PHA 5128 Answer CASE STUDY 3 Question #1: Model

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Ethelbert Nichols
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1 PHA 5128 Answr CASE STUDY 3 Spring 2008 Qustion #1: Aminoglycosids hav a triphasic disposition, but tobramycin concntration-tim profil hr is dscribd via a 2-compartmnt modl sinc th alpha phas could not b charactrizd in th study as in th Figur. Which of th following statmnts is tru? Modl A) Th fast alpha phas is du to th tobramycin passiv diffusion into th clls. B) Th scond phas for tobramycin in this 2-compartmnt modl rprsnts th rturn from th dp compartmnt for aminoglycosids. C) Patints with rnal impairmnt will hav th sam profils sinc tobramycin is mainly liminatd via livr. D) Tobramycin is quickly liminatd from body as indicatd by th flat scond phas in th curv. E) Non of Abov. 1

2 Qustion #2: Discuss why th sampling tim is important to monitor aminoglycosid administration. Plas includ why it is important for th nurs to rcord th xact sampling tim, and whn pak and trough lvls should b drawn. Answr: Th sampling tim is of grat importanc in aminoglycosid administration sinc aminoglycosids hav a small but significant distribution phas. Th most widly accptd mthod is to sampl 1 hour aftr th maintnanc dos has bn initiatd (for a 30 min infusion that would man 30 min aftr th infusion is stoppd). Trough concntrations ar usually obtaind in th half hour bfor th nxt maintnanc dos. It is important to rcord th xact sampling tim, so th clinical pak and trough (sampld 30 aftr nding th infusion and 30 min bfor th nxt maintnanc dos) concntrations can b xtrapolatd to th tru pak and trough concntrations. 2

3 Qustion #3: Vancomycin concntration-tim profil can b dscribd via a thr compartmnt modl. Which profil will rprsnt a 1-hr infusion of vancomycin in th following graph? Answr: (C ) 3

4 Qustion #4: GD, a 75 yar old mal (6 3, 94kg, Cl30mL/min, Vd0.7L/kg), has bn mpirically startd on 500mg vancomycin vry 8hours (multipl i.v. bolus) for th tratmnt of a community acquird Strptococcus pnumonia infction. What would b th xpctd stady-stat pak and trough vancomycin concntrations for GD? Discuss th rsults. What will b th nw dos rgimn to achiv xpct pak concntration (26 mg/l) and tough concntration at stady-stat (11 mg/l)? Answr: V d 0.178ag TBW ( L) Cl 30mL / min 1.8L / h k Cl V d 1.8L / h 0.037h 49L 1 t 1 2 ln h h C C τ τ min D Vd k tau ( 1 ) C k tau 500mg 49L h 8h mg 39.8 L 1 mg 39.8 L h 8h C ln( 26 ) Ln( ) / k ( hr) ~ 24hr C min C ln( 26 ) Ln( ) / k ( hr) ~ 24hr C min k τ D Vd C (1 ) (1 ) 750 mg Q24h mg 29.6 L 750( mg) 4

5 Qustion #5: Drug A is a basic drug. Rcntly, protin binding studis wr prformd in both in vivo (patints with malaria, and plasma AAG concntrations wr consistntly raisd in acut malaria) and in vitro. Th rsults wr shown in Figur 1. A linar rlationship btwn log alpha 1-acid glycoprotin (AAG) concntration and prcntag of fr drug A in vivo was idntifid, which was similar to that obtaind by in vitro addition of AAG to plasma containing drug A (10 mg/l). Thr was no rlation btwn plasma albumin and fr fraction of drug A. Which of following statmnt is FALSE? Figur 1 Rlationship of drug A plasma protin binding (fr/total concntrations; %) to plasma AAG concntration from in vivo study (opn circls). Th closd circls rprsnt in vitro addition of AGP to a plasma sampl containing drug A (10 mg/l) and AAG 0.7 g/l A: Fr drug concntrations will not b affctd if drug A is a low xtraction drug and protin binding changs. 5

6 B: Prcnt of drug A protin binding is much highr in th halthy ldrly than that in th halthy young. C: AAG is an acut phas protin, and is th principal binding protin for drug A. D: If drug A is a high xtraction drug, dos adjustmnt is ndd for patints with highr AAG concntrations in ordr to achiv thraputic ffcts. E: Nwborns hav low protin binding of drug A bcaus of low concntrations of AAG in plasma. Answr: Ag has no ffct on alpha 1-acid glycoprotin concntration, whras plasma albumin lvls dcrasd as a function of ag in both sxs (Plas rfr to Griatrics Slid #11). Fr drug concntration rlats to protin binding fraction as a high xtraction drug. Fr drug concntration dos not dpnd on protin binding fraction as a low xtraction drug. Nwborns hav lowr AAG (Plas rfr to Pdiatric Slid # 21). 6

Answer Homework 5 PHA5127 Fall 1999 Jeff Stark

Answer Homework 5 PHA5127 Fall 1999 Jeff Stark Answr omwork 5 PA527 Fall 999 Jff Stark A patint is bing tratd with Drug X in a clinical stting. Upon admiion, an IV bolus dos of 000mg was givn which yildd an initial concntration of 5.56 µg/ml. A fw