Antihistamines/Decongestants Goldfranks Quiz

A 32yoF presents to the ED following an intentional overdose of an antihistamine. She has a generalized tonic-clonic seizure that resolves following a dose of lorazepam. An EKG demonstrates a QRS interval of 140 msec. Which of the following antihistamines best explains her presentation?

• Loratadine

• Cetirizine

• Doxylamine

• Ranitidine

• Diphenhydramine

Answer explanation

Diphenhydramine is a/w seizures when adults ingest a dose > 1.5g. Diphenhydramine also causes sodium channel blockade, and in overdose, leads to QRS prolongation with findings on the EKG that are similar in appearance to the EKG of patients who overdose on TCAs. Hypertonic sodium bicarb reverses the QRS prolongation that occurs with diphenhydramine overdose.

An 18yoM presents to the ED after having a generalized GTC seizure at home. Vitals are BP 168/90, HR 154, RR 15, temp 100.8. On exam, he has dilated pupils that react only minimally, dry mucous membranes, garbled speech, and a very distended bladder. He also has active hallucinations and appears to be picking at things. An EKG is performed which demonstrates a QRS of 89msec. Which o the following interventions would be the next best step to perform on this patient?

• CT head

• Lumbar puncture

• Administer lorazepam

• Administer CTX, vanc, acyclovir

• Administer physostigmine

Answer explanation

In most circumstances, patients who have an elevated temp, AMS, and a seizure should be treated empirically for encephalitis; they should also have a head CT and LP performed. As this pt has a narrow QRS interval and an exam consistent with antimuscarinic toxicity, we recommend starting by treatment with physostigmine. Physostigmine is both therapeutic and diagnostic. Physostigmine also leads to less interventions (like a lumbar puncture), less imaging, and a shorter hospital stay. Physostigimine is also safer than benzodiazepines in the treatment of antimuscarinic poisoning.

Which of the following imidazolines also acts as a histamine H2 agonist?

• Xylometazoline

• Naphazoline

• Oxymetazoline

• Tetrahydrozoline

• Neumotazoline

Answer explanation

Tetrahydrozoline, which is available without a prescription in the US as an opthhalmic preparation to decrease conjunctival injection, is also a histamine H2 agonist in addition to an alpha adrenergic agonist. Stimulation of H2 increases the production of acid in the stomach. Neumotazoline is not a decongestant.

Which of the following is most likely to cause a false-positive reaction on a urine drug screening immunoassay for phencyclidine?

• Ketamine

• Dextromethorphan

• Amphetamine

• Cocaine

• Marijuana

Answer explanation

False positie results on urine screen immunoassays vary among manufacturers. Many current tests will give a positive result with other arylcyclohexylamine derivatives that are used a phencyclidine substitute. Although ketamine shares chemical and structural similarities to PCP, most testing platforms distinguish the two molecules. Dextromethorphan is the most clinically significant cross-reactant, in that dextromethorphan toxicity resembles PCP toxicity and dextromethorphan is found in many nonprescription cold and cough remedies.

A 25yoF is brought to the ED after being found confused and agitated. She has flushed skin, mydriasis, tachycardia, and dry mouth. Her EKG shows a QRS duration of 130 msec. Which of the following is the most likely cause of her symptoms?

• Levocetirizine

• Loratadine

• Diphenhydramine

• Fexofenadine

• Famotidine

Tags

NGSS.HS-PS1-5

A 40yoM presents with confusion, visual hallucinations, urinary retention, and tachycardia after ingesting an unknown substance. His EKG reveals a QRS interval of 120 msec. Which of the following medications is most appropriate to reverse his symptoms?

• Flumazenil

• Atropine

• Physostigmine

• Activated charcoal

• Naloxone

Which of the following over-the-counter medications is most likely to cause anticholinergic toxicity if taken in large amounts?

• Loratadine

• Diphenhydramine

• Famotidine

• Cetirizine

• Ranitidine