Ciprofloxacin

Ciprofloxacin belongs to the fluoroquinolone family. It is a bactericidal antibiotic, which means that it kills bacteria rather than merely slowing their multiplication. To reproduce, a bacterium must copy its DNA, a long molecule coiled upon itself. Ciprofloxacin blocks two enzymes essential to this copying: DNA gyrase, a type II topoisomerase, and topoisomerase IV.

By neutralizing these enzymes, it prevents bacterial DNA from unwinding and replicating properly, which leads the bacterium to die. Its activity is particularly strong against Gram-negative bacilli, a broad category of bacteria, including Pseudomonas aeruginosa, which is often difficult to treat. This effectiveness explains why it is reserved for specific situations.

The physician prescribes ciprofloxacin to treat bacterial infections that other antibiotics do not always cover. It is used in particular for urinary tract infections and prostatitis, for certain digestive infections such as typhoid fever and salmonellosis, and for infections of the bones and joints. It also serves as prophylaxis against inhalation anthrax and plague.

Taken by mouth, it passes well into the blood: its oral bioavailability reaches 70 to 80 %. The concentration peaks 1 to 1.5 hours after intake, and its elimination half-life is around 4 hours, somewhat longer in older people (3.3 to 6.8 hours). These values explain the dosing schedule and the duration of action of the medicine.

The oral form is most often taken twice a day, at regular intervals. Taking it with a meal reduces digestive discomfort without harming its effectiveness. The prescribed course must be followed through to the end, even if symptoms improve beforehand, and the treatment should not be stopped on one’s own initiative.

Certain foods and medicines interfere with its absorption. Dairy products taken alone, such as milk or yoghurt, and calcium-fortified juices reduce its passage into the blood; it can nonetheless be taken during a meal that contains them. Antacids and calcium, iron or zinc supplements chemically bind it: they must then be spaced at least 2 hours before or 6 hours after ciprofloxacin.

In clinical trials, the most frequent adverse effects remain digestive and moderate. Nausea affects 2.5 % of patients, diarrhoea 1.6 %, vomiting 1 % and skin rash 1 %. Abnormal liver function tests appear in 1.3 % of treated individuals.

A rarer effect deserves particular attention: ciprofloxacin can cause inflammation or rupture of a tendon, especially the Achilles tendon. This event can occur from a few hours to several months after treatment, and is the subject of the highest safety warning from the United States medicines agency. Sudden pain or swelling of a tendon should lead one to stop the effort and seek medical advice.

Other safety warnings of the same level accompany this medicine. It can affect the peripheral nerves and cause a neuropathy, produce neuropsychiatric effects, and worsen myasthenia gravis, a muscle disease. Ciprofloxacin can also prolong the heart’s QT interval, and cases of torsades de pointes, a rhythm disorder, have been reported after marketing.

It can disturb blood sugar in both directions, with hypoglycaemia that is sometimes severe or even fatal when it is added to an oral antidiabetic. The skin becomes more sensitive to the sun and to UV, which exposes one to moderate to severe photosensitivity reactions. Like any antibiotic, it can finally promote diarrhoea due to Clostridioides difficile, a bacterium whose toxins A and B cause forms that are sometimes serious.

Some combinations call for caution, or even prohibition. By blocking a liver enzyme, CYP1A2, ciprofloxacin increases the concentrations of theophylline and caffeine. It also raises those of ciclosporin, an immunosuppressant, whose concentrations require monitoring. This inhibition of CYP1A2 makes the combination with tizanidine, a muscle relaxant, contraindicated, because its concentrations rise sharply. With warfarin, an anticoagulant, the prothrombin time, the INR and any sign of bleeding must be monitored.

Monitoring accompanies the treatment according to the patient’s condition and its duration. It covers signs of tendinitis, mental state, the complete blood count, kidney and liver function and blood sugar. The physician remains attentive to the appearance of diarrhoea that could signal a C. difficile infection. These checks make it possible to adjust or stop the treatment at the right time.