氨茶鹼 / 茶鹼
氨茶鹼與茶鹼屬於**甲基黃嘌呤類衍生物**，在獸醫學中主要用作強效的支氣管擴張劑。它們常被用於治療下呼吸道疾病（如貓氣喘、馬復發性呼吸道阻塞及犬支氣管炎）、氣管塌陷，以及作為心因性肺水腫的輔助治療。 > **臨床要點：** 氨茶鹼本質上是茶鹼的水溶性鹽類（透過加入乙二胺製成）。**100毫克的含水氨茶鹼約含有79毫克的無水茶鹼。** 在兩種劑型之間轉換時，必須仔細計算劑量。 雖然這些藥物非常有效，但其**治療指數狹窄**。毒性與劑量相關，不過犬貓對血清濃度的耐受度通常高於人類。由於不同病患在代謝上存在顯著差異，強烈建議進行治療藥物監測（TDM），特別是對於患有肝臟或心臟疾病的動物。
作用機制: The primary mechanism of action involves the competitive inhibition of **phosphodiesterase (PDE)** enzymes. * **PDE Inhibition** → Decreased breakdown of **cyclic AMP (cAMP)** → Elevated intracellular cAMP levels. * Increased cAMP → Enhanced release of endogenous **epinephrine** → Relaxation of bronchial and pulmonary vascular smooth muscle. * Elevated cAMP also inhibits the release of inflammatory mediators like **histamine** and slow-reacting substance of anaphylaxis (SRS-A) from mast cells. * **Intracellular Calcium Translocation:** Methylxanthines alter intracellular ionized calcium dynamics, contributing to increased diaphragmatic contractility (reducing respiratory fatigue) and weak positive inotropic/chronotropic effects on the heart. * **Additional Effects:** Induces mild diuresis, stimulates the central nervous system (CNS) and respiratory centers, and increases gastric acid secretion.
各物種劑量
- Bronchodilation (Extended-Release) · 20 mg/kg PO once daily in the PM; using Slo-Bid: 25 mg/kg PO once daily in the PM · PO · q24h · Products Theo-Dur and Slo-Bid are no longer available in the USA. Cautious use of dog dose/products is a reasonable alternative.
- Bronchodilation · 6.6. mg/kg PO twice daily; using sustained release tablets (Theo-Dur): 25-50 mg (total dose) per cat PO in the evening · PO · q12h or q24h · Using aminophylline tablets or sustained release tablets
- Tracheal collapse (mild clinical signs, <50% collapse) · aminophylline: 5 mg/kg PO, two times daily. · PO · q12h
- Bronchoconstriction associated with fulminant CHF · Aminophylline 4-8 mg/kg SC, IM, IV q8-12h. · SC/IM/IV · q8-12h
- Cough · Aminophylline: 5 mg/kg PO twice daily · PO · q12h
- Bronchodilation · 4.25 mg/kg PO 2-3 times a day · PO · q8-12h
- Pulmonary edema · Aminophylline 2-7 mg/kg IV q6-12h; Theophylline 5-15 mg/kg PO q12h · IV/PO · q6-12h · IV aminophylline should be diluted in at least 100 mL of D5W or normal saline and administered slowly (not >25 mg/min).
- Pulmonary edema · 11 mg/kg PO or IV q8-12h. · PO/IV · q8-12h · To 'load' may either double the initial dose or give both oral and IV dose at the same time. IV infusion in ~1L fluids over 20-60 mins.
給藥途徑
禁忌症
- Hypersensitivity to any xanthines (including theobromine or caffeine)
- Hypersensitivity to ethylenediamine (specific to aminophylline)
不良反應
- Nausea and vomiting
- Diarrhea
- Insomnia / Restlessness
- Polyphagia (increased appetite)
- Polydipsia and polyuria (increased thirst and urination)
- Tachycardia (rapid heart rate)
- Nervousness, excitability, and tremors (especially in horses)
- Diaphoresis (sweating in horses)
- Ataxia
- Seizures (in severe toxicity)
- Cardiac dysrhythmias (in severe toxicity)
藥物相互作用
- Phenobarbital · May decrease theophylline levels via hepatic enzyme induction.
- Fluoroquinolones (e.g., enrofloxacin, ciprofloxacin) · Can significantly increase theophylline levels. Consider reducing theophylline dose by 30% and monitor for toxicity.
- Macrolides (e.g., erythromycin, clindamycin, lincomycin) · Can increase theophylline levels.
- Cimetidine · Can increase theophylline levels by inhibiting hepatic metabolism.
- Ketamine · Concurrent use can cause an increased incidence of seizures.
- Halothane · Concurrent use may cause an increased incidence of cardiac dysrhythmias.
- Sympathomimetics (e.g., ephedrine, isoproterenol) · Toxic synergism; can lead to severe cardiac arrhythmias.
- Beta-blockers (non-selective, e.g., propranolol) · Can increase theophylline levels and antagonize bronchodilatory effects.
- Corticosteroids · Can increase theophylline levels.
監測
- Therapeutic efficacy (improvement in breathing/cough)
- Clinical signs of toxicity (GI upset, CNS stimulation, tachycardia)
- Serum trough levels at steady state (Target: >8-10 mcg/mL in small animals; do not exceed 15 mcg/mL in horses. Human therapeutic range is 10-20 mcg/mL)
過量
Clinical signs of toxicity are usually associated with serum levels **greater than 20 mcg/mL** in humans, though dogs appear to tolerate higher levels. **Life-threatening signs:** * Tachycardia and severe cardiac arrhythmias * CNS effects including seizures and hyperthermia **Treatment is supportive:** * **Decontamination:** Empty the gut, administer activated charcoal and a cathartic if oral ingestion was recent. * **Seizures:** Maintain an adequate airway and treat with IV **diazepam**. * **Monitoring:** Continuous ECG monitoring for arrhythmias. Monitor and correct fluid/electrolyte imbalances. * **Symptomatic Care:** Hyperthermia may be treated with phenothiazines; severe tachycardia may be treated with **propranolol** if life-threatening.
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