drugs? Wy? Wat typ of distribution (prfusion or prmability) limits t otr drugs? T muscl would most likly tak up Drug A du to its small molcular wigt and no carg. Prmability distribution limits t otr drugs (i.. t carg for Drug B and t ig molcular wigt for Drug C).

5 Cas Study Qustion 3. Wic of t following statmnts bst dscribs a zro-ordr or first-ordr procss: a) T sam fraction of drug is liminatd during a givn tim intrval. First-ordr. S slid 3 in ppt nots. b) T sam amount of drug is liminatd during a givn tim intrval. Zro-ordr. S slid 33 in ppt nots. c) T tim vs. plasma drug concntration profil is as follows: Concntration Tim First-ordr. Not tat y-axis is on a smi-log scal.

PHA 5127 Answers Homework 2 Fall 2001

PHA 5127 Answers Homework 2 Fall 2001 PH 5127 nswrs Homwork 2 Fall 2001 OK, bfor you rad th answrs, many of you spnt a lot of tim on this homwork. Plas, nxt tim if you hav qustions plas com talk/ask us. Thr is no nd to suffr (wll a littl suffring