Pregnancy Currently taking Quinidine or Magnesium additive Renal failure - serum creatinine more than 2 mg/DL or estimated glomerular filtration rate (eGFR) less than 60 ml/min (the worst, ascertained by the participant electronic records in the last 6 months). If the result is near these limits (i.e. serum creatinin 1.5-2) a second analysis will be done near the study enrollment.