I usually carry a tube of antibiotic ointment (such as Neosporin) in my car first aid kit, which is kept in the trunk. There is an expiration date, but does the summer temperature in a closed car have any effect on it?

I couldn't find WHAT the heat does, but every place I found said to keep away from heat and direct sunlight.

I wonder if keeping it insulated would help at all, or would the heat eventually permeate any insulation?

Sue

The temp in my vehicle gets well over 110F in these summer months. No problems for me so far.

Yes the temp will work its way through any insulation its just a matter of time. I use an Igloo cooler to keep my stuff at a more even temp. I park in the garage at night and so it’s only out during the day when I am gone. The insulation on mine is thin on the lid so I cover every thing with an old towel, which really helps it stay cool longer. A couple of blue ice blocks will keep things cool in my low tech. Playmate a couple of days. This is also the way I would bring groceries home during the summer when I lived a long way from where I had to go to shop. If you trade out your blue ice every couple of days you will have a nice cool place to store things in your vehicle. Being able to come back to my truck and get a nice cool drink of water after several hours in the sun at about 100° F is worth the extra effort to me.
The color of your vehicle will make a big difference as well on inside temps. My white truck parked next to my brother in laws black truck at about 100° F has an extremely noticeable difference in temperatures. Adding a silver sunscreen in your windshield and Vent-Shades over your windows (so you can leave them open an inch) will make an unbelievable difference in inside temperatures.

How would you know of any problems? The efficacy of an antibiotic seems hard to measure.

I frequently use the stuff in my car FAK including the antibiotic ointment.