Aminophylline is a 2:1 complex of theophylline and ethyenediamine. Aminophylline has greater water solubility than theophylline. In biological fluids aminophylline dissociates to theophylline hence the pharmacological effects of aminophylline are those of theophylline. Theophylline is a xanthine derivative with the main pharmacological action of direct relaxation of bronchial smooth muscles, relieving bronchospasm. The bronchodilatory effect of theophylline is minimal if bronchospasm is not the cause.
The bronchodilatory effect may be via inhibition of selected phosophodiesterases, which produces an intracellular cyclic AMP. Theophylline also directly stimulates the medullary respiratory centre. Other pharmacological effects of theophylline include stimulation of cardiac muscle (increasing both heart rate and myocardial contractility at higher doses), stimulation of the cental nervous system, transient diuresis, increased gastric secretion, decreased peripheral resistance and cerebral vasoconstriction.
Aminophylline injection BP is indicated for the treatment of reversible bronchospasm associated with chronic bronchitis, emphysema, bronchial asthma and chronic obstructive pulmonary disease. It may also be used for paroxysemal dysponea associated with left heart failure
Aminophylline injection BP is also contraindicated in patients hypertensive to xanthines or to ethylenediamine.Aminophylline injection BP is also contraindicated in patients with coronary artery disease where myocardial stimulation might prove harmful.Aminophylline injection BP is also contraindicated in patients with bronchiolitis (bronchopneumonia)
Use in pregnancy
ADEC Category A: This category includes drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the foetus having been observed. The pharmacokinetics of aminophylline may be altered during pregnancy and therefore serum theophylline concentrations may need to be measured more frequently in patients undergoing aminophylline theraby during pregnancy
Use in children
Children are particularly sensitive to xanthines, especially the CNS stimulant effects. The margin of safety above therapeutic doses is small. Consequently, serum theophylline levels should be carefully monitored in paediatric patients. Rapid intravenous injection is not recommended in children
Cardiovascular system: tachycardia, palpitations, extrasystoles, increased pulse rate, flushing, hypotension, circulatory failure, atrial and ventricular arrhythmia, peripheral vasoconstriction.
Central nervous system: headache, nervousness, insomnia, irritability, restlessness, dizziness, reflex hyperexcitability, seizures, anxiety, tremor, lightheadedness, excitement
Gastrointestinal system: nausea, vomiting, heartburn, epigastric pain, abdominal cramps, anorexia, diarrhea, haematemesis
Genitourinary: increased urination, albuminuriaOther: fever, tachypnea, hypersensitivity induced dermatitis
Dosage and administration
Aminophylline injection BP may be adminidtered by intravenous infusion or by slow intravenous injection at a rate not exceeding 20-25 mg/ml. Recommended doses are given as a guide only. Dosage must be individualized based on patient characteristics, clinical responses and steady state theophylline concentration. Other factors that affect dosage should be considered for example age, smoking history, disease states, diet, drug interactions etc. Doses should be calculated on lean (ideal) body weight. Oral theophylline therapy should be substituted for intravenous therapy as soon as adequate improvement has been made. A loading dose is generally administered over 20-30 minutes, followed by a maintenance dose