I thought a culture was taken (lung wash) and additional tests are pending? I may have understood it wrong.

Best bet would be to call the Vet back and ask how long until the results come in. Its always best to treat them with the correct medication for the actual problem (bacteria, virus, fungus). Its just that sometimes some of these tests and cultures can take 2 weeks or even longer..

If his current symptoms are severe and they have previously been helped by the medication you have, it "may" help to start treatment with what you have to get him through until the culture comes back. You can then adjust the treatment if needed. Some Vets over here treat that way, to get a head start.

However, you have had several treatments already, so at this point the Vet may want to approach this differently.

Find out how long until you get answers. Explain to the Vet how your snake is doing right now, ask if you should treat this to get it under control UNTIL the culture is back, or whether its safe to wait.

It is very difficult to help with medical advice over the internet, esp. if this is a severe case. Its great to get tips and advice, but you should take them and use them to discuss options with the Vet.

Deborah has a very good point, if treatment isn't long enough, all you do is create "resistant" bacteria. Ask the Vet whether longer treatment would be warranted.

Does your Vet have a lot of experience with reptiles ? In a case like this, make sure you use a Vet with good reptile experience !!