fever is the body's response to inflammation or infection. amoxicillin is only effective for a bacterial infection (like strep). it is absolutely no effect on viruses. a person can contract a virus anytime even while taking an antibiotic. fever doesn't really shock or bother medical professionals as much as it does parents but i cannot blindly tell you the significance of this brief transient fever. i do not know anything about your son what you really mean by a "spike" so when in doubt call his medical provider -- someone who knows him his particular case and someone that can offer you the patient-specific advice that you really need.
my son was on day 8 of 1 000mg/day amoxicillian and he spiked a fever. should i be worried? . he presented with high fever and sore throat and was treated for strep. his fever broke the second day but on day 8 of antibiotics he spiked a fever. the ibuprofen i gave him wore off and the fever has not returned. should i return to the doctor?