What is aminophylline (intravenous medication) injection?

Aminophylline Injection: A Bronchodilator for Severe Asthma

Aminophylline injection is an intravenous medication used as a second-line treatment for severe, acute asthma exacerbations when patients continue to deteriorate despite initial therapy with nebulized bronchodilators and systemic corticosteroids. 1, 2

Composition and Pharmacology

Aminophylline is a complex of theophylline and ethylenediamine, with approximately 79% of its weight being anhydrous theophylline. It functions primarily as a bronchodilator by relaxing bronchial smooth muscle. 2, 3

• Standard concentration: 25 mg/mL (equivalent to 19.7 mg/mL anhydrous theophylline)
• pH: 8.8 (8.6 to 9.0)
• Administered via slow intravenous injection or diluted for intravenous infusion

Clinical Use in Asthma Management

Aminophylline is positioned in treatment algorithms for acute severe asthma when patients show:

• Continued deterioration despite initial therapy
• Life-threatening features such as:
  • PEF <33% of predicted or best
  • Silent chest, cyanosis, or feeble respiratory effort
  • Bradycardia or hypotension
  • Exhaustion, confusion, or coma 1

Dosing Protocol

Adults with Acute Severe Asthma:

• Loading dose: 250 mg administered intravenously over 20 minutes
• Maintenance: For smaller patients, 750 mg/24 hours; for larger patients, 1500 mg/24 hours
• Important: Omit the loading dose if the patient is already taking oral theophyllines 1

Children with Acute Severe Asthma:

• Loading dose: 5 mg/kg over 20 minutes
• Maintenance infusion: 1 mg/kg/hour
• Important: Omit the loading dose if the child is already receiving oral theophyllines 1

Monitoring and Precautions

1. Therapeutic Drug Monitoring:

   • Monitor serum theophylline concentrations if infusion continues beyond 24 hours
   • Target serum concentration: 10-20 μg/mL

2. Special Populations Requiring Caution:

   • Patients with cor pulmonale
   • Cardiac decompensation
   • Liver dysfunction
   • Patients taking drugs that reduce theophylline clearance (e.g., cimetidine)
   • In these patients, initial infusion rate should not exceed 17 mg/hr (21 mg/hr as aminophylline) 2

3. Administration Precautions:

   • Do not mix aminophylline in a syringe with other drugs
   • Add separately to intravenous solutions
   • Avoid mixing with alkali-labile drugs (epinephrine HCl, norepinephrine bitartrate, isoproterenol HCl, penicillin G potassium) 2

Efficacy and Evidence Considerations

The evidence for aminophylline's efficacy in acute asthma is mixed:

• Meta-analyses have questioned whether aminophylline adds significant benefit to standard care with nebulized beta-agonists and systemic corticosteroids 4, 3, 5
• Aminophylline may increase adverse effects without improving efficacy when added to inhaled beta-agonists 6
• However, guidelines continue to recommend aminophylline as part of the treatment algorithm for life-threatening asthma not responding to initial therapy 1

Common Side Effects and Toxicity

• Nausea, vomiting
• Headache
• Tachycardia, palpitations
• Tremor
• Seizures (at toxic levels)
• Cardiac arrhythmias (at toxic levels)

Clinical Pearl

While aminophylline remains in treatment guidelines for severe asthma, its use should be reserved for cases not responding to first-line therapies (oxygen, nebulized beta-agonists, systemic corticosteroids). The risk of toxicity must be carefully weighed against potential benefits, particularly since more recent evidence suggests limited additional benefit over modern standard therapy 3, 5.