EpistemisChemical antidotes, environmental poisoning and chelators
Drugs designed to coordinate and bind heavy metals in the blood, counteract acute enzyme inhibition by pesticides or block metabolic pathways of toxic alcohols.
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Atropine and Pralidoxime Combo Duodote, Atropine IVPharmacological Group: Anticholinergic (atropine) and cholinesterase/oxime reactivator (pralidoxime); specific antidotes.
Mechanism of Action: They act synergistically against acute poisoning by organophosphates or nerve warfare agents (sarin, soman). Organophosphates irreversibly inhibit the enzyme acetylcholinesterase (AChE) through phosphorylation of its active serine residue, inducing a massive accumulation of acetylcholine in the synaptic clefts (cholinergic syndrome).
1. Atropine: It is a selective competitive antagonist of muscarinic cholinergic receptors, reversing the peripheral and central cholinergic excess that causes bronchorrhea, bronchospasm, extreme bradycardia, miosis and sialorrhea.
2. Pralidoxime: It is an oxime that exerts a nucleophilic attack on the phosphorus atom of the organophosphate bound to acetylcholinesterase, dephosphorylating and reactivating the functional enzyme before the "aging" phenomenon occurs.
| Routes and Directions | Critical Pharmacokinetics | Main Adverse Effects |
|---|---|---|
| Approved (Crisis): Acute poisoning by organophosphate and carbamate insecticides (with or without manifest severe cholinergic syndrome). | Via: IV, IM (autoinjectors in massive chemical crises). Distribution: Atropine crosses the blood-brain barrier easily. Pralidoxime has very limited central penetration. Elimination: Renal (atropine 50% unchanged; pralidoxime 80% in hours). |
Management with Atropine (Signs of Atropinization): Extreme dryness of the mucous membranes, paralytic mydriasis, intense sinus tachycardia, acute urinary retention, psychosis or atropinic delirium. Pralidoxime: Transient increase in diastolic blood pressure; tachycardia; muscle weakness and hyperventilation. |
Clinical Pearl: The Atropinization Criterion
In the management of poisoning emergencies due to organophosphate pesticides, the fundamental objective of therapy is not the resolution of mydriasis or tachycardia, but rather complete therapeutic atropinization, defined by the resolution of bronchospasm, the cessation of abundant bronchial secretions (bronchorrhea) and the stabilization of heart rate. There is no maximum dose of atropine; Progressive and repeated boluses are administered continuously until the airway is cleared.
Systematic Dosing Scheme
IV Atropine: Start with 1 to 3 mg IV directly, doubling the dose every 3-5 minutes if adequate respiratory response is not obtained. Once atropinization is achieved, start a continuous infusion calculating 10-20% of the total loading dose per hour.
Pralidoxime IV: Administer 1 to 2 g IV slowly infused over 15 to 30 minutes (to avoid hypertensive crises or respiratory arrest due to rapid infusion), followed by a continuous maintenance infusion of 500 mg/hour.
Pharmacological Group: Competitive enzyme inhibitor, toxicology antidote.
Mechanism of Action: It is a potent competitive inhibitor of the hepatic cytoplasmic enzyme alcohol dehydrogenase (ADH), with an affinity for the enzyme approximately 8000 times higher than that of ethanol. By selectively binding to ADH, it blocks the biotransformation of methanol to formaldehyde and its subsequent conversion to formic acid (causing profound metabolic acidosis and blindness due to retinal necrosis) and of ethylene glycol to glycoaldehyde and oxalic acid (causing acute renal tubular necrosis due to the deposition of calcium oxalate crystals).
| Routes and Directions | Critical Pharmacokinetics | Main Adverse Effects |
|---|---|---|
| Approved (Toxicology): Confirmed or highly suspected acute poisoning by methanol or ethylene glycol (alone or in combination with hemodialysis). | Via: IV (diluted infusion). Distribution: It is rapidly distributed in total body water (Vd = 0.6 L/kg). Metabolism: Hepatic extensively by CYP2E1 to inactive metabolites. Fomepizole induces its own metabolism after about 30-40 hours. t1/2: Varies according to plasma concentrations. | Mild Reactions (safe): Temporary mild headache, nausea, dizziness, drowsiness. Local venous irritation: Requires dilution in physiological saline solution. Transient unpleasant metallic taste. |
Pearl of Choice: Fomepizole vs. Ethanol Infusion
Historically, poisoning from non-potable alcohols was treated with intravenous infusions of ethanol to compete for ADH. However, fomepizole has irreplaceable advantages in clinical practice: it does not induce depression of consciousness or drunkenness, it has predictable pharmacokinetics that eliminate the need for continuous monitoring of serum levels, and it does not produce the severe hypoglycemia associated with alcohol therapies.
Fomepizole Clinical Protocol Dosage
Initial Loading Dose: 15 mg/kg IV infused over 30 minutes.
Maintenance: 10 mg/kg IV every 12 hours for a total of 4 doses. From the fifth dose, increase to 15 mg/kg IV every 12 hours due to autoinduction of metabolic clearance.
During Hemodialysis: Double the frequency of administration (give doses every 4 hours during dialysis) since fomepizole is easily cleared by the extracorporeal circuit.
Pharmacological Group: Heavy metal chelating agent, toxicology antidote.
Mechanism of Action: It is a chelator derived from the fungus Streptomyces pilosus that binds selectively and with an extraordinary stability constant to free ferric iron (Fe3+) and linked to ferritin or hemosiderin. By binding to iron, it forms a hydrophilic, stable and non-toxic octahedral coordinated chelate called ferrioxamine, which is easily eliminated from the body through renal glomerular filtration and biliary hydrolysis. It lacks affinity for the iron of hemoglobin, myoglobin or functional cytochromes.
| Routes and Directions | Critical Pharmacokinetics | Main Adverse Effects |
|---|---|---|
| Approved: Acute iron poisoning (accidental massive ingestion, common in pediatrics); Chronic iron overload secondary to repetitive transfusions (transfusion hemochromatosis in thalassemias or severe anemias). | Via: IV (controlled slow infusion), IM, SC (chronic therapy). Absorption: Poor by oral route (<15%, where it can only bind to intestinal iron). Metabolism: Nonspecific plasma enzymes. t1/2: Short: 10-20 minutes. Elimination: Renal (ferrioxamine). | Severe systemic hypotension: Caused by rapid intravenous infusion, due to peripheral vasodilation due to massive release of histamine. Pulmonary toxicity: Acute respiratory distress syndrome (ARDS) associated with prolonged IV infusions (>24 hours). Bacterial infections: Increases susceptibility to sepsis due to Yersinia enterocolitica (which uses ferrioxamine as a siderophore). |
Indicators of Toxicity and Urine Color "Rose Wine"
A characteristic sign of the presence of iron excreted as a ferrioxamine chelate in the patient under treatment is the appearance of a pink wine-colored urine (vin rosé). Systemic treatment is continued steadily until urine returns to normal color and serum iron levels fall safely below 350 µg/dL or total iron binding capacity (TIBC).
Infusion Dosage in Acute Intoxication
IV dose (Infuse through continuous infusion pump): Initial load of 15 mg/kg/hour IV to avoid hypotensive crises. In case of absolute hemodynamic stability, the standard maximum daily cumulative dose is 80 mg/kg/day (exceptionally up to 6 g/day in fulminant poisoning).
Renal Adjustment: In pre-existing oliguric renal failure, ferrioxamine is not excreted efficiently; concomitant hemodialysis is required to purify the circulating soluble chelate.
Epistemis 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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