Monday, June 28, 2010

It's a total eclipse of the voltage gated calcium channel

This is a short one, most the the drugs that you would think act on the heart are covered under other categories.
Anti-Arrhythmics are broken down into four classes. Class I drugs act by blocking sodium channels, and are divided into three sub classes. Ia (Quinidine, Disopyramide and Procainamide), Ib (Lignocaine (also an anaesthetic) and Phenytoin) and Ic (Flecainide and Encainide). Ib drugs associate and disassociate rapidly, Ic drugs more slowly, and Ia have properties in between. Class II are the beta blockers, and they all end in -olol. Amidarone and Sotalol are Class III and they extend action potential of the heart through unclear mechanisms that somehow affect K channels. Finally Verapamil and Diltiazem are Class IV which block calcium channels and slow conduction of the SA and AV nodes.
Digoxin is a cardiac glycoside derived from foxglove (digitalis), it blocks Na/K channels, which slows down AV conduction. This causes the heart to fill more with each contraction, causing it to contract harder and resulting in a greater ejection fraction. It is used in heart failure and as an antiarrythmic, but it is not a particularly pleasant drug.Nitrates are the most common anti anginal drug. They're a smooth muscle relaxant which allows greater cardiac perfusion. They do however have side effects such a postural hypertension and development of tolerance.
And finally calcium channel blockers (antagonists) as oral antihypertensives. These are grouped under the heart because they have a greater effect on the heart that other smooth muscle relaxants do. As described before they are Class IV anti-arrhythmics, but they also cause the arteries to dilate, with little effect on the veins.

That's it for heart pharmacology, for those of you wondering how the magic of Manic Grandiosity happens below is a portrait of my sister and I 'working together' to construct this blog.

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