Tretinoin cream left in heat for 3 hours, can I still use it?

I left tretinoin cream (aluminium tube) in a metal box under the blazing sun of Adelaide Australia for about 3 hours. The metal box gets very hot to the touch after about twenty minutes in the sun. By the time I removed the tube the sun was gone and the tube was warm to the touch. I have no idea how hot it got when the sun was at its strongest. The cream looked a little runny before I cooled it down in the fridge. Would the tretinoin still be effective?? Or should I just get another tube:(