Complementary Alternative Cardiovascular Medicine

Chapter 4 / Herb and Dietary Supplement Interaction 55
Grapefruit Juice
Grapefruit acts on the drug transporter Pgp and, as well, is a potent
inhibitor of cytochrome P450 enzymes (49), producing greatly increased
AUC of a considerable number of medications, notably the calcium
channel blockers amlodipine, felodipine, nifedipine, nimodipine,
nosoldipine, nitredipine (50), and verapamil (51), used for hypertension,
angina, and certain arrythmias. Grapefruit also increases blood concentrations
of cyclosporine (52) and the antiarrythmic quinidine (53). The
mechanism of action of grapefruit is claimed to chiefly involve selective
downregulation of CYP3A4 in the small intestine (54). The active agents
are naringenin (55); the aglycone of naringin, the major bioflavonoid
and bitter principle in grapefruit juice; and two furanocoumarins, 6',7'dihydroxybergamottin
(DHB) (56) and an uncharacterized other
(FC726) (57); DHB exerts multiple effects, whereas FC726 works specifically
on CYP3A4.
LAXATIVE HERBS AND DRUGS
Bulk-forming laxative herbs, such as the hydrocolloidal fiber-containing
guar (Cyamopsis tetragonolobus) gum, psyllium (Plantago spp.),
konjac (Amorphophallus rivieri), and others, taken in sufficient quantity
can delay gastric emptying and reduce the rate of absorption of carbohydrates
and drugs, including digoxin (61).
Laxative herbs that contain stimulant anthranoids, including senna
species (Cassia senna, C. acutifolia, and C. angustifolia), Chinese rhubarb
(Rheum officinale), cascara sagrada (Rhamnus purshiana), frangula
or alder buckthorn (Rhamnus frangula), yellow dock (Rumex crispus),
and drug aloe, the leaf exudates of Aloe vera, can decrease the absorption
of intestinally absorbed drugs resulting from an increased rate of intestinal
transit (62).
CONCLUSION
Patients who are on anticoagulants should avoid consuming ginkgo,
ginseng, dong quai, and danshen products. Those who consume other
herbs, particularly those for which there is any indication of potential for
affecting platelet function, should have their bleeding times monitored
(2). Anyone who is taking critical chronic medication should not use St.
John’s wort, because the herb reduces the bioavailability of many drugs.
The effect of herbal laxatives in decreasing absorption of drugs should
also be considered.