NBME 23 28.8 (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 2/Question#15 (reveal difficulty score)
A child with septicemia has an antibiotic ...
28.8 🔍 / 📺 / 🌳 / 📖
tags: phama_calc pharm_calc

+30 upvote downvote
submitted by ∗wired-in(81)

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Maintenance dose formula is (Css × Cl × tau) ÷ F

where Css is steady-state target plasma conc. of drug, Cl is clearance, tau is dosage interval & F is bioavailability.

Neither dosage interval nor bioavailability is given, so ignoring those & plugging in the numbers (careful to convert units to mg/kg/day):

=(12 ug/mL × 1 mg/1000 ug) × (0.09 L/hr/kg × 1000 mL/1 L × 24 hr/1 day)
= 25.92 mg/kg/day

...which isn't any of the answer choices listed. They must have rounded 0.09 L/hr/kg to 0.1 L/hr/kg, and doing so gives exactly 28.8 mg/kg/day (choice C)

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lispectedwumbologist That's so infuriating I stared at this question for 20 minutes thinking I did something wrong +85

hyoid ^^^^^ +13

seagull lol..my math never worked either. I also just chose the closest number. also, screw this question author for doing that. +10

praderwilli Big mad +10

ht3 this is why you never waste 7 minutes on a question.... because of shit like this +9

yotsubato Why the FUCK did they not just give us a clearance of 0.1 if they're going to fuckin round it anyways... +21

bigjimbo JOKES +1

cr in ur maths, why did u put 24h/1day and not 1day/24h? if the given Cl was 0.09L/hr/kg. I know it just is a math question, but i´d appreciate if someone could explain it. +1

d_holles LMAO games NBME plays +3

hyperfukus magic math!!!!! how TF r we supposed to know when they round and when they don't like wtf im so pissed someone please tell me step isn't like this...with such precise decimal answers and a calculator fxn you would assume they wanted an actual answer! +1

jean_young2019 OMG, I've got the 25.92 mg/kg/day, which isn't any of the answer choices listed. So I chose the D 51.8, because 51.8 is double of 25.9......I thought I must have make a mistake during the calculation ...... +7

atbangura They purposely did that so if you made a mistake with your conversion like I did, you might end up with 2.5 which was one of the answer choices. SMH +7

titanesxvi I did well, but I thought that my mistake was something to do with the conversion and end up choosing 2.5 because it is similar to 25.92 +4

makinallkindzofgainz The fact that we pay these people 60 dollars a pop for poorly formatted and written exams boggles my mind, and yet here I am, about to buy Form 24 +23

qball Me after plugging in the right numbers and not rounding down : https://i.kym-cdn.com/entries/icons/original/000/028/539/DyqSKoaX4AATc2G.jpg +1

frustratedllama Not only do you feel like you're doing sth wrong but then that feeling stays for other questions. sucks so baad +1

fexx 'here.. take 50mg of vyvanse.. I just rounded it up from 30.. dw you'll be fine' (totally doing this with my patients 8-)) +1

cbreland I was so close to picking 2.5 because I thought I did a conversion error. 5 minutes later and still didn't feel comfortable picking 28.8😡 +

yesa 12ug/ml = 12mg/L; 12mg/L x .1L/hr/kg x 24hr/day = 28.8. No need to multiple numerators and denominators by 1000s +

chaosawaits What really grinds my gears is that 3/5 answer choices are closely related to using 0.09 instead of 0.1 (A is 25.92/10, D is 25.92*2, and B is D/10). So basically, we're supposed to know to round 0.09 up to 0.1 but also to not round 12 down to 10. Okay? +

impostersyndromel1000 so you're telling me that I did all my math correctly, got 25.92 then thought I was off by a decimal point and chose 2.5 bc 25.9 wasn't an option and I was actually correct in my math but wrong bc THEY DIDNT PUT THE RIGHT ANSWER? Why is NBME so trash? I hope real exam isnt this bad. +1

+9 upvote downvote
submitted by ∗hungrybox(1277)

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Fucking NBME test writers lmao

Me: "Wait... isn't the answer 25.9? How come I don't see it here."

NBME: "Oh yeah, we rounded it."

Me: "To 30? I don't see that here, either..."

NBME: "No, to 28.8"

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tyrionwill When I got 25.9 and found nothing exactly matched, I guessed that the maintenance dose might be a bit more due to the bioavailability. So this antibiotic probably was not an I.V. formula, but an oral one, with a roughly 90% BA. +2

eradionova Well then it could have been equally likely that it had a 50% BA and the answer would be 51.8 exactly. I almost considered picking that but in the end stuck with the one that was closest to my answer lol +2

+6 upvote downvote
submitted by ∗paperbackwriter(161)

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can we all agree this was far too much math and unit conversion, WHY THE UNIT CONVERSIONS!?! WE ALL CLEARLY PASSED CHEM 101

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+2 upvote downvote
submitted by ∗anechakfspb(77)

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In the question they also don't say whether the antibiotic is administered IV or orally. For an IV dose, F = 100%. For an oral dose, F is typically <100% (FA 2019 p. 233). Based on this, IV maintenance dose would be 25.92 mg/kg/day. However, it is possible that the antibiotic is being given orally and F is closer to 90% (just an example). If this is true, the maintenance dose would be 25.92/0.90 = 28.8. This is obviously based on assumptions, but hopefully another way to explain why the answer is not exactly 25.92.

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veryhungrycaterpillar Oral antibiotics for septicemia? None of the Step 1 question writers are medical doctors, so this actually makes sense. +1

+1 upvote downvote
submitted by ∗hyperfukus(111)

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so should we just skip these? cuz there's prob 10 more i couldve gotten write wasting my life on this one

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faus305 Don't skip it but flag it, give yourself 1 minute and 30 seconds or less to figure it out and if you don't then move on and come back if you have time. Questions like these are what I like to call "time wasters." I got it wrong because I selected 2.5 assuming I made a conversion error when I arrived at 25.9 as my answer. I think the lesson to learn here is that 28 is closer to 25 than 2.5 and NBME are evil people that know I'm not gonna make a conversion error. If you do math in a question and you are SURE you did it write, select the answer closest to the answer your math got you. +

+0 upvote downvote
submitted by ∗isaacyo94(13)

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Another weird thing with this question is that if you multiple the actual answer (25.9) by 2, it gives you exactly 51.8. I did that and almost chose D because of it.

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+0 upvote downvote
submitted by docred123(9)

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Hey can someone please explain this! I am not sure how to do the math, I keep getting tripped up.

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mousie Equation is Maintenance dose = (concentration at steady state) * (Clearance) if you convert all the units to what it wanted them in (mg/kg/day) you'll get 25.92 like weird-in said above I didn't think to round 0.09 to 0.1 of course so I guessed 2.5 assuming I must have done a conversion wrong and was off by a tenth .... BOO bad Q +4

hyperfukus OMG ME TOO!!!!! +

-1 upvote downvote
submitted by ∗diabetes(31)

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12Mg/ml=12mg/L 120.09=1.08 mg/hr/kg 1.0824=25.92 mg/day/kg the nearest nanswer is 28.8

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