Doxycycline 100mg is a broad-spectrum tetracycline antibiotic used to treat many bacterial infections and for certain prophylactic indications when appropriate. It’s commonly prescribed for respiratory tract infections, skin conditions like acne and rosacea, and sexually transmitted infections such as chlamydia, as well as atypical and zoonotic infections including rickettsial diseases, Q fever, and psittacosis. It also has roles in managing cholera and leptospirosis, and may be used for anthrax treatment/prophylaxis. In travel medicine, it can be used for malaria prophylaxis in specific regions based on resistance patterns. Use depends on clinical assessment, local guidelines, and confirmed or suspected pathogen.