Sandbox: antibiotic resistance

Course duration and development of antibiotic resistance

• Completing the antibiotic course even after resolution of symptoms is widely believed to be a must to avoid the development of antibiotic resistant strains by bacteria. But Is this concept true? Dr.Martin J Llewelyn, the professor of infectious diseases at Brighton and Sussex Medical School investigated this concept further.

• The roots of this belief started back in the 1940s with the development of antibiotics. Alexander Fleming himself indicated in his Nobel prize speech that insufficient penicillin for treatment of streptococcal throat infection can cause other patients to get infected with resistant strains of the bacteria. But up till now, streptococci causing throat infection never developed resistance to penicillin after all these years, argues Dr.Llewelyn.
• Two mechanisms are responsible for antibiotic resistance: Targeted selection and collateral selection.
• An example of targeted selection is the resistance developed by Mycobacterium tuberculosis when an insufficient or a single antibiotic is administered. This accounts for a minority of cases of antibiotic resistance.
• Collateral selection occurs when the bacterial flora present normally in the body is affected by the administered antibiotic leaving space for other resistant harmful bacterial strains.
• Collateral selection accounts for most of the cases of antibiotic resistance and it is not dependent at all on the duration of administration of the antibiotic.

• The role of the duration of antibiotic administration on antibiotic resistance is clearly understudied and for most bacterial infections. The conventional duration course was not compared to a shorter course for efficacy and the development of resistant strains in most of the indications of administration of antibiotics.
• Pyelonephritis was treated with quinolones for two weeks, however, trials have shown that 5-7 day course is as efficient.
• Antibiotic treatment efficacy for otitis media was not the same with shorter courses. Antibiotics gave the same clinical results with shorter and longer treatment courses and in fact, shorter courses were associated with lower recurrence rates.
• As regarding hospital acquired pneumonia, research has shown that shorter antibiotic courses might be associated with less chance of developing resistant bacterial strains in the future.
• None of these trials have shown that antibiotic resistance was associated with the shorter courses.
• The author suggested administering antibiotics should be guided by infection biomarkers such as procalcitonin in the inpatient setting and with the symptoms of the patient in the outpatient setting. He also suggests that the message of “completing the course” should be reconsidered and changed.

• However, the topic needs further study to confirm this theory.