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General Toxicology and Toxidromes
GENERAL TOXICOLOGY AND TOXIDROMES Aaron B. Skolnik, MD, and Susan R. Wilcox, MD
CHAPTER 78
XVI. TOXICOLOGY
1. What are the most common causes of death by poisoning? In order from most to least commonly reported, the following categories of drugs are the 10 associated with toxin-related fatalities: n Miscellaneous sedatives n Miscellaneous hypnotics n Miscellaneous antipsychotics n Miscellaneous cardiovascular drugs n Opioids n Acetaminophen combinations n Acetaminophen alone n Miscellaneous antidepressants n Miscellaneous stimulants and street drugs n Miscellaneous muscle relaxants and cyclic antidepressants 2. What are the common toxidromes? Toxidromes are syndromes associated with particular classes of toxins. They may be useful in making the diagnosis of poisoning and initiating treatment as patients are often too ill to wait for the results of laboratory or other testing (Table 78-1). 3. What laboratory testing is indicated in the poisoned patient? Laboratory testing in critically ill poisoned patients should be dictated by the suspected toxin(s) and the findings of the history and physical examination. Laboratory testing should include serum electrolytes and calculation of the anion gap. If the anion gap is elevated, serum osmolarity and calculation of the osmolar gap are often useful. Further laboratory testing might include transaminase and prothrombin time (PT) for a patient who has ingested acetaminophen. Arterial blood gas testing is useful in a critically ill patient poisoned by salicylates as is a carboxyhemoglobin level in a patient with carbon monoxide exposure. Urinalysis may show oxalate crystals suggesting ethylene glycol poisoning or may even fluoresce under a Wood lamp if a patient has ingested a commercial antifreeze preparation. 4. What is the value of serum and urine toxicology screens in the poisoned patient? In many hospitals, a basic serum toxicology screen includes levels of acetaminophen, salicylate, and volatile alcohols. This is a good starting point when ingestants are unknown as it includes treatable toxins for which serum levels guide therapy. Quantitative levels of tricyclic antidepressants are of no value in determining treatment, and many hospitals use a qualitative screen. Urine drug screens are often used to test for metabolites of drugs of abuse and are often not valuable in making a toxicologic diagnosis. Some hospitals have comprehensive blood or urine toxicology testing that can isolate many obscure compounds. However, the results of these tests often become available long after the window for appropriate treatment has closed for patients. It is important to know the availability of toxicologic testing at your hospital and to be aware of the limitations of testing. Cross-reactivity with particular assays may also lead to
545
CHAPTER 78
XVI. TOXICOLOGY
1. What are the most common causes of death by poisoning? In order from most to least commonly reported, the following categories of drugs are the 10 associated with toxin-related fatalities: n Miscellaneous sedatives n Miscellaneous hypnotics n Miscellaneous antipsychotics n Miscellaneous cardiovascular drugs n Opioids n Acetaminophen combinations n Acetaminophen alone n Miscellaneous antidepressants n Miscellaneous stimulants and street drugs n Miscellaneous muscle relaxants and cyclic antidepressants 2. What are the common toxidromes? Toxidromes are syndromes associated with particular classes of toxins. They may be useful in making the diagnosis of poisoning and initiating treatment as patients are often too ill to wait for the results of laboratory or other testing (Table 78-1). 3. What laboratory testing is indicated in the poisoned patient? Laboratory testing in critically ill poisoned patients should be dictated by the suspected toxin(s) and the findings of the history and physical examination. Laboratory testing should include serum electrolytes and calculation of the anion gap. If the anion gap is elevated, serum osmolarity and calculation of the osmolar gap are often useful. Further laboratory testing might include transaminase and prothrombin time (PT) for a patient who has ingested acetaminophen. Arterial blood gas testing is useful in a critically ill patient poisoned by salicylates as is a carboxyhemoglobin level in a patient with carbon monoxide exposure. Urinalysis may show oxalate crystals suggesting ethylene glycol poisoning or may even fluoresce under a Wood lamp if a patient has ingested a commercial antifreeze preparation. 4. What is the value of serum and urine toxicology screens in the poisoned patient? In many hospitals, a basic serum toxicology screen includes levels of acetaminophen, salicylate, and volatile alcohols. This is a good starting point when ingestants are unknown as it includes treatable toxins for which serum levels guide therapy. Quantitative levels of tricyclic antidepressants are of no value in determining treatment, and many hospitals use a qualitative screen. Urine drug screens are often used to test for metabolites of drugs of abuse and are often not valuable in making a toxicologic diagnosis. Some hospitals have comprehensive blood or urine toxicology testing that can isolate many obscure compounds. However, the results of these tests often become available long after the window for appropriate treatment has closed for patients. It is important to know the availability of toxicologic testing at your hospital and to be aware of the limitations of testing. Cross-reactivity with particular assays may also lead to
545