S15C171 - TCA

Question 1

Pathophys of TCA

Answer 1

• inhibition of amine reuptake (NE, serotonin)-antidepressant
• antagonist of postsynaptic histamine receptors (sedation)
• antagonist post-synaptic muscarinic R’s (sedation, coma, agitation, anticholinergic effects)
• antagonist of post-synaptic alpha-adrenergic R’s (sedation, miosis, reflex tachy, ortho HoTN) tx with NE
• inhibition of NE reuptake (agitation, mydrisasis, diaphoresis, tachy, early HTN)
• inhibition of serotonon reuptake (sedation, mydriasis, myoclonus, hyperreflexia)
• inhibits VG sodium channels: wide QRS, impaired contractility, brugada pattern (tx with sodium bicarb, hyeprtonic saline)
• inhibits VG rectifier K channels: prolonged QT, torsades de pointes (tx with MgSO4 and pacing)

Question 2

Pharmacokinetics of TCA

Answer 2

• lipophlic
• cleared by liver
• elimination 1/2 life = 24h (increases to 72h in an OD)
• ingestion 10mg/kg
• toxicity at >2.5mg/kg

Question 3

TCA OD features

Answer 3

• antimuscarinic (anticholinergic, dry mouth, tachy)
• cardiotoxicity (Na ch blocker)
• AMS most common Sx
• serious toxicities occur w/in 6h of ingestion due to: coma, cardiac conduction delays, SVT, HoTN, resp dpn, PVC, v tach, Sz

Question 4

TCA OD Dx

Answer 4

• serum tests can tell presence of tCA
• ECG: tach, RAD, prolonged PR/QRS/QT, or nothing, brugada pattern
• ECG usually resolves after 36h
• if: QRS >100msec, RAD >120 deg or brugada pattern, give sodium bicarb

Question 5

TCA OD Tx

Answer 5

• monitor closely for 6h if asymptomatic
• AC
• sodium bicarb: HoTN, ECG criteria, ventricular dysrhythmias, 1-2mEq/kg until pH 7.5 then 150mEq in 1L of D5 1/2NS
• K
• NO physostigmine
• tx Sz with benzos then barbs (dilantin ineffective)
• HoTN: fluids, then norepi
• torsades: MgSO4
• overdrive pacing if necessary or IV isoproterenol