Medication News & Update
Garlic has long been used by many people for various reasons. While there may be some beneficial health effects most are modest at best if at all. For an excellent article covering this topic please use the following link.
Specific drug info on Garlic from Clinical Pharmacology
Garlic, Allium sativum
Description, Mechanism of Action, Pharmacokinetics
NOTE: All references to garlic powder in this monograph refer to garlic standardized to 1.3% alliin. Not all products available in the US meet these standards.
Description: Garlic is a dietary supplement derived from the bulb of Allium sativum, family Liliaceae. It can be regarded simultaneously as a food and a medicinal herb and has been used as such since the times of the Egyptian pharoahs and the earliest Chinese dynasties. Over 1000 papers have been published in the past 20 years on garlic and related alliums. Extensive clinical and scientific studies partially support the use of garlic for the treatment of hypercholesterolemia, infection, and the prevention of atherosclerosis. Garlic is composed of many natural sulfur compounds, including a sulfur-containing amino acid, alliin (S-allyl-L-cysteine sulfoxide). Alliin is pharmacologically inactive. When garlic is crushed, alliin mixes with the enzyme alliinase and is converted to allicin (diallyl thiosulfinate). Allicin is unstable and upon steam distillation or oil maceration yields various diallyl and dimethyl sulfides plus E-ajoene and Z-ajoene. In general, the total activity of garlic is in its ability to produce allicin, which then produces other active principles. This is referred to as the allicin yield. The allicin yield is decreased when garlic is exposed to heat or acidic environments. Garlic may also contain various amounts of vitamins and minerals. Garlic is listed in the USP and is Generally Recognized As Safe (GRAS) by the FDA.
•Antimicrobial Actions: Infectious microorganisms utilize alcohol dehydrogenase for nutrient digestion and cysteine proteinase for tissue invasion. Allicin has been shown to inhibit these enzymes through a reaction with their sulfhydryl groups. This may explain why garlic can prevent the development of dysentery due to Entamoeba histolytica in hamsters.
•Antihyperlipidemic Actions: Since sulfhydryl-containing compounds are involved in the synthesis of cholesterol, allicin's sulfhydryl binding ability may also explain the cholesterol-lowering action of garlic. The mechanism of action is believed to be through the formation of sulfide bridges by the disulfides found in garlic with 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase or the reductase molecules found in lipids.
•Antiplatelet Actions: It is well documented that garlic inhibits platelet function, probably through inhibition of thromboxane synthesis. Methylallyltrisulfide (MATS) is the chemical substance found in garlic believed to be responsible for this effect. The ajoenes are also thought to possess potent antithrombotic actions.
•Antioxidant Actions: The blood levels of the antioxidant enzymes, catylase and glutathione peroxidase, are increased by the effects of allicin. Thus, garlic, through the effects of allicin, has antioxidant and free-radical scavenging potential.
•Hypoglycemic Actions: Limited animal data suggest that selected consituents in garlic might have some antidiabetic activity, resulting in increased serum insulin concentrations and increased glycogen storage in the liver. Patients with diabetes frequently purchase alternative remedies that have been purported to improve glycemic control, but there is no scientific or controlled evidence in humans of this action. Limited clinical evidence suggests that garlic does not affect blood glucose in those without diabetes.
Pharmacokinetics: Garlic is administered orally and topically. Potency of garlic products can vary substantially from manufacturer to manufacturer due to mode of preparation. An extract standardized to 1.3% alliin is recommended. Fresh garlic yields roughly 0.4% allicin, the desired active ingredient; garlic powder contains roughly 1.3% allicin; dried garlic contains no allicin, but does contain alliin (allicin precursor) and the enzyme (alliinase) necessary to convert alliin to allicin. However, this enzymatic process cannot occur in the acidic environment of the stomach. Dried garlic dosage forms must be enteric coated for protection from gastric fluid and allow enzymatic conversion to occur in the small intestine. Since allicin is unstable in oil, oil-based products should be avoided. A German study found that only 5 of 18 commonly sold garlic preparations contained acceptable amounts of allicin, garlic's major active ingredient. Urinary presence of sulfur compounds has been documented following oral administration of garlic in human subjects.
Description, Mechanism of Action, Pharmacokinetics last revised 4/27/2004 11:52:00 AM
† non-FDA-approved indication
For the treatment of hypercholesterolemia†:
For the prevention of atherosclerosis† (arteriosclerosis†):
For the treatment of Microsporum canis†, sporotrichosis† and tinea pedis†:
Maximum Dosage Limits:
Patients with hepatic impairment:
Patients with renal impairment:
Indications...Dosage last revised 1/23/2003 3:28:00 PM
Administration last revised 7/1/2002
Elderly patients should consult a physician, pharmacist, nutritionist or other health-care professional prior to using a dietary supplement such as garlic. Beneficial effects of chronic garlic intake in healthy individuals 50 to 80 years of age have been demonstrated.
Garlic should be used cautiously in young children as safety has not been established. However, no significant absolute or relative effects on height, weight or blood pressure were noted during an 8 week randomized, double-blind placebo controlled clinical trial with 30 children who received 300 mg of garlic PO tid. There were statistically significant increases in laboratory parameters of albumin (avg. +2 g/L) and hemoglobin (avg. +5.2 g/L).
Garlic should be used cautiously during pregnancy as safety has not been established. However, there are no known contraindications to the use of garlic during pregnancy and lactation. One child reportedly refused breast-feeding after the mother had consumed garlic in excessive amounts, which was possibly transmitted through the breast milk.
Because components in garlic inhibit platelet aggregation and demonstrate antithrombotic activity, use caution when bleeding is a concern. This may include individuals who are receiving anticoagulant therapy or thrombolytic therapy.
Because garlic inhibits platelet function, patients should inform their health care professional that they take garlic prior to scheduling surgery. As with many other platelet inhibitors, discontinue garlic supplements at least 7 days prior to the surgical procedure. It may be wise to discontinue this herb 2—3 weeks prior to an elective procedure when possible.
Limited animal data suggest that selected consituents in garlic might have some antidiabetic activity. Patients with diabetes frequently purchase alternative remedies that have been purported to improve glycemic control, but there is no scientific or controlled evidence in humans of this action. Limited clinical evidence suggests that garlic does not affect blood glucose in those without diabetes. Until more data are available, individuals with diabetes mellitus should use caution in taking dietary supplements containing garlic, and follow their normally recommended strategies for blood glucose monitoring.
Garlic supplementation should be avoided by some patients with human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS). A serious drug interaction between garlic and a HIV protease inhibitor (i.e., saquinavir) has been reported; this interaction may compromise the effectiveness of anti-retroviral therapy and lead to increased rates of HIV drug-resistance (see Drug Interactions).
Contraindications last revised 4/27/2004 11:52:00 AM
Limited animal data suggest that selected constituents in Garlic, Allium sativum might have some antidiabetic activity, resulting in increased serum insulin concentrations and increased glycogen storage in the liver. Patients with diabetes frequently purchase alternative remedies that have been purported to improve glycemic control, but there is no scientific or controlled evidence in humans of this action. Limited clinical evidence suggests that garlic does not affect blood glucose in those without diabetes. Until more data are available, individuals receiving antidiabetic agents should use caution in consuming dietary supplements containing garlic, and follow their normally recommended strategies for blood glucose monitoring.
Garlic, Allium sativum may produce clinically-significant antiplatelet effects . Garlic may theoretically interact with other herbs and dietary supplements that exhibit antiplatelet effects or anticoagulant activity, such as danshen; dong quai, Angelica sinensis, feverfew, Tanacetum parthenium; ginger, Zingiber officinale; ginkgo, Ginkgo biloba; ginseng, Panax ginseng; green tea, horse chestnut, Aesculus hippocastanum; willow bark; and others. NOTE: This list is not inclusive of all herbs or dietary supplements that might have antiplatelet effects or anticoagulant activity. Published clinical data describing dietary supplement interactions are not always available.
Garlic, Allium sativum supplementation may lead to a significant decline in plasma concentrations of the protease-inhibitor saquinavir, leading to saquinavir treatment failures and the potential development of viral resistance. In one study, mean saquinavir concentrations dropped by 51% in the presence of garlic supplementation equivalent to roughly 2 cloves/day (4.64 mg allicin and 11.2 mg allin per capsule given twice daily). HIV-infected patients who are taking saquinavir as the sole protease inhibitor in their HIV treatment regimen should avoid garlic supplements.  No information is available regarding the use of garlic capsules with saquinavir that is enhanced or 'boosted' with ritonavir.
Interactions last revised 9/29/2004 7:12:00 AM
The most common adverse effects associated with the use of garlic in therapeutic doses are related to gastrointestinal complaints. These include dyspepsia, flatulence, halitosis and pyrosis (heartburn). Eructation(belching) was reported in 1 of 20 patients utilizing garlic tablets.
Contact dermatitis may occur from exposure to garlic extract (juice) or bulbs. Patients should be advised to avoid direct contact with skin or to report cases of dermatitis if garlic is used as a topical antiinfective.
Headache and dyspepsia were the most common adverse effects reported by 15 pediatric patients during eight weeks of oral therapy with 900 mg/day of standardized garlic. Minor adverse effects were reported on the midpoint questionnaire by 36% of the placebo group compared to 31% in the garlic extract group; and on the endpoint questionnaire by 13% of the placebo group and 21% of the garlic extract group.
One case of spontaneous spinal epidural hematoma secondary to ingestion of excessive amounts of garlic has been reported. The authors associated the patient's platelet dysfunction with the use of large quantities of garlic.
Adverse Reactions last revised 7/1/2002
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