Posted by Ueli on October 29, 2001 at 21:18:44:
There have been lately some rather confusing posts about Verapamil, so I try to muddle the issue a bit more.
Many call Verapamil a heart or blood pressure medication, this is quite confusing for the context we are using it. Therefore, we should stick to what it does basically: it is a Calcium channel blocker. After all, a hammer is generally called a hammer and not a thumbnail coloring device :-)
What are these calcium channels and why do we want to block them? The nerve receptors on smooth muscles need Ca++ ions so they can react to nerve impulses. The Calcium ions are too big to cross the cell membrane directly, therefore, nature has provided specialized transport channels. Smooth muscles are found around the blood vessels and around the intestines. They are not very strong, not very fast acting, and the main point: they are controlled by the autonomous nervous system. The second kind of muscles we have are the striped ones: These are the one we use to move our bones, they are strong, fast acting and directly controlled by our will. The heart is a special case, because of the heavy work it has to do it is made from striped muscles, however, it is like the smooth muscles controlled by the autonomous nervous system.
Verapamil was developed for heart diseases.
It helps preventing angina pectoris by relaxing and preventing of coronary artery spasm. It is also useful to combat arrhythmia.
High blood pressure is often caused by too tight vessels. By relaxing the overtight smooth muscles around the vessels flow resistance is reduced, and so reducing the pressure needed.
If someone wants to indulge in more medical parlance, go to rxlist.com on Verapamil
For an otherwise healthy Clusterhead the above considerations are of no consequence. Important for us is that the Calcium-depleted muscles around the vessels in the head respond only sluggish to nerve impulses.
At the start of a cluster attack an erroneous signal from the hypothalamus tells the vessels to expand, and in doing so they press on the trigeminal nerve, causing the pain. The pain signal re-enforce (in a way not entirely clear to me) the wrong signal to expand the vessels, and this positive feedback is responsible for the extremely fast raise of an attack. This expansion of the vessels is delayed and less extreme by the action of Verapamil, the feedback is reduced and hence the attack is damped down in intensity, ideally down to none.
The sluggishness of the smooth muscles does not interfere much with the two most popular abortives, Imitrex and oxygen. Imitrex floods the system with a serotonin agonist, mimicking a very strong signal to contract the vessels. When the oxygen content of the blood is higher than normal, the brain issues a command to contract the vessels (as it very closely regulates the amount of oxygen it receives). In both cases it does not matter if the respond time is a fraction of a second longer.
Experience of Verapamil usage for heart and blood pressure conditions give a therapeutic dosage of 120 to 240 mg/day, for hard cases maybe 360 mg. These recommendations - together with the fact that higher doses were not tested for safety - makes many doctors reluctant to up the dose for a clusterhead. However, since most of us have no heart problems, the worst side effect of a higher dose is constipation, but to take care of this there are remedies less severe than castor oil. Some might experience a slowing of the heart rate, but for me this was a good thing: from 95 to 65 at rest. For most the influence on blood pressure is negligible, but for a few this may set an upper limit of the dosage.
Here two quotes from articles about the usefulness of high Verapamil doses for CH everybody should read:
(a repeat from an earlier post, but you didn't read it anyway, LOL)
From Correct management of cluster headaches by Prof Peter Goadsby and Dr Manjit Matharu:
Verapamil is the preventative drug of choice in both episodic and chronic CH. Clinical experience has demonstrated that higher doses than those used in cardiological indications are needed, so outpatient assessment and follow-up is appropriate. The dose is increased until the cluster attacks are suppressed, side-effects intervene or the maximum dose of 960mg daily is achieved.
From Medscape article: The Treatment of Cluster Headache and Facial Pain
Clinical experience suggests that verapamil is the best prophylactic treatment. However, 800 mg or more may be necessary before patients respond.
(You need a password to access Medscape, but it is available to everybody for free. This article gives a good description on the mechanism of a cluster attack.)
Finally a word about normal release versus extended (or slow) release versions of Verapamil: Dr. Goadsby wrote somewhere (sorry, I have no link handy) that - for a reason unknown - the normal release Verapamil helps a clusterhead better than the slow version. Splitting the daily dosis into 3 evenly space doses will give a fairly even concentration throughout the day, as the elimination half life is well over 12 hours.
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