EpistemisSpecific antidotes for drug poisoning
Medicines designed to neutralize, specifically compete with, or reverse the deleterious effects caused by overdoses of prescription xenobiotics.
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Acetylcysteine Fluimucil (sachets), N-Acetylcysteine IVPharmacological Group: Antidote, mucolytic, glutathione precursor.
Mechanism of Action: Acts as the absolute antidote of choice in paracetamol (acetaminophen) overdose. Under overdose conditions, normal hepatic conjugation pathways (sulfation and glucuronidation) become saturated, diverting acetaminophen to the CYP2E1 oxidative pathway that produces the highly reactive and hepatotoxic metabolite NAPQI (N-acetyl-p-benzoquinoneimine). NAPQI rapidly depletes hepatic glutathione stores and binds covalently to hepatocyte proteins, inducing fulminant centrilobular necrosis. Acetylcysteine is deacetylated intracellularly to act as a direct precursor of L-cysteine synthesis, restoring hepatic glutathione reserves and also acting as an alternative nucleophilic substrate that binds directly to free NAPQI, neutralizing its toxicity.
| Routes and Directions | Critical Pharmacokinetics | Main Adverse Effects |
|---|---|---|
| Approved (Medical): Acute paracetamol poisoning (maximum effectiveness in the first 8-10 hours of ingestion); prevention of acute hepatotoxicity from other etiologies (off-label). | Via: IV (preferred in moderate-severe poisoning to avoid vomiting), PO. Metabolism: Extensive hepatic deacetylation to cysteine. t1/2: 5.6 hours (adults). Excretion: Renal (30%). | Anaphylactoid reaction (common in rapid IV infusion): Flushing, pruritus, urticaria, bronchospasm, hypotension (mediated by direct release of non-IgE histamine). Gastrointestinal: Nausea, intense vomiting (orally, intolerable sulfurous "rotten egg" odor). |
Pearl of Emergency Management: Rumack-Matthew Nomogram
To guide the need for treatment with acetylcysteine in acute paracetamol poisoning from a single ingestion, the level of serum paracetamol extracted from 4 hours after ingestion is measured and graphed in the Rumack-Matthew Nomogram. If the plasma level is above the "treatment line" (which starts at 150 µg/mL at 4 hours), the acetylcysteine infusion protocol should be started immediately due to the imminent risk of liver necrosis.
3-Step IV Protocol Dosing
Classic IV Infusion Protocol (Total Dose 300 mg/kg in 21 hours):
1. Loading Dose: 150 mg/kg IV infused in 200 mL of 5% dextrose over exactly 1 hour (reduce rate if anaphylactoid signs).
2. Second Infusion: 50 mg/kg IV dissolved in 500 mL of 5% dextrose administered over the next 4 hours.
3. Third Infusion: 100 mg/kg IV in 1000 mL of 5% dextrose administered over the next 16 hours.
Pharmacological Group: Opioid receptor antagonist, toxicology antidote.
Mechanism of Action: It is a pure competitive antagonist with a very high binding affinity for the opioid receptors of the central nervous system, with special affinity for the mu (µ), kappa and delta opioid receptors. By occupying the receptor, it competitively displaces exogenous opioid ligands (such as morphine, heroin, fentanyl, methadone and oxycodone), immediately reversing the respiratory depression, pupillary miosis and severe sedative effects induced by overdose of these agents.
| Routes and Directions | Critical Pharmacokinetics | Main Adverse Effects |
|---|---|---|
| Approved (Emergency): Complete or partial reversal of CNS and opioid-induced depression, including severe respiratory depression in adults and neonates. Diagnosis: Suspected opioid intoxication in coma of unknown origin. | Via: IV (effect in 1-2 min), IM, SC, Intranasal (nasal Narcan, excellent for non-medical personnel). Oral bioavailability: Practically zero due to an almost absolute first hepatic pass. Metabolism: Hepatic conjugation with glucuronic acid. t1/2: Short: 30 to 90 minutes. | Acute withdrawal syndrome (precipitated): Generalized body pain, profuse sweating, severe diarrhea, rhinorrhea, extreme irritability, agitation, severe tachycardia and arterial hypertension. Cardiovascular: Cardiac arrhythmias or acute non-cardiogenic lung edema (uncommon, after violent reversal). |
Clinical Pearl: Disparity in Half-Life and Risk of Resedation
A critical danger in the management of opioid overdoses is the large disparity between the short half-life of naloxone (~1 hour) and that of the ingested substance (for example, methadone has a half-life of 24-36 hours, and fentanyl depot). After reversal and awakening of the patient, naloxone will be cleared from the body long before the opioid, causing reoccupation of the receptor and recurrence of fatal respiratory depression. A minimum of rigorous medical observation of 4-6 hours is required and, if prolonged-release opioids are suspected, the initiation of a continuous infusion of naloxone.
Out-of-hospital and In-hospital Emergency Dosing
Direct Intravenous Route: 0.4 mg to 2 mg IV. If no response is obtained, the dose may be repeated at 2-3 minute intervals up to a maximum of 10 mg. If the patient has total apnea, start ventilation support with a bag mask and apply rapid boluses.
Intranasal Route: A spray of 4 mg in one nostril, can be repeated in the other nostril every 2-3 minutes if necessary.
Continuous Infusion: Calculate 60% of the initial hourly dose that successfully reversed respiratory depression and infuse it IV continuously.
Pharmacological Group: Specific benzodiazepine receptor antagonist.
Mechanism of Action: It is a derivative of the imidazobenzodiazepine that acts as a competitive antagonist on the allosteric binding site of benzodiazepines in the cellular GABA A receptor of the central nervous system. It competitively blocks the pharmacological effects of benzodiazepine agonists, as well as related non-benzodiazepine agents (such as zolpidem or zopiclone), restoring consciousness and reversing sedation and mild respiratory depression.
| Routes and Directions | Critical Pharmacokinetics | Main Adverse Effects |
|---|---|---|
| Approved: Complete or partial reversal of the sedative effects of benzodiazepines after general anesthesia or short-term diagnostic procedures; management of acute benzodiazepine overdose. | Via: IV exclusively. Distribution: Rapid. Poor protein binding (50%). Metabolism: Hepatic extensive to inactive metabolites. t1/2: Very short: 50 to 60 minutes (requires monitoring due to risk of resedation). Elimination: Renal (90%). | Severe seizures (major warning): Especially in patients with known epilepsy under chronic treatment with benzodiazepines or mixed overdoses with tricyclic antidepressants. Acute withdrawal: Extreme anxiety, panic, psychomotor agitation, sudden sweating and high blood pressure. |
Black Box Warning: Seizure Risk from Flumazenil
Flumazenil can precipitate refractory status epilepticus and death in patients with chronic use of benzodiazepines for seizure control or in mixed intoxications with proconvulsant drugs (such as amitriptyline, imipramine or cocaine). In these scenarios, acute blockade of GABA-mediated inhibition triggers an imbalance of cortical excitability and uncontrollable seizures. Prudent Clinical Use: Flumazenil should not be used routinely in comas of unknown origin or when multiple substance abuse is suspected.
Adult Dosage in Emergencies
Initial Dose: 0.2 mg IV administered slowly over 15 seconds. If the desired level of consciousness is not achieved after 45 seconds, a second dose of 0.3 mg IV may be injected. Successive doses of 0.5 mg IV may be repeated at 1-minute intervals until a maximum cumulative dose of 3 mg is reached.
Pregnancy: Category C. Use only in critical situations Breastfeeding: CompatibleEpistemis is educational review material. It is not a medical device, does not diagnose or prescribe treatment, and does not replace formal medical training, current clinical guidelines, or professional clinical judgment.
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- Immunology, Oncology and Toxicology
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- Clinical Toxicology