Query is taking lot of time with not in clause

[shahbaz khan]

Beloq mentioned query is taking huge amount of time with not in clause.Without this it is taking significantly low time.How should i improve on this.

set @clinicid:=3;
set @location := (select entity_id from hlclocations where locsiteid=@clinicid and loctypelviid=5);
select
s.sitedesc,
hlcitems.itemcode,
hlcitems.itemdesc,
0 TranIn,
0 TranOut,
0 Sales,
0 Consumption,
0 Adjustment
,hlcinventory.invtotalqty closing
,hlcinventory.invtotalqty opening


from hlcinventory
inner join ( select hlcinventory.invitemid invitemid,
Max(hlcinventory.invcreatedat) MaxDate from hlcinventory
where (hlcinventory.invlocid = @location and invdcnid = @clinicid and
(hlcinventory.invcreatedat < '2009-07-01'))
group by hlcinventory.invitemid ) Q1 on (hlcinventory.invcreatedat=Q1.MaxDate and hlcinventory.invitemid=Q1.invitemid)
inner join hlcitems on (hlcinventory.invitemid = hlcitems.entity_id)
inner join hlcsites s on s.entity_id=@clinicid
where hlcitems.entity_id not in (select group_concat(invitemid) from hlcinventory where
invcreatedat between '2009-07-01 00:00:00' and '2009-07-05 23:59:59'
and invlocid = @location and invdcnid = @clinicid)
and invlocid = @location and invdcnid = @clinicid
group by itemcode
order by itemcode;