Pharmacokinetics (Elimination) PDF

**PHARMACOKINETICS (elimination)** Pharmacokinetics refers to the movement and modification of a medication inside the body. So once the medication is administered: - first it has to be absorbed into the circulation - then distributed to various tissues throughout the body - metabolized or...

**PHARMACOKINETICS (elimination)** Pharmacokinetics refers to the movement and modification of a medication inside the body. So once the medication is administered: - first it has to be absorbed into the circulation - then distributed to various tissues throughout the body - metabolized or broken down - and finally, eliminated or excreted in the urine or feces. You can remember this with the acronym **[ADME]**; which stands for: 1. Absorption 2. Distribution 3. Metabolism 4. and Elimination. Let's focus on **[elimination]**, which is the process of removing medications and their metabolites from the body through excretion. - This is [done primarily by **the kidneys**], through **[glomerular filtration]**, meaning that certain medications can be filtered out as the blood flows through the glomerulus. - In addition, as [the filtrate makes its way through **the renal tubules**], [other medications from **the peritubular capillaries** get actively secreted into **the tubular lumen**], while [others are passively reabsorbed into the blood]. Ultimately, **[the medications that are filtered, secreted, and not reabsorbed]**, end up being **[excreted from the body via urine]**. Aside from the kidneys, medications [can also be eliminated through **the gastrointestinal** or **GI tract**]. - So orally administered medications that [do not get absorbed along the GI tract are directly passed in **feces**]. On the other hand, [some medications undergo a process of **enterohepatic circulation**], when a medication is transferred by the liver into the bile. - After that, [bile carrying the medication is released into the GI tract] - where the medication can be reabsorbed, entering the portal circulation - to ultimately return to the liver. - At this point, [the process of enterohepatic circulation **occurs again**], and the liver transfers the medication back into the bile to be secreted into the GI tract, until it's [ultimately eliminated from the body through **the feces**]. - Lastly, small amounts of certain medications can be [cleared out of the body through **the lungs**] as we exhale air, as well as **[through sweat]**, **[saliva]**, **[tears]**, and even **[breast milk]**. Now, there are several factors that can affect the elimination of medications. - First of all, **[impaired renal function]** or any [condition that **decreases the cardiac output**] - can result in decreased glomerular filtration rate, which can lead to the buildup of medications inside the body. - Urine pH also affects elimination. - For example, if the urine is alkaline, acidic medications don't get reabsorbed, so they get excreted in the urine instead. - Another factor affecting elimination is **[impaired hepatic function]**, which [affects the liver's ability to metabolize or break down the medication]. As a result, **[the elimination process can slow down and lead to increased levels of the medication inside the body for a longer period of time]**. - Finally, if certain medications are administered together, they can affect each other's elimination. An example of this is **[probenecid]**, which is often given along with **[penicillin]**. - That's because probenecid slows down the elimination of penicillin, letting it [**stay longer in the bloodstream**, and **increasing its effectiveness**]. \*\*\* Now, let's look at **[the half-life of a medication]**, which is the time required for the blood concentration of a medication to be reduced by half and this mainly depends on [the pharmacokinetic phases of **metabolism** and **elimination**]. - So, for example, if [a medication's half-life is **two hours**], this means that it takes two hours for the concentration of that medication to **[drop from 100 to 50 mg/liter]**. Alright, before administering any medication to your client, remember to keep in mind some of the general pharmacokinetic principles that relate to how the medication is eliminated from your client's body. - First, review their medical history, taking note of any existing liver or renal disorders, as well as [conditions that can affect renal blood flow, like **hypertension** or **atherosclerosis**]. - Next, review all of your client's medications and supplements, and [check for **potentially nephrotoxic medications** like: ] - aminoglycosides - and NSAIDs - Also remember to consider other client characteristics that could affect elimination. - For example, as **[a person grows older]**, the number of working nephrons decreases. - On the flip side, [a **newborn's kidneys** are functionally immature] - Now, you'll also need to **[teach your client about their medication]**, including symptoms of medication toxicity that should be reported. - Explain the importance of **[recognizing symptoms of renal impairment]** like: - sudden changes in urinary output - dark-colored urine - or lower extremity swelling. - Likewise, teach them to **[recognize symptoms of liver impairment]**, including: - Nausea - abdominal discomfort - anorexia - and yellowing of the skin or eyes. - Lastly, because some medications could be present in breast milk, be sure to ask your client if they are breastfeeding, or have any plans to breastfeed. - For clients that need to take medication while breastfeeding, [elimination rate helps determine when they should take it]. - For medication with a **[short half-life]**, recommend that they take the medication **[just after a nursing session]** so the medication will be eliminated by the next feeding. - On the other hand, if your client is taking medication with a **[long half-life]**, advise them that the best time to take the medication is **[just before their baby's longest sleep period]**. - Also remind them to avoid sustained release medications and to take **[the lowest effective dose]** for the shortest possible duration. - If you are unsure whether a medication is incompatible with breastfeeding, [check with the healthcare provider, pharmacist, or lactation consultant]. - Another key step before starting a new medication is to review the ordered renal function tests, including: - BUN - Creatinine - GFR and CrCl (creatinine and creatinine clearance) - and urinalysis as well as **[liver function tests]**, including: - AST - ALT - alkaline phosphatase - GGT - and LDH. Report abnormal lab results to your client's healthcare provider. - Once your client has started their medication[, keep a close eye on their urine output and laboratory test results]. - **[Routinely assess]** [for factors that influence medication elimination, and use this information to evaluate the therapeutic response]. Quick review... Pharmacokinetics refers to the movement and modification of a medication inside the body, and involves: - Absorption - Distribution - Metabolism - and elimination. 1. [Renal and liver function are the primary factors that influence the elimination of medications from the body]. 2. [Most medications are eliminated by the **kidneys**], however some are eliminated through the **feces**, **exhaled air**, **sweat**, **saliva**, and **breast milk**. 3. Nursing considerations for medication elimination include: - reviewing the client's medical history, - current medications, - laboratory test results - and considering the client's age and stage of development. 4. Client education focuses on recognition of medication toxicity and symptoms of renal and hepatic insufficiency, as well as safe medication administration when breastfeeding.