Propranolol
Propranolol is a **non-selective beta-adrenergic antagonist** (beta-blocker) used primarily in veterinary medicine for its **antiarrhythmic properties**. It is classified as a Class II antiarrhythmic agent. * **Primary Uses:** Management of supraventricular and ventricular tachyarrhythmias (e.g., APCs, VPCs, atrial fibrillation), hypertrophic cardiomyopathy (HCM), and systemic hypertension. * **Endocrine Uses:** Frequently used to control the cardiovascular and neuromuscular signs of sympathetic overstimulation in **feline hyperthyroidism** and pheochromocytoma. * **Behavioral Uses:** Occasionally used off-label for situational anxiety or loud-noise phobias in dogs. > **Clinical Pearl:** Because propranolol is non-selective, it blocks both cardiac and pulmonary receptors. It should be used with extreme caution or avoided in patients with feline asthma or other bronchospastic airway diseases.
Mecanismo: Propranolol acts via **competitive blockade of both $\beta_1$ and $\beta_2$ adrenergic receptors**. * **$\beta_1$ Blockade (Cardiac):** $\rightarrow$ Decreases sinus heart rate (negative chronotropy) $\rightarrow$ Depresses AV node conduction (negative dromotropy) $\rightarrow$ Decreases myocardial contractility (negative inotropy) $\rightarrow$ Ultimately reduces cardiac output and myocardial oxygen demand. * **$\beta_2$ Blockade (Pulmonary/Vascular):** $\rightarrow$ Can cause bronchoconstriction and peripheral vasoconstriction. * **Additional Effects:** Possesses **membrane-stabilizing (quinidine-like) effects** at higher doses, which alters the cardiac action potential. It lacks intrinsic sympathomimetic activity (ISA) and inhibits glycogenolysis.
Dosificación por especie
- Susceptible cardiac arrhythmias · 0.02 mg/kg IV slowly (up to a maximum of 1 mg/kg) · IV · As needed
- Susceptible cardiac arrhythmias · 2.5 mg (up to 10 mg) total dose per cat q 8-12h. · PO · q8-12h
- Susceptible cardiac arrhythmias · 0.02 mg/kg IV over one minute; can repeat up to a maximum of four times as needed based upon response · IV · As needed
- Adjunctive therapy in heart failure · 2.5-10 mg (total dose) PO q8h (start low and titrate) · PO · q8h
- Adjunctive therapy of hypertension · 2.5-5 mg (total dose) PO q8-12h · PO · q8-12h
- Adjunctive therapy in feline hyperthyroidism · 2 mg/kg (6.25 mg per cat) once daily · PO · q24h · To control neuromuscular and cardiovascular effects
- Hypertrophic cardiomyopathy · 0.5-2 mg/kg PO or SC once a day to twice a day · PO/SC · q12-24h
- Hypertrophic cardiomyopathy · 0.2-2 mg/kg PO q8-12h. · PO · q8-12h
- V-Tach · 0.05-0.16 mg/kg IV · IV · Single dose · Negative inotropic and chronotropic effects may be undesirable.
- V-Tach · 0.03-0.15 mg/kg IV · IV · Single dose · Considered not as effective as lidocaine; decreases ventricular rate even if it does not restore sinus rhythm. Use with caution in animals with airway disease.
Vías de administración
Contraindicaciones
- Overt heart failure
- Hypersensitivity to beta-blockers
- Greater than 1st degree heart block
- Sinus bradycardia
- Congestive heart failure (unless secondary to a tachyarrhythmia responsive to beta-blockers)
- Bronchospastic lung disease (e.g., feline asthma)
- Bradyarrhythmias
- Acute or decompensated congestive heart failure
- Concurrent administration with alpha-adrenergic agonists (e.g., adrenaline)
Efectos adversos
- Bradycardia
- Lethargy and depression
- Impaired AV conduction
- Congestive heart failure (CHF) or worsening of heart failure
- Hypotension
- Syncope
- Diarrhea
- Hypoglycemia
- Bronchoconstriction
- AV block
- Myocardial depression
- Heart failure
- Hypoglycaemia
- Bronchospasm
- Diarrhoea
- Peripheral vasoconstriction
- Depression
Interacciones farmacológicas
- Antacids · May reduce oral propranolol absorption; separate doses by at least one hour
- Anesthetics, General · Additive myocardial depression may occur
- Anticholinergics · May negate cardiac effects of beta-blockers
- Calcium Channel Blockers · Concurrent use should be done with caution due to additive negative inotropic effects, particularly in patients with cardiomyopathy or CHF
- Cimetidine · May decrease the metabolism of propranolol and increase blood levels · moderate
- Diuretics · May increase risk for hypotension · moderate
- Epinephrine · Unopposed alpha effects of epinephrine may lead to rapid increases in blood pressure and decrease in heart rate
- Fluoxetine · May decrease propranolol metabolism; complete heart block reported in one human
- Insulin and Antidiabetic Drugs · Propranolol may prolong the hypoglycemic effects of insulin therapy
- Lidocaine · Clearance may be impaired by propranolol · major
- Methimazole, Propylthiouracil · Propranolol doses may need to be decreased when initiating therapy
- Phenobarbital · May increase the metabolism of propranolol · moderate
Monitorización
- ECG (Electrocardiogram)
- Signs of toxicity (bradycardia, hypotension, lethargy)
- Blood pressure (especially if administering IV)
- Heart rate and rhythm (ECG)
- Blood pressure
- Signs of congestive heart failure (e.g., respiratory rate/effort)
- Blood glucose (especially in diabetic patients receiving insulin)
Sobredosis
**Clinical Signs:** The most predominant expected signs are **hypotension** and **bradycardia**. Other possible effects include CNS depression (ranging from depressed consciousness to seizures), bronchospasm, hypoglycemia, hyperkalemia, respiratory depression, pulmonary edema, AV block, or asystole. **Treatment:** * **Decontamination:** If recent oral ingestion, consider emptying the gut and administering activated charcoal. * **Monitoring:** Monitor ECG, blood glucose, potassium, and blood pressure. * **Cardiovascular Support:** Use IV fluids and pressor agents for hypotension. Treat bradycardia with **atropine**; if atropine fails, cautiously administer **isoproterenol**. A transvenous pacemaker may be necessary. * **Heart Failure:** Treat with digoxin, diuretics, oxygen, and IV aminophylline if necessary. * **Antidotal Therapy:** **Glucagon** (5-10 mg IV; human dose) may increase heart rate and blood pressure, reducing the cardiodepressant effects of propranolol. * **Seizures:** Generally respond to IV diazepam.
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