Download Vitamin K Content in Common Foods

CE Offering/Pharmacology
in adverse side effects secondary to potent
vasodilation, including headaches and palpitations. Patients should therefore avoid
the combination of grapefruit juice and
cilostazol.7
The HMG Co-A reductase inhibitors
(statins) are one of the most prescribed
classes of drugs in the world. Simvastatin
(Zocor), lovastatin (Mevacor) and atorvastatin (Lipitor) are all metabolized by CYP
3A4. Taking grapefruit juice with any of
these three statins may increase the risk of
statin-induced myopathies and rhabdomyolysis. Of the three, lovastatin and simvastatin have the strongest risk for interacting
with grapefruit juice.7 Atorvastatin has a
moderate risk of toxicity with grapefruit
juice. If the patient does not want to forego grapefruit juice, substitute pravastatin
(Pravachol), fluvastatin (Lescol) or rosuvastatin (Crestor). These three statins are
metabolized by CYP isoenzymes not affected by grapefruit juice and will not cause
potential toxicity.8,9
U.S. and Canadian prescribing information advises grapefruit avoidance by
patients who take the calcium channel
blockers nisoldipine (Sular) or nifedipine
capsules (Adalat), but not nifedipine tablets (Procardia XL), felodipine (Plendil) or
verapamil (Calan, Verelan). Substituting
amlodipine (Norvasc) for any of the above
would negate the concern about calcium
channel blocker side effects, including
exacerbated peripheral edema, tachycardia,
hypotension and headaches.6
Diazepam (Valium), midazolam (Versed),
quazepam (Doral) and triazolam (Halcion)
each interact with grapefruit juice. Watch
for possible increased sedation with these
medications. Choose alprazolam if a benzodiazepine is necessary and the patient
continues to drink grapefruit juice.10
Prescribing information for the immunosuppressants cyclosporine (Neoral,
Sandimmune) and tacrolimus (Prograf)
advises avoiding grapefruit juice because of
significantly increased bioavailability and
serum concentrations. Signs of toxicity with
cyclosporine include nephrotoxicity, hepatotoxicity and increased immunosuppression.
Signs of toxicity with tacrolimus include
hypertension, tremor, headache and insomnia. This interaction is theoretically possible
with sirolimus (Rapamune) as well.6
Calcium Supplements
Calcium supplements are among the
top 25 over-the-counter products sold
in the United States, and levothyroxine
(Synthroid, Levothroid, Levoxyl, etc.), is
among the top five brand-name drugs sold.
Table 2
Vitamin K Content in Common Foods
Foods with high amounts of vitamin K:
• Vegetables: broccoli, Brussels sprouts, cabbage, collard greens,
endive (raw), kale (raw leaf), kohlrabi, lettuce (bib, red leaf), mustard greens (raw), parsley, spinach, turnip greens (raw), watercress (raw), Swiss chard
• Oils and fats: mayonnaise, canola oil, soybean oil
• Beverages: tea (green tea; brewing green tea may alter vitamin K
content, but no consensus has been reached)
Foods with moderate amounts of vitamin K:
• Vegetables: asparagus, avocado, red cabbage, green peas, dill pickles, iceburg lettuce
• Fats and oils: margarine and olive oil
Foods with low amounts of vitamin K:
• Vegetables: green beans, carrots, cauliflower, celery, corn, cucumber (without peel), eggplant,
mushrooms, onions, green pepper, potato, pumpkin, sauerkraut (canned), tomato
• Fruits
• Meat
• Dairy products
• Oils and fats: corn oil, peanut oil, safflower oil, sesame oil, sunflower oil
• Beverages: coffee, cola, fruit juices, milk, tea (black)
Source: Clotcare Online Resource (www.clotcare.com)
More women than men have osteopenia or
osteoporosis, and more women than men
have hypothyroidism. For this reason, it
would appear that women would be more
likely to take calcium supplements along
with their levothyroxine. This is a harmful
combination because calcium carbonate
supplements can reduce the utilization of
thyroid hormone, especially when a patient
takes it in high doses and in the morning.11
Levothyroxine is best absorbed on an
empty stomach, so it should be taken in
the morning 1 hour prior to breakfast. To
minimize the interaction between calcium
carbonate and levothyroxine, separate the
doses by at least 4 hours. Taking 500 mg of
calcium at lunch and dinner minimizes any
impairment in drug effectiveness.12 High
amounts of soy in the diet can also inhibit thyroid hormone synthesis, especially
if the patient also has low iodine levels.
Advise patients who require thyroid medication and calcium supplementation to
eat soy in small amounts and only at the
evening meal.11 Consuming large amounts
of healthful brassica vegetables (broccoli,
cauliflower and Brussels sprouts) can also
reduce the utilization of thyroid hormone.11
Vitamin K and Warfarin
The interaction between warfarin
(Coumadin) and foods that contain vita-
min K has been well documented in the
literature. Vitamin K is an essential cofactor
in the hepatic production of clotting factors
II, VII, IX and X. As a result of vitamin K
antagonism, warfarin inhibits the production of these four clotting factors. The oral
formulation of warfarin is widely used for
the long-term prevention of thromboembolic disease.13
Because vitamin K and warfarin are
antagonists, the amount of vitamin K in
the diet can diminish warfarin’s anticoagulant effects. The most important concept to
remember about the interaction between
vitamin K and warfarin is consistency.
When patients adhere to a steady diet of
vitamin K-containing foods, their INR levels should not be a concern. Advise patients
to report any significant changes in dietary
vitamin K intake to maintain a therapeutic
INR. Table 2 provides examples of vitamin
K content in popular foods.
The interaction between warfarin and
vitamin K leads to two significant practice
pearls. First, for patients who take warfarin
and have fluctuating INRs, add a low dose
(100 mcg per day) of vitamin K. This will
make the patient less sensitive to changes
in dietary vitamin K and lead to fewer fluctuations in INR. Don’t advise patients to
avoid foods that contain vitamin K. Instead,
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