Why do I need a blood test when taking theophylline?
Theophylline is commonly used as a third-line agent in the management of asthma, after beta-agonists and anti-inflammatories. Unfortunately, its therapeutic level is quite close to its toxic level. This means that the dose that the asthmatic needs to get the full benefit of the drug is not very much lower than the dose which causes side effects which range from unpleasant to dangerous. This would not be such a problem if there weren’t such large variations in the rate at which people metabolize theophylline. Apparently, if a group of people are given the same dose of theophylline, the concentration of the drug in their bloodstreams may vary by up to a factor of seven. Therefore, the best way to monitor that the asthmatic is receiving the optimal amount of theophylline is to take a blood level concentration.
