What is ampicillin used to treat?
Ampicillin is a versatile, broad-spectrum antibiotic from the penicillin family, effective against a wide array of Gram-positive and Gram-negative bacteria. Its utility in treating bacterial infections is well-documented, though its effectiveness is dependent on the specific bacterial strain's susceptibility. It is important to note that ampicillin, like other antibiotics, is only effective against bacterial infections and will not treat viral illnesses such as the common cold or flu.
Key indications and uses
Ampicillin is a mainstay in the treatment of several infectious diseases. The specific use and administration method (oral, intravenous, or intramuscular) depend on the type and severity of the infection.
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Bacterial Meningitis: Ampicillin is used to treat bacterial meningitis caused by susceptible organisms like E. coli, Group B Streptococci, and Listeria monocytogenes. For severe cases, it is often administered intravenously. In some instances, it may be used in combination with aminoglycosides to increase effectiveness against Gram-negative bacteria.
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Respiratory Tract Infections: It is prescribed for infections of the throat, sinuses, and lungs, including community-acquired pneumonia (CAP) caused by susceptible bacteria such as Streptococcus pneumoniae and Haemophilus influenzae. For uncomplicated pediatric CAP, ampicillin is often recommended as a first-line therapy.
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Gastrointestinal Infections: Ampicillin can be used to combat bacterial infections of the gastrointestinal tract, such as those caused by Salmonella and Shigella species. Both oral and intravenous routes may be used depending on the severity.
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Urinary Tract Infections (UTIs): Susceptible strains of E. coli and Proteus mirabilis that cause UTIs can be treated with ampicillin. For uncomplicated UTIs, sufficient urinary concentrations can be achieved to eradicate the bacteria.
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Sepsis and Endocarditis: Ampicillin is effective against sepsis and endocarditis caused by susceptible Gram-positive organisms, including certain Streptococcus and Enterococcus species. In some neonatal settings, ampicillin in combination with gentamicin is a first-line treatment for sepsis.
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Infections in Infants: Ampicillin is a commonly used antibiotic in the neonatal intensive care unit (NICU) for the treatment of bacterial infections, including early-onset sepsis and meningitis.
Ampicillin vs. Amoxicillin
While both are aminopenicillins, ampicillin and amoxicillin have key differences, particularly concerning absorption and resistance patterns. These differences influence which drug a healthcare provider might prescribe.
| Feature | Ampicillin | Amoxicillin |
|---|---|---|
| Oral Absorption | Poorly absorbed from the gastrointestinal tract; requires empty stomach for better absorption. | Better and more reliably absorbed from the gastrointestinal tract; can be taken with or without food. |
| Bioavailability | Lower systemic availability after oral administration. | Higher systemic bioavailability after oral administration. |
| Frequency | Typically dosed more frequently, such as every 6 hours, for oral administration. | Typically dosed less frequently, such as every 8 hours, for oral administration. |
| Beta-Lactamase Susceptibility | Susceptible to degradation by beta-lactamase enzymes produced by resistant bacteria. | Also susceptible to beta-lactamase, but often combined with clavulanic acid to overcome resistance. |
| Administration | Available in oral, intramuscular (IM), and intravenous (IV) forms. | Available primarily for oral use, though not available in an IV form in the US. |
| Side Effects | More prone to causing diarrhea compared to amoxicillin due to poorer absorption and more residue in the gut. | Less commonly causes gastrointestinal side effects like diarrhea. |
How ampicillin works: The mechanism of action
Ampicillin is a bactericidal antibiotic, meaning it works by killing bacteria rather than simply stopping their growth. Its mechanism of action targets the bacterial cell wall, which is essential for the organism's survival.
- Binding to Penicillin-Binding Proteins (PBPs): Ampicillin binds to and inhibits penicillin-binding proteins (PBPs), which are enzymes crucial for building the peptidoglycan structure of the bacterial cell wall.
- Inhibiting Cell Wall Synthesis: By acylating and inactivating these transpeptidase enzymes, ampicillin prevents the final cross-linking step in the synthesis of the peptidoglycan.
- Causing Cell Lysis: The compromised cell wall weakens the bacterium, leading to cell lysis and death.
The challenge of antibiotic resistance
Over the decades, the widespread use of ampicillin has led to the emergence of bacterial resistance. One common mechanism involves bacteria producing beta-lactamase enzymes that break down the beta-lactam ring of the ampicillin molecule, rendering it ineffective. To combat this, ampicillin is often combined with a beta-lactamase inhibitor like sulbactam, as seen in the intravenous medication ampicillin/sulbactam (formerly branded Unasyn). Continued efforts in antibiotic stewardship are crucial to preserve the effectiveness of ampicillin and other antibiotics.
Conclusion
Ampicillin is a valuable penicillin-class antibiotic with a broad spectrum of activity against many bacterial infections, from respiratory ailments and meningitis to UTIs and sepsis. Its effectiveness, however, is tempered by the rise of antibiotic resistance, which has led to the development of combination therapies to increase its efficacy. The decision to use ampicillin or a related antibiotic depends on the specific type of infection, the patient's condition, and local resistance patterns, highlighting the need for accurate diagnostic testing.
