Garlic
Garlic (Allium sativum)
Generic Name
Garlic (Allium sativum)
Mechanism
- Cardiovascular protection:
- Directly inhibits *3‑hydroxy‑3‑methylglutaryl‑CoA (HMG‑CoA) reductase*, producing modest LDL‑cholesterol ↓ and triglyceride ↓.
- Suppresses platelet aggregation by inhibiting thromboxane A₂ synthesis and enhancing nitric‑oxide‑mediated vasodilation.
- Antioxidant scavenging of reactive oxygen species → ↓ endothelial dysfunction.
- Antimicrobial activity:
- Allicin and ajoene disrupt bacterial cell walls and interfere with thiol‑dependent enzymes, providing virucidal, antibacterial, and antifungal effects.
- Anti‑inflammatory & cytoprotective:
- Down‑regulates NF‑κB and COX‑2, reducing prostaglandin synthesis.
- Attenuates ischemia–reperfusion injury and hepatic inflammation via Nrf2 activation.
- Antioxidant & anticancer:
- DATS induces apoptosis in tumor cell lines through mitochondrial cytochrome‑c release and caspase activation.
- Inhibits carcinogen activation by up‑regulating phase II detoxification enzymes (glutathione S‑transferase, UDP‑glucuronosyltransferase).
Pharmacokinetics
| Parameter | Typical Findings |
| Absorption | Peak plasma levels of allicin (after ingestion of 2–4 g raw garlic) reach 30–40 µM within 1–2 h; however, allicin is unstable and rapidly converted to DATS, ajoene, and polysulfides. |
| Metabolism | Extensive conversion in the GI tract and liver via *glutathione* conjugation and *sulfotransferase* pathways; mainly cytochrome P450 3A4 independent. |
| Distribution | Widely distributed; lipophilic metabolites cross cellular membranes easily. |
| Elimination | Primarily renally excreted (≈ 40 %) and hepatically metabolized; terminal half‑life of active metabolites ~ 7–12 h. |
| Drug interactions | Mildly induces CYP3A4; potent inhibits platelet function and may potentiate anticoagulants (warfarin, DOACs). |
Indications
- Cardiovascular prophylaxis: Primary and secondary prevention of atherosclerotic disease (LDL‑cholesterol ↓ 10‑20 %, triglycerides ↓ 15‑25 %).
- Hypertension adjunct: Modest blood‑pressure reduction (1–3 mm Hg systolic, 1‑2 mm Hg diastolic).
- Hyperlipidemia adjunct: Often paired with statins to enhance lipid lowering.
- Chronic periodontal disease: Local antimicrobial effects on plaque biofilm.
- Gastro‑intestinal prophylaxis: Mild protective effect against NSAID‑induced ulcers.
- Cancer risk modulation: Observational support for reduced incidence of certain cancers (esophageal, colorectal, breast).
Contraindications
- Bleeding disorders: Risk of hemorrhage; avoid in hemophilia, thrombocytopenia.
- Anticoagulant therapy: Contraindicated or requires dose adjustment in patients on warfarin, DOACs, or antiplatelet agents (aspirin, clopidogrel).
- Peri‑operative period: Stop ≥5 days before surgery to reduce surgical bleeding.
- Pregnancy & lactation: Limited safety data; use only if risk outweighs benefit.
- Severe liver disease: May precipitate drug‑induced cholestatic hepatitis.
- Allergy: Prior hypersensitivity to Allium species mandates avoidance.
Dosing
| Form | Dose | Frequency | Notes |
| Aged Garlic Extract (AGE) | 300–600 mg/day | Once daily | Standardized for S‑allicin content. |
| Raw garlic | 2–3 g per day | 1–2 × daily | Better for cardiovascular benefit but may result in stronger side effects. |
| Allicin‑containing supplement | 600–1200 mg/day | 1–2 × daily | Used in clinical studies for lipid lowering. |
| Capsule (alliin) | 500 mg/day | Twice daily | Non‑bioactive until ingested & converted. |
| Topical | 1–3 % garlic oil solution | 2–3 × daily | For skin infections or wounds. |
• Start low, titrate up: Begin with 250 mg/day to assess tolerability.
• Timing: Take with food to mitigate GI effects; avoid at bedtime to reduce halitosis.
Adverse Effects
| Category | Specific Effects |
| Common |
• 2–3 % incidence of GI upset (nausea, belching) • Metallic taste & garlic breath • Hypersensitivity rash (rare) |
| Serious |
• GI bleeding (with anticoagulants) • Cholestatic hepatitis (1–2 / 100,000) • Hemorrhagic complications (perioperative) • Hypoglycemia in diabetics • Possible arrhythmias at very high doses (≤ 5 g/day) |
Monitoring
| Parameter | Frequency | Target/Alert |
| Coagulation profile (PT/INR, aPTT) | Prior to initiation & 1‑2 weeks after dose change | ↑ 1.5× baseline may necessitate dose adjustment. |
| Liver enzymes (ALT/AST, ALP) | Baseline & 1‑3 months | ALT > 3× ULN or ALP > 2× ULN – discontinue. |
| Platelet count | Baseline & 4‑6 weeks | ↓ > 30 % → reassess. |
| Cholesterol panel | Baseline, 4‑6 weeks, then every 3 months | LDL reduction of ≥10 % desired. |
| Fasting glucose | Baseline & 3‑months in diabetics | Hypoglycemia symptoms—adjust diabetic meds. |
| Blood pressure | Baseline & at each visit | ≥ 5 mm Hg systolic drop may warrant dose reduction. |
Clinical Pearls
- Synergistic lipid‑lowering: Pairing garlic with statins can enhance LDL‑cholesterol reduction but watch for *rhabdomyolysis* (creatine kinase ↑ >10× ULN).
- Anticoagulant caution: Garlic’s platelet‑inhibitory effect can potentiate warfarin; check INR 3‑4 days after starting garlic and consider *dose reduction* or *hold* in the peri‑operative period.
- Bioavailability matters: Allicin is volatile; aged garlic extract, encapsulated garlic, or immediate‑release allicin guarantees more predictable pharmacodynamics.
- Allium allergy check: For patients with known *pollen‑food* syndrome, a skin‑prick test for garlic can prevent anaphylaxis.
- Food interactions: Foods high in *CYP3A4* inducers (e.g., *grapefruit*) can dampen garlic’s efficacy; conversely, *bile‑salt inhibitors* may reduce absorption.
- Kidney disease: Reduce dose to avoid potential accumulation of sulfur metabolites.
- Use in diabetes: A modest hypoglycemic effect—monitor blood glucose and adjust oral hypoglycemics to avoid hypoglycemia.
--
• This drug card provides an evidence‑based, high‑yield summary of garlic’s pharmacology suitable for academic and clinical reference.