What are the risks of taking Lequin 500mg that is 7 months expired?

Do you mean Levaquin ?

http://www.drugs.com/levaquin.html

|What is Levaquin? 
 ?  Levaquin is an antibiotic in a class of drugs called
fluoroquinolones. It fights bacteria in the body.
 ?  Levaquin is used to treat various types of bacterial infections. |

No researcher is going to touch this with a 10 foot pole.  Expiration
dates are issued by the manufacturer for a multitude of reasons and
they don't publish them.  Discuss this issue with your pharmacist. 
S/He will likely know the chemical and composition factors that
determine the expiration date of that particular drug.

Examples:

Active or inert ingredient breakdown
half life of active ingredient when exposed to air or light
chemical change in active ingredient over time
yada, yada, yada