I don't suggest you just shove a syringe (or anything) down a chameleon's throat.
Nobody suggested that.
I went to great lengths to caution that the procedure needs to be gentle.
It is certainly far less stressful than badgering a chameleon for 20 or 30 minutes to get it to eat a drop of something at a time.
Buy what is formulated for your animal or "Make" a concoction that is close to your animals natural diet.
Take a look at the ingredients on the labels of formulated diets and compare and see a) how "natural" the diet formulation is (there will be no insects at all) and b) how insectivore ingredients compare with carnivore ingredients. Many veterinarians use "carnivore care" from oxbow quite successfully for treating all their insectivorous lizard patients. This formulation is for all carnivores.
As for my formulation- I've proven it works effectively on several occasions. The most extraordinary was when I got a group of a dozen "bottom of the barrel, probably going to die" melleri from an importer one time. They were severely dehydrated and emaciated and heavily parisitized. I cleaned them up and used the formulation I described for 2 weeks to assist feed all 12, while still offering a few insects. At the end of 2 weeks all had gained significant weight- some more than doubling their weight at the start. The first breedings I ever did with melleri came from this group which were sold to me for almost nothing because they were thought to be almost certain to die- and looked it on arrival.
I've used the formulation for other insect eating lizards over the years as well that required assist feed, and other groups of recently imported chameleons back when I treated groups in a "shotgun" fashion of worming and sometimes using flagyl as an antibiotic (if the animal is weak and emaciated when using flagyl I assist feed my formulation for the duration of treatment- it helps with hydration, provides energy and keeps the digestive system active and provides acidophilus for the gut fauna that is destroyed by the flagyl) and acclimation and had really great results.
That was then this is now- I no longer purchase large groups of fresh imports, and if I did, I'd use a commercial product. But I would still use my tried and tested home formulation for individual animals that needed the help if the situation arose. Because it has always worked really really well...
And yeah- I assist fed my formulation using the procedure I described of gently inserting the syringe way all the way down and did it very safely and minimized stress and harassment of my lizards unlike pestering assist feed methods...
Lastly, kindly remember that the OP has sought advice from the very best veterinarian that he could find ("the best in his country"). It would be kind of foolish to disregard that veterinarian's advice completely without consulting another veterinarian...
IMO, The info supplied is good for someone experienced ONLY. Knowing where the glottis is, size of syringe and knowing a safe amount to size of an animal would also be useful. Yes you can generally give more but you can still give to much...
Much easier for a newer keeper to put a tip of a syringe at the front of the mouth and administer a couple drops, allow the animal time to swallow and repeat. Patience is all that is needed.
Good points. Sometimes I forget what is easy for me may not be easy for everyone.
Also for the OP- seems like after 2 months it might be a good idea to try to get the lizard bowl feeding on it's own...
Assist feed really isn't a good long term solution, and in spite of my defending your veterinarian's advice, neither is dog food...
My comments about formulation should be taken from the perspective of assist feeding for a couple of weeks tops... For most lizards, that should be enough to turn things around to where it can feed on it's own in spite of difficulty...