Samples must be separated within 24hrs of collection.
Sample stability:
-
1 week at 2-8 o C
-
60 days at -20 o C
Units: umol/L
Therapeutic interval:
|
Asthma: |
55-110 |
|
Neonatal apnoea: |
33-66 |
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: 8%
Principle: Immunoturbidometric assay
Reagents: Roche TDM Theophylline kit
Analyser: Cobas c502
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 Caffeine test has now been withdrawn.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 <110 umol/L but with greater risk for toxicity. Most clinicians choose an initial target of 55 umol/L.
Factors that reduce theophylline clearance include: prematurity, age >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.
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427