When pt is in renal failure, need to be at lower dosage with less frequency 15. Discuss the importance of understanding the time course of drug responses (plasma drug levels, single-dose time course , drug half-life, and drug levels produced with repeated doses). Explain why clinicians often monitor plasma drug levels and describe how these levels are regulated to prevent drug toxicity. Plasma drug levels: o Clinicians monitor the plasma drug levels in efforts to regulate drug responses/dosage.
Minimum effective concentration (MEC): when the plasma drug level is below the therapeutic effect level.. too low to illicit a response. Toxic concentration: plasma drug levels are too high and toxic effects occur Therapeutic range: the wider the range the safer. The narrower the range the more unsafe it is. Drug concentration in plasma should be between the minimum effective concentration for obtaining desired drug action and the minimum toxic concentration. Meaning, there should be enough drug present to produce therapeutic response, but not so much that toxicity results. o Because one cannot measure drug concentration at the active site since the site of action of most drugs is not in the blood. However, drug concentrations at sites of action are related to drug responses. o Most drugs have a direct correlation between the level of drug in plasma and the intensity of therapeutic and toxic effects. Single-dose time course: (did not go over this in class) o How plasma drug levels change over time after a single dose o Drug levels rise as the medication undergoes absorption and decline as it is metabolized and excreted from the body. Metabolism and excretion are the processes most responsible for causing plasma drug levels to fall, and so are the primary determinants of how long drug effects will persist. o Plasma levels go up and then come back down. Drug half-life o An index of just how rapidly the amount of drug in the body decline occurs. The time required for the amount of drug in the body to decrease by 50%. 50% is lost every X time. o It can be minutes to weeks. o This is important in determining the dosing interval (how much time separates each dose). o Drugs with shorter half-life needs to be administered more frequently. o 4 half-lives to be eliminated from the body, or to reach a plateau Drug levels produced with repeated doses o Multiple dosing leads to drug accumulation o The process by which plateau drug levels are achieved Drug build up until a plateau or steady level has been achieved. When the amount of drug eliminated between doses equals the dose administered, average drug levels will remain constant and plateau will have been reached. In other words when the amount lost between doses grows to be as large as the amount administered.
Time to plateau: if the drug is administered repeatedly in the same dose, plateau will be reached in approximately four half-lives. And as long as dosage remains constant, the time required to reach plateau is independent of dosage size. For a drug with a long half-
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- Spring '17
- Pharmacology, Pharmacokinetics, Receptors, Nursing Process