It sounds like you are managing his problems very well!
The short answer to your question is that I usually ADD IN the tramadol to the metacam. So, I keep the patient on the metacam and add the tramadol on top of that. The dose for tramadol is 1-4 mg/kg by mouth every 8 to 12 hours. I start low and very gradually (over weeks to months) build up if I need to.
So, for a 72lb dog, he weighs 32.7kg. Tramadol comes as a 50mg tablet, so I would start him at 1 tablet every 12 hours and see how he did with that for a week or two before considering increasing the dose.
If my patient did not find relief with the Metacam PLUS Tramadol combination, then I would add in gabapentin.
In terms of treating arthritis pain, my general treatment is as follows:
1. Be lean!
Every extra pound that a dog carries on sore joints just makes the problem worse. So, the single most effective thing you can do to help a dog with sore joints is to make sure he is slim - even a little bit on the skinny side of normal. It is just going to make him so much younger! It sounds like you are already taking care of this! Check to see how much he weighed when he was 2 years old. Has he gained since then?
2. Try glucosamine.
This supplement is very safe, and is helpful in the majority of dogs. For a 60-80lb dog, I usually suggest 500mg given 3 times daily. It usually takes 6-8 weeks on this supplement to see improvement. It can be added to what you are giving.
Here are some links:
3. Improve muscle mass with swimming.
If your dog likes to swim this is such a great exercise because it builds up the muscles around the joint, which stabilizes them, but causes none of the strain in the joints that running does.
4. Consider prescription medications.
Your veterinarian has a selection of very effective and safe medications to treat the pain and inflammation of arthritis.
Some common nonsteroidal anti-inflammatory drugs (NSAIDs) that might be prescribed are:
Metacam - http://www.petplace.com/drug-library/meloxicam-metacam/page1.aspx
Etogesic - http://www.petplace.com/drug-library/etodolac-etogesic/page1.aspx
Deramaxx - http://www.petplace.com/drug-library/deracoxib-deramaxx/page1.aspx
Previcox - http://www.petplace.com/drug-library/firocoxib-previcox/page1.aspx
Other options to consider are:
Tramadol - http://www.petplace.com/drug-library/tramadol-hydrochloride-ultram/page1.aspx
Gabapentin (which can be given together with Tramadol) - http://en.wikipedia.org/wiki/Gabapentin
Of these, I would have to say that my favourite is Metacam. I have had SUCH good results with it, and can only think of one dog that had vomiting on it, out of several hundred dogs that I have had on this drug.
Some dogs do better no one NSAID than another, so you could consider switchign from Metacam to another NSAID if adding the tramadol +/- gabapentin does not work.
6. Cartrophen/Adequan -
It's great that you dog is on this! This injectible drug is a polysulfated glycosaminoglycan (p-gag) and I have used it in hundreds of patients. I have never had one vomit! In an exhaustive study of 70 000 dogs, exactly TWO dogs vomited, and one had diarrhea upon injection. I have found improvement in about 80% of dog that have been on this medication and strongly recommend it.
More about it here:
7. Also, many people with joint pain report that a warm compress is soothing, and your dog may appreciate that too.
You can do this by making a wet towel compress. Place a small wet towel, folded into a zip-lok bag (unzipped!) and heat for about 2 minutes in the microwave. Remove and press all the air out. Make sure it is not too hot! You may want to put another towel around it, and then gently place over your dog's sore area.
8. Provide your dog with a padded bed large enough to stretch out on so he can sleep in luxury!
9. To help your dog to get up the stairs at night, I would recommend using a "sling" that you can make yourself if this is an issue for him.
Take a long bath towel, and fold it 3 or 4 times lengthwise, so that you have a long and thin shape. Put this under his belly, as far back as possible, so it is under his hips. Now, bring the ends up over his back so that you can hold the ends above him. With this, you can lift almost all his weight by using this sling, and thus really help him up the stairs. He can walk himself, with you right beside him taking his weight on the sling to help him. This is a really good way to help him up stairs or up into the car - or any time he has to go UP!
For further information about hip dysplasia, I will give you these links: http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=1916
For further information about arthritis I will give you these links:
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.
Best wishes to you and to your dog!