Prescription principles and gram-positive flora
Rational pharmacotherapy of infectious diseases is based on the mandatory isolation and precise identification of the microorganism. Only after this step does the physician select the drug of choice.
Among gram-positive cocci, streptococci and staphylococci are of the greatest clinical significance. For Streptococcus and Pneumococcus, the gold standard of therapy remains benzylpenicillin.
The approach to treating infections caused by Staphylococcus strictly depends on its enzymatic activity and resistance profile:
- If the strain does not produce $\beta$-lactamase, benzylpenicillin is used.
- When $\beta$-lactamase is produced, oxacillin is prescribed.
- If methicillin-resistant strains (MRSA) are identified, vancomycin becomes the salvage drug.
Gram-positive rods also require a specific approach. For example, in anthrax (Bacillus anthracis), benzylpenicillin is most effective, whereas in diphtheria (Corynebacterium diphtheriae), the administration of macrolides is indicated.
Gram-negative microorganisms
Gram-negative flora often requires the prescription of broader-spectrum or targeted agents.
- Cocci: Meningococcal infection (Neisseria meningitidis) responds well to benzylpenicillin. In gonorrhea (Neisseria gonorrhoeae), the first-line drugs are ceftriaxone and ciprofloxacin.
- Enteric group: To eradicate Escherichia coli, ciprofloxacin or third-generation cephalosporins are used. Infections caused by Salmonella and Shigella require the administration of ciprofloxacin. If meningitis is caused by Klebsiella, second-generation cephalosporins are indicated.
- Specific rods: Pseudomonas aeruginosa (Pseudomonas aeruginosa) is characterized by high natural resistance, which is why anti-pseudomonal penicillins (ureidopenicillins, carboxypenicillins) or ceftazidime are used against it. For pneumonia and meningitis caused by Haemophilus influenzae, third-generation cephalosporins, inhibitor-protected aminopenicillins (amoxicillin + clavulanic acid), or co-trimoxazole are prescribed.
Highly dangerous, zoonotic, and atypical infections
Causative agents of highly dangerous infections require the immediate administration of potent etiotropic therapy:
- Yersinia pestis (plague): streptomycin, tetracyclines.
- Francisella tularensis (tularemia): streptomycin.
- Vibrio cholerae (cholera): doxycycline, ciprofloxacin.
- Brucella (brucellosis): a combination of doxycycline and rifampicin.
Intracellular and atypical pathogens are inaccessible to classical $\beta$-lactams, which is why other pharmacological groups take the lead here:
- Rickettsiae (epidemic typhus, Rocky Mountain spotted fever, Q fever) and Borrelia burgdorferi (Lyme disease): doxycycline.
- Chlamydia: doxycycline or azithromycin.
- Mycoplasma pneumoniae: macrolides or doxycycline.
- Legionella pneumophilia: macrolides.
Spirochetes, specifically Treponema pallidum (Treponema pallidum), which causes syphilis, retain high sensitivity to benzylpenicillin.
Anaerobes, fungi, and specific regimens
For the treatment of infections caused by specific pathogens, clear therapeutic regimens have been developed:
- Anaerobes: For infections associated with Bacteroides fragilis, clindamycin or metronidazole is used. Clostridial infections require a differentiated approach: gas gangrene (Clostridium perfringens) and tetanus (Clostridium tetani) are treated with benzylpenicillin, while pseudomembranous colitis (Clostridium difficile) is treated with metronidazole.
- Pneumocystis: To eradicate Pneumocystis carinii, the drug of choice is co-trimoxazole.
- Helicobacter: Eradication of Helicobacter pylori is carried out using combination therapy that includes amoxicillin and clarithromycin.
- Tuberculosis: Mycobacterium tuberculosis requires a prolonged multi-drug regimen, the baseline drugs of which are isoniazid, rifampin, ethambutol, and pyrazinamide.
Briefly: answers to topical questions
Which antibiotic groups possess anti-pseudomonal activity?
Anti-pseudomonal activity is exhibited by several groups of antibacterial drugs.
- Penicillins — ureidopenicillins, carboxypenicillins, and inhibitor-protected drugs (piperacillin/tazobactam).
- Cephalosporins — ceftazidime, cefepime, ceftobiprole, cefoperazone/sulbactam.
- Carbapenems — meropenem, imipenem (ertapenem does not possess such activity).
- Fluoroquinolones — ciprofloxacin, levofloxacin.
- Aminoglycosides — amikacin (used in combination).
Which drugs are included in the standard Helicobacter pylori eradication regimen?
The standard Helicobacter pylori eradication regimen includes strictly standardized triple or quadruple drug combinations.
- Antibacterial agents — amoxicillin, clarithromycin, metronidazole.
- Proton pump inhibitors — for example, omeprazole.
- Bismuth preparations — used as an additional component.
If the first-line therapy fails, a second-line eradication regimen is prescribed, including reserve antibiotics and proton pump inhibitors.
How to treat pseudomembranous colitis caused by Clostridium difficile?
To treat pseudomembranous colitis caused by Clostridium difficile, antibacterial drugs and detoxification therapy are used.
- Metronidazole — is the first-line drug for the treatment of this infection.
- Vancomycin — serves as an alternative. It is administered orally (per os as a solution), utilizing its property of poor absorption for local action in the intestinal lumen.
Which antifungal drugs are used to treat systemic candidiasis?
For the treatment of systemic candidiasis, the drugs of choice are:
- Fluconazole — the first-line drug in systemic candidiasis.
- Itraconazole — exhibits activity in systemic candidiasis.
- Caspofungin — used as initial therapy for candidemia.
Sources also indicate antifungal drugs for the treatment of candidiasis in general: amphotericin B, nystatin, levorin, and clotrimazole.
Which antiviral drugs are the drugs of choice for cytomegalovirus infection?
Direct-acting antivirals are the drugs of choice for the treatment and prevention of cytomegalovirus infection.
- Ganciclovir is the mainstay of treatment in immunocompromised patients, for manifest forms, primary episodes, or relapses.
- Valganciclovir is a prodrug of ganciclovir. It is the drug of choice for treating CMV retinitis in patients with AIDS and is also used to prevent CMV esophagitis after organ transplantation.
To remember staphylococcal therapy, use the "BOV" rule: Without lactamase (No enzyme) — Benzylpenicillin, Produces lactamase — Oxacillin, Highly resistant (MRSA) — Vancomycin.
Class and exam questions
Which drug is the drug of choice for syphilis?
Benzylpenicillin remains the first-line drug for the treatment of infection caused by Treponema pallidum.
How to treat infections caused by intracellular pathogens (chlamydia, mycoplasmas)?
Since $\beta$-lactams are ineffective against them, the drugs of choice are macrolides (e.g., azithromycin) and tetracyclines (doxycycline).
Which antibiotics are active against Pseudomonas aeruginosa?
Ureidopenicillin, carboxypenicillins, and antipseudomonal cephalosporins (ceftazidime) are used against Pseudomonas aeruginosa.
What are the special features of tuberculosis treatment?
Treatment of Mycobacterium tuberculosis always requires a multi-drug regimen. First-line drugs include isoniazid, rifampin, ethambutol, and pyrazinamide.
What else to study on this topic
- Mechanisms of staphylococcal resistance ($\beta$-lactamase production and MRSA)
- Characteristics of antipseudomonal penicillins and cephalosporins
- Principles of combined eradication therapy for Helicobacter pylori
- Pharmacology of first-line antituberculosis drugs
- Specifics of treating anaerobic infections (Clostridia and Bacteroides)
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