How a drug is absorbed by your body into the blood depends on the way it is taken:<\/p>\n
- \n
- A pill is usually absorbed into the blood through the stomach walls after it is swallowed \u2013 these can become active in a few minutes but usually take an hour or two to reach the highest concentration in the blood.<\/li>\n
- IV drugs are injected directly into the blood work much faster \u2013 sometimes in seconds or minutes.<\/li>\n<\/ul>\n
However a drug is taken, it will reach a peak level and then these levels will go down as the body breaks down the active ingredients, usually as the circulating blood is filtered by the liver or kidneys.<\/p>\n
This basic process happens with every drug \u2013 alcohol, nicotine, aspirin, HIV drugs\u2026<\/p>\n
Drugs are always absorbed more quickly than the body can break them down, so the highest concentration is reached relatively quickly, and then it takes longer to leave the body.<\/p>\n
Drug absorption<\/h2>\n
![\"Drug](\"https:\/\/i-base.info\/ttfa\/files\/2009\/07\/absorption.gif\")
<\/p>\n- \n
- After taking a drug, levels peak quickly then drop slowly as the drug is eliminated (cleared from the body) \u2013 every drug has its own absorption curve.<\/li>\n
- The highest concentration<\/strong> is called the Cmax<\/strong>.<\/li>\n
- The total exposure to drug over the dosing period<\/strong> is call the Area Under the Curve (AUC)<\/strong><\/li>\n
- The time taken to get to the highest concentration<\/strong> is called the Tmax<\/strong><\/li>\n
- The time taken to reduce the highest concentration by half<\/strong> (by 50%) is called a drug’s ‘half-life’ or T\u00bd<\/strong>.<\/li>\n
- It takes approximately 5 half-lives for a drug to be cleared to negligible levels, but in theory, tiny quantities can be in the body for much longer.<\/li>\n
- When a drug is taken routinely as treatment, the lowest concentration just before the next dose<\/strong> is called the Cmin or Ctrough<\/strong> (trough level).<\/li>\n<\/ul>\n
Drug absorption after multiple doses<\/h2>\n
![\"Drug](\"https:\/\/i-base.info\/ttfa\/files\/2009\/07\/multiple.gif\")
<\/p>\n- \n
- Each dose taken on time makes sure that the drug stays above the lowest useful level <\/strong>(called the Minimum Effective Concentration or MEC<\/strong>).<\/li>\n
- Remember that all these results are averages.<\/li>\n
- Some people absorb drugs more quickly or more slowly than the average.<\/li>\n
- Some people clear drugs more quickly or more slowly than the average.<\/li>\n
- These results are usually only calculated in blood and blood levels do not always relate to how active a drug is inside a cell. With nucleoside analogues<\/strong>, the level of the active drug inside the cell is more important than blood levels \u2013 graphs for drugs levels inside cells would follow a similar pattern, but are more difficult to measure With some nucleosides, the levels in blood or plasma do not match the levels inside cells.<\/li>\n<\/ul>\n
Pharmacokinetics<\/h2>\n
Pharmacokinetics is the name for ways that drugs are absorbed and eliminated by the body.<\/strong><\/p>\n
Although drugs behave differently in different parts of the body (blood, brain, genital fluids, inside different cells etc) the basic principles of absorption and elimination are similar.<\/p>\n
Studies\u00a0 looking at drug levels in genital fluids use the same terms and measurement as drug levels in blood (Cmin, Cmax etc). Importantly, a drug behaves differently in each compartment.<\/p>\n
Some drugs are rapidly absorbed in blood but might take a day to reach maximum levels in genital fluids. Some drugs have much higher concentrations in genital fluids than they in blood.<\/p>\n","protected":false},"excerpt":{"rendered":"
If you understand what happens when you take a drug through the following graphs, you will understand the science behind adherence. What happens to drugs in the body? When you take a drug, it is absorbed into the blood and …<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":315,"menu_order":10,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-345","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages\/345","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/comments?post=345"}],"version-history":[{"count":0,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages\/345\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages\/315"}],"wp:attachment":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/media?parent=345"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- The total exposure to drug over the dosing period<\/strong> is call the Area Under the Curve (AUC)<\/strong><\/li>\n