Syntax:
{DEALLOCATE | DROP} PREPARE stmt_name

To deallocate a prepared statement, use the DEALLOCATE PREPARE
statement. Attempting to execute a prepared statement after
deallocating it results in an error.

If you terminate a client session without deallocating a previously
prepared statement, the server deallocates it automatically.

URL: http://dev.mysql.com/doc/refman/5.0/en/sqlps.html

