Two medicines, side by side
Erythromycin vs metronidazole
Erythromycin and metronidazole are both labeled for bacterial infections. Drugs@FDA records approvals of erythromycin since 1964 and of metronidazole since 1963. Pharmacies paid $1.96 per erythromycin 250 mg tablet and $0.102 per metronidazole 250 mg tablet (NADAC, October 7, 2026). Metronidazole's other strengths are brand-only: $2.60 per mL (Likmez 500 mg/5 mL suspension). In FDA's classes, erythromycin is a macrolide and metronidazole a nitroimidazole antimicrobial.
Check it at the source: the erythromycin FDA label on DailyMed (effective August 1, 2024); the metronidazole FDA label on DailyMed (effective September 3, 2024).
Highlights of the erythromycin record
Erythromycin (Erythrocin) · label of August 1, 2024
Used for
From the label: indicationsTo reduce the development of drug-resistant bacteria and maintain the effectiveness of erythromycin tablets and other antibacterial drugs, erythromycin tablets should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. […]
On the market
- Earliest approval on file
- June 25, 1964
- Generic labelers
- 38 labelers
- Pharmacy cost
- $1.96 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 2
Highlights of the metronidazole record
Metronidazole (Flagyl) · label of September 3, 2024
Metronidazole has been shown to be carcinogenic in mice and rats (see PRECAUTIONS ). Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the INDICATIONS AND USAGE section below.
Used for
From the label: indicationsSymptomatic Trichomoniasis. Metronidazole tablets are indicated for the treatment of T. vaginalis infection in females and males when the presence of the trichomonad has been confirmed by appropriate laboratory procedures (wet smears and/or cultures). Asymptomatic Trichomoniasis. […]
On the market
- Earliest approval on file
- July 18, 1963
- Generic labelers
- 55 labelers
- Pharmacy cost
- $0.102 per tablet
Supply and safety
- Shortage
- In shortage
- Recalls
- 7
Source: FDA drug labels via openFDA (Erythromycin label of August 1, 2024, Metronidazole label of September 3, 2024); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do erythromycin and metronidazole differ on the record?
In FDA's classes, erythromycin is a macrolide and metronidazole a nitroimidazole antimicrobial.
Only the metronidazole label carries a boxed warning.
Generics: erythromycin since 1964; metronidazole since 1984 (Drugs@FDA).
| Erythromycin | Metronidazole | |
|---|---|---|
| Labeled for | Bacterial infections, Acne | Bacterial infections |
| Pharmacologic class | Macrolide, Macrolide Antimicrobial | Nitroimidazole Antimicrobial |
| How it works (label) | n/a | n/a |
| Half-life (label) | n/a | The elimination half-life, measured during the first 3 days of life, was inversely related to gestational age. |
| Earliest approval on file (Drugs@FDA) | June 25, 1964 | July 18, 1963 |
| First generic approved | June 24, 1964 | December 6, 1984 |
| Generic labelers (NDC) | 38 labelers | 55 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $1.96 per tablet (Erythromycin 250 mg tablet) | $0.102 per tablet (Metronidazole 250 mg tablet) |
| 12-month price change | +12% | +10% |
| Boxed warning | No | Yes |
| Shortage now | No current entry | In shortage |
| Recalls recorded | 2 | 7 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 18,956 | 63,553 |
| DEA schedule | none | none |
Source: Drugs@FDA, FDA NDC Directory, CMS NADAC of October 7, 2026, FDA shortages and recalls, FAERS via openFDA (FDA files October 8, 2026)
What next?
- Alternatives to erythromycin
- every medicine labeled for the same conditions