Interactions between theophylline and other drugs may be pharmacodynamic but are more often related to pharmacogenetics, and it is the alteration of theophylline clearance by other drugs that leads to an increase or decrease in serum theophylline concentrations, hence the need for prompt monitoring of their blood concentrations.

Blood samples are taken after the peak blood concentration reached steady state 2～4h after administration, and then monitored every 4h. The effective blood concentration for the treatment of acute asthma attacks was 10～20 mg/L. The effective blood concentration for the prevention of asthma attacks and for the treatment of apnea in premature infants was 5～10 mg/L. The effective blood concentration for the treatment of acute asthma attacks is 10-20 mg/L, and for the prevention of asthma attacks and the treatment of apnea in preterm infants is 5-10 mg/L. The blood concentration should not be more than 20 mg/L, otherwise the probability of adverse reactions increases significantly.

（1）Any time signs or symptoms of theophylline toxicity occur;

（2）For those with persistent symptoms of wheezing, before a dose increase is proposed in consideration of the possibility that blood levels may be below therapeutic concentrations;

（3）After administration from initiation of therapy to adjustment to the final dose;

（4）When a change in treatment regimen is required due to the development of a new disease, worsening of a chronic disease, or a condition that may alter theophylline clearance;

（5）Infants under 1 year of age with immature theophylline metabolic pathways should be given special attention to dosage and monitoring of serum theophylline concentrations (Recommendation Class B).

See the following table for oral theophylline dosage adjustments based on blood concentration as a guide (Recommendation Class A)

Table 6 Table of oral aminophylline dosimetry based on blood concentration as a guide

The narrow therapeutic window for theophylline limits its intravenous use in pediatrics, but its safety for oral administration and its multimodal pharmacological effects have maintained its place in therapeutic areas such as asthma, where heterogeneity is evident.

Intravenous use of theophylline in the treatment of acute asthma exacerbations should be guided by a balanced approach based on clinical improvement, alertness to adverse effects, and blood levels, with the goal of achieving safe and rational use.