Thanks for the answers to my questons.
The fact that he's not lethargic and is still otherwise acting normal is a good thing.
We can pretty much rule out certain conditions such as kennel cough or an irritated throat or pneumonia ; unfortunately, however, there are going to be a number of other possible explanations for a cough of 10 months duration, even if there aren't any other symptoms.
In no particular order, they are:
1. Problems with the heart whereby the heart can enlarge compressing the trachea and/or fluid is building up in the chest. Or heartworm disease which is transmitted by mosquitoes.
It is possible that a good physical exam might detect a heart murmur or irregular heart rate but these are not present in every case.
An x-ray and/or an ultrasound may be needed though to diagnose this problem.
Bronchitis which is similar to asthma in a person.
These dogs are reacting to something in their environment that triggers inflammation in their lungs.. If this is the case, then control vs cure is what might be expected and the treatment is often different for each dog.
We typically diagnose this condition based on x-ray findings, breed of dog (this condition is more common is certain small dogs, than Labs or Goldens, for example), duration of cough, and non-response to other medications which might be tried such as antibiotics.
Some of these dogs will respond to anti-cough medications (see below for a suggested option). Others will respond to bronchodilators such as Aminophylline which would have to be dispensed by your vet. Sometimes antibiotics can improve the situation since secondary bacterial infections can occur while other dogs will improve on steroids such as humans would use for asthma.
Sometimes this is a trial and error sort of process since every patient doesn't react in the same way when certain medications are given.
3. Collapsing trachea is primarily seen in smaller dogs; this is exactly what it sounds like. This is a manageable condition for the most part unless surgical intervention is done to correct the problem. This is sometimes difficult to diagnose on an x-ray but is also managed rather than cured (unless surgical correction is performed).
Many of the above treatments for bronchitis are also used for these dogs. Carrying extra weight can be a problem for dogs with this condition and can make it worse.
Use a harness instead of a collar.
Avoid any potentially irritating substances such as cigarette smoke or excessive dust.
4. Fungal infections can cause coughing but may be more or less common depending on where you live. I would have expected him to have gotten much worse, though, if this were the problem.
As to over the counter treatment options, cough suppressants can be given although I'm often hesitant to use them unless or until the underlying cause for the cough has been identified.
However, acceptable ones to use include Dextromethorphan (LINK).
The dose would be 0.25 to 1 mg/lb 2-3 times a day. You just want to double check labels and ensure that the formulations only contain this ingredient although inclusion of Guaifensin is fine.
Anti-histamines are also safe to give which can help dry up secretions similar to a human. The dose of Benadryl, for example, would be 10 mg/lb twice a day with sedation a common side effect.
I hope this helps although, again, my apologies for the delayed reply. Deb