JUNE 2012 ANTIBIOTIC TREATMENT GUIDE INFORMATION SHEET ON BACTERIAL RESISTANCE THIS OPTIMAL USAGE GUIDE IS PROVIDED FOR INFORMATION PURPOSES ONLY AND SHOULD NOT REPLACE THE JUDGMENT OF A PROFESSIONAL. This information sheet is intended for health professionals involved in primary care services. It was developed as a guide for antibiotics prescription in ambulatory and long-term care settings, where treatment is usually empirically based. The information presented here refers to the clinical guides on antibiotic treatment (inesss.qc.ca), which take bacterial resistance into account. CONTEXT Some bacteria have developed means to resist the effects of antibiotics, through mechanisms such as the production of enzymes ANTIBIOTIC GUIDE TREATMENT that inactivate antibiotics or the modification of their cell wall structure, making the pathogen “impervious” to the antibiotic. The increase in antibiotics resistance witnessed over the last decades is worrisome. The widespread and non-optimal use of anti- biotics has promoted the emergence of bacterial resistance and has contributed to the global increase of infection-related morta- lity. Administering antibiotics to animals (veterinary medicine or agriculture) further contributes to the problem. The link between antibiotics use and the emergence of bacterial resistance has been clearly established. Furthermore, several factors contribute to resistance propagation, including inadequate hygiene practices, the proximity of hospitalized patients, international travel, etc. Since individual antibiotics prescriptions can have a direct collective impact, it is important that health care professionals con- sider this aspect of public health when writing a prescription. It is a concrete way to help in the fight against bacterial resistance. DEFINITIONS AND CLINICAL IMPLICATIONS Bacteria develop resistance through either genetic mutation or the acquisition of genetic material. The use of antibiotics promotes the emergence of resistance by eliminating sensitive bacteria and contributing to the selection of resistant bacteria. This phenomenon is called “selective pressure.” MAIN RESISTANCE MECHANISMS Enzyme inhibition (e.g., Staphylococcus aureus) Efflux pumps Production of an enzyme that inactivates or destroys (e.g., Staphylococcus aureus and Streptococcus the antibiotic pneumoniae) Presence of membrane transporters that carry Examples: the antibiotic ( ) out of the cell and keep it from β-lactams ( ) reaching adequate concentrations. These pumps β-lactamases can break down penicillins and are specific to one or several antibiotics classes. cephalosporins, inactivating them. Aminoglycosides Examples: Three enzymes have the capacity to inhibit these antibiotics. Tetracycline Tetracycline, doxycycline Macrolides Alteration of the antibiotic target site Azithromycin, clarithromycin (e.g., Staphylococcus aureus and Streptococcus Fluoroquinolones pneumoniae) Ciprofloxacin, levofloxacin Modification of the site of action on the cellular membrane or in the cytosol, leading to decreased affinity for the antibiotic ( ). Decreased permeability of the cellular membrane (e.g., Escherichia coli) Examples: Closing of the membrane pores used by the Penicillin antibiotic ( ) to enter the cell. The alteration of penicillin-binding proteins (PBP) decreases the affinity for the antibiotic. Examples: Fluoroquinolones Fluoroquinolones The spontaneous mutation of only one DNA gyrase or Ciprofloxacin, levofloxacin topoisomerase IV amino acid leads to fluoroquinolone resistance. Macrolides Intracellular modifications of the ribosomal target site inside Adapted from: Yim G., Attack of the Superbugs: Antibiotic Resistance, www.scq.ubc.ca. the bacterium may decrease the effect of macrolides. In practice, there are two main definitions for bacterial resistance. Microbiological resistance (in vitro) occurs when a bacterial strain is able to grow despite the presence of an antibiotic. This resistance depends on a few parameters, among which the serum concentration reached by a given antibiotic plays a signifi- cant role. In cases of life-threatening infections (bacteraemia, meningitis), the concept of in vitro resistance becomes extremely important. Clinical resistance (in vivo) is defined as the lack of sign and symptom improvement (fever, overall condition, etc.) after 72 hours of treatment. This type of resistance is more relevant to common medical practice, since it indicates treatment failure of the course of antibiotics. In certain cases, microbiological resistance does not translate into clinical resistance. In that regard, the tissue concentration of the antibiotic has a major impact and must be considered along with the antibiogram. Here are some examples: Macrolides and some fluoroquinolones are significantly concentrated in the respiratory tract. Therefore, these molecules may remain clinically effective despitein vitro resistance. Except for moxifloxacin, fluoroquinolones reach high concentrations in the urinary tract because they are mostly elimina- ted unchanged by the kidney. Urine concentrations may exceed the bacterial resistance threshold. Streptococcus pneumoniae may acquire resistance to penicillin by altering the affinity of the antibiotic’s binding site. This type of resistance is usually overcome by administering high-dose amoxicillin, for example in cases of acute otitis media. FACTORS CONTRIBUTING TO EMERGENCE AND PROPAGATION INFORMATION SHEET ON INFORMATION BACTERIAL RESISTANCE PRESCRIPTION- PATIENT- HOSPITAL ENVIRONMENT- ASSOCIATED FACTORS ASSOCIATED FACTORS ASSOCIATED FACTORS § Liberal use of antibiotics § Recent exposure to an antibiotic from § Failure to follow the policies and § Use of broad-spectrum antibiotics any class (promotes the emergence of measures recommended for infec- resistance, usually within the same class) tion control, including hand washing, § Use of antibiotics with a long tissue half-life (e.g., azithromycin, long-las- § Child under two years old hygiene practices and health measures ting subtherapeutic residual concen- § Child attending a daycare centre § Failure to follow policies and pro- cedures related to intra- and inter-ins- tration after treatment completion) § Immunosuppression titution communication when transfer- § Suboptimal use of antibiotics (dura- § Lack of compliance with treatment ring patients tion of treatment too short or too due to adverse effects, excessively long, subtherapeutic dose) complex dosage, drug unavailability § International travel QUESTIONS TO ASK BEFORE PRESCRIBING AN ANTIBIOTIC § What is the likelihood of a bacterial etiology? § Which bacteria are the most likely cause for this type of infection? PATHOGEN § Is it recommended to confirm bacterial etiology before starting treatment? § What is the usual sensitivity profile of the pathogens involved? § Which antibiotics are the most likely to be effective against these bacteria? § Has the patient taken antibiotics within the last three months, and if yes, which ones? § Does the patient attend a place with a higher risk of bacterial resistance, such as daycare centres? § Has the patient travelled in an area with known bacterial resistance? PATIENT § Is the patient a known carrier of resistant bacteria? § Does the patient present significant comorbidities or immunosuppression? § Is the patient at risk of not taking the medication properly? § What is the first-line antibiotic for this type of infection? § What are the main pharmacokinetic parameters (tissue distribution, elimination route, etc.) of the ANTIBIOTIC antibiotic considered? § Is there a risk of drug interaction that may modify its efficacy? § What are the appropriate dose and duration for the treatment? EXAMPLES OF CLINICAL SITUATIONS TYPE OF SIGNS OF A ANTIBIOTICS PREFERRED EMPIRICAL TREATMENT APPROACHES INFECTION RESISTANT INVOLVED AND COMMENTS (pathogen) PATHOGEN ACUTE OTITIS MEDIA IN Children under Pneumococcal resistance is stable in Québec. When treatment CHILDREN AND two years old is indicated, resistance may easily be countered by increasing COMMUNITY- Daycare atten- the dose of AMOXICILLIN (90 mg/kg/day): adequate concen- ACQUIRED PENICILLINS dance trations in the middle ear and in the lung parenchyma for the PNEUMONIA IN treatment of pneumococci with intermediate resistance to peni- CHILDREN Recent antibio- cillin and of most highly penicillin-resistant pneumococci. (Streptococcus tic treatment pneumoniae) Macrolides remain the first-line treatment for patients with a low risk for complications. Due to high macrolide concentra- tions in lung tissues, microbiological resistance does not always lead to clinical resistance. INFORMATION SHEET ON INFORMATION BACTERIAL RESISTANCE Macrolides It is recommended to select an agent from another class when a taken within MACROLIDES macrolide has been used within the last three months. the previous 3 months Another treatment option should be considered in cases where microbiological resistance has been confirmed through culture COMMUNITY- results. ACQUIRED PNEUMONIA IN A higher risk of emergence of macrolide resistance has been shown ADULTS when using azythromycin as opposed to using clarithromycin. (Streptococcus pneumoniae) It is recommended to select an agent from another class when a fluoroquinolone has been used within the last three months. Fluoroquino- Fluoroquinolones should be reserved for higher-risk patients lone taken FLUORO- who are known or suspected carriers of first-line-agent resistant within the pre- QUINOLONES strains of Streptococcus pneumoniae.
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