Cephalexin: Pharmacology and Side Effects

General Description

Cephalexin is an FDA-approved first-generation cephalosporin antibiotic that can be used to treat a variety of bacterial infections, such as pneumonia and other chest infections, skin infections, urinary tract infections (UTIs), respiratory tract infections, and otitis media. It can also be used to treat bone infections caused by Staphylococcus aureus or Proteus mirabilis.

Figure 1. Cephalexin

Pharmacology

Cephalexin is a β-lactam antibiotic that is structurally characterized by a β-lactam ring. Within bacterial cells, peptidoglycan provides mechanical stability to the cell wall. Cephalexin, along with other β-lactam antibiotics, utilizes its β-lactam ring to inhibit peptidoglycan synthesis, a key process in the formation of bacterial cell walls. Its β-lactam ring binds to penicillin-binding proteins (PBPs), which effectively blocks the final stage of peptidoglycan synthesis, called the transpeptidation reaction. This reaction is essential for the cross-linking of bacterial peptidoglycan. By inhibiting this process, cephalexin undermines cell viability and ultimately leads to bacterial cell death.

Despite this, bacteria can develop resistance to cephalexin through various mechanisms, including the following pathways:

(1) Bacteria express "β-lactamases" to degrade β-lactam antibiotics.

(2) Bacteria modify PBP proteins to change the binding affinity of cephalexin to its target site.

(3) Bacteria synthesize efflux pumps to expel drugs from the cells.

Side Effects

Common side effects of Cephalexin include:

• Gastrointestinal reactions (abdominal pain, diarrhea, indigestion, nausea, vomiting, gastritis)

• Redness, blistering, peeling or loosening of the skin

• Abnormal vaginal discharge, itching or odor

Rare side effects include:

• Muscle or joint pain

• Blood in the stool

• Immunogenic hemolytic anemia

• Toxic tendinopathy

• Acute generalized exanthematous pustulosis

Serious side effects include:

• Severe stomach pain, watery or bloody diarrhea

• Unexplained bruises on the skin

• Yellowing of the skin and dark urine (may be a liver problem)

• Serious allergic reactions (trouble breathing, swelling of the face, lips, tongue or throat, hives)

If any of the above serious adverse reactions occur, please contact your doctor immediately.

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