$a; $b;
$stmt->bindParam(1, $a);
$stmt->bindParam(2, $b);
$a = 1;
$b = 2;
$stmt->execute();
$a = 3;
$b = 4;
$stmt->execute();
foreach ($foo as $bar => $baz) {
　$a = $bar;
　$b = $baz;
　$stmt->execute();
}

これでいいよ