Drug Monitoring

Interactions of St. John's wort with various drugs depend on concentrations of active components. Herbal remedies are not prepared following rigorous pharmaceutical standards. Wide variations in the active component of St. John's wort in various commercial preparations have been reported. Draves and Walker (59) reported that in commercial tablets of St. John's wort, the percentage of active components varied from 31.3 to 80.2% of the claim of active ingredients based on labeling of the bottle. Studies have demonstrated that cytochrome P 450 enzyme induction by St. John's wort depends on the hyperforin content, and products that do not contain substantial amount of hyperforin (<1%) may not show clinically significant interactions with drugs (22). Arold et al. (60) demonstrated that low hyperforin containing St. John's wort had no significant interaction with alprazolam, caffeine, tolbutamide and digoxin. Moreover, hyperforin is photosensitive and unstable in aqueous solution while degradation is dependent on the pH of the solution (61).

Because interaction between St. John's wort and drugs may depend on the concentrations of active components of St. John's wort, measurement of active components of St. John's wort in human serum may have clinical implications. Bauer et al. described a high performance liquid chromatographic method (isocratic reverse phased-HPLC) for determination of hypericin, pseudohypericin using fluorimetric detection and hyperforin by UV detection. The limit of detection was 0.25 ng/mL of hypericin and pseudohypericin and 10ng/mL for hyperforin in human plasma (62). Pirker et al. also used liquid-liquid extraction using n-hexane and ethyl acetate (70:30 by vol) and reverse phase HPLC with UV fluorescence and mass spectrometric (electrospray ionization) detection for quantification of active components of St. John's wort in human plasma. The linearity for hypericin determination was 8.2-28.7 ng/mL for hypericin and 21.6-242.6 ng/mL for hyperforin (63). Several liquid chromatographic methods have also been reported for determination of active components of St. John's wort in various commercial preparations (64,65).

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