{"id":105,"date":"2019-04-24T12:39:34","date_gmt":"2019-04-24T12:39:34","guid":{"rendered":"https:\/\/sepia2.unil.ch\/pharmacology\/?page_id=105"},"modified":"2020-09-04T03:00:35","modified_gmt":"2020-09-04T03:00:35","slug":"halflife","status":"publish","type":"page","link":"https:\/\/sepia2.unil.ch\/pharmacology\/parameters\/halflife\/","title":{"rendered":"Half-life"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\"> &#8220;Time it takes for the plasma concentration or the amount of drug in the body to be reduced by 50%&#8221; <\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Descriptio<\/h3>\n\n\n\n<div class=\"wp-block-columns has-2-columns is-layout-flex wp-container-core-columns-is-layout-9d6595d7 wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<p>\nBy definition, the plasma concentration of a drug  is halved after one \nelimination half-life. Therefore, in each  succeeding half-life, less \ndrug is eliminated. After one half-life the  amount of drug remaining in\n the body is 50% after two half-lives 25%,  etc. After 4 half-lives the \namount of drug (6.25%) is considered to be  negligible regarding its \ntherapeutic effects. \n\n<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-video\"><video height=\"346\" style=\"aspect-ratio: 346 \/ 346;\" width=\"346\" controls src=\"https:\/\/sepia2.unil.ch\/pharmacology\/wp-content\/uploads\/2019\/04\/halflife_Trim.mp4\"><\/video><\/figure>\n<\/div>\n<\/div>\n\n\n\n<p>The half-life of a drug depends on its <a href=\"\/pharmacology\/clearance\">clearance<\/a> and <a href=\"\/pharmacology\/volumeofdistribution\">volume of distribution<\/a>. The elimination half-life is considered to be independent of the amount of drug in the body.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Clinical implications<\/h3>\n\n\n\n<p>Half-life determines the length of the drug effect. It also indicates whether accumulation of the drug will occur under a <a href=\"\/pharmacology\/repeated-administration\">multiple dosage regimen<\/a> and it is essential to decide on the appropriate dosing interval.<\/p>\n\n\n\n<p><p class=\"hiddenTitle\">Chart Pharmacokinetics<\/p>\n<div>\n\n    <div id=\"chartContainer\">\n        <canvas id=\"chart\"><\/canvas>\n        <div class=\"\" id=\"divSliderContainer\"><\/div>\n    <\/div>\n\n    <script>\n\n        let chart;\n        let baseDataChartValues = [];\n        let dataChart = [];\n        let dataChartStoredValues = [];\n        let labelsChart = [];\n\n        let dose = 1000;\n        let baseDose = 1000;\n\n        let mDose = 1000;\n        let baseMDose = 1000;\n\n        let tau = 6;\n        let baseTau = 6;\n\n        let vd = 50;\n        let baseVd = 50;\n\n        let cl = 10;\n        let baseCl = 10;\n\n        let f = 0.7;\n        let baseF = 0.7;\n\n        let ka = 1.5;\n        let tH;\n\n        const maxTime = 20;\n\n        function getPlasmaConcentration(h) {\n            let formulaPlasmaConcentration = (dose*f*ka\/(vd*(ka-cl\/vd))*(Math.exp(-cl\/vd*h)));\n\n            return formulaPlasmaConcentration;\n        }\n\n        \/*\n         *\n         * t1\/2 = ln(2) * (volume of distribution \/ clearance)\n         *\n         *\/\n        function getHalfLife() {\n            tH = Math.log(2)*(vd\/cl);\n            return (Math.round(tH * 100) \/ 100);\n        }\n\n        function updateSlider(updateStored = false) {\n            dataChart = [];\n            if(updateStored) dataChartStoredValues = [];\n\n            for(let i = 0; i <= maxTime; i++) {\n                let concentration = getPlasmaConcentration(i);\n                dataChart.push(concentration);\n                if(updateStored) dataChartStoredValues.push(concentration);\n            }\n\n            chart.data.datasets[0].data = dataChart;\n            chart.data.datasets[1].data = dataChartStoredValues;\n\n            $( \"#slider-vd\" ).slider( \"option\", \"value\", vd);\n            $( \"#slider-cl\" ).slider( \"option\", \"value\", cl);\n            chart.update();\n        }\n\n        let sliderVd = '<div id=\"slider-vd\" class=\"sliderRange\">' +\n                            '<span id=\"custom-handle-vd\" class=\"ui-slider-handle customHandle\"><\/span>' +\n                            '<span class=\"spanUnit\" id=\"\">Vd<\/span>' +\n                        '<\/div>';\n\n        $('#divSliderContainer').append(sliderVd);\n\nlet sliderCl = '<div id=\"slider-cl\" class=\"sliderRange\">' +\n                            '<span id=\"custom-handle-cl\" class=\"ui-slider-handle customHandle\"><\/span>' +\n                            '<span class=\"spanUnit\" id=\"\">CL<\/span>' +\n                        '<\/div>';\n\n        $('#divSliderContainer').append(sliderCl);\n\n\n   \n\n        $(function() {\n\n            let handleVd = $('#custom-handle-vd');\n\n            $( \"#slider-vd\" ).slider({\n                orientation: \"vertical\",\n                range: \"true\",\n                min: 10,\n                max: 100,\n                step: 0.1,\n                value: vd,\n                create: function() {\n                    handleVd.text( $( this ).slider( \"value\" ) );\n                },\n                slide: function( event, ui ) {\n                    vd = ui.value;\n                    handleVd.text( ui.value );\n                    updateSlider();\n                }\n            });\n\n            let handleCl = $('#custom-handle-cl');\n\n            $( \"#slider-cl\" ).slider({\n                orientation: \"vertical\",\n                range: \"true\",\n                min: 1,\n                max: 25,\n                step: 0.1,\n                value: cl,\n                create: function() {\n                    handleCl.text( $( this ).slider( \"value\" ) );\n                },\n                slide: function( event, ui ) {\n                    cl = ui.value;\n                    handleCl.text( ui.value );\n                    updateSlider();\n                }\n            });\n\n        });\n        \n        \n\n        Chart.pluginService.register({\n            beforeInit: function(chart) {\n\n                for(let i = 0; i <= maxTime; i++) {\n                    labelsChart.push(i);\n                    dataChart.push(getPlasmaConcentration(i));\n\n                    dataChartStoredValues = dataChart;\n                    baseDataChartValues = dataChart;\n                }\n\n            }\n        });\n\n        chart = new Chart(document.getElementById(\"chart\"), {\n            type: 'line',\n            data: {\n                labels: labelsChart,\n                datasets: [{\n                    label: \"Plasma Concentration\",\n                    data: dataChart,\n                    borderColor: colorDatasetMain.borderColor,\n                    fillColor: colorDatasetMain.fillColor,\n                    strokeColor: colorDatasetMain.strokeColor,\n                    highlightFill: colorDatasetMain.highlightFill,\n                    highlightStroke: colorDatasetMain.highlightStroke,\n                    borderWidth: \"1\",\n                    pointRadius: 0,\n                    fill: false\n                }, {\n                    label: \"Plasma Concentration\",\n                    data: dataChartStoredValues,\n                    borderColor: colorDatasetStored.borderColor,\n                    fillColor: colorDatasetStored.fillColor,\n                    strokeColor: colorDatasetStored.strokeColor,\n                    highlightFill: colorDatasetStored.highlightFill,\n                    highlightStroke: colorDatasetStored.highlightStroke,\n                    borderWidth: \"1\",\n                    pointRadius: 0,\n                    fill: false\n                }]\n            },\n            options: {\n                scales: {\n                    xAxes: [{\n                        scaleLabel: {\n                            display: true,\n                            labelString: 'H [hour]'\n                        }\n                    }],\n                    yAxes: [{\n                        scaleLabel: {\n                            display: true,\n                            labelString: 'C [mg\/l]'\n                        }\n                    }]\n                },\n                responsive: true,\n                maintainAspectRatio: false\n            }\n        });\n\n    <\/script>\n\n<\/div><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Related terms<\/h3>\n\n\n\n<p>Elimination rate constant ( \u03bb ): Fractional rate of  drug removal from the body. This rate is constant in first-order  kinetics and is independent of drug concentration in the body.  \u03bb is the  slope of the plasma concentration-time line (on a logarithmic y scale). <\/p>\n\n\n\n<p>Apparent half-life (t<sub>1\/2<\/sub>): In some cases, such as for <a href=\"\/pharmacology\/extravascular-administration\">controlled-release preparations<\/a>, the rate of decline of the drug plasma concentration is not due to elimination alone. Other factors such as <a href=\"\/pharmacology\/absorption\">absorption rate<\/a>\n or distribution rate influence plasma concentration decay. In such \nconditions, the observed half-life is called apparent half-life.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Assessment<\/h3>\n\n\n\n<div class=\"wp-block-blocks-latex-block-latex\"><script type=\"text\/x-mathjax-config\">   MathJax.Hub.Config({tex2jax: {inlineMath: [['$','$'], ['\\\\(','\\\\)']]}}); <\/script><p class=\"formula\">$$t_{1\\over2}={\\color{Pink}{ln(2)}\\over{\\color{RoyalBlue}{\\lambda}}}={\\color{Pink}{ln(2)}*{\\color{RoyalBlue}{Vd}\\over{\\color{RoyalBlue}{CL}}}}={\\color{Pink}{0.693}}*{\\color{RoyalBlue}{Vd}\\over{\\color{RoyalBlue}{CL}}}$$<\/p><\/div>\n\n\n\n<p><strong>Vd<\/strong> = <a href=\"\/pharmacology\/volumeofdistribution\">volume of distribution<\/a> <\/p>\n\n\n\n<p><strong>CL<\/strong> = <a href=\"\/pharmacology\/clearance\">clearance<\/a> <\/p>\n\n\n\n<p> <strong>\u03bb<\/strong> = elimination rate constant = CL\/Vd <\/p>\n","protected":false},"excerpt":{"rendered":"<p>&#8220;Time it takes for the plasma concentration or the amount of drug in the body to be reduced by 50%&#8221; Descriptio By definition, the plasma concentration of a drug is halved after one elimination half-life. Therefore, in each succeeding half-life, less drug is eliminated. After one half-life the amount of drug remaining in the body &hellip; <\/p>\n<p class=\"link-more\"><a href=\"https:\/\/sepia2.unil.ch\/pharmacology\/parameters\/halflife\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Half-life&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":7,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-105","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/pages\/105","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/comments?post=105"}],"version-history":[{"count":30,"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/pages\/105\/revisions"}],"predecessor-version":[{"id":1286,"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/pages\/105\/revisions\/1286"}],"up":[{"embeddable":true,"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/pages\/7"}],"wp:attachment":[{"href":"https:\/\/sepia2.unil.ch\/pharmacology\/wp-json\/wp\/v2\/media?parent=105"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}