美托洛爾
**美托洛爾 (Metoprolol)** 是一種心臟選擇性（**β1-特異性**）腎上腺素受體阻斷劑，廣泛應用於獸醫學中的多種心血管疾病管理。 主要臨床應用包括： * 控制**心室上性心搏過速**及心室性期前收縮 (PVCs/VPCs)。 * 治療**全身性高血壓**。 * 治療貓的**肥厚性心肌病 (HCM)**，有助於減少動態左心室流出道阻塞並改善舒張期充盈時間。 由於其相對的 β1-選擇性，在患有併發**支氣管收縮疾病**（如貓氣喘）的病患中，美托洛爾通常被認為比非選擇性 β-阻斷劑（如普萘洛爾 propranolol）更安全，但在較高劑量下可能會失去選擇性，仍需謹慎使用。
作用機制: Metoprolol competitively blocks **beta1-adrenergic receptors** located primarily in the myocardium. **Mechanism Pathway:** Blockade of beta1-receptors → decreased activation of adenylyl cyclase → reduced intracellular cAMP → decreased intracellular calcium influx. This results in: * **Negative chronotropy**: Decreased sinus heart rate. * **Negative dromotropy**: Slowed atrioventricular (AV) conduction. * **Negative inotropy**: Decreased myocardial contractility and cardiac output. * Decreased myocardial oxygen demand and reduced blood pressure. *Clinical Pearl*: Metoprolol lacks intrinsic sympathomimetic activity (ISA) and membrane-stabilizing activity. At higher dosages, its cardioselectivity diminishes, leading to **beta2-receptor blockade** in bronchial smooth muscle → potential bronchoconstriction.
各物種劑量
- As an oral beta blocker · 2-15 mg (total dose) PO q8h · PO · q8h
- For rate control in chronic atrial fibrillation · 0.25-1 mg/kg PO q1224h. · PO · q1224h · Note: 'q1224h' is transcribed exactly as it appears in the source text, likely a typo for q12-24h.
- For CHF (early/mild or well-controlled) · 0.2 mg/kg PO twice daily, with slow titration upwards every 2-3 weeks up to 0.4-6.6 mg/kg PO three times a day. · PO · BID to TID · Many dogs will not tolerate this upward titration.
- To decrease the incidence of atrial fibrillation and flutter in dogs undergoing valve surgery · 0.4-1 mg/kg PO q24h · PO · q24h · Using sustained release metoprolol (ToprolXR) administered before and as soon as feasible after surgery.
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給藥途徑
禁忌症
- Overt or unstable heart failure
- Hypersensitivity to beta-blockers
- Greater than first-degree heart block
- Sinus bradycardia
不良反應
- Bradycardia
- Lethargy and depression
- Impaired AV conduction
- Congestive heart failure (CHF) or worsening of heart failure
- Hypotension
- Hypoglycemia
- Bronchoconstriction (at high doses)
- Syncope
- Diarrhea
藥物相互作用
- General Anesthetics · Increased risk for heart failure and hypotension due to additive myocardial depressant effects.
- Calcium-Channel Blockers (e.g., diltiazem, verapamil, amlodipine) · Concurrent use should be done with caution; additive negative inotropic and chronotropic effects, particularly in patients with preexisting cardiomyopathy or CHF.
- Digoxin · May increase negative effects on SA or AV node conduction.
- Diuretics (thiazides, furosemide) · May increase the hypotensive effect of metoprolol.
- Hydralazine · May increase the risks for pulmonary hypertension in uremic patients.
- Quinidine · May increase metoprolol plasma concentrations.
- Reserpine · Potential for additive effects including hypotension and bradycardia.
- SSRI Antidepressants (e.g., fluoxetine, sertraline, paroxetine) · May increase metoprolol plasma concentrations.
- Sympathomimetics (e.g., metaproterenol, terbutaline, epinephrine, phenylpropanolamine) · May have their actions blocked by metoprolol, and they may in turn reduce the efficacy of the beta-blocker.
監測
- Cardiac function
- Pulse rate
- ECG (if necessary)
- Blood pressure (if indicated)
- Signs of toxicity (bradycardia, hypotension, lethargy)
過量
Overdosage primarily results in extensions of the drug's pharmacologic effects: **hypotension, bradycardia, bronchospasm, cardiac failure, and potentially hypoglycemia**. **Treatment:** * **Decontamination**: If recent oral ingestion, consider emptying the gut and administering activated charcoal. *Caution*: Inducing emesis can be risky as coma and seizures may develop rapidly. * **Monitoring**: Continuous ECG, blood pressure, blood glucose, and potassium. * **Cardiovascular Support**: Treat symptomatically. Use IV fluids and pressor agents for hypotension. * **Bradycardia**: Treat with atropine. If atropine fails, isoproterenol may be given cautiously. A transvenous pacemaker may be necessary. * **Cardiac Failure**: May be treated with digitalis glycosides, diuretics, and oxygen. * **Antidote**: Glucagon (5-10 mg IV - human dose) may increase heart rate and blood pressure and reduce the cardiodepressant effects of metoprolol.
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