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The American Society of Health-System Pharmacists reports a shortage of isosorbide dinitrate immediate-release tablets. Unlike most drug shortages, there are three manufacturers of these generic tablets for angina pectoris instead of just one. None gave a reason for the shortage. It could be that there is a shortage of the active principal ingredient per se, or that the API is being used for the more expensive slow-release formulations that are still patent-protected monopolies, but I emphasize that this is only speculation on my part.
A beta-blocker is the first choice for treatment, a calcium channel blocker is often second, and a nitrate may be second or third choice. It is very important to start nitrates at a low dose and use them at the lowest effective dose, because they only work for a few hours before the body's receptors in the arteries and veins will no longer respond until they have been gone from the circulation for about half a day. A feature of isosorbide is that it affects the veins more than the arteries, which helps reduce the load on the heart and allows it to get sufficient oxygen to prevent angina. Simultaneously it helps dilate the arteries in the heart like other nitrates, improving the oxygen supply. Finally dilation of the arteries throughout the body lower blood pressure and make the heart's work easier. It is hard to predict how much of an isosorbide dinitrate tablet is going to be available to the body. It must first be converted to the active mononitrate form in the liver. Anywhere from 10-90% may be converted, with an average of 25%.
When used with a calcium channel blocker, a nitrate may result in a blood pressure that is too low. This is also true when a nitrate is used with sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra).
1 comment:
Ray, thank you for the information. My pharmacy started experiencing supply shortages in May and told me they could not deliver until August. I switched pharmacies and they ordered 1,000 tablets to have on hand for me or so they say. Post by pass I am on 80mg Lisinopril, 100mg Cozaar, 120mg Innopran XL, plus Uroxatral, Propranolol, Diazapem and 3X20mg Isosorbide Dinitrate all of them on a daily basis and I am lucky if my BP is 202/101. It has been as high as 262/138 post by-pass, worse than before by pass. I think someone messed up so I guess I live day to day and wait for the "Big One". Maybe that is a bad attitude but that is how I feel. Isosorbide Dinitrate actually is the only thing combined with the other meds that showed a significant drop in my BP occasionally as low as 165/101 so I guess I feel dependent on it. Now with the supply shortages I feel there is a conspiracy to get rid of those of us who need the drug to sustain life.
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