ANTIHISTAMINES - rEMERGs

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Peripheral Anticholinergic Effects‣ Tachycardia: decreases vagal stimulation to heart‣ Hyperthermia: agitation + inability to sweat‣ Mydriasis:‣ Can’t see: loss of accomodation + mydriasis‣ Dry, flushed skin‣ Hypertension‣ Urinary retension‣ Decreased bowel activity: ileus, absent bowel soundsCardiovascular Effects‣ Sinus tachycardia very common (vagolytic effects)‣ May be hypertensive or hypotensive‣ Wide QRS and prolonged QT can occur Thought to be a function of Na+ channel blockade Treat with bicarbNotes on Diphenhydramine (Bendadryl) Overdoses‣ Retrospective review of 136 cases: 55% developed CNS depression, 15%developed catatonic stupor‣ Pediatric patients more susceptible to seizures, respiratory complications, CNSstimulation, and anticholinergic symptoms‣ Wide QRS, prolonged QT, ventricular dysrhytmias have all occurred‣ Vertical and horizontal nystagmus noted‣ Rhabdomyolysis has occurred: patients were very agitatedDry as a bone:dry skinRed as a beet: flushedMad as a hatter: agitationBlind as a bat: mydriasis,accomodationHot as a hare: feverMANAGEMENT General‣‣‣‣‣‣‣‣‣‣Cardiac monitorWatch for seizures, prolonged QT, wide QRSNeed [APAP] level b/c of cold preps often have acetaminophenWatch temp and HR as predictors of who will be more toxicMost managed with only supportive careActivated charcoal is indicated (may require intubation and NG administration ifthere is significant CNS depression)Consider MDAC as anticholinergic effects with delay gastric motility and GIabsorptionFluids for dehydrationFluids +/- pressors for hypotensionGastric Lavage only for MASSIVE overdose that presents early
‣ Benzos for severe agitation‣ Benzos for seizures‣ Temp: cold water mist, fansCardiac Toxicity‣ Wide QRS, prolonged QT‣ Bolus bicarbonate until effect‣ Hypertonic salinePhysostigmine‣ Acetylcholinesterase inhibitor (central and peripheral) which increases the amountof acetylcholine in the synapse‣ Can effectively reverse anticholinergic toxicity‣ Initially was used to counteract atropine poisoning‣ Only used for SEVERE toxicity: benefit must clearly outweigh the risks‣ Risks: cholinergic crisis (DUMBELS)‣ Contraindications: wide QRS, history of exposure to TCAs or any IA or ICantiarrthmics, exposure to any other potential Na+ channel blocker (cocaine,carbamezepine, thioridazine, etc), underlying cardiac conduction disorders‣ Increased mortality when TCAs on board (how can you be sure they aren’t?)‣ Must be on cardiac monitor with atropine at bedside for cholinergic crisis‣ Dose: 1-2 mg in adults, 0.5 mg in children; repeat q10 min prnDECONGESTANTSPHARMACOLOGY Sympathomimetics that act on alpha adrenergic receptors to produce vasoconstriction in themucous membranes and improve airflow In therapuetic doses they can have systemic affects in addition to local effects Ephedrine and Pseudoephedrine: alpha 1,2 and beta 1,2 agonism Phenylephrine: powerful alpha agonist with very little beta effects Phenylpropanolamine: alpha 1,2 agonism with no beta agonism Imidazoline sympathomimetics: topical applicaitons (oxymetazoline, tetrahydrozoline,naphazoline); pure alpha 2 agonist that are primarily used as nasal decongestants NOTE: weight lifters and athletes are abusing these Onset of symptoms usually within few hours and resolve by 8-24hrsCLINICAL MANIFESTATIONS Rarely cause systemic toxicity b/c of poor absorption CNS stimulation common Cardiac stimulation: tachycardia, HTN Bradycardia possible with pure alpha agonists (reflexic response to hypertension) Requires 4-5 Xs recommended dose to see significant effects Headache is most common initial symptom that is reported by those that become toxic Severe exposures: ventricular arrythmias, seizure, intracranial hemorrhages, ischemic gut, MisMANAGEMENT Activated charcoal Benzodiazepines for sedation, seizures
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