General Choice of Antibiotics Against Common Microorganisms

This table is not meant to be a definitive guide for clinical treatment but a general indication of the main antimicrobial actions and thus of the overall usefulness of commonly used antibiotics.

Microorganism(s)a First-choice antibiotic(s)b Second-choice antibiotic(s)b
Gram-Positive Cocci
Staphylococcus (boils, infection of wounds, etc.)
Non-β-lactamase-producing Benzylpenicillin (penicillin G) or phenoxymethylpenicillin (penicillin V) A cephalosporin or vancomycin
β-lactamase-producing A β-lactamase-resistant penicillin (i.e. flucloxacillin) A cephalosporin or vancomycin, or a macrolide, or a quinolone
Methicillin-resistant Vancomycin ± gentamicin ± rifampicin (rifampin) Co-trimoxazole, or ciprofloxacin, or a macrolide ± fusidic acid, or rifampicin
Methicillin/vancomycin-resistant Quinupristin/dalfopristin or linezolid
Streptococcus, haemolytic types (septic infections, i.e. bacteraemia, scarlet fever, toxic shock syndrome) Benzylpenicillin or phenoxymethylpenicillin ± an aminoglycoside A cephalosporin, or a macrolide, or vancomycin.
Enterococcus (endocarditis) Benzylpenicillin + gentamicin Vancomycin
Pneumococcus (pneumonia) Benzylpenicillin or phenoxymethylpenicillin or ampicillin, or a macrolide A cephalosporin
Microorganism(s)a First-choice antibiotic(s)b Second-choice antibiotic(s)b
Gram-Negative Cocci
Morasella catarrhalis (sinusitis) Amoxicillin + clavulanic acid Ciproxafloxacin
Neisseria gonorrhoeae (gonorrhoea) Amoxicillin + clavulanic acid, or ceftriaxone Cefotaxime, or a quinolone
Neisseria meningitidis (meningitis) Benzylpenicillin Chloramphenicol, or cefotaxime, or minocycline
Microorganism(s)a First-choice antibiotic(s)b Second-choice antibiotic(s)b
Gram-Positive Rods
Corynebacterium (diphtheria) A macrolide Benzylpenicillin
Clostridium (tetanus, gangrene) Benzylpenicillin A tetracycline, or a cephalosporin
Listeria monocytogenes
(rare cause of meningitis and generalised infection in neonates)
Amoxicillin ± an aminoglycoside Erythromycin ±an aminoglycoside
Microorganism(s)a First-choice antibiotic(s)b Second-choice antibiotic(s)b
Gram-Negative Rods
Enterobacteriaceae (coliform organisms)
Escherichia coli, Enterobacter, Klebsiella
Infections of urinary tract An oral cephalosporin, or a quinolone Extended-spectrum penicillin
Septicaemia An aminoglycoside (intravenous) or cefuroxime Imipenem or a quinolone
Shigella (dysentery) A quinolone Ampicillin or trimethoprim
Salmonella (typhoid, paratyphoid) A quinolone or ceftriaxone Amoxicillin or chloramphenicol or trimethoprim
Haemophilus influenzae
(infections of the respiratory tract, ear, sinuses; meningitis)
Ampicillin or cefuroxime Cefuroxime (not for meningitis) or chloramphenicol
Bordetella pertussis (whooping cough) A macrolide Ampicillin
Pasteurella multocida
(wound infections, abscess)
Amoxicillin + clavulanic acid Ampicillin
Vibrio cholerae (cholera) A tetracycline A quinolone
Legionella pneumophila
(pneumonia, legionnaires disease)
A macrolide ± rifampicin
Helicobacter pylori
(associated with peptic ulcer)
Metronidazole + amoxicillin + ranitidinec (2-week regimen) Clarithromycin + metronidazole
Pseudomonas aeruginosa
Urinary tract infection A quinolone Antipseudomonal penicillins
Other infections (of burns etc.) Antipseudomonal penicillins + tobramycind Imipenem ± an aminoglycoside, or ceftazidime
Brucella (brucellosis) Doxycycline + rifampicin
Bacteroides fragilis
Oropharyngeal infection Benzylpenicillin Metronidazole or clindamycin
Gastrointestinal infection Metronidazole, clindamycin Imipenem
Gram-negative anaerobic rods (other than B. fragilis) Benzylpenicillin or metronidazole A cephalosporin or clindamycin
Campylobacter (diarrhoea) A macrolide or a quinolone A tetracycline or gentamicin
Microorganism(s)a First-choice antibiotic(s)b Second-choice antibiotic(s)b
Treponema (syphilis, yaws) Benzylpenicillin A macrolide or ceftriaxone
Borrelia recurrentis (relapsing fever) A tetracycline Benzylpenicillin
Borrelia burgdorferi (Lyme disease) A tetracycline
Leptospira (Weil's disease) Benzylpenicillin A tetracycline
(typhus, tick-bite fever, Q fever, etc.)
A tetracycline A quinolone
Microorganism(s)a First-choice antibiotic(s)b Second-choice antibiotic(s)b
Other Organisms
Mycoplasma pneumoniae A tetracycline or a macrolide Ciprofloxacin
Chlamydia (trachoma, psittacosis, urogenital infections) A tetracycline
Actinomyces (abscesses) Benzylpenicillin A tetracycline
Pneumocystis (pneumonia, especially in AIDS patients) Co-trimoxazole (high dose) Pentamidine or atovaquone or trimetrexate
Nocardia (lung disease, brain abscess) Co-trimoxazole

a Only the main diseases caused by each organism are mentioned (in parentheses).
b ± signifies that an agent is to be used with or without another agent; if agents are to be used concomitantly, a plus sign only is used.
c An antiulcer drug, not an antibiotic.
d Not in the same syringe.