$insert = array("firstname"=>"value",
	"lastname"=> "value2");

insertDB("user", $insert);
function insertDB($table, $data) {
	global $dbh;
	$fields = array(); $params = array(); $boundparam = array();
	foreach($data as $field => $value) {
		$fields[] ="`".$field."`";
		$params[] = $value;
		$boundparam[] = "?";
	}
	
	$sql = "INSERT INTO `".$table."`".
		" (".implode(",",$fields).") VALUES (".implode(",",$boundparam).")";
	
	$stmt = $dbh->prepare($sql);
	return $stmt->execute($params);
}