Chapter 1 – A Hypertensive Crisis

Physiologic & Pharmacologic Background

  • Sympathomimetic cascade
    • Stimulation of adrenergic receptors (α, β₁, β₂) → ↑ catecholamine-mediated effects
    • β₁ agonism
    • Predominantly cardiac
    • ↑ HR (chronotropy), ↑ contractility (inotropy) → ↑ CO → ↑ SBP
    • β₂ agonism
    • Predominantly vascular & bronchial smooth muscle
    • Vasodilation in skeletal muscle beds but, when combined with β₁ effects, overall systemic BP may still rise
  • Monoamine oxidase (MAO)
    • Enzyme responsible for oxidative deamination of monoamines (NE, EPI, DA, 5-HT, tyramine)
    • Two isoforms: MAO-A (NE, 5-HT) and MAO-B (DA)

MAO-Inhibitors (MAOIs)

  • Core function: Block MAO-A ± MAO-B → ↑ synaptic monoamines
  • Therapeutic targets
    • Depression ("atypical" pattern), anxiety disorders
    • Parkinson’s disease (selective MAO-B inhibitors such as selegiline)
  • Key clinical outcome stated in transcript: “MAO inhibitors are effective”

Hypertensive Crisis Mechanism

  • When MAO is inhibited, dietary or exogenous sympathomimetics are not degraded ➔ catecholamine surge ➔ hypertensive crisis
    • Defined clinically as acute rise in BP, often \text{SBP}>180\,\text{mmHg} or/and \text{DBP}>120\,\text{mmHg} with or without acute end-organ damage
  • Contributors highlighted in transcript
    • β₁/β₂ agonists (e.g., albuterol, isoproterenol, epinephrine-containing local anesthetics)
    • Caffeine
    • Adenosine receptor antagonist ➔ disinhibition of catecholamine release
    • Phosphodiesterase inhibition ➔ ↑ cAMP in vascular smooth muscle ➔ additive pressor response

Drug–Drug & Drug–Diet Interactions (Extended Context)

  • Sympathomimetic medications
    • OTC decongestants (pseudoephedrine, phenylephrine)
    • ADHD stimulants (methylphenidate, amphetamine)
    • Weight-loss agents (phentermine, ephedra)
  • Tyramine-rich foods (aged cheese, cured meats, soy, draft beer)
    • Tyramine displaces NE from vesicles → sudden release; normally degraded by gut MAO-A
  • Other xanthines (theophylline) and caffeinated beverages
  • Rule of thumb: avoid any agent that can “boost” NE/EPI while on an MAOI

Clinical Manifestations of Crisis

  • Sudden, pounding headache, occipital or temporal
  • Severe HTN: visual changes, epistaxis
  • Autonomic hyperactivity: diaphoresis, palpitations, tachycardia
  • Possible progression → intracranial hemorrhage, acute heart failure

Management Overview

  • Immediate discontinuation of offending agent(s)
  • Phentolamine or nitroprusside IV for BP control
  • Non-selective β-blocker alone is contraindicated (unopposed α-vasoconstriction)

Patient Counseling & Practical Implications

  • Provide detailed list of restricted foods & OTC preparations
  • Warn about caffeine intake; recommend ≤100100–150 mg150\,\text{mg} caffeine/day or complete avoidance
  • Instruct on wearing medical alert identifying MAOI therapy

Ethical & Safety Considerations

  • Prescriber responsibility to review full medication list (polypharmacy)
  • Pharmacist double-check prior to dispensing decongestants/stimulants

Quick‐Reference Equations & Numbers

  • Threshold for hypertensive urgency: BP≥180/120 mmHg\text{BP}\geq 180/120\,\text{mmHg}
  • Catecholamine store time after MAOI initiation: ≈2\approx 2–3 weeks3\,\text{weeks} for enzyme resynthesis after discontinuation

Mnemonic Connections

  • “MAOI + TCA” → MaTeC (Massive Amine Tyramine Crisis) to recall additive risk

Key Takeaways

  • MAOIs effective but high-risk for hypertensive crisis when combined with β₁/β₂ agonists or caffeine.
  • Educate, monitor, and avoid sympathomimetics to mitigate life-threatening complications.