Doxycycline is a broad-spectrum antibiotic that belongs to the tetracycline class of drugs. It is commonly used to treat a wide variety of bacterial infections, including respiratory infections (like pneumonia and bronchitis), skin infections, urinary tract infections, and certain sexually transmitted diseases such as chlamydia and gonorrhea. Additionally, doxycycline is used to prevent malaria and treat conditions like Lyme disease and acne. It works by inhibiting bacterial protein synthesis, thereby preventing the bacteria from growing and multiplying. Doxycycline is generally well tolerated, but it can cause side effects like nausea, photosensitivity (increased sensitivity to sunlight), and gastrointestinal discomfort. It is typically taken orally, in the form of tablets or capsules, and is often prescribed in a dosage of 100 mg.