Diltiazem is classified as an antiarrythmic or calcium channel blockers. Antiarrythmics/calcium channel blockers will act upon the heart by relaxing the heart muscle and slowly down the electrical system. The electrical system is most likely going hair wire like in atrial fibrillation; so at the AV junction it just calms everything down. It is used in Atrial Fibrillation, high blood pressure and ACS. Since it acts on your heart by changing your rhythm it can lower your blood pressure and thus you can feel dizzy. Everybody is different and how you react to the medication is different than everyone else. So it is hard to predict how you will react, but generally speaking we have a good idea.
Kidney disease and liver disease can have a great impact on your medication since all medicines are excreted from the body from these organs. If you have any of these conditions let your doctor know. The medicine can build up in your body and cause you to have more medicine than expected in your system when the next dose is due. This will compound and make you feel dizzy and pass out. So talking to your doctor and becoming a partner in your health is crucial.
Seek medical attention right away if you feel your heart is slow, you feel weak, have chest pain, shortness of breath lightheaded or fainting.
They come in time release capsules as well regular tablets. Breaking open the capsule changes how your medicine absorbed in your body and is no longer time released. If your having trouble swallowing there are alternatives and talking with your doctor will help greatly.
Below are pictures for easy identification.