Herbal Toxicity and Drug-Herb Interactions

[Audio] In this lesson we'll discuss drug-herb interactions involving antihypertensive medications..

[Audio] What are the major determinants of blood pressure? Blood pressure is mainly affected by cardiac output and peripheral resistance. Cardiac output is mainly determined by heart rate and cardiac contractility. Drugs (and/or herbs) that increase or decrease heart rate are referred to as positive or negative chronotropes/chronotropic drugs, respectively. Drugs (and/or herbs) that increase or decrease cardiac contractility are referred to as positive or negative inotropes/inotropic drugs, respectively. Peripheral vascular resistance is mainly affected by vascular tone..

[Audio] So, what causes increased blood pressure? Increased heart rate, increased contractility, vasoconstriction, increased blood volume. What causes decreased blood pressure? Decreased heart rate, decreased contractility, vasodilation, decreased blood volume. Knowing these processes and definitions allows us to better understand the mechanisms of action of antihypertensive drugs and the mechanisms by which herbs may interact with them..

[Audio] There are many types of antihypertensive drugs with various and sometimes overlapping mechanisms of action..

[Audio] The names of these drug classifications are very helpful in letting us know their mechanisms of action..

[Audio] What types of herbs interact with antihypertensive drugs? Herbs that affect the blood pressure or the determinants of blood pressure ( heart rate, vascular tone, cardiac contractility, blood volume)..

[Audio] Many herbs that clear heat also act to lower blood pressure. The mechanism of action includes suppression of sympathetic stimulation, dilation of blood vessels, and diuresis. However, it is important to keep in mind that the antihypertensive actions of some of these herbs are only documented by in vitro studies via intravenous injection, and may not be replicated in clinical situations in vivo How can we be sure that these interactions will: 1) even occur at all; 2) be clinically significant; or 3) impact our patients' health. We cannot be sure. In fact, since many herbs (and/ or their chemical constituents) have not been extensively studied in human clinical trials, most of the interactions we will learn are "potential" or "theoretical" based on observed or expected mechanism of action. The following slides will list herbs with potential interactions with antihypertensive medications..

Clear Deficiency Heat. Di Gu Pi Inhibition of ACE Qing Hao Decreased cardiac contractility, decreased heart rate.

Clear Heat, Cool Blood. Mu Dan Pi prolonged effect Sheng Di Huang Xuan Shen Vasodilation, decreased heart rate.

Clear Heat, Drain Fire. Qing Xiang Zi moderate effect Xia Ku Cao Rapid onset Zhi Mu.

Clear Heat, Dry Damp. Huang Bai Antihypertensive effect from derivative Xyloponin Huang Lian Huang Qin Vasodilation, sympathetic inhibition Long Dan Cao.

Clear Heat, Resolve Toxicity. Lian Qiao Shan Dou Gen Ye Ju Hua Vasodilation, adrenaline inhibition Effect duration: 2 hours.

Regulate Blood, Stop Bleeding. Ce Bai Ye Vasodilation Huai Hua Mi Decreased heart rate Pu Huang Decreased heart rate No effect from PO administration.

Extinguish Wind, Stop Tremors. Di Long Gou Teng Decreased heart rate, reduced PVR Some CCB effect similar to verapamil Reduces SBP & DBP.

A r om a tic. Transform Damp Hou Po Reduced BP 20mmHg for 10 minutes (in cats) Open Orifices Niu Huang.

Release Exterior. Cool Ge Gen Mu Zei Warm Xin Yi Hua.

Transform Phlegm. Phlegm Heat Chuan Bei Mu Mild effect Pang Da Hai.

Dispel Wind Damp. Du Huo Marked effect, 1 to2 hours duration Qing Feng Teng Rapid onset Quick development of tolerance.

Drain Damp. Ban Ban Lian Diuretic Marked, prolonged effect Bian Xu Diuretic, increased urine output.

Tonifying. Tonify Yang Du Zhong Vasodilation Dry-fried form more effect Tolerance develops.

Relieve Food Stagnation Lai Fu Zi Slow, prolonged effect Shan Zha Vasodilation Downward Draining Huo Ma Ren Mild effect.

Expel Parasites Bing Lang Inhibition of ACE Stabilize and Bind Lian Zi Lian Zi Xin.

[Audio] These charts were made from information found in the Chen book..

Herbs with Hypotensive Effect. Bai Guo Di Yu Ku Lian Pi Qing Mu Xiang Xi Xian Cao Bai Ji Li Er Cha Kun Bu Ren Dong Teng Xiang Fu Bi Ba Fo Shou Lai Fu Zi Ren Shen Xie Cao Bi Cheng Qie Gao Ben Lian Zi Xin San Qi Xin Yi Hua Chang Shan Ge Gen Ling Yang Jiao Sang Bai Pi Xu Chang Qing Che Qian Zi Gou Teng Ling Zhi Sang Ji Sheng Xuan Shen Chen Xiang Hu Jiao Lu Lu Tong Sha Yuan Zi Ye Ju Hua Chi Shao Hu Zhang Man Jing Zi Shan Dou Gen Yin Yang Huo Chou Wu Tong Huai Hua Mu Dan Pi Shan Zha Yu Zhu Chuan Bei Mu Huang Bai Mu Zei Sheng Jiang Yuan Zhi Chuan Wu Huang Lian Niu Bang Zi Shui Niu Jiao Ci Wu Jia Huang Qin Niu Huang Suan Zao Ren Da Ji Huo Ma Ren Pang Da Hai Tian Ma Di Gu Pi Jing Tian San Qi Qing Feng Teng Tu Si Zi Di Long Jue Ming Zi Qing Hao Wu Zhu Yu.

[Audio] Many herbs have blood pressure-lowering effects. Fewer herbs have demonstrated blood pressure-raising effects..

[Audio] We should be mindful of factors that may interfere with mechanisms of drug action or potentiation of side effects. For example, ARBs, ACE inhibitors, K-sparing diuretics can all cause hyperkalemia. We should use caution administering herbs with high concentrations of potassium, especially if the patient is taking more than one of these drugs, or the if the patient has impaired kidney function..

[Audio] These herbs are contraindicated for those with hypertension..

[Audio] These herbs are cautioned for those with hypertension..

[Audio] How do we monitor for signs of clinically significant interaction? Obviously, we should have patients monitor their blood pressure and track changes. (If they are not already doing so, it is helpful to have patients write down/electronically record their home blood pressure readings. Blood pressure changes, if they occur, will likely happen over time. It is unlikely that administering an herb that has an interaction with an antihypertensive medication will suddenly or dramatically increase or decrease a patient's blood pressure. We also want to monitor factors that influence blood pressure: heart rate & rhythm, cardiac output, kidney function ( fluid retention, electrolyte balance). With an interaction that causes additive hypotensive effects, patients may become dizzy or lightheaded. They may feel tired, sleepy, or confused. Drug-herb interactions with antihypertensive medications may be used synergistically to provide additional blood pressure control. Communication is important. You, as the herbal medicine practitioner should be aware of the patients medications, and you or the patient should inform the patient's prescriber of any herbal therapies administered..

References. Chen, J., Chen, T. & Crampton, L. (2012). Chinese medical herbology and pharmacology . City of Industry, Calif: Art of Medicine Press. Clinical Pharmacology. www.clinicalpharmacology.com Finkel, R., Clark, M. A., & Cubeddu, L. X. (2009). Pharmacology. Philadelphia: Lippincott Williams & Wilkins. Jennes, F. & Flaws, B. (2004). Herb toxicities & drug interactions : a formula approach . Boulder, CO: Blue Poppy Press. Katzung, B., Masters, S. & Trevor, A. (2009). Basic & clinical pharmacology . New York London: McGraw-Hill Medical..