Antibiotic Therapy Overview and Choices

Antibiotic Therapy Overview

• Antibiotic therapy began with Sir Alexander Fleming's discovery of penicillin in 1945, which won him a Nobel Prize.
• Before penicillin, sulfa antibiotics were used, but their numerous adverse effects limited their effectiveness.
• Antibiotics have been widely used since the 1940s.

Key Considerations in Antibiotic Choice

• Proper antibiotic choice depends on identifying the organism causing the infection, ensuring antimicrobial susceptibility, and using the narrowest effective spectrum.
• Host factors, including allergies, age, renal and liver function, the site of infection, pregnancy, and metabolic disorders (particularly diabetes) must be considered.

Types of Antibiotics

• Penicillins (e.g., penicillin G, penicillin V, amoxicillin, cloxacillin, oxacillin, ampicillin, piperacillin, methicillin)
• Cephalosporins
• Carbapenems
• Monobactams
• Glycopeptides
• Aminoglycosides
• Fluoroquinolones

Determining Antimicrobial Susceptibility

• Disk diffusion method: Bacteria are spread on a plate, and antibiotic-impregnated disks are placed on the surface. The diameter of the inhibition zone helps determine antibiotic effectiveness.
• Epsilometer (E-test): A strip with a gradient of antibiotic concentrations is placed on the plate, and the zone of inhibition where the strip intersects with the bacteria indicates the minimum inhibitory concentration (MIC).

Additional Considerations

• Minimum bactericidal concentration (MBC): Specialized testing may be needed for fastidious organisms, such as obligate anaerobes, Haemophilus species, pneumococci, and MRSA, as these are difficult to grow under standard conditions.
• Pharmacodynamic profile: Assess area under the curve/time curve to MIC (AUC/MIC), maximal serum concentration/MIC (Cmax/MIC), and time during dosing interval that plasma concentration exceeds MIC (t/MIC).
  • Concentration-dependent antibiotics (e.g., fluoroquinolones, aminoglycosides) efficacy increases with drug concentration
  • Time-dependent antibiotics (e.g., beta-lactams, vancomycin) efficacy is proportional to the duration the drug concentration is above the MIC.
• Site of infection: Some antibiotics are not effective in certain sites, so the infection site should be considered.
• Immune system: Antibiotics can suppress immune functions in immunocompromised patients.
• Combinations: Some clinicians advocate antibiotic combinations (e.g., penicillin + aminoglycosides, oxacillin + aminoglycosides); however, antagonism is possible.
• Adverse effects: Approximately 5% of patients experience adverse effects from antibiotics. Combinations of antibiotics increase costs and adverse effects.
• Anaphylaxis: Beta-lactams are the most common antibiotics linked with anaphylaxis.

Vaccine Recommendations for Healthcare Workers

• Hepatitis B Virus (HBV): Mandatory in the USA since 1991. The vaccine is available for those exposed and those who wish to update their immunity.
  • The vaccine contains the HBV surface antigen and cannot spread the virus.
  • The vaccination series consists of 3 doses at 0, 1, and 6 months.
• Influenza: Annual vaccination is needed, usually starting in the fall, and includes strains A and B.
• Rubella: Avoid pregnancy for two months after vaccination.
• Varicella: Two doses of the vaccine are administered with 2 months between doses, and pregnancy should be postponed after the second dose.
• Tetanus: Recommended toxoid vaccine every 10 years.
• Pneumococcal: Recommended for immunocompromised adults and those over 65.

Monitoring the Response to Antibiotics

• Clinically assess any improvements or worsening of symptoms
• Monitor drug levels (e.g., vancomycin)
• Perform laboratory tests regularly (e.g., white blood cell (WBC) counts, liver enzymes, kidney function tests)

Cost Considerations

• If all other factors are equal, choose the least expensive drug.

Additional information regarding the presentation

• Needle Stick Injuries: Hepatitis B—30%, Hepatitis C—3%, HIV—0.3%.
• Host Factors: Include allergies, prior adverse reactions to drugs, and aspects of immune condition.
• Age: Renal function decreases, and some antibiotics must be avoided in children.
• Generic/Metabolic: In patients with G6PD deficiency, avoid sulfa drugs.
• Pregnancy: Certain antibiotics can be used safely(e.g penicillins, cephalosporins, erythromycin) While others need to be avoided (e.g teratogenic drugs, aminoglycosides, tetracyclines).
• Renal and Liver Function: Some antibiotics (e.g., aminoglycosides) need to be used with caution, and renal function monitored.
• Vaccination response and booster shots needed to maintain immunity.