MECHANISM OF ACTION
Theophylline may induce the metabolism of
carbamazepine. Carbamazepine may induce the metabolism of theophylline.
DISCUSSION
In one case report, concurrent administration of carbamazepine
and theophylline resulted in sub-therapeutic levels of theophylline, a
decrease in theophylline half-life, and a worsening of the patient's
clinical condition. In another report, a patient maintained on carbamazepine
for eight months experienced a convulsion eight days after beginning
theophylline therapy. The patient had previously received theophylline three
times without adverse effect. In a follow-up study in this patient,
concurrent administration of theophylline and carbamazepine resulted in
decreases in carbamazepine levels by 29.6-36.7%, a decrease in carbamazepine
half-life by 11.8%, and another grand mal seizure. Theophylline levels in
this patient were high; however, not enough information is given in the
report to determine if carbamazepine inhibited the metabolism of
theophylline.
CLINICAL EFFECTS
Decreased levels of carbamazepine and theophylline may
result in decreased clinical effectiveness of these agents.
SEVERITY LEVEL
2-Severe Interaction: Action is required to reduce the risk
of severe adverse interaction.
PATIENT MANAGEMENT
During concurrent therapy, theophylline and
carbamazepine serum concentrations should be monitored. The dosage of one or
both agents may need to be adjusted.
PREDISPOSING FACTORS
None determined.
REFERENCES