Two medicines, side by side
Ampicillin vs azithromycin
Ampicillin and azithromycin are both labeled for bacterial infections. Drugs@FDA records approvals of ampicillin since 1966 and of azithromycin since 1991. Pharmacies paid $0.441 per ampicillin 500 mg capsule and $0.266 per azithromycin 250 mg tablet (NADAC, October 7, 2026); the strengths differ, so the two prices are not like for like. Azithromycin's other strengths are brand-only: $98.51 per mL (Azasite 1% eye drops). In FDA's classes, ampicillin is a penicillin-class antibacterial and azithromycin a macrolide antimicrobial.
Check it at the source: the ampicillin FDA label on DailyMed (effective February 21, 2025); the azithromycin FDA label on DailyMed (effective December 4, 2025).
Highlights of the ampicillin record
Ampicillin (Penbritin-S) · label of February 21, 2025
Used for
From the label: indicationsAmpicillin for injection is indicated in the treatment of infections caused by susceptible strains of the designated organisms in the following conditions: Respiratory Tract Infections caused by Streptococcus pneumoniae. Staphylococcus aureus (penicillinase and nonpenicillinase-producing), H. influenzae, and Group A beta-hemolytic streptococci. […]
On the market
- Earliest approval on file
- December 29, 1966
- Generic labelers
- 17 labelers
- Pharmacy cost
- $0.441 per capsule
Supply and safety
- Shortage
- A presentation being discontinued
- Recalls
- 3
Highlights of the azithromycin record
Azithromycin (Zithromax) · label of December 4, 2025
Used for
From the label: indicationsAzithromycin tablets are macrolide antibacterial drug indicated for the treatment of patients with mild to moderate infections caused by susceptible strains of the designated microorganisms in the specific conditions listed below. […]
On the market
- Earliest approval on file
- November 1, 1991
- Generic labelers
- 55 labelers
- Pharmacy cost
- $0.266 per tablet
Supply and safety
- Shortage
- A presentation being discontinued
- Recalls
- 11
Source: FDA drug labels via openFDA (Ampicillin label of February 21, 2025, Azithromycin label of December 4, 2025); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do ampicillin and azithromycin differ on the record?
In FDA's classes, ampicillin is a penicillin-class antibacterial and azithromycin a macrolide antimicrobial.
Half-life, in each label's words: Ampicillin, “Due to maturational changes in renal function, ampicillin half-life decreases as postmenstrual age (a sum of …”; Azithromycin, “Elimination Plasma concentrations of azithromycin following single 500 mg oral and IV doses declined in a polyphasic …”
Generics: ampicillin since 1971; azithromycin since 2005 (Drugs@FDA).
| Ampicillin | Azithromycin | |
|---|---|---|
| Labeled for | Bacterial infections, Urinary tract infections | Bacterial infections |
| Pharmacologic class | Penicillin-class Antibacterial | Macrolide Antimicrobial |
| How it works (label) | n/a | Azithromycin is a macrolide antibacterial drug. [see Microbiology ( 12.4 )] |
| Half-life (label) | Due to maturational changes in renal function, ampicillin half-life decreases as postmenstrual age (a sum of gestational age and postnatal age) increases for infants with postnatal age of less than 28 days. | Elimination Plasma concentrations of azithromycin following single 500 mg oral and IV doses declined in a polyphasic pattern resulting in a mean apparent plasma clearance of 630 mL/min and terminal elimination half-life … |
| Earliest approval on file (Drugs@FDA) | December 29, 1966 | November 1, 1991 |
| First generic approved | March 3, 1971 | November 14, 2005 |
| Generic labelers (NDC) | 17 labelers | 55 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $0.441 per capsule (Ampicillin 500 mg capsule) | $0.266 per tablet (Azithromycin 250 mg tablet) |
| 12-month price change | -8% | -26% |
| Boxed warning | No | No |
| Shortage now | A presentation being discontinued | A presentation being discontinued |
| Recalls recorded | 3 | 11 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 8,240 | 59,712 |
| 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 ampicillin
- every medicine labeled for the same conditions