麻黃鹼
麻黃鹼是一種非兒茶酚胺類的擬交感神經胺。在獸醫學中，它主要用於治療犬貓的**尿道括約肌機制不全 (USMI)**，儘管苯丙醇胺 (PPA) 因中樞神經副作用較低而更常被首選。 此外，它也可作為注射型**升壓劑**以對抗麻醉引起的低血壓，並可作為**支氣管擴張劑**用於呼吸道疾病。 > **臨床要點：** 由於麻黃鹼比許多其他擬交感神經藥物更容易穿透血腦屏障，它可能會引起輕度至中度的中樞神經刺激，在某些病患身上表現為焦躁不安或激動。
作用機制: Ephedrine is a **mixed-acting sympathomimetic**. - **Indirect Action (Primary):** It enters the sympathetic nerve terminal and promotes the release of stored **norepinephrine** into the synaptic cleft. - **Direct Action (Secondary):** It directly stimulates **α- and β-adrenergic receptors**. **Key Pathways:** - **α1-receptors** → Smooth muscle contraction → Increased internal urethral sphincter tone (improving continence) and peripheral vasoconstriction (increasing blood pressure). - **β1-receptors** → Positive inotropic and chronotropic effects on the heart → Increased cardiac output. - **β2-receptors** → Smooth muscle relaxation → Bronchodilation. > **Note:** Because it relies heavily on endogenous norepinephrine stores, repeated frequent dosing can deplete these stores, leading to **tachyphylaxis** (diminished response over time).
各物種劑量
- Treatment of bronchospasm (emergency treatment) · 2-5 mg PO · PO · Once
- Treatment of urinary incontinence · 2-4 mg (total dose) PO q8h · PO · q8h
- Treatment of urinary incontinence · 2-4 mg/kg PO q6-12h or 2-4 mg (total dose) PO q8h · PO · q6-12h or q8h
- Treatment of urinary incontinence · 2-4 mg per cat PO q8-12h · PO · q8-12h
- Treatment of hypotension associated with anesthesia · 0.15-0.25 mg/kg IV boluses OR CRI at 5-10 micrograms/kg/minute · IV · To effect or CRI · Dilute into 5 mL of a balanced electrolyte solution or saline and give small increment IV boluses until desirable blood pressure achieved.
- Hypotension during anaesthesia · Dose not specified in monograph · IV/IM · As needed · Perioperative · Use with caution.
- Nasal congestion (cat 'flu') · Dose not specified in monograph · topical · Not specified · Short-term · Proposed for treatment of nasal congestion; may be of some benefit.
- Treatment of bronchospasm (maintenance therapy) · 1-2 mg/kg PO q8-12h · PO · q8-12h
- Treatment of bronchospasm · 2 mg/kg PO q8-12h · PO · q8-12h
- Treatment of urinary incontinence · 5-15 mg (total dose) PO q8h · PO · q8h
給藥途徑
禁忌症
- Severe cardiovascular disease
- Cardiac arrhythmias
- Pregnancy
- Lactation
- Glaucoma
不良反應
- Restlessness
- Irritability
- Tachycardia
- Hypertension
- Anorexia
- Tachyphylaxis (decreased response to subsequent doses)
- Panting
- Mydriasis (dilated pupils)
- CNS stimulation (restlessness, agitation)
- Atrial fibrillation
- Vasoconstriction
- Reduction of intestinal wall motility and tone
藥物相互作用
- Acepromazine (and other phenothiazines) · Phenothiazines block alpha-adrenergic receptors; concomitant use can lead to unopposed beta-activity causing vasodilation and increased cardiac rate.
- Alpha-blockers (e.g., phentolamine, prazosin) · May negate the therapeutic effects of ephedrine.
- General Anesthetics (cyclopropane, halogenated hydrocarbons) · Increased risk of arrhythmias. Propranolol may be administered should these occur.
- Beta-blockers · Concomitant use may diminish the effects of both drugs.
- Digoxin · Increased risk of arrhythmias if used concurrently. · major
- Monoamine Oxidase Inhibitors (including amitraz) · Should not be given within two weeks of receiving MAOIs; severe hypertension and hyperpyrexia are possible.
- Other Sympathomimetic Agents (e.g., phenylpropanolamine) · Should not be administered together as increased toxicity may result.
- Reserpine · May reverse the pressor effects of ephedrine.
- Theophylline · May increase the risk for theophylline toxicity. · moderate
- Tricyclic Antidepressants · May decrease the pressor effects of ephedrine.
- Urinary Alkalinizers (e.g., sodium bicarbonate, citrates, carbonic anhydrase inhibitors) · May reduce urinary excretion of ephedrine and prolong its duration of activity, potentially requiring dosage adjustments.
監測
- Clinical effectiveness (resolution of incontinence, improved blood pressure, or bronchodilation)
- Heart rate and rhythm
- Blood pressure
- Behavioral changes (restlessness, irritability)
- Heart rate and rhythm (ECG during anaesthesia)
- Resolution of urinary incontinence
- Signs of CNS stimulation or excessive panting
過量
Clinical signs of overdosage may consist of an exacerbation of adverse effects (restlessness, tachycardia). In a **very large overdose**, severe cardiovascular signs (hypertension leading to rebound hypotension, bradycardias to tachycardias, and cardiovascular collapse) or CNS effects (ranging from severe stimulation to coma) can be seen. **Treatment:** - If the overdose was recent, empty the stomach using usual precautions. - Administer activated charcoal and a cathartic. - Treat clinical signs supportively as they occur.
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