Ephedra (Ephedra sinica)
The predominant active constituent in ephedra, also known as ma
huang in Chinese medicine, is ephedrine. Its sympathomimetic effects are used, often
in combination with caffeine, to promote weight loss, increase energy, and treat
respiratory conditions such as asthma and bronchitis. In 1998, 2% of obese Americans
and 1% of the general population took over-the-counter weight loss products containing
ephedra.[24]
Current usage rates of ephedra are
probably higher in light of an FDA proposal in 2001 to withdraw approval of phenyl-propanolamine,
another popular over-the-counter weight loss agent.
Ephedra is far less safe than other commonly used herbal medications.
It has been associated with numerous adverse events, including fatal cardiac and
central nervous system complications.[25]
Hypertension,
tachycardia, vasoconstriction, and vasospasm are the putative causes of myocardial
infarction and stroke in these patients.[26]
Ephedra
may also affect cardiovascular function by causing myocarditis.[27]
Many of these adverse events are reported in healthy patients taking typical doses
of ephedra ( Table 15-5
).
Long-term use results in
TABLE 15-5 -- Adverse events associated with ephedra in 11 patients
|
Patient No. |
Age/Sex |
Estimated Dose of Ephedra Alkaloids (mg/day) |
Duration of Use |
Adverse Event |
Outcome |
Preexisting Conditions or Concurrent Risks |
|
1 |
35/F |
45 |
1 wk |
Subarachnoid hemorrhage |
Permanent disability |
None |
|
2 |
22/M |
20–60 |
Unknown |
Arrhythmia |
Permanent disability |
Asthma |
|
|
|
|
Cardiac arrest |
|
|
|
3 |
28/F |
21 |
1 day |
Cardiac arrest |
Permanent disability |
None |
|
4 |
43/M |
60 |
7 mo |
Cardiac arrest |
Death |
Family history of coronary artery disease |
|
5 |
37/F |
36 |
1 wk |
Severe hypertension |
Death |
None |
|
|
|
|
Cardiac arrest |
|
|
|
|
|
|
Hypokalemia |
|
|
|
6 |
59/F |
36 |
3 wk |
Acute myocardial infarction |
Coronary artery bypass surgery |
Hypertension |
|
7 |
38/M |
20 |
1 yr |
Arrhythmia |
Death |
None |
|
|
|
|
Cardiac arrest |
|
|
|
8 |
47/F |
44–65 |
9 mo |
Hypertension |
Permanent disability |
Concomitant ingestion of caffeine and ethanol |
|
|
|
|
Bilateral lacunar infarctions |
|
|
|
9 |
29/M |
30 |
2 wk |
Stroke |
Permanent disability |
Concomitant use of dehydroepiandrosterone and androstenedione |
|
10 |
39/M |
Unknown |
Unknown |
Hemorrhagic stroke |
Permanent disability |
None |
|
11 |
47/M |
Unknown |
3 wk |
Hemorrhagic stroke |
Permanent disability |
Possible hypertension |
|
From Haller CA, Benowitz NL: Adverse cardiovascular
and central nervous system events associated with dietary supplements containing
ephedra alkaloids. N Engl J Med 343:1833, 2000. |
tachyphylaxis from depletion of endogenous catecholamine stores and may contribute
to intraoperative hemodynamic instability. In these situations, direct-acting sympathomimetics
are the first-line therapy for hypotension and bradycardia. Halothane should be
avoided in patients who have recently taken ephedra because of the increased risk
of ventricular arrhythmias. Concomitant use of ephedra and monoamine oxidase inhibitors
can result in life-threatening hyperpyrexia, hypertension, and coma. Heavy ephedra
use can result in nephrolithiasis, which by some estimates accounts for 0.06% of
all kidney stones.[28]
[29]
The pharmacokinetics of ephedrine have been studied in humans.
[30]
[31]
The elimination
half-life of ephedrine (5.2 hours) is approximately the same whether given as an
alkaloid in ephedra or as purified ephedrine hydrochloride. However, absorption
may be slower (absorption rate constant of 0.49/hour versus 1.73/hour) when ephedrine
is consumed as part of an herbal medication. Given this information, ephedra should
be discontinued at least 24 hours before surgery.
