Keflex is the brand name of the drug cephalexin. Cephalexin is an antibiotic in a class called cephalosporins. These work by preventing bacteria from reproducing. The Merck Manual, a reference manual for drugs, states that cephalexin is a first-generation cephalosporin. As an antibiotic similar to penicillin, cephalexin may cause allergic reactions as well as more generalized side effects.
Cephalexin behaves in a similar way to penicillin. According to information in the Merck Manual, patients may experience an adverse reaction to cephalexin if they have an allergy to penicillin. Symptoms of an allergic reaction to cephalexin may include angioedema, swelling especially in the face, and urticaria, known as hives. In addition a patient may go into anaphylactic shock. This condition is a life-threatening reaction that begins quickly and involves a drop in blood pressure and heart rate as well as slowed breathing. Patients experiencing any of these side effects should seek medical attention immediately.
Systemic Side Effects
Serious systemic side effects may occur while taking cephalexin. The most common of these is diarrhea. Other gastrointestinal side effects include stomach pain, changes in stool color, nausea and vomiting. Some patients may vomit blood. The Mayo Clinic notes that serious neuromuscular effects may occur, including joint and muscle pain and possibly arthritis. Patients may experience neurological side effects such as dizziness. Skin may blister or peel, or patients may notice skin rashes or lesions that the Mayo Clinic describes as red with a purple color in the middle. Patients may also experience the symptoms of a cold such as chills, cough, fever, sore throat and excessive tiredness. Individuals who notice any of the above side effects should visit a medical professional.
Initial Side Effects
Some side effects may not be as serious because they subside once patients become accustomed to the medication. The Mayo Clinic notes that patients may experience belching and indigestion while taking cephalexin. Some patients may feel anxious, irritable, shaky or nervous. Other neurological effects include restlessness and hallucinations. Some patients may have difficulty sleeping. Muscle and joint pain may initially occur after beginning cephalexin. According to the Merck Manual, cephalexin may also increase pain during sex, cause itching around the genital area and result in white or brown vaginal discharge. If any of these side effects persist or worsen, individuals should consult with a physician.