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OBJECTIVE: To determine the methodological quality of clinical trials that examined possible interactions of St John's wort with conventional drugs, and to examine the results of these trials. DESIGN: Systematic review. DATA SOURCES: Electronic databases from inception to April 2004, reference lists from published reports, and experts in the field. STUDY SELECTION: Eligible studies were prospective clinical trials evaluating the pharmacokinetic effect of St John's wort on the metabolism of conventional drugs. DATA EXTRACTION: Two reviewers selected studies for inclusion and independently extracted data. DATA SYNTHESIS: 22 pharmacokinetic trials studied an average of 12 (SD 5) participants; 17 trials studied healthy volunteers and five studied patients. Most (17) studies used a "before and after" design; four studies used control groups other than the active group. Three studies randomised the sequence of administration or the participants to study arms or periods; three studies blinded participants or investigators. In 15 trials, investigators independently assayed the herb. Of 19 trials with available plasma data, three found no important interaction (change in area under the curve < 20%) and 17 found a decrease in systemic bioavailability of the conventional drug; in seven studies the 95% confidence interval excluded a decrease of < 20%. CONCLUSION: Clinicians and patients should beware of possible decreases in the systemic bioavailability of conventional drugs when taken concomitantly with St John's wort.

BACKGROUND: Health authorities create and maintain administrative databases. Despite the potential advantages of these databases, the validity of the information they include must be considered.OBJECTIVE: To examine the validity of diagnosing chronic obstructive pulmonary disease (COPD) from a large administrative database.METHODS: Physician services and prescription claims data related to COPD and asthma were extracted from the Quebec universal medical insurance register (Régie de l'assurance-maladie du Québec; RAMQ) from the period of April 1, 1994 to March 31, 1999. Before obtaining the data, criteria for the validity of the COPD diagnosis in the database were formulated based on the epidemiology of COPD in the province. The extent to which the database satisfied these criteria are described within the present paper.RESULTS: For patients aged 65 years or older, COPD was two times more prevalent in the RAMQ database than in the 1994/1995 National Population Health Survey. One in three patients with a RAMQ-diagnosis of COPD also had a RAMQ-diagnosis of asthma, and 47% of patients aged 65 years or older with a RAMQ-diagnosis of COPD did not fill any prescription for beta-2-agonists. In addition, 42% of patients with a RAMQ-diagnosis of COPD who never had a RAMQ-diagnosis of asthma appeared only once with that diagnosis in the database. Of all patients aged 65 years or older with a RAMQ-diagnosis of COPD, 37% and 23% met the operational definitions of 'possible COPD' and 'probable COPD', respectively.CONCLUSIONS: Most RAMQ-diagnoses of COPD lack validity; therefore, the validity of database diagnoses should be routinely ascertained before using administrative databases in clinical and health services research.