map.on('draw:created',function (e) {
    var type = e.layerType,
    layer = e.layer;

    var coordinates = layer.getLatLngs();
    var sql_coordinates =[];

    for (var i in coordinates){
    sql_coordinates.push(coordinates[i].lng+" "+coordinates[i].lat);
    $('#coords').val(sql_coordinates);
    alert(sql_coordinates);
    };
});

<input type="hidden" name="coords" id="coords" />

<?php

// Parametre de  connection
$host = 'localhost';
$database = 'metiers';
$user = 'postgres';
$pass = '';
$port = '5432';

$dns = 'pgsql:host='.$host .';port='.$port .';dbname='.$database;

// récupération des variables
$coords = $_POST['coords'];

try
{
$bdd = new PDO("pgsql:host=$host;dbname=$database",$user,$pass);
$bdd->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

//Requete d'insertion

$req = $bdd->prepare('INSERT INTO city.conduites_ep_l93(coords) VALUES(?)');

$req->execute(array($coords));

}
catch(Exception $e)
{
    echo "Connection a la BDD impossible : ", $e->getMessage();
die();
}

header('Location:index.html');

?>

Update city.conduites_ep_l93 SET geom = ST_GeomFromText('MULTILINESTRING((coords))',2154);

ERROR:  parse error - invalid geometry
HINT:  "MULTILINESTRING((co" <-- parse error at position 19 within geometry
********** Erreur **********

ERROR: parse error - invalid geometry
État SQL :XX000
Astuce : "MULTILINESTRING((co" <-- parse error at position 19 within geometry