Posted by Ueli (195.162.175.19) on January 09, 2002 at 00:52:36:
In Reply to: would this make sense? posted by don on January 08, 2002 at 22:12:02:
The elimination half life time of Verapamil for a single dose is 2.8 to 7.4 h (hours). But this increases soon to 4.5 to 12 h when taking it regularly, due to a depletion of the enzyme used to degrade it. For clusterheads, who take more Verapamil than used in the studies, the half live is probably on the high side.
Assume someone takes 100 mg of instant release Verapamil every 8 hours. After a sufficient long time a quasi steady state will evolve: The serum concentration will take the shape of a saw tooth, with a peak right after taking a pill and sloping down to a low just before the next pill. These high and low values depend on the half life time (T½) and are
for T½ = 12 h: equivalent to a single dose of 270 mg (high) and 170 mg (low) and
for T½ = 6 h: 166 mg and 66 mg.
In calculating these values I assumed a truly instant release. But the resorption time of Verapamil is about 1 to 2 h, and this degrades the saw tooth concentration curve to a smoother wave shape, with less pronounced peeks and troughs. But the average values remain about the same. For the extended release version the peak is smoothed out even further, but since this is usually taken only once per day the variation between max and min concentration is about the same.
An interesting question is how long does it take to reach the steady state concentration. For T½ = 6 h after only one day 90% of the steady state is reached. For T½ = 12 h it takes 2 to 3 days.
Why then does it take 1 or 2 weeks for Verapamil to take full effect? Probably because it takes a longer time to saturate the Calcium channels.
Since the resorption times of both regular and sustained release Verapamil are short compared to the serum concentration buildup times, it does not matter which one to choose in regard of getting relieve as fast as possible.
BUT there are 2 good reasons to choose the regular release version:
1) The worlds foremost expert on cluster headaches, Dr. Peter Goadsby, recommends it. He doesn't know exactly why it's better, but it has probably something to do with the different concentrations of the metabolites of Verapamil.
2) It is cheaper.
Doctors often think along the line of heart diseases when prescribing Verapamil, and for some heart conditions the sustained release version is more or less mandatory.
If you are interested in the pharmacology of Verapamil, visit the link below for a few hours :-)