If the fever is above 39 degree Celsius I will bring to PD. Normally PD will prescribe paracetamol plus brufen for high fever. If fever lasts for 72 hours, you should bring baby to PD for a blood test to rule out any serious infection or dengue.
Anytime my kid is feeling warm, I just bug my pedia and send a text message asking her what I should do. And she normally tells me to only administer paracetamol if fever is 37.8C. But a fever of 40C, then that's cause for alarm already.