Yew - Drug Monograph

Introduction

Yew refers to plants of the genus Taxus (family Taxaceae), most commonly Taxus baccata (European yew), T. canadensis (Canadian yew), and T. cuspidata (Japanese yew). Although not an approved pharmaceutical, yew is clinically relevant in two distinct domains: (1) as a source of severe plant poisoning through ingestion of its taxine alkaloids, and (2) as the botanical origin of the taxane class of antineoplastic agents (paclitaxel, docetaxel, cabazitaxel). This monograph focuses primarily on yew as a toxicologic agent, with reference to its pharmaceutical derivatives.

Drug Class and Overview

• Toxicologic class: Cardiotoxic plant alkaloid poisoning (taxine alkaloids).
• Botanical source: All Taxus species; nearly all plant parts (needles, bark, seeds) are toxic except the fleshy red aril of the berry.
• Pharmaceutical derivatives: Paclitaxel (Taxol), docetaxel (Taxotere), and cabazitaxel (Jevtana) — microtubule-stabilizing chemotherapy agents originally isolated from Taxus brevifolia (Pacific yew) bark or semi-synthesized from yew precursors.
• Distinguishing feature: Yew is one of the few plants whose primary lethal mechanism is direct cardiac ion channel blockade, producing rapid-onset bradyarrhythmias and refractory cardiovascular collapse.

Mechanism of Action

The principal toxic constituents are taxine A and taxine B (pseudo-alkaloids), with taxine B considered the most cardiotoxic. Their pharmacologic actions include:

• Sodium channel blockade in cardiac myocytes, reducing action potential upstroke and conduction velocity.
• Calcium channel antagonism, decreasing sinoatrial node automaticity and myocardial contractility.
• Resultant bradycardia, AV conduction block, hypotension, ventricular arrhythmias, and asystole.

The pharmaceutical derivative paclitaxel acts by a completely different mechanism — reversible binding to β-tubulin, promoting microtubule polymerization and stabilization, thereby arresting mitosis in dividing cells.

Indications

• No approved therapeutic indication for yew plant material itself.
• Yew poisoning management: Recognition and supportive care of acute Taxus ingestion (clinical toxicology).
• Derivative indications (paclitaxel/docetaxel/cabazitaxel): Ovarian, breast, lung, prostate, gastric, and other malignancies — refer to individual agent monographs.

Dosage and Administration

• No therapeutic dose; yew is not administered as a drug.
• Toxic dose: Highly variable; case literature suggests ingestion of approximately 50 g of yew needles (or roughly 50–100 berries with seeds chewed) may be lethal in adults, though fatalities have been reported with smaller amounts and survival with larger amounts.
• Pediatric considerations: Children are particularly vulnerable due to lower body weight; even a small number of chewed needles or seeds may produce serious toxicity.
• Pregnancy: No established safe exposure; ingestion should be treated as a medical emergency.

Pharmacokinetics

• Absorption: Taxine alkaloids are absorbed from the gastrointestinal tract following ingestion of plant material; onset of symptoms typically within 30 minutes to 2 hours.
• Distribution: Limited human data; taxines appear to distribute to cardiac tissue, consistent with their cardiotoxic profile.
• Metabolism: Not well characterized in humans; hepatic metabolism is presumed.
• Elimination: Not well characterized; renal and biliary routes have been proposed.
• Half-life: Not established for taxines in humans.

Contraindications

• Ingestion of any part of the Taxus plant other than the red aril of ripe berries (which is considered non-toxic).
• Use of yew extracts, "natural remedies," or homeopathic preparations containing yew is not recommended outside of regulated pharmaceutical derivatives.

Warnings and Precautions

• Cardiovascular collapse: Yew poisoning can progress rapidly from mild GI symptoms to fatal arrhythmia within hours.
• No effective antidote: Management is entirely supportive.
• Delayed presentation risk: Initial GI symptoms (nausea, vomiting, abdominal pain, dizziness) may be followed by a deceptive latent phase before sudden cardiovascular deterioration.
• Misidentification risk: Yew is commonly grown as an ornamental shrub; clippings and pruned branches may be inadvertently ingested by humans or animals.
• Animal toxicity: Livestock, horses, and domestic animals are also susceptible to yew poisoning.

Drug Interactions

• No clinically established drug interactions for yew plant ingestion.
• Theoretically, concurrent use of other sodium-channel-blocking agents (e.g., class I antiarrhythmics, tricyclic antidepressants) or calcium-channel blockers could potentiate cardiotoxicity, but this is based on mechanistic reasoning rather than clinical trial data.
• Paclitaxel interactions (relevant to derivatives): CYP3A4 and CYP2C8 substrates; numerous interactions with azole antifungals, macrolides, protease inhibitors, and grapefruit juice — refer to paclitaxel prescribing information.

Adverse Effects

Yew poisoning (acute ingestion):

• Common: Nausea, vomiting, abdominal pain, dizziness, mydriasis, flushing.
• Serious/rare: Severe bradycardia, AV block, ventricular tachycardia/fibrillation, hypotension, seizures, coma, death.

Paclitaxel/docetaxel (derivative agents):

• Common: Myelosuppression, peripheral neuropathy, alopecia, arthralgia/myalgia, hypersensitivity reactions, mucositis.
• Serious: Anaphylaxis, febrile neutropenia, cardiotoxicity (less prominent than with taxines), peripheral neuropathy.

Monitoring Parameters

For suspected yew poisoning:

• Continuous cardiac monitoring (telemetry) for at least 24 hours, even after apparent recovery.
• Vital signs: Heart rate, blood pressure, respiratory rate, oxygen saturation.
• 12-lead ECG: Serial assessment for QRS widening, PR prolongation, AV block, QT changes.
• Serum electrolytes: Particularly potassium and magnesium (to assess arrhythmia risk).
• Renal and hepatic function: Baseline and as clinically indicated.
• Bicarbonate and pH: To detect metabolic acidosis from cardiovascular compromise.

Patient Education

• Never ingest any part of a yew plant except the soft red flesh of ripe berries; the seeds inside berries are toxic and should not be chewed.
• Keep yew shrubs out of reach of children and pets.
• Do not use yew clippings, homemade extracts, or "natural" yew preparations for self-medication.
• Seek immediate emergency medical care for any suspected yew ingestion, even if the person initially feels well.
• Inform clinicians of any recent exposure to ornamental shrubs or plant material when presenting with unexplained cardiac symptoms.

Clinical Pearls

1. Yew poisoning is a "sudden death" toxidrome: Patients may appear stable and then deteriorate rapidly with refractory bradyarrhythmias — early aggressive monitoring is essential.
2. There is no antidote: Treatment is supportive (IV fluids, atropine for bradycardia, vasopressors, pacing, and standard ACLS protocols); extracorporeal membrane oxygenation (ECMO) has been used successfully in case reports of severe refractory cardiac arrest.
3. The red aril is the only non-toxic part: Public folklore that "yew berries are poisonous" is partially incorrect — the fleshy red cup is edible, but the seed within is toxic, and the leaves/bark are highly toxic.
4. Yew is the source of taxanes: Paclitaxel was originally isolated from Pacific yew bark; this discovery transformed oncology but also raised conservation concerns that led to semi-synthetic production methods.
5. Differential diagnosis: Yew poisoning should be considered in unexplained cardiac arrest near gardens, cemeteries, or landscaped areas, particularly when digoxin toxicity has been excluded.

References

1. World Health Organization / International Programme on Chemical Safety (INCHEM). Taxus baccata (Yew). Poisons Information Monograph.
2. Goldfrank's Toxicologic Emergencies (current edition). Plant-related cardiac toxins: Taxus species. McGraw-Hill.
3. Dart RC, ed. Medical Toxicology. Lippincott Williams & Wilkins. Chapter on plant poisoning.
4. U.S. Food and Drug Administration. Prescribing Information: Paclitaxel (Taxol). Bristol-Myers Squibb.
5. U.S. Food and Drug Administration. Prescribing Information: Docetaxel (Taxotere). Sanofi-Aventis.
6. European Association of Poisons Centres and Clinical Toxicologists (EAPCCT). Position statements on plant poisoning management.
7. Krenzelok EP, Jacobsen TD, Aronis J. Yew (Taxus) ingestion: a review of the literature and case reports. Journal of Toxicology: Clinical Toxicology.
8. Cummins RO, Haulman J, Quan L, et al. Near-fatal yew berry intoxication treated with extracorporeal circulation. American Journal of Emergency Medicine (representative case literature).
9. American Heart Association. Advanced Cardiovascular Life Support (ACLS) guidelines for bradyarrhythmia and cardiac arrest management.
10. National Library of Medicine / PubMed. Search strategy: "Taxus baccata poisoning" and "taxine alkaloid cardiotoxicity."