17.17: Pharmaceutical Poisoning: Treatment Strategies

Treatment strategies for poisoning are a critical aspect of emergency medicine, focusing on preventing the absorption of toxins and enhancing their elimination. When a poisoning incident occurs, the first response is to halt exposure and decontaminate the patient, particularly through gastrointestinal (GI) methods if the poison was ingested.

Gastrointestinal Decontamination Techniques:

Activated charcoal is the cornerstone of GI decontamination. It works through adsorption, binding the toxin to prevent its absorption into the bloodstream. With a large surface area due to its internal pore structure, activated charcoal can adsorb many toxins, reducing their biological effects. It's typically administered in doses of 0.5–2 grams per kilogram of the patient's body weight. Despite its benefits, activated charcoal isn't effective against all substances, particularly alcohols, corrosives, hydrocarbons, and metals. Also, it may lead to adverse effects like vomiting and aspiration, and it is not recommended for patients with GI perforations or those who require endoscopy.

Whole-bowel irrigation is another method to flush out the GI tract using a polyethylene glycol solution. This is particularly helpful in cases of ingestion of sustained-release medications, heavy metals, or in "body packers" — individuals who have ingested packets of illicit drugs. However, it is contraindicated in patients with bowel obstruction and can lead to complications like pulmonary aspiration.

Gastric lavage, which involves flushing out the stomach's contents with saline, is now less commonly used due to potential risks such as mechanical trauma and pulmonary aspiration.

Enhancement of Elimination Methods:

Once a toxin is absorbed, strategies to accelerate its elimination are employed. Urinary alkalinization, for example, increases the renal excretion of weak acids such as salicylates. This method involves infusing sodium bicarbonate to make the urine more alkaline, trapping the poison in the urine for excretion. For certain poisons, extracorporeal removal techniques like hemodialysis or hemoperfusion are used to cleanse the blood directly. Hemodialysis is effective for removing water-soluble, low molecular weight toxins with minimal protein binding. It is indicated in severe or life-threatening poisonings or when other elimination methods are ineffective or contraindicated.

Antidotal therapy comprises specific antidotes that counteract the poison's effects. N-acetylcysteine for acetaminophen poisoning and naloxone for opioid overdose are prime examples. These agents can reverse the toxic dynamics by various mechanisms, including competing for receptor sites or altering drug metabolism.

In summary, the management of poisoning requires a nuanced understanding of various decontamination and elimination procedures, tailored to the nature of the toxin and the patient's condition.

Poisoning management involves immediate exposure cessation, thorough skin and eye washing, and GI decontamination.

GI decontamination prevents poison absorption through adsorption, whole-bowel irrigation, and gastric lavage.

Adsorption happens when the poison binds to an adsorbent’s surface. Activated charcoal, a common adsorbent with surface carbon moieties, is effective in most acute drug overdoses.

Whole-bowel irrigation involves enteral administration of an iso-osmotic polyethylene glycol solution to purge the intestines.

Gastric lavage uses a tube inserted into the stomach to flush and remove its contents with normal saline.

These decontamination procedures carry risks such as pulmonary aspiration, mechanical injury, and death.

On the other hand, if poison is absorbed, elimination enhancement procedures are used.

Urine alkalinization using sodium bicarbonate expedites weakly acidic drug elimination.

Antidotal therapy employs specific antagonists like N-acetyl-L-cysteine for acetaminophen poisoning and naloxone for heroin overdose.

Finally, hemodialysis removes waste and toxic metabolites from the blood.