Propanolol
(again)
bác sĩ Ân Đặng
Ds Lê Văn Nhân viết:
Thưa quý anh chị,
Bác sĩ Trần-mạnh-Ngô đã chịu khó hội đủ các chuyên gia về cách dùng propanolol
cho migraine. Chúng ta đã nghe bs Nguyễn-văn-Đích về nội khoa, bs Thái-minh-Trung
về tâm thần, hôm nay xin giới thiệu bài của 1 nephrologist: bs Ân-Đặng:
Chúng tôi xin cảm ơn bs Trần-mạnh-Ngô và bs Ân-Đặng cũng như 2 bs Nguyễn-văn-Đích
và Thái-minh-Trung.
Bs Ân Đặng viết:
In response to your question, propanolol has FDA-approved indications
for the treatment of hypertension, angina, post-MI, tachyarrhythmias (as
a Class II antiarrhythmic agent), and hypercatecholamine states (hyperthyroidism,
pheochromocytoma, congestive heart failure, etc.). It is also used to
treat essential tremor, prevent migraine attacks, lower portal vein pressure
in portal hypertension, and reduce symptoms of anxiety (It might be helpful
in post-traumatic stress disorder). Being a beta-blocker, propanolol lowers
blood pressure and heart rate even when it is administered only for preventing
migraine. It must be used with caution in combination with other classes
of antihypertensives. I would not combine propanolol with another beta-blocker
or verapamil due to high risk of heart block.
Propanolol is no longer widely used in treating hypertension for the following
reasons:
1) Its non-selective blockade of both beta-1 and beta-2
receptors causes more side effects compared to newer, more cardioselective
agents. For example, beta-2 blockade by propanolol leads to acute bronchospasm--not
recommended for asthmatic/COPD patients.
2) Its relatively short duration of action requires frequent
dosing (at least tid), increasing the likelihood of patient noncompliance.
Propanolol can be prescribed in its long-acting form, known as Inderal-LA.
However, Inderal-LA is not as well known as atenolol and metoprolol.
3) Its bioavailability is variable due extensive first-pass
metabolism in the liver, making its effect less predictable in patients
with impaired hepatic function.
4) It has been available on the market as a generic drug for many years
and therefore is no longer promoted by the pharmaceutical industry. Unfortunately,
doctors tend to remember new drugs heavily promoted by pharmaceutical
companies who feed them well or give them gifts/perks. No pharmaceutical
representative who wants to keep his/her job will tell doctors to prescribe
generic propanolol, even though all neurologists and internists are well
aware of its utility in preventing migraine attacks. When I was a resident
working in Neurology clinics, I prescribed Inderal and Inderal-LA to many
migraine patients, as instructed by my Internal Medicine and Neurology
faculties.
According to the first article mentioned below, the mechanisms of the
antimigraine effect of propranolol have not been established. "The
antimigraine effect may be due to inhibition of vasodilatation or arteriolar
spasms over the cortex. Beta-adrenergic receptors have been demonstrated
in the pial vessels of the brain." Propanolol is a highly lipophilic
drug which can cross the blood-brain barrier readily, but I have not found
any literature stating that this property is the reason why it is preferred
in preventing migraine. Other beta-blockers, as well as calcium channel
blockers e.g. nifedipine, can be also prescribed for migraine prophylaxis.
It's just that propanolol has a proven track record of preventing migraine
and is available on all drug formularies. Therefore, physicians rely on
it by experience ... despite not getting free dinners from the maker of
Coreg!
For further details on propanolol, click on the following links:
http://www.mentalhealth.com/drug/p30-i02.html
http://en.wikipedia.org/wiki/Propranolol
An Dang, M.D.
Nephrology
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