What is the difference between a pill you swallow and a lozenge that dissolves in themouth? On the surface there would seem to be little difference, but the difference is huge.

When you take a pill or capsule it is physically broken down in the stomach, passes to the small intestine and subjected to intestinal enzymes, gets absorbed by the hepatic (liver) circulation, transported to the liver where it is metabolized and broken down further leaving only a small percentage of the original drug intact to eventually reach its intended target and to do its job.
This pass through the liver before reaching the general circulation is called first-pass metabolism. It is this reason you may have to take 100 mg of drug just to get an effective dose of 1 mg to reach its intended target when you take a medication through the oral route. First pass metabolism is affected by the health of the liver and also by other medication and or toxins the liver has to process at any time.
The medication in a troche enters the circulation through the oral mucosa. The medication then enters the central circulation and then carried to other parts of the body reaching their intended targets first before ever reaching the liver. Compared to swallowing a pill, troches are absorbed quickly reach peak blood levels in 30 to 60 minutes.
Troches provide a different dosage form that avoids first-pass metabolism and medications delivered by way of a troche enter the blood stream more quickly and absorption through the oral mucosa is more predictable and not subjected to the effects of meals on drug absorption as it is for pills or capsules that are swallowed.