Methoxsalen Caffeine

Oral methoxsalen and S-methoxypsoralen markedly reduce caffeine clearance but the clinical significance of this is uncertain. Topical methoxsalen does not interact with caffeine. 

A study in patients receiving PUVA therapy (methoxsalen either orally, in 4 patients, or topically as a bath in 7 patients, plus UVA) found that die clearance of a single 150-mg dose of caffeine was markedly reduced in the patients given oral methoxsalen but not altered in those given topical methoxsalen. ... 

Both methoxsalen and 5-methoxypsoralen inhibit the hepatic metabolism of caffeine by the cytochrome P450 isoenzyme CYP1A2, thereby markedly increasing caffeine levels. ... 

The practical consequences of this interaction are as yet uncertain, but it seems possible that the toxic effects of caffeine will be increased. In excess, caffeine (including that from tea, coffee and cola drinks) can cause jitteriness, headache and insomnia. The interaction does not appear to occur with topical methoxsalen. 

Caffeine is metabolized by the isoenzyme CYP1A2. Drugs that inhibit this isoenzyme (including fluvoxamine, ciprofloxacin, cimetidine, amiodarone, fluoroquinolones, furafylline, interferon, methoxsalen, and mibefradil) may slow the metabolism of caffeine. In persons drinking multiple cups of coffee daily, high levels of caffeine could accumulate (Carrillo and Benitez 2000). 

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