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Chapter: Modern Pharmacology with Clinical Applications: Herbal Medicine

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Herbal Preparations: Kava

Kava-kava (Piper methysticum) is a South Pacific island shrub the rhizome or root of which was used in the past as a ceremonial beverage and that today is popular as an anxiolytic.

Kava

 

Kava-kava (Piper methysticum) is a South Pacific island shrub the rhizome or root of which was used in the past as a ceremonial beverage and that today is popular as an anxiolytic. Historically, women prepared the kava by pounding and then chewing it. After being allowed to ferment in bowls, the kava was drunk by male islanders to mark a special event. The herb would induce a pleas-ant euphoric tranquility and contribute to the group’s social cohesion. The active ingredients are thought to be kavapyrones (also known as kavalactones), a family of related synergistically active compounds that include kawain and methysticin.

 

Mechanism of Action

 

The exact mechanism of action is unclear, but it is thought that kavapyrones may act in the amygdala, pro-ducing a tranquilizing and muscle relaxant effect.

Despite inducing mild sedation and euphoria, there is usually no cognitive or memory impairment at typical doses. Chewing the root results in a local anesthetic ef-fect with temporary numbness. High doses may cause gait impairment, dilated pupils, and eventually impaired motor performance.

 

Indications

 

Kava may be effective for the short-term treatment of anxiety. A number of small trials have shown extracts, standardized to 70% kavapyrones, to be significantly and consistently more effective than placebo. Addi-tional studies suggest that kava acts centrally as a mus-cle relaxant and likely has neuroprotective and nonopi-oid analgesic properties.

 

Adverse Reactions, Contraindications, and Interactions

 

Although kava was considered relatively safe until re-cently, GI upset, headache, allergic skin reactions, ele-vated liver function tests, and rare extrapyramidal re-actions may occur. It should be avoided in patients with known liver disease. Slowed reflexes and diminished judgment may occur at high doses. Heavy chronic use may produce a psychological (rather than physiologi-cal) habituation and a pellagralike skin condition known as kava dermatitis characterized by reddened eyes and dry flaking skin with a yellow discoloration; flavokawains A and B are yellow pigments isolated from kava and are likely causative. Despite the resem-blance to pellagra, niacin does not reverse this condi-tion.

 

Heavy kava users have also been observed to lose weight and have low plasma protein levels and low platelet and lymphocyte counts. Pulmonary hyperten-sion and shortness of breath have rarely occurred. Kava should be avoided in pregnant women and children, since the consequences of use are unknown. A recent cause for concern is an uncommon idiosyncratic liver toxicity associated with kava use; in some cases, this has been severe enough to warrant liver transplantation. It is unclear whether kava alone is to blame, but the safety of this herb is under review. Several European coun-tries, where this problem was first reported, have either suspended sales or are acting to make kava a prescrip-tion drug.

 

Kava should not be used with alcohol, benzodi-azepines, barbiturates or other sedatives because of their additive effects. In one case, coma resulted from mixing alprazolam and kava. Patients have complained that kava, while relaxing the body, may be less effective for mental anxiety with obsessive or racing thoughts than are the benzodiazepines.

Dosage

 

Kava preparations are frequently standardized to 30 to 70% kavapyrones. Doses of 100 mg (70% kavapyrones) three times daily are often used for anxiety. Kava is sometimes drunk as a tea (2–4 g of root placed in 150 mL of hot water followed by straining). Treatment may take several weeks to be fully effective, but should be limited to no more than 3 months of drug administration.

 

Conclusion

 

Kava appears to act somewhat like an herbal tranquil-izer to produce a calm, relaxed state, often with mild eu-phoria. At recommended doses it has little effect on cognitive performance. Although it is safe for most adults, prolonged or excessive use may create psycho-logical dependency and health problems.

 

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