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Bronchodilator Pregnancy: C — theophylline levels altered in pregnancy; monitor closely

Aminophylline

Brand names: Phyllocontin

Adult dose

Dose: Loading: 5mg/kg IV over 20–30 min. Infusion: 500mcg/kg/h
Route: IV (slow infusion)
Frequency: Loading dose then continuous infusion
Max: 1g loading (max); infusion rate titrated to levels
Loading dose ONLY if NOT already on theophylline. If on oral theophylline: do NOT give loading dose (risk of toxicity). Monitor levels: target 10–20 mg/L. Reduce infusion rate in HF, cirrhosis, elderly, and severe COPD.

Dose adjustments

Renal

No adjustment required — hepatically metabolised.

Hepatic

Reduce infusion rate by 50% in hepatic impairment.

Clinical pearls

  • Aminophylline = theophylline + ethylenediamine (80% theophylline). Levels reported as theophylline equivalents.
  • Narrow therapeutic index: therapeutic 10–20 mg/L; toxic >20 mg/L. Measure level 6h after starting infusion.
  • MAGICS trial: IV magnesium sulphate now preferred over aminophylline in severe acute asthma — fewer adverse effects, similar efficacy.
  • Role limited in modern practice: use only for life-threatening asthma unresponsive to maximal first-line therapy.

Contraindications

  • Porphyria
  • Already on oral theophylline (do not give loading dose)
  • Hypersensitivity to theophylline or ethylenediamine

Side effects

  • Nausea, vomiting, GI discomfort (at levels >15 mg/L)
  • Tachycardia, palpitations, arrhythmias
  • Headache, insomnia
  • Seizures (at toxic levels >30 mg/L)
  • Hypokalaemia (potentiates salbutamol)

Interactions

  • Ciprofloxacin / erythromycin: markedly increase theophylline levels — halve aminophylline dose or avoid
  • Rifampicin / phenytoin: reduce theophylline levels
  • Cimetidine: increases theophylline levels
  • Salbutamol: additive hypokalaemia — monitor K+

Monitoring

  • Theophylline level (trough and at 6h)
  • HR (ECG)
  • K+
  • BP

Reference: BTS/SIGN Asthma 2023; NICE BNF 84. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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