Kava and Digoxin: Safe Herb-Drug Combo?

observational-study PMID: 17079360

Kava and Digoxin: Safe Herb-Drug Combo?

Quick Summary: This study checked if kava supplements change how the heart drug digoxin works in the body. Researchers tested kava on healthy people and found it didn't significantly affect digoxin's levels or processing, unlike some other herbs and drugs. This suggests kava is unlikely to cause major interactions with digoxin through a key body process called P-glycoprotein (P-gp), which helps pump drugs out of cells.

What The Research Found

Scientists wanted to see if kava or goldenseal herbs mess with digoxin, a medication used for heart conditions like irregular heartbeat or heart failure. Digoxin is processed by P-gp, a protein that acts like a gatekeeper for drugs in your body.

Kava (at 1227 mg per day) caused no big changes in how much digoxin stayed in the blood, its peak levels, or how quickly it left the body—no surprises here.
Goldenseal (at 3210 mg per day) slightly raised digoxin's peak blood level by 14%, but didn't change other key measures.
As expected, the antibiotic clarithromycin boosted digoxin levels (up to 42% more exposure), while the drug rifampin lowered them (up to 33% less peak level). These proved the test worked right.
Overall, kava didn't act as a strong P-gp modulator, meaning it probably won't speed up or slow down digoxin's effects much.

In plain terms: Kava seems neutral when it comes to digoxin, reducing worries about mixing them.

Study Details

Who was studied: 20 healthy adults with no health issues—these were volunteers in good shape, not people already on heart meds.
How long: Each herb phase lasted 14 days, with a 30-day break (washout) between tests. Control drugs ran for 7 days each. They measured digoxin effects before and after.
What they took:
Kava: 1227 mg daily (a standard extract taken by mouth).
Goldenseal: 3210 mg daily (also a standard extract).
Digoxin: A single 0.5 mg dose by mouth, with blood tests over 24 hours to track levels.
Controls: Rifampin (600 mg daily) to mimic speeding up drug clearance, and clarithromycin (1000 mg daily) to slow it down.

The setup was randomized and crossover-style, so everyone tried different things in random order to keep it fair.

What This Means For You

If you're taking digoxin for heart problems and want to try kava for stress or anxiety relief, this study is good news—it shows no major clash at typical doses. Kava won't likely make your digoxin too strong or too weak via P-gp.

Talk to your doctor first: Even if safe here, everyone's body is different, and kava can affect the liver in other ways.
Watch for other interactions: This only tested P-gp; kava might mix with alcohol, sedatives, or liver meds.
Dose matters: Stick to around 1200 mg daily if using kava, and choose quality extracts to match the study.
For heart patients: If you're on digoxin, don't self-medicate with herbs—get personalized advice to avoid risks.

Bottom line: Kava looks low-risk for digoxin users, but professional guidance keeps you safe.

Study Limitations

This research isn't perfect, so take it with a grain of salt:
- Small group: Only 20 healthy folks, so results might not fit everyone, especially those with heart disease or on long-term digoxin.
- Short time frame: 14 days of kava might not show full effects if you take it longer.
- Specific products: They used exact extracts—your kava supplement could act differently if it's not standardized.
- Indirect testing: They measured digoxin in blood as a stand-in for P-gp activity, not the protein itself, so it's not 100% direct.
- No details on ages or backgrounds: We don't know if older people or certain groups would react the same.

More studies on real patients could confirm this for everyday use. Always check with a healthcare pro before mixing herbs and meds.

Key Findings

This study found that kava kava supplementation (1227 mg/day for 14 days) did not significantly alter digoxin pharmacokinetics in healthy volunteers, suggesting no potent modulation of P-glycoprotein (P-gp) activity. In contrast, goldenseal increased digoxin's maximum concentration (C_max) by 14% (p < 0.05), though other parameters remained unchanged. Rifampin (a P-gp inducer) reduced digoxin exposure, while clarithromycin (a P-gp inhibitor) increased it, validating the model.

Study Design

This was a randomized, controlled, crossover observational study involving 20 healthy volunteers. Participants received goldenseal (3210 mg/day) or kava kava (1227 mg/day) for 14 days, followed by 30-day washout periods. Rifampin (600 mg/day) and clarithromycin (1000 mg/day) were used as positive controls for P-gp induction and inhibition, respectively. Digoxin (0.5 mg oral dose) was administered pre- and post-supplementation, with plasma concentrations measured over 24 hours.

Dosage & Administration

Kava kava: 1227 mg/day (standardized extract) orally for 14 days.
Goldenseal: 3210 mg/day (standardized extract) orally for 14 days.
Positive controls:
Rifampin: 600 mg/day for 7 days (P-gp inducer).
Clarithromycin: 1000 mg/day for 7 days (P-gp inhibitor).
Digoxin: 0.5 mg oral dose administered before and after each supplementation period.

Results & Efficacy

Rifampin: Reduced digoxin AUC_0-3 by 32%, AUC_0-24 by 25%, C_max by 33%, and CL/F by 24% (p < 0.01 for all).
Clarithromycin: Increased AUC_0-3 by 42%, AUC_0-24 by 38%, C_max by 36%, CL/F by 31%, and t_1/2 by 29% (p < 0.01).
Kava kava: No statistically significant changes in AUC, CL/F, t_1/2, or C_max (p > 0.05).
Goldenseal: 14% increase in C_max (p < 0.05), but no other significant effects.

Limitations

Small sample size: Only 20 participants, limiting generalizability and statistical power.
Healthy volunteers: Findings may not apply to populations on chronic digoxin therapy.
Short supplementation duration: 14 days may be insufficient to fully induce or inhibit P-gp.
Formulation specificity: Results apply only to the standardized extracts tested; other kava or goldenseal products might differ.
Indirect P-gp assessment: Relied on digoxin pharmacokinetics as a surrogate, not direct P-gp activity measurements.

Clinical Relevance

For individuals taking digoxin (e.g., for heart failure or arrhythmias), this study suggests that kava kava at 1227 mg/day does not meaningfully interact via P-gp modulation. However, goldenseal's 14% increase in C_max warrants caution, though it was not clinically significant. Supplement users should still consult healthcare providers when combining herbs with medications, as individual variability and non-P-gp mechanisms may exist. The study underscores that kava, at this dose and formulation, is unlikely to cause critical herb-drug interactions involving P-gp.

Note: Demographics (age, sex, ethnicity) were not reported in the provided summary. All results are based on the study’s predefined statistical thresholds (p < 0.01 for controls, p < 0.05 for goldenseal).