May Meeting, Riverview

As we straggled in and began munching our heart healthy lunch, Sheila Turkell answered questions. For instance, herbs can be quite potent and they can interact with other medications, but since they don’t have to be approved we don’t even know exactly how potent they are.

Sheila opened the meeting, issued the usual call for volunteers for Mended Hearts, and introduced our featured speaker, pharmacist James Hode, RPh, and his topic, anticoagulants and their drug interactions. He gave us a detailed handout and referred to it as he spoke.

Many of us, we told him, take Coumadin (generic: warfarin), Plavix (clopidogrel) or daily aspirin; none are on low-molecular-weight heparin. These are drugs prescribed to inhibit clotting if clots are likely to cause heart attack or stroke.

A diagram in the handout helped explain how these drugs work. Coumadin and heparin work in different ways to inhibit the formation of thrombin, the most important part of blood clots. Thrombin reacts with platelets, which is where Plavix and aspirin act. Disrupting any part of the process prevents clots.

Doctors titrate Coumadin depending on the diagnosis. For most patients the target is an INR (measured by a standard blood test) of 1.5 to 2.5 (higher INR means “thinner” blood: less clotting). Most patients reach this target with 2.5 to 5 mg a day.

Drug interactions for anticoagulants center on two things: Vitamin K, and the Cytochrome P450 system.

Cytochrome P450 is a group of enzymes in the liver that metabolize drugs and other substances, usually changing them into something less active. Some drugs can alter the effectiveness of these enzymes.

Vitamin K is found in green leafy vegetables and is also produced in your gut flora (the bacteria in your intestines) and in your liver. It makes your blood “thicker” - more likely to clot. Coumadin works by counteracting Vitamin K.

Normally your coagulation is naturally balanced: proteins S and C inhibit coagulation, while Vitamin K promotes it. Research published just recently suggests a maintenance dose of Vitamin K for patients on Coumadin to make them less sensitive to small changes.

Diet should be adjusted for patients taking Coumadin to avoid too much Vitamin K. That doesn’t mean foods containing Vitamin K are prohibited, just don’t eat a lot of them.

High protein diets can increase clotting. Coumadin binds to protein (albumin) in the blood and when it does it becomes less active. Consuming more protein binds more Coumadin, so the dosage may have to be increased.

Important: limit grapefruit (and grapefruit juice) to about 8 ounces a day. It increases the activity of many drugs, including Coumadin and calcium channel blockers, by interfering with the Cytochrome P450 pathways that eliminate the drugs.

Alcohol, caffeine and other food substances increase the activity of Coumadin. Others, including the hydrocarbons in grilled meats, counteract it. Avoid excess.

Proton pump inhibitors (PPI) reduce stomach acidity and may be prescribed to prevent stomach bleeding due to anticoagulants. Recent research has found that they inactivate Plavix. Plavix itself is inactive; its active form (which reduces clotting by inactivating platelets) is made in the liver through the Cytochrome P450 system. PPIs (especially Prilosec and Nexium) use up the enzymes that activate Plavix.

Many drugs, including antifungals and antibiotics, increase or decrease warfarin activity. Your doctors should be told about all the drugs you’re taking. Stay away from alternative medicine products because they’re untested and their effects are not predictable.

We got a lot of information, a better understanding of interactions, more detail than described here, and a comprehensive handout to keep and refer to.