Use of Dietary Supplements by Patients Taking Digoxin: RESULTS

21 Nov
2010

dietary supplements

Patient CharacteristicsOf the 447 potential participants identified in the chart review, 143 could not be contacted, and 132 were exclud­ed for various reasons: declined to participate in the study, were excluded by their doctors, lacked sufficient proficiency in English, were no longer taking digoxin, had died, were in poor health, or were deaf. A total of 172 patients were enrolled for the study in person (n = 33, 19.2%) or by phone (n = 139, 80.8%) between June 2001 and November 2003. Participants’ demographic character­istics, including digoxin use and concurrent illnesses, are summarized in Table 1. As expected, the most common indications for digoxin therapy were heart failure and/or atrial fibrillation (a total of 143 patients, 83.1%). Despite their digoxin therapy, most patients (151 or 87.8%) had experienced symptoms commonly associated with heart failure and/or atrial fibrillation in the month before the survey, including light-headedness, dizziness, loss of consciousness, heart palpitations, shortness of breath, fatigue, coughing, lung congestion, and swelling in the legs or ankles. Eighteen (10.5%) of the patients were unsure of the reason for digoxin therapy. Impaired renal function, thyroid disorder, and acute diarrhea were the relevant concurrent disorders most commonly reported. Twelve of the patients reported having cancer, but none had undergone chemotherapy in the month or year before the study. Only 47 (27.3%) of the patients had undergone testing for serum digoxin level in the past year.

Use of Nonprescription Medications

Table 2 summarizes the use of nonprescription medications (OTC drugs and/or dietary supplements) by the patients in the month before the study. Use of OTC drugs and/or nonherbal supplements was reported by 153 (89.0%) patients; nonherbal supplements (vitamins and minerals) were the most popular (used by 121 patients, 70.3% of the total sample). Common OTC medications included acetaminophen (19/172 patients, 11.0%) and acetylsalicylic acid (51/172 patients, 29.7%), neither of which is known to interact with digoxin.
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Table 1. Characteristics of 172 Adult Patients Taking Digoxin for Heart Conditions



Characteristic


No.

(%)

of
Patients*



Demographic


Mean age ± SD (range) (years) Sex Men
Women


65.2±12.0


122 50


(22-90)


(70.9)

(29.1)



Primary indication for digoxin


Heart failure alone


60


(34.9)


Atrial fibrillation alone


55


(32.0)


Heart
failure


+

atrial
fibrillation


28


(16.3)


Not sure


18


(10.5)


Othert


11


(6.4)



Concurrent illness


Acute diarrhea


32


(18.6)


Thyroid disorder


26


(15.1)


Hypothyroidism


21


(12.2)


Hyperthyroidism


3


(1.7)


Not sure


2


(1.2)


Impaired renal function


17


(9.9)


Malignancy


12


(7.0)



Digoxin therapy (mean ± SD, range)


Duration* (years)


5.9±7.2


(0.25-52)


Dose (|jg/day)


174.8±77.9


(62.5-500)


Average no. of tests of digoxin level
per year


0.75±1.59


(0-12)


Patients with test of digoxin level in
past year


47


(27.3)


SD

=


standard deviation. *Except where indicated otherwise.


tDilated idiopathic cardiomyopathy,
pacemaker, leaky valve, coronary artery bypass graft(s),


enlarged heart, coronary artery
dissection, or myocardial infarction.



ФА

total
of


23


patients


(13.4%)

were
unsure how long they had been taking digoxin.

Potentially interacting OTC medications and nonherbal supplements, namely antacids, potassium supplements, quinine, and kaolin-pectin, were used by 50 (29.1%) of the participants; antacids and potassium supplements were the most popular of these (Table 2). For 34 (68.0%) of these 50 patients, usage of OTC medi­cations and nonherbal supplements in the month before the study was similar to usage over the previous year; only 9 (18.0%) of the 50 patients reported increased use.

Table 2. Use of Nonprescription Medications, in the Month Preceding the Study, by 172 Patients Receiving Digoxin Therapy



Substance


No.

(%)

of
Patients


Regular use of any nonprescription
product


153


(89.0)


Use of nonherbal supplements


121


(70.3)



Potentially interacting over-the-counter productstt


Any


50


(29.1)


Antacid


37


(21.5)


Potassium supplement


15


(8.7)


Quinine


4


(2.3)


Kaolin-pectin


2


(1.2)


Any, but excluding potassium


41


(23.8)



Herbal supplements


Any§


37


(21.5)


Potentially interacting^


4


(2.3)


Ginseng (any type)


2


(1.2)



Cassia angustifolia


1


(0.6)


Cascara sagrada bark


1


(0.6)


Licorice root


1


(0.6)


*Over-the-counter products or dietary
supplements or both.


tIncludes antacids, potassium
supplements, quinine, and kaolin-pectin


*Some patients used more than one
potentially interacting substance.



§


Echinacea,

evening primrose oil, saw palmetto, strauss heartdrops, lecithin,
cranberry capsules,


garlic,
Ginkgo biloba,

fenugreek, apple cider, chamomile, flaxseed, chondroitin.



^Includes ginseng,

Cassia angustifolia,

cascara sagrada bark, and licorice root.

Thirty-seven (21.5%) of all 172 patients reported having used herbal supplements in the previous month, but only 4/172 patients (2.3%) reported that they had used a herbal supplement that potentially interacts with digoxin. The most popular herbal supplements were Echinacea, evening primrose oil (Oenothera biennis), and saw palmetto (Serenoa repens). Of the 37 patients who used herbal supple­ments, 27 had used only 1 such supplement, 9 had used between 2 and 6 supplements, and 1 reported using 10 herbal supplements. The 135 participants who did not use herbal supplements gave the following reasons: not wanting to use additional medication (28 or 20.7%), not believing in the efficacy of herbal supplements (20 or 14.8%), being concerned about the safety of herbal supplements (17 or 12.6%), not knowing enough about herbal supplements (12 or 8.9%), being aware of herb-digoxin interactions (11 or 8.1%), counselling by physicians (8 or 5.9%), counselling by pharmacists (1 or 0.7%), and other reasons (7 or 5.2%). Thirty-one (23.0%) of the nonusers provided no reason.
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