Side Effects of Long-Term Antibiotic Use

Antibiotics are chemicals that have the ability to inhibit the growth of microorganisms, especially bacteria, and are either produced naturally by other microorganisms or synthetically in a laboratory. Although antibiotics are commonly prescribed for 7 to 14 days to treat most illnesses, long-term use may be necessary to treat certain chronic infections. Prolonged use of antibiotics can have several side effects, so it is important for both the doctor and patient to weigh the pros and cons of prolonged antibiotic use. 

Changes in Normal Flora

Several surface tissues, such as skin and mucous membrane, as well as certain internal organs such as the intestines, are colonized with large amounts of microorganisms, predominantly bacteria and yeasts. These microorganisms are part of the normal flora. However, excessive and prolonged use of antibiotics, especially broad spectrum antibiotics which act against several different types of bacteria, can lead to eradication of the normal flora from their habitats. According to Todar’s Online Textbook of Bacteriology, lack of normal flora could lead to vitamin deficiencies, especially vitamin K and vitamin B12. It can also suppress the natural immunity of the body, making the individual more susceptible to infectious diseases.

The decrease in the population of beneficial bacteria can also lead to overgrowth of unwanted microorganisms such as Candida, and can lead to conditions like oral thrush and Candida vaginosis.

Adverse Physiological Effects

Both long-term and short-term use of antibiotics can lead to several changes in the body. Although most allergic reactions such as skin rash and swelling of the face appear within first 48 hours of the antibiotic use, other changes–such as lack of appetite, nausea and mild diarrhea–can last for a long time, so prolonged use of antibiotics can be very distressing to the patient.

For their study, the team used mice to look at the effects of four antibiotics commonly given to lab animals.

Previously, it was thought the antibiotics only killed gut bacteria and blocked some immune functions in the gut. But the new study shows they also destroy cells in the intestinal epithelium.

The intestinal epithelium is a velvet-like layer of specialized cells that lines the intestine and helps absorb water, glucose and essential nutrients into the bloodstream. It is also a barrier between the rest of the body and the huge colonies of bacteria that live in the gut.

The velvet-like appearance of the intestinal epithelium is due to the millions of tiny projections called villi that maximize the surface area of the epithelium.

The intestinal epithelium is home to an abundance of immune cells that live alongside the trillions of gut bacteria with whom they are in constant dialogue to maintain the delicate stability of the partnership between the host body and its bacterial colonies.

Antibiotics Disrupt Mitochondria and Host-microbe Signaling

The team also discovered that antibiotics affect a gene that is critical to the communication between host and gut bacteria. Prof. Morgun notes:

“When the host microbe communication system gets out of balance it can lead to a chain of seemingly unrelated problems.”

Disruption in host-microbe dialog can not only disrupt digestion, cause diarrhea and ulcerative colitis, but new research is also linking it to immune function, obesity, food absorption, depression, sepsis, asthma and allergies.

The team also found that the antibiotics and bacteria that have developed resistance to them cause significant changes to mitochondria, leading to more cell death.

Mitochondria are tiny compartments inside cells that act like batteries – they convert food into energy for the cell. They also play an important role in cell signaling and growth and need to function properly for good health.

In evolutionary terms, mitochondria are descended from bacteria, which may explain why antibiotics attack cell components that most closely resemble them.

Studies like this support the idea that killing bad bacteria with antibiotics is perhaps not a good way to deal with infection – given the increasing list of side-effects and problems they cause. Prof. Morgun suggests boosting the healthy bacteria so they outcompete the unwanted ones might be a better approach.