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Guanethidine
Aka: Guanethidine, Ismelin
- See Also
- Peripheral Presynaptic Alpha Adrenergic Antagonist
- Sympathetic Nervous System
- Alpha Adrenergic Receptor
- Postsynaptic Alpha Adrenergic Antagonist (e.g. Prazosin)
- Reserpine (Serpasil)
- Guanadrel (Hylorel)
- Mechanism
- Transiently increases Norepinephrine release from nerve terminals (with transient Hypertension and Tachycardia)
- Subsequent decreased Norepinephrine release via depletion of Norepinephrine from nerve stores
- Prevents Norepinephrine release at nerve endings
- Poorly crosses blood brain barrier
- No sedation (contrast with Reserpine)
- Pharmacokinetics
- Bioavailability 30% after oral dose
- Half is Metabolized
- Half-life: 5 days (very long)
- Adverse effects persists for weeks after stopping agent
- Indications
- Rarely used in United States
- May have a place in Severe Hypertension, but has been replaced by newer agents with fewer adverse effects
- Contraindications
- Pheochromocytoma
- Severe Hypertension
- Adverse Effects
- Transient Hypertension and Tachycardia (see mechanism above)
- Hypotension
- Reflex Tachycardia mechanism blocked by loss of Norepinephrine release
- Decreased Cardiac Output
- Bradycardia
- COPD Exacerbation
- Nasal congestion (significantly increased)
-
Drug Interactions
- Tricyclic Antidepressants (TCA)
- TCAs block Guanethidine entry into cells
- References
- Olson (2020) Clinical Pharmacology, MedMaster, Miami, p. 64-5