Metronidazole

No longer first-line. StatPearls: "Metronidazole is no longer recommended as first-line therapy for C difficile infections and should only be considered in cases where vancomycin or fidaxomicin are unavailable." IV metronidazole is an adjunct in fulminant disease and may be needed if ileus is present.

Anaerobic cover — combined with a fluoroquinolone, or with trimethoprim-sulfamethoxazole as an alternative.

Its status in C. difficile has changed and the change is the teaching point: "Metronidazole is no longer recommended as first-line therapy for C difficile infections." The current order, per the IDSA/SHEA 2021 focused update as reported by StatPearls, is fidaxomicin 200 mg twice daily for 10 days first; oral vancomycin 125 mg every 6 hours for 10 days if fidaxomicin is unavailable; and metronidazole only when neither can be obtained. The one place it retains a defined role is fulminant disease, where "adjunctive therapy with intravenous metronidazole 500 mg every 8 hours is recommended" alongside oral and rectal vancomycin — where the intravenous route reaches an inflamed colon that oral drug may not. There is an irony worth naming for students: metronidazole’s demotion sits inside the same stewardship story that created the problem, since antibiotic overuse is the most critical modifiable risk factor for C. difficile in the first place, and "overuse increases the risk of adverse drug effects, C. difficile infection, and contributes significantly to the rise of antimicrobial resistance."

Anaerobic coverage — relevant to polymicrobial diabetic-foot and contiguous infection.

Metronidazole is on this page for two separate reasons, and its pelvic inflammatory disease role — the one the first-line chip refers to — is the one students omit. It is in every PID regimen CDC recommends for outpatient care — 500 mg orally twice daily for 14 days — and in parenteral regimen 1 at 500 mg orally or intravenously every 12 hours. The disorder-side reason is microbiological: PID is polymicrobial, and bacterial vaginosis organisms and anaerobes are "also common" in its microbiology alongside gonorrhea, chlamydia and Mycoplasma genitalium. A regimen of ceftriaxone plus doxycycline alone leaves the anaerobic half untreated. Trichomoniasis is treated with this same class, and the metronidazole class page owns it — the regimen, the way it differs by sex, and the pregnancy guidance. This page does not carry those details. The disulfiram-like alcohol reaction, peripheral neuropathy and metallic taste belong to the class page; the fetched STI guideline pages carry no alcohol counselling, so it is not attributed to them here.

The original β-lactams — bactericidal cell-wall inhibitors. The defining nursing job is screening for and recognizing allergy, from rash to anaphylaxis.

β-lactam cousins of penicillin, organized by generation — each generation trades some gram-positive reach for broader gram-negative coverage.

Powerful, broad-spectrum DNA-synthesis blockers — but a boxed warning for disabling tendon, nerve, and CNS effects means they’re reserved when alternatives exist.

Suppress viral replication rather than kill viruses outright. The nursing essentials: hydrate with acyclovir, start early (flu within 48 h), and remember most antivirals suppress — they don’t cure.

Powerful IV drugs for serious Gram-negative infection — but nephrotoxic and ototoxic. Levels matter.

Broad, generally safe protein-synthesis inhibitors — a penicillin-allergy alternative. Watch QT and CYP3A4.