slow postgresql query

gistfile1.txt

        Column         |            Type             |                     Modifiers                     | Storage  | Stats target | Description
------------------------+-----------------------------+---------------------------------------------------+----------+--------------+-------------
 id                     | integer                     | not null default nextval('tags_id_seq'::regclass) | plain    |              |
 type                   | character varying(255)      |                                                   | extended |              |
 label                  | character varying(255)      |                                                   | extended |               |
 created_at             | timestamp without time zone | not null                                          | plain    |              |
 updated_at             | timestamp without time zone | not null                                          | plain    |              |
Indexes:
    "tags_pkey" PRIMARY KEY, btree (id)
    "add_unique_index_label" UNIQUE, btree (label)
    "index_tags_on_label" btree (label)
    "index_tags_on_type" btree (type)
Has OIDs: no


52118303 rows 



QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.00..17534.00 rows=20 width=1585) (actual time=66438.975..83816.000 rows=1 loops=1)
   ->  Index Scan using add_unique_index_label on tags  (cost=0.00..4569360.65 rows=5212 width=1585) (actual time=66438.971..83815.994 rows=1 loops=1)
         Filter: ((label)::text ~~* 'rs556'::text)
         Rows Removed by Filter: 52118302
 Total runtime: 83816.047 ms