Parameters not replacing properly in NpgsqlCommand

I'm trying to replace parameters in a string to execute in an Npgsql query.

The problem is, when it replaces the parameter by its value in the string it adds unnecessary parentheses and so the query returns an error.

NAME_SCHEMA_DB and NAME_ADMIN_DB are string constants and ExecuteCommand just takes an NpgsqlCommand and executes it.

This is my code:

String qdropSchema = @"DROP SCHEMA IF EXISTS @name_schem CASCADE";
String qCreateSchema = @"CREATE SCHEMA @name_schem AUTHORIZATION @name_admin";


DbCommand commandeDrop = new NpgsqlCommand(qdropSchema);
commandDrop.Parameters.Add(new NpgsqlParameter("@name_schem", NAME_SCHEMA_DB));

DbCommand commandCreate = new NpgsqlCommand(qCreateSchema);
commandCreate.Parameters.Add(new NpgsqlParameter("@name_schem", NAME_SCHEMA_DB));
commandCreate.Parameters.Add(new NpgsqlParameter("@name_admin", NAME_ADMIN_DB));


ExecuteCommand(commandDrop);
ExecuteCommand(commandCreate);

This is what the SQL query it tries to run when it reaches ExecuteCommand(commandDrop)

DROP SCHEMA IF EXISTS (('test_schemaName')) CASCADE;

I 'm not sure why it adds the extra parentheses and single quotes. Normally, I'd want the query it runs to be

DROP SCHEMA IF EXISTS test_schemaName CASCADE;