UMEM Educational Pearls - Toxicology

With the aging population, bisphosphonate use will continue to increase. They promote bone growth by inhibiting osteoclast action and resorption of bone. Unfortunately, they have their side effects and the FDA has sent out a recent warning that affects us all:

• [Posted 01/07/2008] FDA informed healthcare professionals and patients of the possibility of severe and sometimes incapacitating bone, joint, and/or muscle (musculoskeletal) pain in patients taking bisphosphonates.

If a patient presents with severe bone/joint pain, check the med list to see if they are on a bisphosphonate - they may not be faking the pain. This can occur days, weeks or even years after initiation of dose

Levetiracetam

• A new anticonvulsant that is 100% renally eliminated
• Does not require therapeutic drug monitoring like phenytoin
• The IV form does not cause skin necrosis or have cardiotoxicity like phenytoin
• Is being investigated in benzodiazepine-refracory status epilepticus (1)
• Fairly safe drug even in overdose (Barrueto et al ;) )

 

Knake et al. Intravenous levetriacetam in thetreatment of benzodiazepine-refractory status epilepticus. J Neurol Neurosurg Psychiatry 2007 Sept 26; Epub

                                      Phenytoin po      Phenytoin IV       Fosphenytoin

Time to therapeutic       6.4 hrs                  1.7 hrs                 1.3 hrs

Adverse Events              0.69/pt                   1.86/pt                 1.87/pt

Also to take into account  is that the adverse events with IV phenytoin include soft-tissue necrosis if there is extravasation of infusion. The cardiotoxicity seen with phenytoin and fosphenytoin is largely due to the propylene glycol diluent and thus not seen with oral loading or even in oral overdosing.

You decide, at least you have the data to properly evaluate the risk:benefit ratio.

Ketorolac: an NSAID that gained popularity since it is not an opioid, has excellent anti-inflammatory/analgesic effects and is given IM or IV. Also has been used in renal colic secondary to smooth muscle relaxation (Prostaglandin mediated) in the ureters. You should know:

• When given IV or IM still causes PUD and has caused GI perforations.
• Renal Insufficiency is larger concern with this NSAID than others.
• Consider misoprostol for GI complications.
• Use for acute pain, limit the number doses given and don't prescribe for more than 3 days. I generally don't prescribe it at all, use another NSAID for outpatient treatment.

 

Corelli et al. Renal Insufficiency and ketorolac. Ann Pharmacother. 1993; 27(9): 1055-7

Lithium: Hypothyroidism (5-15% of pts) and goiter (37% of pts), mechanism unclear

Amiodarone (37% Iodine by weight): Hyper or Hypothroidism

Beta-Blockers: by blocking peripheral conversion of T4 to T3 cause hypothyroidism

Corticosteroid: same as beta-blockers but can also cause transient thyrotoxicosis (Jod-Basedow effect)

Iodine, Iodinated contrast, radiactive iodine all can cause hypothyroidism but iodinated contrast material can actually induce thyrotoxicosis and thyroid storm from unknown mechanism.

Everything you need to know about anti-emetics, mechanism of action, potency and toxicity:

1) 5-HT3 Blockers - Ondansetron, Granistron

- The most potent anti-emetic, only toxicity is really cost

2) Dopamine Blockers - Metoclopramide

- Can titrate to high doses, causes dystonia, akathisia and mild QT prolongation

3) Anticholinergic - Promethazine, meclizine, diphenhydramine

- Cannot titrate, most sedating, urinary retention in elderly, mild QT prolongation

• Risk Factors for RCIN: Renal insufficiency, >60 yr old, DM, Renal Transplant, Hypovolemia, EF <30%, concomitant nephrotoxic drugs
• Consider Prophylaxis with anyone of three methods (no method has been found superior.
  • Normal Saline: 1 ml/kg/h IV pre and post study
  • NaHCO3: 3 ml/kg IV bolus over 1 hr then 1 ml/kg/h pre and post
  • IV Acetylcysteine 150 mg/kg bolus over 1hr then 50 mg/kg over 4h

A short list of some of the unique food poisonings and the toxicologic effects:

• Ciguatera toxin (fish): hot-cold sensation reversal
• Tetrodotoxin (fugu, puffer fish): paresthesias progressing to paralysis and dysrythmias
• Scrombroid (spoiled fish): flushed face due to histamine ingestion
• Paralytic Shellfish Poisoning (mussels, clams, etc): acts like curare, toxin is saxitoxin
• Amnestic shellfish poisoning (mussels): exactly what it says, loss of memory - very cool

Sulfonylureas

• Sulfonylureas cause insuline release via cAMP/protein kinase C
• All sulfonylurea overdoses should be admitted for 24 hrs regardless of symptoms
• Antidote for recurrent hypoglycemia due to sulfonylureas (overdose or therapeutic misadventure) is octreotide, after your glucose
• Octreotide, a somatostatin analogue, turns of insulin secretion completely
• Octreotide 50 mcg SQ q 6 hrs for 24 hrs then observe for hypoglycemia 12-24 hrs

Fasono et al. Comparison of Octreotide and Standard Therapy Versus Standard Therapy Alone for the Treatment of Sulfonylurea-Induced Hypoglycemia. Ann Emerg Med 2007 Aug 29.

Carbamazepine

• Anticonvulsant that can be monitored (you can draw a level)
• Toxicity resembles a TCA with seizures and cardiac conduction delays
• > 40 mcg/mL assoc with coma, seizures, respiratory failure and cardiac toxicity
• Treat widened QRS comples with sodium bicarbonate
• Adsorbs very well to activated charcoal, multi-dose may be required

SSRI Toxicity

Things to watch for in patients that are taking SSRI:

• Therapeutic administration usually safe
• Hyponatremia is a common adverse effect (ADH secretion regulated by serotonin)
• Serotonin Syndrome is a possibilty in combination with other serotnergic drugs
• One SSRI is more problematic than the rest => Citalopram and Escitalopram
  • The only SSRI that can cause QT prolongation (even 24hrs after OD) and can cause seizures
  • This is the only SSRI with significant toxicity and unfortunately is the most commonly Rx by psych

GHB

• Sedating and amnestic, has become notorious in chemical submission (date rape)
• Very fast onset and rapid resolution though respiratory depression can occur 
• Difficult to test for with few labs and quickly eliminated through urine 
• Best chance to catch it is if the patient's first urine void is collected and tested

Valproic Acid (Depakote) - Increased use for both seizure disorder, migraine prophylaxis and bipolar disorder - Causes hyperammonemia with or without hepatic insufficiency (Liver enzymes could be normal!) - Hyperammonemia can occur at therapeutic concentrations and overdose - If the patient is sedated and has hyperammonemia, consider carnitine therapy antidotal - Carnitine IV or PO: 50-100 mg/kg bolus or divided bid, safe to give

Isopropanol (Commonly Rubbing Alcohol)

• Rubbing alcohol is 70% isopropanol, like drinking Bacardi 151 (151 proof)
• This is NOT a toxic alcohol in the traditional sense
• This causes a large ketosis, large osmol gap but NO anion gap and no acidosis
• This is because isopropanol is metabolized to acetone (a ketone) not an acid
• Toxicity: inebriation, hemorrhagic gastritis, sedation to the point of death/intubation

Ciguatera Poisoning - The most commonly reported cause of fishborne poisoning - Most commonly big-game fish: sea bass, grouper, red snapper, yellow-tail, kingfish and sturgeon - Ciguatoxin is bioaccumulated (thus big fish) and is heat and acid stable (unaffected by cooking) - Symptoms: 6-12 hrs post-ingestion GI, paresthesias, metallic taste, ataxia and paresis of legs are possible - The classic symptom is dysesthesias (sensory reversal where cold gives intense burning sensation) - Treatment: Supportive, consider mannitol, calcium, gabapentin - Avoid the following as it may exacerbate symptoms: opioids, barbiturates, steroids

Ethanol withdrawal can be measure objectively with the CIWA-Ar Scale. It is a prospectively validated tool to measure whether or not a patient is in ethanol withdrawal and can assist with management. Score Treatment <10 Does not require treatment 10-15 Treatment with either oral or intravenous benzodiazepines, outpatient > 15 Intravenous benzodiazepines with likely admission You must also take into account the patient's history, comorbidities and previous history of ethanol withdrawal/delirium tremens. ***The CIWA Score Sheet has been attached to this pearl***

Attachments

• 0709201013_ciwa-ar.pdf (10 Kb)

There are few medications/toxins that can cause clinically significant diabetes or hyperglycemia, here is the list: Vacor (PNU, an off the market rat poison) Streptozocin Alloxan Pentamidine Quinolones (gatifloxacin>moxifloxacin>ciprofloxacin) Olanzapine Antidote for Vacor, streptozocin, Alloxan: Niacinamide Antidote for Quinolones, Olanzapine: Remove agent, supportive care

Scombroid is one of the most common seafood poisonings. A classic EM board question. - Caused by ingestion of histamine in fish muscle - Naturally occurring histidine is converted to histamine by bacteria in unrefrigerated fish - Most common fish: tuna, mackerel, bonito, mahi mahi, blue fish and yellow tail - Symptoms: Within minutes to hours - flushing, urticaria, perioral burning, N/V/D - Treatment: Antihistamines, fluids, bronchodilators. Epinephrine and steroid for severe reactions.

- Classic Clinical Finding: Cyanosis out of proportion to clinical symptoms (look real blue but not SOB) - Causative Agents: Benzocaine (and other local anesthetics), dapsone, nitrites, phenazopyridine (Pyridium) - When do you treat: significant tissue hypoxia (MI, CVA, Dysrhythmias), and if MetHb >20% asymptomatic - Treatment: Methylene Blue 1-2 mg/kg (0.1 -0.2 mL/kg of 1% methylene blue) over minutes

- Few medications are uniformly lethal after a certain amount is ingested. - Colchicine is one of those medications, >0.8 mg/kg ingested=100%mortality regardless of treatment. - Many people prescribe it without knowing the adverse effect profile. - In fact, the prescribing instructions tell you to take the patient to toxicity (nausea and vomiting). - After an acute overdose this would be the sequence of events assuming surivival: Phase Signs & Symptoms i Nausea, vomiting, diarrhea, dehydration, leukocytosis (0-24hrs) II Sudden cardiac death (24-36hrs), pancytopenia, renal failure sepsis, ARDS, rhabdo (1-7d) III Alopecia, myopathy, neuropathy, myoneuropathy (>7d) - Colchicine prevents/destroys microtubule spindle formation and thus acts like a chemotherapeutic agent killing the cells that replicate most. - Think twice when prescribing this medication to someone, especially a patient at risk for suicide or medication noncompliance (where they think a little is good so more is better).