Antibiotics target bacteria, not viruses. Since the common cold and influenza are viral, antibiotics will not shorten them or relieve symptoms, and taking them unnecessarily can cause side effects and drive antibiotic resistance.
Management of a cold or flu focuses on rest, fluids, and over-the-counter remedies used as directed to ease symptoms. For confirmed influenza in certain higher-risk people, a doctor may consider a specific antiviral medicine, which is different from an antibiotic.
Antibiotics become relevant only if a bacterial complication develops, such as a bacterial sinus infection, ear infection, or pneumonia. A doctor decides this based on examination and your overall picture. Do not pressure for or self-start antibiotics for a simple cold.