{"id":46,"date":"2019-09-18T16:19:17","date_gmt":"2019-09-18T20:19:17","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/nursingpharmacology\/chapter\/1-9-examining-effect\/"},"modified":"2022-01-06T15:43:31","modified_gmt":"2022-01-06T20:43:31","slug":"1-9-examining-effect","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/nursingpharmacology\/chapter\/1-9-examining-effect\/","title":{"raw":"1.9 Examining Effect","rendered":"1.9 Examining Effect"},"content":{"raw":"

Onset, Peak, and Duration<\/h2>\r\nDosing considerations play an important role in understanding the effect that a medication may have on a client. During administration, the nurse must pay close attention to the desired effect and therapeutic response, as well as the safe dose range for any medication.\u00a0 The nurse should have an understanding of medication [pb_glossary id=\"525\"]efficacy[\/pb_glossary]<\/strong> in order to ensure its appropriateness.\u00a0 If a nurse is provided different medication choices according to a provider's written protocol, the nurse should select the option with the anticipated desired therapeutic response. Additionally, the nurse must be aware of the overall [pb_glossary id=\"526\"]dose response[\/pb_glossary]<\/strong> based on the dosage selected.\r\n\r\nThree additional principles related to the effect of a medication on a client are onset, peak, and duration.\r\n\r\n[pb_glossary id=\"527\"]Onset[\/pb_glossary]:<\/strong> the onset of medication refers to when the medication first begins to take effect\r\n\r\n[pb_glossary id=\"528\"]Peak [\/pb_glossary]:<\/strong> the peak of medication refers to the maximum concentration of medication in the body, and the point at which the client shows evidence of greatest therapeutic effect\r\n\r\n[pb_glossary id=\"529\"]Duration[\/pb_glossary]:<\/strong> the duration of medication refers to the length of time the medication produces its desired therapeutic effect\r\n\r\nConsider this client care example and apply the principles of onset, peak, and duration: Gurmeet, a 67-year-old female client, who has just undergone hip replacement surgery earlier today, rings the call light to request medication for pain. She notes her pain is \"excruciating, a definite 9 out of 10.\" Her brow is furrowed, and she is grimacing in obvious discomfort. As the nurse providing care for Gurmeet, you examine her post-operative medication orders and consider the pain medication options available to you. In reviewing the various options, it is important to consider how quickly a medication will work (onset), when the medication will reach maximum effectiveness (peak), and how long the pain relief will last (duration). Understanding these principles is important in effectively relieving the client's pain and constructing an overall plan of care.\r\n
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Clinical Reasoning and Decision-Making Activity 1.9\"Image<\/h2>\r\n<\/header>\r\n
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  1. At 0500, your client, who had a total knee replacement yesterday, rates his pain while walking as 7 out of 10.\u00a0 Physical therapy is scheduled at 0900. The client has acetaminophen (Tylenol) 650 mg ordered every four hours as needed for discomfort.\u00a0 What should you consider in relation to the administration and timing of this client's pain medication?<\/li>\r\n<\/ol>\r\n

    2. Your client is prescribed NPH insulin<\/a> to be given at breakfast and supper.\u00a0 As a student nurse, you know that insulin is used to decrease blood sugar levels in clients with diabetes mellitus. During report, you hear that the client has been ill with GI upset during the night, and the nursing assistant just informed you he refused his breakfast tray.\u00a0 While reviewing this medication order, you consider the purpose of the medication and information related to the medication's onset, peak, and duration. When reviewing the drug reference, you find the NPH insulin has an onset of about 1 - 3 hours after medication administration.\u00a0 \u00a0What should you consider in relation to the administration and timing of the client's insulin?<\/p>\r\n

    Note: Answers to these activities can be found in the \"Answer Key<\/a>\" sections at the end of the book.<\/p>\r\n\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n

    Duration and Dosing<\/h3>\r\nNow let's consider the implication of duration and dosing. Remember the duration of medication is correlated with the elimination. If a medication has a short half-life (and thus is eliminated more quickly from the body), the therapeutic effect is shorter. These medications may require repeated dosing throughout the day in order to achieve steady blood levels of active free drug and a sustained therapeutic effect.\u00a0 Other medications have a longer half-life (and thus a longer therapeutic duration) and are only given once or twice per day. For example, oxycodone immediate release is prescribed every 4 to 6 hours for the therapeutic effect of immediate relief of severe pain, whereas oxycodone ER (extended-release) is prescribed every 12 hours for the therapeutic effect of sustained relief of severe pain.\r\n

    Monitoring Therapeutic Drug Levels<\/h2>\r\nNow that the basic concepts of medication onset, peak, and duration have been discussed, it is important to understand the value of the therapeutic window and therapeutic index in medication administration.\r\n\r\n[caption id=\"attachment_48\" align=\"alignright\" width=\"282\"]\"Image Figure 1.9 Therapeutic Window[\/caption]\r\n

    Therapeutic Window<\/h3>\r\nFor every drug, there exists a dose that is minimally effective (the Effective Concentration) and another dose that is toxic (the Toxic Concentration). Between these doses is the [pb_glossary id=\"530\"]therapeutic window[\/pb_glossary],<\/strong> \u00a0where the safest and most effective treatment will occur (see Figure 1.9).[footnote]\"Therapeutic Window<\/a>\" by Shefaa Alasfoor is licensed under CC BY-SA 3.0<\/a>[\/footnote]\u00a0 Think of this area as the dosing \"sweet spot.\"\r\n\r\nFor example, warfarin (Coumadin) is a medication used to prevent blood clotting and is monitored using a blood test called INR. Too high a dose of warfarin would cause the INR to increase above the therapeutic window and put the client at risk of bleeding. Conversely, too low a dose of warfarin would cause the INR to be below the therapeutic window and put the client at risk of clotting.\u00a0 It is vital that the nurse frequently monitor INR levels for a client receiving warfarin to ensure the dosage appropriately reaches the therapeutic window and does not place the client at risk for bleeding or clotting.\r\n

    Peak and Trough Levels<\/h4>\r\nNow let's apply the idea of the therapeutic window to the administration of medications requiring the monitoring of peak and trough levels, which is required in the administration of some IV antibiotics. It is important for the dosage of these medications to be titrated<\/strong> to achieve a desired therapeutic effect for the client.\u00a0 Titration is often accomplished by closely monitoring the blood levels of the medication. A drug is said to be within the \"therapeutic window\" when the serum blood levels of an active drug remain consistently above the level of effective concentration (so that the medication is achieving its desired therapeutic effect) and consistently below the toxic level (so that no toxic effects are occurring). A [pb_glossary id=\"528\"]peak[\/pb_glossary]<\/strong> drug level is drawn at the time when the medication is being administered and is known to be at the highest level in the bloodstream.\u00a0 A [pb_glossary id=\"941\"]trough[\/pb_glossary]<\/strong> level is drawn when the drug is at its lowest in the bloodstream right before the next dose is given. Medications have a predicted reference range of normal values for peak and trough levels. These numbers assist the pharmacist and provider in gauging how the body is metabolizing, protein-binding, and excreting the drug, and assist in the adjustment of the prescribed drug doses to keep the medication within the therapeutic window.\u00a0 When administering IV medications that require peak or trough levels, it is vital for the nurse to time the administration of\u00a0 the medication according to the timing of these blood draws.\u00a0 [footnote]This work is a derivative of Principles of Pharmacology<\/a> by LibreTexts<\/a> licensed under CC BY-NC-SA 4.0<\/a>.[\/footnote]<\/sup>\r\n

    Therapeutic Index<\/h3>\r\n[pb_glossary id=\"531\"]Therapeutic Index[\/pb_glossary] <\/strong>is a quantitative measurement of the relative safety of a drug.\u00a0 It is a comparison of the amount of drug that produces a therapeutic effect versus the amount of drug that produces a toxic effect.\r\n