Since the intestine is the place where the drug is absorbed, yes, absolutely, diarrhea should adversely impact your absorption of the drug.

schwad01, the first sentence in your post could have been written by my husband. He has had antibiotics 4 times in the last 4-5 years -- 3 times for illness and once following surgery. Each event for which antibiotics were given, brought his physical condition progressively lower.

The last illness was an acute bronchitis for which he received IV fluids, IV and oral antibiotics, and 7 weeks of nebulized steroids. It seemed to be the last straw; during the early stages of bronchitis his neurologic condition descended into true disability with increased confusion and more severe memory loss. His physical weakness and unsteadiness worsened tremendously with the nebulized steroids and never quite returned to baseline ... He fell out of bed 3 mornings in a row after starting that treatment. (Later, a functional medicine doctor attributed that decline in muscle function to the Pulmicort; she said she had seen this before in people over 80.) He was dehydrated and was not allowed proper rehydration, only given 1/2 liter on his first visit to Casualty/ Emergency, 1 liter on his second visit. The doctor was not even going to grant him that much, but I argued until he allowed it. I am aware that confusion and memory loss can occur in dehydration, but the doctors could not be convinced to give him more IV fluids, despite that he had stopped drinking water (due to nausea) the day before, and it became impossible to assure his oral water intake because he was confused and didn’t understand the need. Of note, he was not taking levodopa at the time. He started taking it in earnest some time after this illness.

We've learned our lesson. This last winter we made sure to keep him warm at all times -- evidently the lymphocytes retreat into secondary lymphatic organs when the body gets chilled. Also, he took immune boosters that increase glutathione production. This strategy worked beautifully. He didn't catch any infections this last winter, not so much as a sniffle, even when I caught a bit of a cold.

Because you mentioned diarrhea, schwad01, I’m also posting on page 2 of another thread that was started years ago, linked here:
Hey, anyone dealt with this issue?