SN instructed patient about Sulfamethoxazole. Call your doctor right away if you notice any of these side effects: Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing, Blistering, peeling, or red skin rash, Dark urine or pale stools, nausea, vomiting, loss of appetite, stomach pain, yellow skin or eyes, Chest pain, cough, or trouble breathing, Confusion, weakness, Muscle twitching, Severe diarrhea, stomach pain, cramps, bloating, Skin rash, purple spots on your skin, or very pale or yellow skin, Sore throat, fever, muscle pain, Uneven heartbeat, numbness or tingling in your hands, feet, or lips, Unusual bleeding, bruising, or weakness. If you notice these less serious side effects, talk with your doctor: Mild nausea, vomiting, or loss of appetite.