Serious Antibiotic Side Effects

Penicillin was the first antibiotic developed by Alexander Fleming in the early part of the 20th century. It wasn't until Ernst Chain and Howard Florey made improvements to it that it became a world standard for killing disease-causing bacteria in World War II. Penicillin still is widely used in various forms and under brand names such as Amoxil, Nafcil, Veetids, Bactocill, Ticar, Geocillin, Pfizerpen, Cloxapen, Pipracil, Crysticillin, Principen, Dynapen and Staphcillin. Since penicillin's development, many other antibiotics have been created.

A woman with a cold sleeps while in the foreground, medications are visible. (Image: Tafiphoto/iStock/Getty Images)

Skin (Integumentary) System

Antibiotics may contribute to serious side effects in the skin that require medical attention. Some of them, such as a skin rash, hives, scaly or red skin, facial swelling, welts, skin discoloration or redness, require you to cease taking the medication and to seek emergency medical help. Hive-like swelling also may occur on various parts of the body, including the genitals, face, feet, eyelids, legs, lips, hands, throat or tongue. You should report any of these to a doctor. These types of side effects occur from antibiotics such as those in the penicillin family, vancomycin and rifaximin.

Gastrointestinal System

Many antibiotics may cause diarrhea as a side effect. Prolonged use of antibiotics with the side effect will cause dehydration and possible long-term damage to the gastrointestinal system. The body loses its natural bacterial flora with antibiotic use and irritation within the natural mucosa of the intestinal wall occurs. Monitoring the diarrhea is essential to ward off dehydration, which is loss of body fluids through watery stools. Other gastrointestinal side effects may include severe cramps or pain in the abdomen, vomiting and nausea.


Stronger antibiotics than those in the penicillin family, such as moxifloxacin hydrochloride, which may be prescribed for such ailments as acute bacterial sinusitis, bacteriological effects on bronchitis, pneumonia and infections of the skin, can cause some psychiatric side effects. These may include discouragement, a feeling that you or your surroundings aren't real, sad feelings, empty feelings, changes in mood, changes in mental state, irritability, nervousness, overreacting emotionally, moods that change rapidly, feeling like you are detached from your body and concentration difficulties.

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