Willow Bark
Willow Bark
Generic Name
Willow Bark
Mechanism
- Salicin, the primary active compound, is hydrolyzed to salicylic acid in the gut.
- Salicylic acid competitively inhibits cyclooxygenase‑1 (COX‑1) and cyclooxygenase‑2 (COX‑2), reducing prostaglandin synthesis.
- Decreased prostaglandin levels lead to:
- ↓ pain transmission and sensitization
- ↓ fever (antipyretic effect)
- ↓ inflammatory mediator release
Pharmacokinetics
| Parameter | Approximate Value |
| Absorption | 70–90 % oral; peak plasma 1–2 h post‑dose |
| Distribution | Widely distributed; plasma protein binding ~20–30 % |
| Metabolism | Liver → salicylate glucuronide/sulfate conjugates |
| Elimination | Renal (≈70 %) and biliary; t½ ≈ 2–3 h for salicylates |
| Special Populations | Reduced clearance in hepatic/renal impairment; increased exposure in pregnancy (3rd trimester) |
Indications
- Mild to moderate musculoskeletal pain (e.g., low‑back pain, osteoarthritis)
- Tension‑type headaches
- Low‑grade fevers where NSAIDs are contraindicated
- Adjunctive therapy in chronic inflammatory conditions (limited evidence)
Contraindications
- Severe hepatic or renal impairment
- Active peptic ulcer disease or significant GI bleeding risk
- Known allergy to aspirin or salicylates
- Pregnancy after 20 weeks (risk of premature ductus arteriosus closure)
- Children/teens with viral illnesses (risk of Reye’s syndrome)
- Concurrent use with anticoagulants/antiplatelet agents → ↑ bleeding risk
- Hypersensitivity to bark or other *Salix* spp.
Dosing
| Form | Typical Dose | Frequency | Notes |
| Standardized dried bark | 300–600 mg (≈ 100–200 mg salicin) | 1–4 × daily | Max 1.2 g/day |
| Extract (200 mg salicin Eq.) | 1–2 × daily | 1–4 × daily | Use when weight‑based dosing is required |
| Syrup (herbal) | 5 mL (≈ 30 mg salicin) | 3–4 × daily | For pediatric/elderly patients |
• Take with food or milk to minimize GI irritation; slight reduction in peak plasma concentration.
• Avoid alcohol concurrently; may increase GI bleeding risk.
Adverse Effects
| Category | Adverse Effect | Frequency/Severity |
| Common | Nausea, dyspepsia, loose stools | 5–10 % |
| Mild epistaxis or gum bleeding | <5 % | |
| Headache, dizziness | <5 % | |
| Serious | Peptic ulcer, GI hemorrhage | <1 % |
| Renal dysfunction (acute interstitial nephritis) | <0.5 % | |
| Hypersensitivity (rash, angioedema) | <0.5 % | |
| Reye’s syndrome (in children) | Rare |
Monitoring
- Baseline & periodic liver function tests (ALT/AST)
- Renal function (CrCl, BUN/Creatinine)
- Complete blood count (CBC) for anemia/bleeding
- INR/PT if on warfarin or other anticoagulants
- GI symptom diary for early detection of ulceration
- Blood pressure (occasionally affected by vasodilatory effects)
Clinical Pearls
- Standardization matters: Use extracts calibrated to salicin content for dose consistency.
- Food interaction: While food reduces GI upset, it can delay absorption; timing may be individualized.
- Pregnancy caution: Reserve for 1st trimester; avoid after 20 weeks unless benefits outweigh risks.
- Anticoagulant synergy: Concomitant aspirin or warfarin increases bleeding risk; monitor INR and consider dose reduction.
- Pediatric use: Only under strict supervision; avoid if the child has a viral illness due to Reye’s risk.
- Alternative to NSAIDs: For patients with NSAID intolerance but needing analgesia, willow bark offers a milder anti‑inflammatory profile with lower GI toxicity.
- Evidence gap: While traditionally used, high‑quality randomized trials are limited; consider willow bark as adjunctive rather than first‑line therapy for osteoarthritis.
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