Morning Rounds \u00b7 Pharmacokinetics \u00b7 Round 04<\/title>\n<link href=\"https:\/\/fonts.googleapis.com\/css2?family=Playfair+Display:ital,wght@0,400;0,600;0,700;1,400;1,600&family=Source+Serif+4:ital,wght@0,300;0,400;0,600;1,400&display=swap\" rel=\"stylesheet\">\n<style>\n#npk04 *,#npk04 *::before,#npk04 *::after{box-sizing:border-box;margin:0;padding:0}\n#npk04{\n --ob:#1A5F7A;--ob-light:#236E8C;--ob-pale:#E6F3F7;--ob-dark:#114455;\n --correct:#2D6B47;--correct-bg:#EAF6EF;--correct-border:#3A9960;\n --wrong:#B83232;--wrong-bg:#FDF0F0;--wrong-border:#E53935;\n --ink:#0F2A35;--ink-mid:#2A4D5A;--ink-soft:#5A7D8A;\n --line:#B8D8E3;--cream:#F2F8FA;--warm:#F8FCFD;\n font-family:'Source Serif 4',Georgia,serif;\n font-size:16px;color:var(--ink);background:var(--cream);\n line-height:1.7;padding:0 0 64px;\n}\n#npk04 .mr-header{background:linear-gradient(135deg,var(--ob-dark) 0%,var(--ob) 60%,var(--ob-light) 100%);color:#E4F4F9;padding:36px 24px 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.mr-band-c{background:var(--correct-bg);color:var(--correct)}\n#npk04 .mr-band-w{background:var(--wrong-bg);color:var(--wrong)}\n#npk04 .mr-band-s{background:var(--ob-pale);color:var(--ob)}\n#npk04 .mr-retry{display:block;margin:18px auto 4px;background:transparent;border:2px solid var(--ob);color:var(--ob);border-radius:8px;padding:9px 28px;font-family:'Playfair Display',serif;font-size:0.92rem;font-weight:700;cursor:pointer;}\n#npk04 .mr-retry:hover{background:var(--ob);color:#E4F4F9}\n@media(max-width:480px){\n #npk04 .mr-title{font-size:1.4rem}\n #npk04 .mr-num{font-size:1.7rem}\n #npk04 .mr-stem{font-size:0.9rem}\n #npk04 .mr-opt-text{font-size:0.86rem}\n}\n<\/style>\n\n<div id=\"npk04\">\n\n <div class=\"mr-header\">\n <div class=\"mr-series-tag\">Numerical Series · Pharmacokinetics<\/div>\n <div class=\"mr-eyebrow\">Morning Rounds · Round 04 of 07<\/div>\n <div class=\"mr-title\">Clearance &<br><em>Steady-State Concentration<\/em><\/div>\n <div class=\"mr-subtitle\">Five calculations · Infusion rates, units traps, renal clearance & the Css formula<\/div>\n <div class=\"mr-chips\">\n <span class=\"mr-chip\">5 Questions<\/span>\n <span class=\"mr-chip\">+4 \/ −1 scoring<\/span>\n <span class=\"mr-chip\">Options reshuffled<\/span>\n <\/div>\n <\/div>\n\n <div class=\"mr-sentinel\" id=\"npk04-sentinel\"><\/div>\n\n <div class=\"mr-progress\" id=\"npk04-progress\">\n <div class=\"mr-prog-inner\">\n <div class=\"mr-pips\" id=\"npk04-pips\"><\/div>\n <\/div>\n <\/div>\n\n <div class=\"mr-body\">\n <div id=\"npk04-cases\"><\/div>\n <div class=\"mr-submit-wrap\">\n <button class=\"mr-btn\" id=\"npk04-submit\">Submit for Debrief<\/button>\n <\/div>\n <div class=\"mr-score\" id=\"npk04-score\">\n <div class=\"mr-score-in\">\n <div class=\"mr-score-ey\">Round Complete<\/div>\n <div class=\"mr-ring\" id=\"npk04-ring\">\n <div class=\"mr-ring-in\">\n <span class=\"mr-ring-pct\" id=\"npk04-pct\">0%<\/span>\n <span class=\"mr-ring-sub\">net<\/span>\n <\/div>\n <\/div>\n <div class=\"mr-score-title\">Your Debrief<\/div>\n <div class=\"mr-score-net\" id=\"npk04-net\"><\/div>\n <div class=\"mr-verdict\" id=\"npk04-verdict\"><\/div>\n <div class=\"mr-bands\">\n <span class=\"mr-band mr-band-c\" id=\"npk04-ct-c\"><\/span>\n <span class=\"mr-band mr-band-w\" id=\"npk04-ct-w\"><\/span>\n <span class=\"mr-band mr-band-s\" id=\"npk04-ct-s\"><\/span>\n <\/div>\n <button class=\"mr-retry\" id=\"npk04-retry\">↻ New Round<\/button>\n <\/div>\n <\/div>\n <\/div>\n\n<\/div>\n\n<script>\n(function () {\n 'use strict';\n\n var NS = 'npk04';\n var TOTAL = 5;\n var MAX = 20;\n var LTRS = ['A','B','C','D'];\n\n var QS = [\n\n {\n id: 1,\n tag: 'Steady State — Infusion Rate ÷ Clearance',\n stem: 'Drug Y is infused at <strong>200 mg\/hour<\/strong>. Its clearance is <strong>100 mL\/min<\/strong>. What is the <strong>steady-state plasma concentration (C<sub>ss<\/sub>)<\/strong>?',\n correct: '33.33 mg\/L',\n opts: [\n '33.33 mg\/L',\n '50 mg\/L',\n '2 mg\/L',\n '200 mg\/L'\n ],\n exp: 'Formula: <strong>C<sub>ss<\/sub> = Infusion rate ÷ Clearance<\/strong>. The trap here is a <strong>units mismatch<\/strong> — infusion rate is in mg\/hour, clearance is in mL\/min. Convert first.<span class=\"calc\">Clearance: 100 mL\/min × 60 min\/hr = <strong>6000 mL\/hr = 6 L\/hr<\/strong><br><br>C<sub>ss<\/sub> = 200 mg\/hr ÷ 6 L\/hr = <strong>33.33 mg\/L<\/strong><\/span>The distractor 50 mg\/L comes from dividing 200 by 4 (confusing 100 mL\/min with L\/hr directly). The distractor 2 mg\/L comes from dividing by 100 without unit conversion. This question appeared in your original Telegram set — the unit conversion is the entire exam point. Always reconcile time units (per hour vs per minute) and volume units (mL vs L) before dividing.'\n },\n\n {\n id: 2,\n tag: 'Clearance — Basic Definition & Calculation',\n stem: 'A drug has a <strong>volume of distribution of 50 L<\/strong> and a <strong>half-life of 5 hours<\/strong>. What is its <strong>total body clearance<\/strong>?',\n correct: '6.93 L\/hour',\n opts: [\n '6.93 L\/hour',\n '10 L\/hour',\n '0.693 L\/hour',\n '250 mL\/min'\n ],\n exp: 'Clearance links Vd and half-life via the elimination rate constant:<span class=\"calc\">k = 0.693 ÷ t½ = 0.693 ÷ 5 hr = 0.1386 hr−1<br><br>Clearance (CL) = k × Vd<br>= 0.1386 hr−1 × 50 L<br>= <strong>6.93 L\/hr<\/strong><\/span>This is the fundamental relationship: <strong>CL = 0.693 × Vd ÷ t½<\/strong>. Rearranged, it gives you t½ = 0.693 × Vd ÷ CL — which explains why half-life increases when Vd rises (drug accumulates in tissues) or when CL falls (organ failure). The distractor 10 L\/hr comes from dividing 50 by 5 without the 0.693 factor. The distractor 250 mL\/min is a unit-converted version of 15 L\/hr — wrong calculation but plausible-looking units.'\n },\n\n {\n id: 3,\n tag: 'Renal Clearance — Dose Adjustment in Renal Failure',\n stem: 'A drug is <strong>100% renally excreted<\/strong> with normal renal clearance of <strong>120 mL\/min<\/strong>. A patient has a GFR of <strong>30 mL\/min<\/strong> (25% of normal). If the usual dose is <strong>400 mg every 8 hours<\/strong>, what is the most appropriate dose adjustment?',\n correct: '100 mg every 8 hours (reduce dose to 25% of normal)',\n opts: [\n '100 mg every 8 hours (reduce dose to 25% of normal)',\n '400 mg every 32 hours (extend interval to 4 times normal)',\n '200 mg every 16 hours (halve dose and double interval)',\n '400 mg every 8 hours; no adjustment needed as the liver compensates'\n ],\n exp: 'When a drug is <strong>100% renally cleared<\/strong>, clearance falls proportionally with GFR.<span class=\"calc\">Residual function = 30 ÷ 120 = <strong>25% of normal clearance<\/strong><\/span>Two strategies exist for dose adjustment in renal failure:<br><br><strong>1. Dose reduction<\/strong> (keep interval, reduce dose): 25% of 400 mg = <strong>100 mg every 8 hours<\/strong> — maintains the same dosing frequency, lowers peak and trough proportionally.<br><br><strong>2. Interval extension<\/strong> (keep dose, extend interval): give 400 mg every 8 ÷ 0.25 = <strong>32 hours<\/strong>.<br><br>Both are pharmacokinetically valid; the choice depends on whether the drug needs stable levels (aminoglycosides prefer interval extension to allow trough-driven toxicity monitoring). The liver does <em>not<\/em> compensate for renal clearance of renally-excreted drugs — trap D is dangerous clinical reasoning.'\n },\n\n {\n id: 4,\n tag: 'Clearance — Hepatic Extraction & First-Pass',\n stem: 'Drug A has a <strong>hepatic extraction ratio of 0.9<\/strong> (high extraction). Drug B has a <strong>hepatic extraction ratio of 0.1<\/strong> (low extraction). A patient develops <strong>severe liver cirrhosis<\/strong> with reduced liver blood flow. Which drug\\'s oral bioavailability is <strong>most dramatically increased<\/strong>, and why?',\n correct: 'Drug A; high-extraction drugs depend on liver blood flow for first-pass metabolism, so reduced flow in cirrhosis dramatically increases oral bioavailability',\n opts: [\n 'Drug A; high-extraction drugs depend on liver blood flow for first-pass metabolism, so reduced flow in cirrhosis dramatically increases oral bioavailability',\n 'Drug B; low-extraction drugs are more sensitive to changes in liver blood flow because they are not efficiently cleared even under normal conditions',\n 'Both equally; liver cirrhosis reduces hepatic enzyme activity uniformly regardless of extraction ratio, affecting all drugs proportionally',\n 'Drug A; high-extraction drugs have poor oral bioavailability normally because they are rapidly cleared by renal excretion, which is impaired in cirrhosis'\n ],\n exp: 'This is the <strong>flow-dependent vs capacity-dependent clearance<\/strong> distinction — a high-yield conceptual question.<br><br><strong>High-extraction drugs (ER > 0.7)<\/strong>: clearance = liver blood flow. Nearly all drug presented to the liver is extracted in one pass. Oral bioavailability is normally very low (e.g. propranolol ~25%, morphine ~25%, lignocaine ~35%). In cirrhosis, <em>two things happen<\/em>: (1) reduced blood flow → less first-pass; (2) portosystemic shunting bypasses the liver entirely. Result: <strong>dramatic rise in bioavailability<\/strong> → toxicity on normal doses.<br><br><strong>Low-extraction drugs (ER < 0.3)<\/strong>: clearance depends on enzyme capacity, not blood flow. Cirrhosis does reduce enzyme activity, but the effect on bioavailability is modest because first-pass was never dramatic to begin with (e.g. warfarin, diazepam).<br><br>Exam anchor: <strong>propranolol, morphine, lignocaine, labetalol<\/strong> = high extraction = dangerous in cirrhosis.'\n },\n\n {\n id: 5,\n tag: 'Steady State — Effect of Changing Infusion Rate',\n stem: 'A patient is receiving Drug Z at <strong>60 mg\/hour<\/strong> and has reached steady-state plasma concentration of <strong>10 mg\/L<\/strong>. The infusion rate is doubled to <strong>120 mg\/hour<\/strong>. What will the <strong>new steady-state concentration<\/strong> be, and how long will it take to reach it?',\n correct: '20 mg\/L; the time to reach the new steady state is still 4–5 half-lives of the drug',\n opts: [\n '20 mg\/L; the time to reach the new steady state is still 4–5 half-lives of the drug',\n '20 mg\/L; the new steady state is reached immediately because the patient is already at equilibrium',\n '40 mg\/L; doubling the infusion rate quadruples the steady-state concentration due to non-linear kinetics',\n '15 mg\/L; the new steady state is the average of the old concentration and the theoretical maximum'\n ],\n exp: 'Two separate facts tested here simultaneously:<br><br><strong>Fact 1 — New C<sub>ss<\/sub>:<\/strong> In first-order kinetics, C<sub>ss<\/sub> is directly proportional to infusion rate.<span class=\"calc\">New C<sub>ss<\/sub> = Old C<sub>ss<\/sub> × (New rate ÷ Old rate)<br>= 10 mg\/L × (120 ÷ 60)<br>= <strong>20 mg\/L<\/strong><\/span><strong>Fact 2 — Time to new steady state:<\/strong> This is the one candidates get wrong. Being at steady state does <em>not<\/em> mean you reach the new steady state instantly. The system must re-equilibrate, and this always takes <strong>4–5 half-lives<\/strong> from the moment of the rate change — the same as starting from zero.<br><br>Trap C (quadrupling) would be true for <strong>zero-order kinetics<\/strong> or Michaelis-Menten saturation — where doubling dose causes disproportionate concentration rise. Phenytoin at high doses behaves this way, which is why phenytoin dose adjustments must be small and cautious.'\n }\n\n ];\n\n var answers = {}, answered = 0, shuffled = {}, done = false;\n\n function gid(s) { return document.getElementById(NS + '-' + s); }\n function byId(s) { return document.getElementById(s); }\n\n function shuffleArr(arr) {\n var a = arr.slice(), i, j, t;\n for (i = a.length - 1; i > 0; i--) {\n j = Math.floor(Math.random() * (i + 1));\n t = a[i]; a[i] = a[j]; a[j] = t;\n }\n return a;\n }\n\n function countVal(v) {\n var n = 0, k;\n for (k in answers) { if (answers[k] === v) n++; }\n return n;\n }\n\n function buildPips() {\n var cont = gid('pips'), i, q, wLine, wPip, line, pip;\n cont.innerHTML = '';\n for (i = 0; i < QS.length; i++) {\n q = QS[i];\n if (i > 0) {\n wLine = document.createElement('div');\n wLine.className = 'mr-pip-wrap';\n line = document.createElement('div');\n line.className = 'mr-pip-line';\n line.id = NS + '-pl' + q.id;\n wLine.appendChild(line);\n cont.appendChild(wLine);\n }\n wPip = document.createElement('div');\n wPip.className = 'mr-pip-wrap';\n pip = document.createElement('div');\n pip.className = 'mr-pip';\n pip.id = NS + '-pip' + q.id;\n pip.textContent = String(q.id);\n wPip.appendChild(pip);\n cont.appendChild(wPip);\n }\n }\n\n function build() {\n var cont, i, q, opts, card, top, numDiv, meta, tag, stem,\n rule, optsDiv, expDiv, lbl, txt, j, optEl, ltrSpan, txtSpan;\n\n cont = gid('cases');\n cont.innerHTML = '';\n answers = {}; answered = 0; shuffled = {}; done = false;\n gid('score').style.display = 'none';\n buildPips();\n\n for (i = 0; i < QS.length; i++) {\n q = QS[i];\n opts = shuffleArr(q.opts);\n shuffled[q.id] = opts;\n\n card = document.createElement('div');\n card.className = 'mr-case';\n\n top = document.createElement('div');\n top.className = 'mr-case-top';\n\n numDiv = document.createElement('div');\n numDiv.className = 'mr-num';\n numDiv.textContent = q.id < 10 ? 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'c' : 'w';\n answered++;\n\n for (i = 0; i < opts.length; i++) {\n el = byId(NS + '-o' + qid + '-' + i);\n if (opts[i] === q.correct) {\n el.className = 'mr-opt correct locked';\n } else if (i === oi) {\n el.className = 'mr-opt wrong locked';\n } else {\n el.className = 'mr-opt dimmed locked';\n }\n }\n\n byId(NS + '-exp' + qid).style.display = 'block';\n byId(NS + '-pip' + qid).className = 'mr-pip ' + (correct ? 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#npk04 .mr-opt-text{font-size:0.86rem}\n}\n<\/style>\n\n<div id=\"npk04\">\n\n <div class=\"mr-header\">\n <div class=\"mr-series-tag\">Numerical Series · Pharmacokinetics<\/div>\n <div class=\"mr-eyebrow\">Morning Rounds · Round 04 of 07<\/div>\n <div class=\"mr-title\">Clearance &<br><em>Steady-State Concentration<\/em><\/div>\n <div class=\"mr-subtitle\">Five calculations · Infusion rates, units traps, renal clearance & the Css formula<\/div>\n <div class=\"mr-chips\">\n <span class=\"mr-chip\">5 Questions<\/span>\n <span class=\"mr-chip\">+4 \/ −1 scoring<\/span>\n <span class=\"mr-chip\">Options reshuffled<\/span>\n <\/div>\n <\/div>\n\n <div class=\"mr-sentinel\" id=\"npk04-sentinel\"><\/div>\n\n <div class=\"mr-progress\" id=\"npk04-progress\">\n <div class=\"mr-prog-inner\">\n <div class=\"mr-pips\" id=\"npk04-pips\"><\/div>\n <\/div>\n <\/div>\n\n <div class=\"mr-body\">\n <div id=\"npk04-cases\"><\/div>\n <div class=\"mr-submit-wrap\">\n <button class=\"mr-btn\" id=\"npk04-submit\">Submit for Debrief<\/button>\n <\/div>\n <div class=\"mr-score\" id=\"npk04-score\">\n <div class=\"mr-score-in\">\n <div class=\"mr-score-ey\">Round Complete<\/div>\n <div class=\"mr-ring\" id=\"npk04-ring\">\n <div class=\"mr-ring-in\">\n <span class=\"mr-ring-pct\" id=\"npk04-pct\">0%<\/span>\n <span class=\"mr-ring-sub\">net<\/span>\n <\/div>\n <\/div>\n <div class=\"mr-score-title\">Your Debrief<\/div>\n <div class=\"mr-score-net\" id=\"npk04-net\"><\/div>\n <div class=\"mr-verdict\" id=\"npk04-verdict\"><\/div>\n <div class=\"mr-bands\">\n <span class=\"mr-band mr-band-c\" id=\"npk04-ct-c\"><\/span>\n <span class=\"mr-band mr-band-w\" id=\"npk04-ct-w\"><\/span>\n <span class=\"mr-band mr-band-s\" id=\"npk04-ct-s\"><\/span>\n <\/div>\n <button class=\"mr-retry\" id=\"npk04-retry\">↻ New Round<\/button>\n <\/div>\n <\/div>\n <\/div>\n\n<\/div>\n\n<script>\n(function () {\n 'use strict';\n\n var NS = 'npk04';\n var TOTAL = 5;\n var MAX = 20;\n var LTRS = ['A','B','C','D'];\n\n var QS = [\n\n {\n id: 1,\n tag: 'Steady State — Infusion Rate ÷ Clearance',\n stem: 'Drug Y is infused at <strong>200 mg\/hour<\/strong>. Its clearance is <strong>100 mL\/min<\/strong>. What is the <strong>steady-state plasma concentration (C<sub>ss<\/sub>)<\/strong>?',\n correct: '33.33 mg\/L',\n opts: [\n '33.33 mg\/L',\n '50 mg\/L',\n '2 mg\/L',\n '200 mg\/L'\n ],\n exp: 'Formula: <strong>C<sub>ss<\/sub> = Infusion rate ÷ Clearance<\/strong>. The trap here is a <strong>units mismatch<\/strong> — infusion rate is in mg\/hour, clearance is in mL\/min. Convert first.<span class=\"calc\">Clearance: 100 mL\/min × 60 min\/hr = <strong>6000 mL\/hr = 6 L\/hr<\/strong><br><br>C<sub>ss<\/sub> = 200 mg\/hr ÷ 6 L\/hr = <strong>33.33 mg\/L<\/strong><\/span>The distractor 50 mg\/L comes from dividing 200 by 4 (confusing 100 mL\/min with L\/hr directly). The distractor 2 mg\/L comes from dividing by 100 without unit conversion. This question appeared in your original Telegram set — the unit conversion is the entire exam point. Always reconcile time units (per hour vs per minute) and volume units (mL vs L) before dividing.'\n },\n\n {\n id: 2,\n tag: 'Clearance — Basic Definition & Calculation',\n stem: 'A drug has a <strong>volume of distribution of 50 L<\/strong> and a <strong>half-life of 5 hours<\/strong>. What is its <strong>total body clearance<\/strong>?',\n correct: '6.93 L\/hour',\n opts: [\n '6.93 L\/hour',\n '10 L\/hour',\n '0.693 L\/hour',\n '250 mL\/min'\n ],\n exp: 'Clearance links Vd and half-life via the elimination rate constant:<span class=\"calc\">k = 0.693 ÷ t½ = 0.693 ÷ 5 hr = 0.1386 hr−1<br><br>Clearance (CL) = k × Vd<br>= 0.1386 hr−1 × 50 L<br>= <strong>6.93 L\/hr<\/strong><\/span>This is the fundamental relationship: <strong>CL = 0.693 × Vd ÷ t½<\/strong>. Rearranged, it gives you t½ = 0.693 × Vd ÷ CL — which explains why half-life increases when Vd rises (drug accumulates in tissues) or when CL falls (organ failure). The distractor 10 L\/hr comes from dividing 50 by 5 without the 0.693 factor. The distractor 250 mL\/min is a unit-converted version of 15 L\/hr — wrong calculation but plausible-looking units.'\n },\n\n {\n id: 3,\n tag: 'Renal Clearance — Dose Adjustment in Renal Failure',\n stem: 'A drug is <strong>100% renally excreted<\/strong> with normal renal clearance of <strong>120 mL\/min<\/strong>. A patient has a GFR of <strong>30 mL\/min<\/strong> (25% of normal). If the usual dose is <strong>400 mg every 8 hours<\/strong>, what is the most appropriate dose adjustment?',\n correct: '100 mg every 8 hours (reduce dose to 25% of normal)',\n opts: [\n '100 mg every 8 hours (reduce dose to 25% of normal)',\n '400 mg every 32 hours (extend interval to 4 times normal)',\n '200 mg every 16 hours (halve dose and double interval)',\n '400 mg every 8 hours; no adjustment needed as the liver compensates'\n ],\n exp: 'When a drug is <strong>100% renally cleared<\/strong>, clearance falls proportionally with GFR.<span class=\"calc\">Residual function = 30 ÷ 120 = <strong>25% of normal clearance<\/strong><\/span>Two strategies exist for dose adjustment in renal failure:<br><br><strong>1. Dose reduction<\/strong> (keep interval, reduce dose): 25% of 400 mg = <strong>100 mg every 8 hours<\/strong> — maintains the same dosing frequency, lowers peak and trough proportionally.<br><br><strong>2. Interval extension<\/strong> (keep dose, extend interval): give 400 mg every 8 ÷ 0.25 = <strong>32 hours<\/strong>.<br><br>Both are pharmacokinetically valid; the choice depends on whether the drug needs stable levels (aminoglycosides prefer interval extension to allow trough-driven toxicity monitoring). The liver does <em>not<\/em> compensate for renal clearance of renally-excreted drugs — trap D is dangerous clinical reasoning.'\n },\n\n {\n id: 4,\n tag: 'Clearance — Hepatic Extraction & First-Pass',\n stem: 'Drug A has a <strong>hepatic extraction ratio of 0.9<\/strong> (high extraction). Drug B has a <strong>hepatic extraction ratio of 0.1<\/strong> (low extraction). A patient develops <strong>severe liver cirrhosis<\/strong> with reduced liver blood flow. Which drug\\'s oral bioavailability is <strong>most dramatically increased<\/strong>, and why?',\n correct: 'Drug A; high-extraction drugs depend on liver blood flow for first-pass metabolism, so reduced flow in cirrhosis dramatically increases oral bioavailability',\n opts: [\n 'Drug A; high-extraction drugs depend on liver blood flow for first-pass metabolism, so reduced flow in cirrhosis dramatically increases oral bioavailability',\n 'Drug B; low-extraction drugs are more sensitive to changes in liver blood flow because they are not efficiently cleared even under normal conditions',\n 'Both equally; liver cirrhosis reduces hepatic enzyme activity uniformly regardless of extraction ratio, affecting all drugs proportionally',\n 'Drug A; high-extraction drugs have poor oral bioavailability normally because they are rapidly cleared by renal excretion, which is impaired in cirrhosis'\n ],\n exp: 'This is the <strong>flow-dependent vs capacity-dependent clearance<\/strong> distinction — a high-yield conceptual question.<br><br><strong>High-extraction drugs (ER > 0.7)<\/strong>: clearance = liver blood flow. Nearly all drug presented to the liver is extracted in one pass. Oral bioavailability is normally very low (e.g. propranolol ~25%, morphine ~25%, lignocaine ~35%). In cirrhosis, <em>two things happen<\/em>: (1) reduced blood flow → less first-pass; (2) portosystemic shunting bypasses the liver entirely. Result: <strong>dramatic rise in bioavailability<\/strong> → toxicity on normal doses.<br><br><strong>Low-extraction drugs (ER < 0.3)<\/strong>: clearance depends on enzyme capacity, not blood flow. Cirrhosis does reduce enzyme activity, but the effect on bioavailability is modest because first-pass was never dramatic to begin with (e.g. warfarin, diazepam).<br><br>Exam anchor: <strong>propranolol, morphine, lignocaine, labetalol<\/strong> = high extraction = dangerous in cirrhosis.'\n },\n\n {\n id: 5,\n tag: 'Steady State — Effect of Changing Infusion Rate',\n stem: 'A patient is receiving Drug Z at <strong>60 mg\/hour<\/strong> and has reached steady-state plasma concentration of <strong>10 mg\/L<\/strong>. The infusion rate is doubled to <strong>120 mg\/hour<\/strong>. What will the <strong>new steady-state concentration<\/strong> be, and how long will it take to reach it?',\n correct: '20 mg\/L; the time to reach the new steady state is still 4–5 half-lives of the drug',\n opts: [\n '20 mg\/L; the time to reach the new steady state is still 4–5 half-lives of the drug',\n '20 mg\/L; the new steady state is reached immediately because the patient is already at equilibrium',\n '40 mg\/L; doubling the infusion rate quadruples the steady-state concentration due to non-linear kinetics',\n '15 mg\/L; the new steady state is the average of the old concentration and the theoretical maximum'\n ],\n exp: 'Two separate facts tested here simultaneously:<br><br><strong>Fact 1 — New C<sub>ss<\/sub>:<\/strong> In first-order kinetics, C<sub>ss<\/sub> is directly proportional to infusion rate.<span class=\"calc\">New C<sub>ss<\/sub> = Old C<sub>ss<\/sub> × (New rate ÷ Old rate)<br>= 10 mg\/L × (120 ÷ 60)<br>= <strong>20 mg\/L<\/strong><\/span><strong>Fact 2 — Time to new steady state:<\/strong> This is the one candidates get wrong. Being at steady state does <em>not<\/em> mean you reach the new steady state instantly. The system must re-equilibrate, and this always takes <strong>4–5 half-lives<\/strong> from the moment of the rate change — the same as starting from zero.<br><br>Trap C (quadrupling) would be true for <strong>zero-order kinetics<\/strong> or Michaelis-Menten saturation — where doubling dose causes disproportionate concentration rise. Phenytoin at high doses behaves this way, which is why phenytoin dose adjustments must be small and cautious.'\n }\n\n ];\n\n var answers = {}, answered = 0, shuffled = {}, done = false;\n\n function gid(s) { return document.getElementById(NS + '-' + s); }\n function byId(s) { return document.getElementById(s); }\n\n function shuffleArr(arr) {\n var a = arr.slice(), i, j, t;\n for (i = a.length - 1; i > 0; i--) {\n j = Math.floor(Math.random() * (i + 1));\n t = a[i]; a[i] = a[j]; a[j] = t;\n }\n return a;\n }\n\n function countVal(v) {\n var n = 0, k;\n for (k in answers) { if (answers[k] === v) n++; }\n return n;\n }\n\n function buildPips() {\n var cont = gid('pips'), i, q, wLine, wPip, line, pip;\n cont.innerHTML = '';\n for (i = 0; i < QS.length; i++) {\n q = QS[i];\n if (i > 0) {\n wLine = document.createElement('div');\n wLine.className = 'mr-pip-wrap';\n line = document.createElement('div');\n line.className = 'mr-pip-line';\n line.id = NS + '-pl' + q.id;\n wLine.appendChild(line);\n cont.appendChild(wLine);\n }\n wPip = document.createElement('div');\n wPip.className = 'mr-pip-wrap';\n pip = document.createElement('div');\n pip.className = 'mr-pip';\n pip.id = NS + '-pip' + q.id;\n pip.textContent = String(q.id);\n wPip.appendChild(pip);\n cont.appendChild(wPip);\n }\n }\n\n function build() {\n var cont, i, q, opts, card, top, numDiv, meta, tag, stem,\n rule, optsDiv, expDiv, lbl, txt, j, optEl, ltrSpan, txtSpan;\n\n cont = gid('cases');\n cont.innerHTML = '';\n answers = {}; answered = 0; shuffled = {}; done = false;\n gid('score').style.display = 'none';\n buildPips();\n\n for (i = 0; i < QS.length; i++) {\n q = QS[i];\n opts = shuffleArr(q.opts);\n shuffled[q.id] = opts;\n\n card = document.createElement('div');\n card.className = 'mr-case';\n\n top = document.createElement('div');\n top.className = 'mr-case-top';\n\n numDiv = document.createElement('div');\n numDiv.className = 'mr-num';\n numDiv.textContent = q.id < 10 ? 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