In one study
theophylline clearance was reduced by 19% after 6 weeks of treatment with
intramuscular methotrexate 15 mg weekly. A few patients complained of nausea and the
theophylline dosage had to be reduced in one.
The
clinical significance of this interaction is unclear as reductions of this
magnitude are rarely significant. It seems most likely to affect those patients with
theophylline levels at the top of the therapeutic range.