Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Max may be constipated. It's not a commonly seen problem in dogs but it can happen.
If you want to know for sure if he is actually constipated, then you could perform a rectal on him. Lubricate the index finger of a latex glove with K/Y or Vaseline and gently insert your finger into his anal opening about 1 inch or so. I would have someone helping you since you don't want to get injured. If you feel really firm, hard stool then he may very well be constipated. However, if you don't feel hard fecal material, then something else may be going on.
In any event oral laxatives aren't likely to be terribly effective as the sole option if he's lethargic and not eating but may be of help if you can remove some fecal material.
There are several manual methods to removing stools from a dog's colon if you're up for the challenge:
1. Sometimes if you can remove enough hard feces that are present right at the anal opening, the patient is able to evacuate the remainder. Gently insert your index finger into his anus as I mentioned above up to your first or second knuckle, and try to hook your finger into fecal material and gently retract it. You may need to perform this procedure several times.
Ii understand that this is not something that everyone will feel comfortable doing.
2. If you have a large syringe or turkey baster, you can also give him a warm water enema. Obviously, this is not for the faint hearted either. I would lubricate the end of the syringe or baster as I mentioned above, gently insert into his rectum about 1 inch and gently squeeze the warm water into him.
You may also need to repeat this procedure several times to loosen up the hard stool.
Every step should be done gently so as not to hurt him.
3. You can give him an over the counter, human enema if it has DSS (docusate sodium) on the label. Another enema option would be a single pediatric glycerin suppository.
I can provide oral laxative options below which may help if he's not badly constipated or which can help to move things along. Mineral oil isn't a great product for this particular problem and I would avoid its use.
1. Laxatone or Laxaire (or similar products) which are hairball laxatives for cats. These products will work very well on a smaller dog. They are available at pet or grain stores. You would give 1-3 inches 2-3 times a day.
2. Canned pumpkin (NOT the pie mix); ½ -1 tsp daily in food
3. Over the counter, human Miralax 1/4-1/2th tsp twice daily can work very well.
4. Oral Docusate Sodium (Colace) 25 mg once or twice a day for small dogs.
Also encourage him to drink if you can; either pedialyte (although it doesn't have a great taste) or low sodium chicken broth are options in addition to plain water.
I hope this helps. Deb