A drug that is already approved for use against nicotine addiction also works against alcohol dependence, suggests a new US study on rats. The effect is yet to be tested on humans.

The study was led by Dr Selena Bartlett, director of the Preclinical Development Group at the Gallo Clinic and Research Center, affiliated to the University of California, San Francisco (UCSF) and is published in the early online edition of the Proceedings of the National Academy of Sciences (PNAS) .

One dose of the drug, called varenicline cut drinking by 50 per cent, and the animals did not go back to excess drinking after the drug was stopped, which is what often happens when people try to reduce alcohol dependence with the currently approved drugs.

Varenicline has the brand name Chantix in the US and Canada, and is known as Champix in Europe. It is marketed by Pfizer.

Also, unlike naltrexone, the currently approved most effective drug for treating alcohol dependence, varenicline did not kill appetite, said the researchers.

In the study, 18 rats were given intermittent access to unlimited amounts of 40 per cent proof alcohol for 4 months. Over this period the rats had a total of 37 binge drinking sessions.

Intermittent access is more likely to induce craving. The rats increased their consumption steadily; each time they had access they drank more alcohol. The withdrawal during the periods when they did not have access made them drink more when they did.

But when they were given varenicline (every other day for a week), the rats cut their drinking in half and when the drug was stopped, they did not immediately start drinking more.

The researchers said they think varenicline works on the brain's reward system in a different way to other anti alcohol dependence drugs. They think varenicline turns down the reward system rather than replaces it.

The researchers also conducted two othe experiments. One showed that the drug reduced alcohol dependence in 7 rats with continuous access to alcohol and another showed it reduced dependence in 30 rats that had learned to drink alcohol in response to stress.

Bartlett said:

"The biggest thrill is that this drug, which has already proved safe for people trying to stop smoking, is now a potential drug to fight alcohol dependence."

"Alcoholism takes a tremendous toll, and so few drugs are available to counter it," she said.

85 per cent of alcoholics are also smokers, so if clinical trials can confirm varenicline's effectiveness against alcohol dependence (Bartlett and colleagues are planning to do this, together with Markus Heilig at the National Institute on Alcohol Abuse and Alcoholism), and it gets federal approval, patients will be able to get one drug to treat both conditions.

Speculating on their findings, Bartlett said that the drug's effectiveness against both drinking and smoking is probably because it targets the reward centre in the brain that is triggered by both nicotine and alcohol, a centre that is known as the ventral tegmental area, or VTA, which releases the "feel good" neurotransmitter dopamine into the nucleus accumbens. This is the effect induced by addictive drugs such as morphine, cocaine, alcohol and nicotine.

Although alcohol and nicotine act in different ways, the result is still the release of dopamine. Nicotine binds directly to the neuronal nicotinic acetylcholine receptor, while alcohol stimulates the production of the neurotransmitter acetylcholine which then activates the same receptor. Both actions release more dopamine.

Varenicline, like nicotine, also binds directly to the receptor, which blocks it from being activated by either nicotine or alcohol.

Because it has already been approved as a treatment for nicotine dependence, the drug's safety has already been established, which means it should not take as long to get it tested and approved as a treatment for alcohol dependence said the researchers.

Varenicline has been on the market for about a year. It is derived from the alkaloid cytisine, found in many garden trees and shrubs of the Faboideae subfamily such as laburnum, genista (broom) and sophora.

"Varenicline, alpha4 beta2 nicotinic acetylcholine receptor partial agonist, selectively decreases ethanol consumption and seeking."
P Steensland et al.
Proc Natl Acad Sci 2007;July 9 (Early Online)

Click here for the Proceedings of the National Academy of Sciences.

Click here to learn more about alcohol addiction (BBC Health pages).

Written by: Catharine Paddock
Writer: Medical News Today