Pyrantel Theophylline

An interaction of pyrantel with theophylline has been reported (3). 

An 8-year-old boy with status asthmaticus was given intravenous aminophylline and then switched to mod-ified-release oral theophylline on day 3, when his serum theophylline concentration was 15 pg/ml. On day 4 he was given a single dose of pyrantel 160 mg (for A. lumbricoides infection) at the same time as his second oral dose of theophylline. About 2.5 hours later his serum theophylline concentration was 24 pg/ml, and a further 1.5 hours later it had risen to 30 pg/ml. No further theophylline was given and no theophyUine toxicity occurred. 

Not understood. One suggestion is that the pyrantel inhibited the liver enzymes concerned with the metabolism of the theophylline, thereby increasing its levels. However, this is unlikely as the interaction occurred so rapidly. Another suggestion was that pyrantel may have increased drug release from the sustained-release theophylline preparation. 

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