The interviewer administered the survey (in person or by telephone), using a standardized questionnaire with questions about relevant exposures and symptoms during the month before the survey date. The questionnaire consisted mostly of checklists and fill-in-the-blank entries; the interview lasted about 10 to 15 minutes. Data collected included demographic characteristics, indication for digox- in therapy, duration of digoxin therapy, dose of digoxin, disease states (e.g., symptoms potentially related to heart failure or atrial fibrillation or both), number and date(s) of hospital admissions in the previous month, concurrent illnesses (impaired renal function, malignancy, thyroid disorder, acute diarrhea), symptoms potentially related to digoxin toxicity (anorexia, nausea, vomiting, diarrhea, changes in vision, headache, weakness or dizziness, mental disturbances), dosage of nonprescription medications used in the past month, and whether usage patterns for nonprescription medications had changed over the past month. Participants were asked specifically about their use of 4 OTC products and 30 herbal supplements that have been reported as potentially interacting with digoxin (see Appendix 1) and about their use of any other nonprescription medications not specifically listed. In addition, patient-specific records in the provincial prescription database (PharmaNet) were reviewed to obtain information on the use of prescription medications during the month before the survey date.
Descriptive statistics were used to summarize demographic data, prevalence of diseases, concurrent illnesses, and the use of medications (prescription and nonprescription) with the potential of influencing digoxin therapy. Because herbal supplements were of special interest, nonherbal supplements were grouped with OTC medications in the detailed analysis of nonpre- scription medication use. To evaluate the associated risk of digoxin toxicity, case patients were identified as those reporting one or more symptoms potentially related to digoxin toxicity in the month before the interview. Univariate analysis was used to compare the prevalence of exposures between patients who did and those who did not report symptoms potentially related to digoxin toxicity. The x2 test and Fisher’s exact test were employed, where appropriate, for categorical data; Student’s t test was used for continuous variables. Statistical analyses were performed using SPSS software (version 12.0 for Windows, SPSS Inc, Chicago, Illinois). A p value less than 0.05 was deemed significant. levitra professional