... in mice, gut bacteria can influence whether cancer treatments work.
Working independently, two teams of scientists showed that three cancer treatments rely on gut bacteria to mobilise the immune system and kill tumour cells—not just in the gut, but also in the blood (lymphomas) and skin (melanomas). Remove the bacteria with antibiotics, and you also neuter the drugs.
Cyclophosphamide, oxaliplatin and "immunotherapy—a cocktail of substances that stimulates the immune system to attack cancer cells" all depend upon the bacteria in your gut to work. Antibiotics kill gut bacteria and make the treatments ineffective.
I don't know how doctors and pharmacists can keep track of all the drugs and their effects upon the body and on other drugs. I can't remember the names of my cocktails. I know one of those little devils put my tongue to sleep before it put my brain into a dream state.
I can just see them all now, in the pharmacy, concocting my cocktail.
The three witches, casting a spell
Double, double, toil and trouble;
Fire burn, and cauldron bubble.
There are broad-spectrum antibiotics and there are antibiotics that are specific for certain kinds of bacteria. The specific antibiotics would not necessarily kill the particular gut bacteria in question, or interfere with cancer drugs.
Broad-spectrum antibiotics need to be used with caution and preferably not for a long time. But doctors know this.