chemical structure of quinidine
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Duraquin

Quinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent in the heart. It is a stereoisomer of quinine, originally derived from the bark of the cinchona tree. more...

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Like all other class I antiarrhythmic agents, quinidine primarily works by blocking the fast inward sodium current (INa). Quinidine's effect on INa is known as a use dependent block. This means that at higher heart rates, the block increases, while at lower heart rates the block decreases. The effect of blocking the fast inward sodium current causes the phase 0 depolarization of the cardiac action potential to decrease (decreased Vmax).

Quinidine also blocks the slowly inactivating tetrodotoxin-sensitive Na current, the slow inward calcium current (ICa), the rapid (IKr) and slow (IKs) components of the delayed potassium rectifier current, the inward potassium rectifier current (IKI), the ATP-sensitive potassium channel (IKATP) and Ito.

The effect of quinidine on the ion channels is to prolong the cardiac action potential, thereby prolonging the QT interval on the surface EKG.

The half life of oral quinidine is 6 to 8 hours, and it is eliminated by the cytochrome P450 system in the liver. About 20 percent is excreted unchanged via the kidneys.

Qunidine-induced thrombocytopenia (low platelet count) is mediated by the immune system, and may lead to thrombocytic purpura.

Read more at Wikipedia.org


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The Latest Heartburn Drug: Dressed Up In Purple, But Just Another Knock-Off - Nexium - Brief Article
From Healthfacts, 9/1/01 by Maryann Napoli

The ads should be familiar by now. A large group of purple-clad middle-aged people is standing, scattered along the rocky edge of the ocean. RELIEVE THE HEARTBURN, HEAL THE DAMAGE. The camera pans in on one woman,: "I didn't know acid reflux could wear away the lining of my esophagus." The waves repetitively splashing against the rocks drive home the point. Now people with heartburn have another costly drug (about $143 a month) at their disposal called Nexium.

Nexium is a knock-off of several other high-priced heartburn drugs, namely, Prilosec, Prevacid, Protonix, and Aciphex. All are from a drug class called proton pump inhibitors (PPIs), which block stomach-acid production by inhibiting the acid-producing cells known as parietal cells.

It's tempting to dismiss Nexium as just another "me too" drug, one chemical notch away from the other PPIs, and one more example of a pharmaceutical company trying to make us think it has come up with something new. But actually Nexium signals a new pharmaceutical industry twist. Normally, a company makes a me-too drug to cut into a competitor's profits, but in this case, both Prilosec and Nexium are made by the same company. AstraZeneca's reason for competing with its own product is obvious. Prilosec (called Losec in Canada) will soon go off patent, and generic versions will become available at about two-thirds the cost.

Gone is the pretense that carried the day for Prozac's competitors, who claimed that their me-too antidepressants (Zoloft, Paxil, etc) had fewer side effects. There is no significant difference in side effects between Prilosec and Nexium. Both drugs come in delayed-release form, so AstraZeneca has not introduced a new format. In fact, Nexium offers no innovation; the drug owes its existence entirely to AstraZeneca's need to retain the company's considerable share of the $8.3 billion PPI Market.

Both Prilosec and Nexium are to be prescribed for "the treatment of heartburn and other symptoms associated with gastroesophageal reflux disease (GERD)." Both drugs can be prescribed for the short-term treatment (4-8 weeks) of erosive esophagitis which has been diagnosed by endoscopy. Both can also be prescribed for the "maintenance of healing of erosive esophagitis." Both are purple.

The deja vu aspect of Nexium doesn't trouble the Food and Drug Administration. An FDA spokesman explained in a telephone interview that the agency sticks solely to the question of whether the data submitted by a drug company shows that the drug is more effective than a placebo and that its benefits outweigh its risks. A drug company is not required by the FDA to show that its "new" drug is an improvement over existing drugs.

The Nexium ads directed at physicians misleadingly imply that the new drug is more powerful than Prilosec. "We've captured the essence of Prilosec and created a NEW PPI...introducing Nexium the POWERFUL new PPI from the makers of Prilosec..."

AstraZeneca did take the unusual step of conducting studies to compare its two PPIs against each other. The results were modest. Only two of the four comparative clinical trials showed that Nexium had any advantage over Prilosec. And the improvement was only in the 5-8% range. No doubt, AstraZeneca is hoping that few doctors will notice how slight Nexium's advantage is over Prilosec and continue prescribing the expensive drug when the generic versions of Prilosec arrive.

What to do:

If your doctor has prescribed Nexium, read about the supporting studies and see how many people were treated successfully. (You won't find this information in the fine print on the back page of the Nexium magazine ads.) Go to the Nexium Web site (www.purplepill.com) and download the FDA-required four-page prescribing information by clicking into "important product information." Or, call 1(800) 236-9933. Note that the studies lasted only six months.

See below for a partial list of drugs and supplements that can aggravate heartburn.

Numerous commonly prescribed drugs and over-the-counter products can worsen the symptoms of gastroesophageal reflux disease, or GERD, because they reduce the lower esophageal sphincter's ability to completely contract and close. Other drugs and supplements, if taken regularly, can further damage an eroded esophagus due to repeated direct contact with the lining of the esophagus.

Here's a list of each based on information provided by the Mayo Clinic's G.I. Digest:

Drugs That May Worsen GERD

Anticholinergics for digestive diseases (e.g., Bentyl, Atropine). Anticholinergics are drugs that block the effects of acetylcholine, a substance produced by the body which is responsible for certain nervous system activities;

Sedatives (e.g., phenobarbital, sold under dozens of brand names) and Tranquilizers (e.g., Valium, etc);

Theophylline (sold under more than 40 different brand names in the U.S. and Canada) for the treatment of asthma and other chronic obstructive pulmonary diseases;

Calcium Channel Blockers for angina and hypertension (e.g., Procardia, Adalat, Cardizem);

Progesterone, a hormone usually taken in conjunction with estrogen to counteract the latter drug's cancer-causing effect on the uterus;

And opioids for pain relief (e.g., morphine).

Drug That Can Damage the Esophagus

Potassium supplements;

Iron supplements;

Antibiotics (e.g., tetracycline);

Nonsteroidal anti-inflammatory drugs, such as aspirin, acetaminophen, ibuprofen, etc.;

Fosamax, an osteoporosis drug. (See last month's HealthFacts for ways to minimize esophageal damage);

And Quinidine for heart rhythm disorders (e.g., Duraquin, Quinaglute Dura-Tabs, Quinidex).

---

Maryann Napoli is the associate director of the Center for Medical Consumers in New York City.

COPYRIGHT 2001 Center for Medical Consumers, Inc.
COPYRIGHT 2001 Gale Group

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