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Related Concept Videos

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers01:12

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

Class III antiarrhythmic drugs are a group of medications that can prolong action potentials in the heart. They achieve this by blocking potassium channels or enhancing inward currents from sodium channels. However, these drugs have a unique property of "reverse use-dependence," which is most pronounced at slower heart rates and can lead to torsades de pointes—a specific type of arrhythmia. However, it is essential to note that excessive QT interval prolongation—a measure of the heart's...
Therapeutic Drug Monitoring: Affecting Factors01:29

Therapeutic Drug Monitoring: Affecting Factors

Therapeutic Drug Monitoring (TDM) is the clinical practice of measuring specific drug levels in a patient's blood or body tissues to manage and optimize therapy. TDM is crucial for drugs with narrow therapeutic windows, like warfarin and phenytoin, where incorrect doses can lead to treatment failure or severe side effects. This monitoring ensures the dosage administered is within a safe and effective range. The factors affecting therapeutic drug monitoring include:Patient-Specific Factors:a.
Pharmacokinetic–Pharmacodynamic Relationship: Influence of Elimination Half-Life on Effect Duration01:23

Pharmacokinetic–Pharmacodynamic Relationship: Influence of Elimination Half-Life on Effect Duration

Drug elimination from the body primarily occurs through metabolic and excretion pathways. Hepatic metabolism transforms lipophilic drugs into hydrophilic forms for excretion, typically via enzymatic processes classified as phase I (modification) and phase II (conjugation). Renal excretion eliminates drugs and metabolites through filtration and secretion in the kidneys. Impairment in liver or kidney function can hinder these processes, delaying drug clearance and extending the drug’s half-life.
Pharmacogenetic Phenotypes: Alterations in Pharmacokinetics, Drug Targets and Biologic Milieu01:29

Pharmacogenetic Phenotypes: Alterations in Pharmacokinetics, Drug Targets and Biologic Milieu

Genetic variations significantly influence drug response through pharmacokinetics, receptor interactions, and biologic milieu modifications. Pharmacokinetic alterations impact drug metabolism and clearance, affecting efficacy and toxicity. Variants in drug-metabolizing enzymes, such as CYP2C9 and CYP2C19, alter drug activation and elimination. For example, CYP2C9 loss-of-function variants require lower warfarin doses to prevent excessive bleeding, while CYP2C19 variants reduce clopidogrel...
Pharmacokinetic–Pharmacodynamic Relationship: Duration of Dose-Effect Relationship01:14

Pharmacokinetic–Pharmacodynamic Relationship: Duration of Dose-Effect Relationship

For drugs producing a quantal response, onset occurs when plasma concentration reaches a minimum effective level (Cmin). The drug's action duration depends on how long the plasma concentration remains above Cmin.Two primary factors influence this duration: dose size and the rate of drug removal from the action site. Both depend on the drug's redistribution to poorly perfused tissues and elimination processes. A larger dose promotes rapid onset and prolongs the effect's duration.Consider a...
Drug toxicity: Drug–Drug Interaction01:30

Drug toxicity: Drug–Drug Interaction

Drug–drug interactions can precipitate toxicity through multiple mechanisms. Absorption interactions alter how drugs enter the body, exemplified when ranitidine increases the absorption of basic drugs, while cholestyramine decreases the levels of propranolol. Protein binding interactions occur when drugs share the same binding sites on plasma proteins. Drugs like aspirin and warfarin, when bound in excess, can lead to increased free drug concentrations, enhancing the potential for...

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Related Experiment Videos

Prolonged QT interval and methadone: implications for palliative care.

Andrew Wilcock1, James M Beattie

  • 1University of Nottingham and Hayward House Macmillan Specialist Palliative Care Unit, Nottingham University Hospitals NHS Trust, Nottingham, UK. andrew.wilcock@nottingham.ac.uk

Current Opinion in Supportive and Palliative Care
|October 3, 2009
PubMed
Summary

Methadone use in palliative care may contribute to unexpected deaths through respiratory depression or torsade de pointes. Close patient monitoring and awareness of QT interval prolongation risks are crucial for safe methadone administration.

Related Experiment Videos

Area of Science:

  • Palliative Care Medicine
  • Clinical Pharmacology
  • Cardiology

Background:

  • Methadone is frequently used in palliative care for pain management.
  • Unexpected deaths have been observed in patients receiving methadone.
  • Cardiac arrhythmias, specifically torsade de pointes, are a potential concern.

Purpose of the Study:

  • To review current literature on methadone and QT interval prolongation.
  • To assess the risk of torsade de pointes associated with methadone.
  • To provide guidance for palliative care clinicians regarding methadone use.

Main Methods:

  • Literature review of recent studies on methadone, QT interval, and torsade de pointes.
  • Analysis of reported adverse events and mortality data.
  • Evaluation of existing clinical guidelines and expert opinions.

Main Results:

  • A higher incidence of unexpected deaths in methadone-treated patients is noted.
  • Torsade de pointes is a potential contributing factor to mortality, alongside respiratory depression.
  • Current guidelines for risk minimization are largely based on expert opinion due to limited robust evidence.
  • Routine ECG screening is debated, but recommended with risk factors for QT prolongation.

Conclusions:

  • Safe methadone use necessitates understanding its pharmacology and vigilant patient monitoring to prevent overdose.
  • Clinicians must be aware of methadone's Summary of Product Characteristics regarding QT prolongation and general ECG monitoring advice.
  • Balancing methadone's benefits and risks requires careful consideration of individual patient circumstances.
  • Clinicians should recognize symptoms like palpitations, syncope, or seizure-like activity in patients on methadone.