Diagnostic Use
Aminophylline is an alternative name for theophylline.
Theophylline (like caffeine), is a methylxanthine which inhibits the breakdown of cyclic AMP. The increased cyclic AMP concentration stimulates the CNS and heart, and relaxes smooth muscle (including that of the bronchus and vascular bed). It has been used in management of acute asthma.
Both caffeine and theophylline can be used to treat neonatal apnoea, a condition commonly found in low birth weight babies. Because metabolism converts theophylline to caffeine, measuring theophylline in infants may significantly underestimate the total methylxanthine load, and toxicity may go unnoticed. Caffeine test has now been withdrawn.
The therapeutic intervals quoted above is for steady state peak levels, mainly to assess toxicity. The steady-state peak level is the peak level after the patient has been on the drug for at least 3 doses. Note that for asthma, some patients are already well controlled on concentration of 27.5-55 umol/L and thus no need to increase the dose. 65% of the maximum available bronchodilatory effect can be achieved at level of around 55umol/L. For this reason, those at level close to or >110 umol/L will experience about the same therapeutic benefit as those with 65, acute pulmonary edema , congestive heart failure, cor pulmonale, hepatic cirrhosis, severe obstructive pulmonary disease. Examples of drug-drug interaction include cimetidine, macrolide antibiotics like erythromycin, quinolones which can cause increase level. Cigarette smoking and cannabis smoking enhance theophylline clearance.
Reference Intervals
Units: umol/L
Therapeutic interval:
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Asthma:
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55-110
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Neonatal apnoea:
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33-66
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The therapeutic interval applies to steady state peak level (peak level after at least 3 doses have been given), mainly to assess toxicity :
Peak values are attained at:
- Slow release: 5 – 6 h post dose.
- Uncoated, non-sustained release preparation: 2 h post dose.
Uncertainty of Measurement
Uncertainty of Measurement: 8%