Hi, Metronidazole is an antibiotic that is primarily used to treat infections caused by bacteria and some parasites. It is not typically used to treat swelling or pain caused by spider bites. If you have been bitten by a spider and are experiencing swelling and pain that is spreading, it is important to seek medical attention as soon as possible. Depending on the severity of the reaction and the type of spider, you may require specific medical treatment, such as antivenom. In the meantime, you can try to reduce the swelling by applying a cool compress to the affected area and taking over-the-counter pain relievers like ibuprofen or acetaminophen. It is also important to keep the affected area clean and avoid scratching or further irritating the bite. However, please note that spider bites can be serious and even life-threatening in some cases, so it is important to seek professional medical advice if you are unsure or if your symptoms worsen. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician