Cefixime

Cefixime is a third-generation oral cephalosporin, a bactericidal antibiotic: it kills the bacterium rather than merely slowing its growth. Its target is the bacterial wall. To keep their shape and withstand pressure, bacteria build a reinforced wall by cross-linking peptidoglycan units, a rigid mesh that surrounds the cell. This cross-linking is carried out by enzymes called penicillin-binding proteins, or PBPs, which are peptidoglycan transpeptidases.

Cefixime binds to these PBPs and blocks their activity. Cross-linking no longer takes place, the wall weakens, and the bacterium dies. It has another strength: it resists hydrolysis by certain beta-lactamases, the enzymes that some germs make to destroy antibiotics. This stability makes it active against bacteria that have become resistant to several penicillins.

Cefixime treats well-defined bacterial infections. It is approved for uncomplicated urinary tract infections, otitis media, pharyngitis and tonsillitis, acute exacerbations of chronic bronchitis, and uncomplicated gonorrhea, cervical or urethral. The doctor chooses it when the bacterium responsible is among those it reaches.

An antibiotic fights only bacteria, never viruses: it has no effect on a cold or the flu. Prescribing it wisely also limits the emergence of resistance, an issue that goes beyond each individual patient. The length of treatment depends on the infection and is followed through to the end.

In adults, the usual dose is 400 mg per day, in a single daily intake. In children, it is 8 mg per kilo per day, in one intake or split into two intakes of 4 mg per kilo every twelve hours. The tablet and the suspension absorb about 40 to 50 percent of the dose, with or without food. For the capsule, a meal reduces absorption, with a drop of about 15 percent in total exposure and 25 percent in peak concentration.

Regularity makes for effectiveness: taking the dose at a fixed time keeps a stable concentration. The serum peak occurs in the hours following intake, and the mean half-life is three to four hours, sometimes up to nine hours. Even if symptoms improve quickly, you must not stop the treatment on your own: a shortened infection can return and favor resistant bacteria.

The most frequent effects concern digestion. In clinical trials, diarrhea was observed in 16 percent of patients, nausea in 7 percent, loose or frequent stools in 6 percent, flatulence in 4 percent, abdominal pain in 3 percent, and dyspepsia in 3 percent. These disturbances reflect the antibiotic’s action on the intestinal flora.

A rarer effect deserves attention. Like nearly all antibiotics, cefixime can cause diarrhea linked to the bacterium Clostridioides difficile, of variable intensity, from mild diarrhea to severe or even fatal colitis; cases of pseudomembranous colitis have been documented. Severe or persistent diarrhea, during or after treatment, should lead to seeking medical advice rather than restarting the medication on your own.

Once in the blood, cefixime is bound to serum proteins at about 65 percent. It is eliminated mainly by the kidneys: about half of the absorbed dose is found unchanged in the urine within twenty-four hours, which explains its value in urinary tract infections. More than 10 percent of the dose also passes into the bile.

Cephalosporins, including cefixime, can be accompanied by a fall in prothrombin activity, that is, the blood’s ability to clot, which depends on vitamin K. In at-risk patients, prothrombin time is monitored, and vitamin K is given if needed.

Two drug interactions are worth knowing. Combined with warfarin or other anticoagulants, cefixime can prolong prothrombin time, with or without bleeding: monitoring of coagulation is then increased. With carbamazepine, an antiepileptic, elevated blood levels have been reported in pharmacovigilance, and measuring carbamazepine levels is advised.

Cefixime can also distort certain laboratory tests. It gives false positives for glucose in urine with Benedict’s or Fehling’s solutions, false positives for ketone bodies with nitroprusside tests, and, like other cephalosporins, can make a direct Coombs test positive. Reporting this treatment to the laboratory avoids misinterpreting a result.