Pitfalls in the interpretation of serum theophylline levels
C. Lam, Z. Ben-Zvi, S. Barnett and M. Kattan
In two groups of patients, noncompliance with drug regimens resulted in
misinterpretation of serum theophylline levels. All six chronic asthmatics
in the first group, found in a retrospective review of 43 outpatient
charts, had outpatient serum theophylline levels in the therapeutic range
(10 to 20 microgram/mL) and at least a 7-microgram/mL greater inpatient
theophylline level while receiving the same dosage. When hospitalized,
four of these patients had serum theophylline levels in the toxic range
(greater than 20 microgram/mL). In the second group four hospitalized
patients had persistently low serum theophylline levels despite an adequate
theophylline dose. When compliance was enforced, serum theophylline levels
rose significantly. Compliance cannot be assumed in the outpatient with a
serum theophylline level in the therapeutic range or in the hospitalized
patient. Determination of serum theophylline level after supervised drug
administration is recommended in inpatients requiring unusually high doses
of theophylline or in those whose condition is poorly controlled despite
having serum theophylline levels in the therapeutic range (10 to 20
microgram/mL).