Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
Ampicillin vs AMOXICILLIN PEDIATRIC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Ampicillin is a penicillin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity, and disrupting peptidoglycan cross-linking.
Amoxicillin is a semisynthetic penicillin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs). It blocks the transpeptidation step in peptidoglycan cross-linking, leading to cell lysis and death.
Respiratory tract infections,Urinary tract infections,Meningitis,Septicemia,Endocarditis,Gastrointestinal infections,Intra-abdominal infections,Skin and soft tissue infections,Prophylaxis for bacterial endocarditis (off-label),Listeriosis
Treatment of infections caused by susceptible strains of microorganisms in conditions such as otitis media, sinusitis, pharyngitis, tonsillitis, pneumonia, bronchitis, urinary tract infections, skin and skin structure infections, and gonorrhea,Prophylaxis of infective endocarditis in patients undergoing dental or upper respiratory tract procedures (off-label but per ADA/AHA guidelines),Eradication of Helicobacter pylori (as part of combination therapy)
250-500 mg orally every 6 hours; 1-2 g IV/IM every 4-6 hours.
250-500 mg orally every 8 hours or 500-875 mg orally every 12 hours for adults.
Terminal elimination half-life: 1-1.8 hours in adults with normal renal function; prolonged to 7-20 hours in end-stage renal disease (Cr Cl <10 m L/min).
Terminal elimination half-life: 1-1.5 hours in children with normal renal function; prolonged to 7-21 hours in anuria.
Ampicillin is primarily excreted unchanged in the urine via renal tubular secretion and glomerular filtration. A small portion is metabolized by hydrolysis to penicilloic acid, but hepatic metabolism is minimal.
Amoxicillin is primarily metabolized by hydrolysis to penicilloic acid, which is then excreted renally. It does not undergo extensive hepatic metabolism; renal clearance involves tubular secretion and glomerular filtration.
Renal: 90% unchanged via glomerular filtration and tubular secretion; biliary: 10% (small amount).
Renal: 60-80% unchanged via glomerular filtration and tubular secretion; biliary: minor (<10%); fecal: <5%.
17-20% bound to serum albumin.
17-20% bound to serum proteins, primarily albumin.
0.28-0.31 L/kg (higher in neonates and critically ill patients).
0.3-0.5 L/kg; reflects distribution into extracellular fluid and well-perfused tissues; crosses placenta and distributes into pleural, synovial, and peritoneal fluids.
Oral: 50% (fasting); reduced by 25-50% with food. IM: ~100% (complete absorption).
Oral: 75-90% (absorption is rapid but incomplete; food does not significantly affect absorption).
Cr Cl 10-50 m L/min: administer every 6-12 hours; Cr Cl <10 m L/min: administer every 12-24 hours.
Cr Cl 10-30 m L/min: administer every 12 hours. Cr Cl <10 m L/min: administer every 24 hours. Hemodialysis: administer dose after dialysis.
No adjustment needed for hepatic impairment; dose as in normal hepatic function.
No specific dose adjustment required for Child-Pugh A or B. Child-Pugh C: consider dose reduction based on clinical response.
Neonates: 25-50 mg/kg IV/IM every 12 hours (first week), every 8 hours (1-4 weeks); Infants/Children: 25-100 mg/kg/day IV/IM divided every 6-8 hours; Oral: 50-100 mg/kg/day divided every 6-8 hours.
Neonates <4 weeks: 30 mg/kg/day divided every 12 hours. Infants and children >4 weeks: 20-50 mg/kg/day divided every 8 hours (mild-moderate infection) up to 80-100 mg/kg/day divided every 6-8 hours (severe infection).
Cr Cl >50 m L/min: no adjustment; Cr Cl 10-50 m L/min: administer every 6-12 hours; Cr Cl <10 m L/min: administer every 12-24 hours; maximum 2 g/day.
No specific dose adjustment based solely on age; assess renal function and adjust accordingly due to age-related decline in GFR.
Serious and occasionally fatal hypersensitivity reactions (anaphylaxis) have been reported in patients on penicillin therapy. Clostridium difficile-associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents.
No FDA black box warning.
Serious hypersensitivity reactions (anaphylaxis) requiring emergency treatment,Clostridium difficile-associated diarrhea (CDAD) may occur,Prolonged use may result in superinfection with non-susceptible organisms,Use with caution in patients with renal impairment (dose adjustment needed),Skin rash is common in patients with mononucleosis or concurrent allopurinol use
Serious hypersensitivity reactions (anaphylaxis) may occur; discontinue therapy if allergic reaction occurs. Clostridium difficile-associated diarrhea (CDAD) can occur. Adjust dose in renal impairment. Use caution in patients with mononucleosis due to high incidence of morbilliform rash. Prolonged use may result in superinfection.
Hypersensitivity to ampicillin or any penicillin,Hypersensitivity to cephalosporins (cross-allergenicity possible),Infections caused by penicillinase-producing bacteria (including methicillin-resistant Staphylococci)
Hypersensitivity to amoxicillin or any penicillin derivative; history of anaphylactic reaction to beta-lactams.
Food decreases absorption of oral ampicillin; take on an empty stomach. No specific food restrictions aside from timing. Avoid alcohol as it may increase gastrointestinal irritation.
Amoxicillin absorption is not significantly affected by food; may be taken with or without meals. However, to minimize gastrointestinal upset, administer with a small amount of food if needed. Avoid acidic beverages (e.g., fruit juices) within 1 hour of dosing as they may degrade the antibiotic.
Ampicillin is FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects. In humans, ample data across all trimesters indicate no increased risk of major birth defects, though there is a theoretical risk of altered gut flora and maternal-fetal effects from high doses. No documented teratogenicity from controlled studies in pregnant women.
Amoxicillin is classified as FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. Human data from pregnant women indicate no increased risk of major birth defects across all trimesters. Caution in first trimester due to limited data, but generally considered safe.
Ampicillin is excreted in breast milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.2–0.3. Amount ingested by the infant is estimated to be <0.1% of a therapeutic neonatal dose. The American Academy of Pediatrics considers it compatible with breastfeeding. Monitor infant for potential diarrhea, rash, or candidiasis.
Amoxicillin is excreted into breast milk in low concentrations (M/P ratio approximately 0.01-0.02). Considered compatible with breastfeeding; minimal risk of infant effects such as diarrhea or allergic sensitization. Monitor infant for potential gastrointestinal disturbances.
Pregnancy increases renal clearance and volume of distribution for ampicillin, potentially lowering serum concentrations. For standard infections, no dose adjustment is routinely needed. However, for serious infections (e.g., meningitis, endocarditis), higher doses or more frequent intervals may be required to achieve therapeutic levels. Consider therapeutic drug monitoring in severe cases.
Physiologic changes in pregnancy (increased renal blood flow, glomerular filtration rate, and volume of distribution) may lower serum concentrations. Standard dosing is generally adequate, but severe infections may require dose adjustment. No specific dose reduction recommended; monitor clinical response.
Ampicillin is a bactericidal antibiotic that inhibits cell wall synthesis. It is effective against Gram-positive cocci (except penicillinase-producing staphylococci) and some Gram-negative bacilli. Use with probenecid to increase serum levels. Monitor for rash, which may indicate mononucleosis. Dose adjustment required in renal impairment (Cr Cl <30 m L/min). Administer IV slowly over 10-15 minutes to avoid phlebitis.
Amoxicillin pediatric suspension is dosed based on body weight; typical dose is 20-40 mg/kg/day in divided doses every 8 hours. For high-dose therapy (e.g., resistant pneumococcus), 80-90 mg/kg/day in two divided doses. Shake suspension well before each dose. Use within 14 days after reconstitution; discard unused portion. Not for patients with severe renal impairment (Cr Cl <30 m L/min) without dose adjustment. Monitor for rash, diarrhea, and hypersensitivity reactions.
Take ampicillin exactly as prescribed, even if you feel better.,Complete the full course of therapy to prevent resistance.,Take on an empty stomach (1 hour before or 2 hours after meals) for best absorption.,Oral suspension must be refrigerated; shake well before each use.,Discard any unused oral suspension after 14 days.,Report any skin rash, diarrhea, or difficulty breathing to your doctor immediately.,Do not use if you are allergic to penicillins or cephalosporins.,Avoid alcohol while on this medication to reduce risk of side effects.,May reduce the effectiveness of oral contraceptives; use additional birth control.
Take this medication exactly as prescribed; complete the full course even if your child feels better.,Shake the bottle well before each dose; measure the dose with the provided dosing device.,Refrigerate the suspension after mixing; do not freeze. Discard any unused portion after 14 days.,Do not give this medication if your child is allergic to penicillins or cephalosporins.,Common side effects include diarrhea, nausea, and rash. Contact your doctor if severe diarrhea or signs of allergic reaction occur.,This medication may reduce the effectiveness of oral contraceptives; use additional birth control if applicable.,Inform your doctor if your child has kidney disease, phenylketonuria (some suspensions contain phenylalanine), or is pregnant/breastfeeding.
"The coadministration of ampicillin, a broad-spectrum penicillin antibiotic, with streptozocin, a nitrosourea antineoplastic agent used in pancreatic islet cell carcinoma, may reduce serum concentrations of streptozocin. This interaction is hypothesized to result from ampicillin-induced alterations in gut microbiota, leading to reduced enterohepatic recirculation of streptozocin metabolites or interference with renal tubular secretion of the active drug. Clinically, this could diminish the anticancer efficacy of streptozocin, potentially compromising tumor response."
"Ampicillin may reduce the serum concentration of Kanamycin via direct chemical inactivation in body fluids, particularly in patients with renal impairment. This interaction can lead to subtherapeutic aminoglycoside levels, potentially compromising antibacterial efficacy and promoting bacterial resistance. Clinically, this necessitates careful monitoring of Kanamycin levels and dose adjustments to maintain therapeutic effect."
"Ampicillin, a beta-lactam antibiotic, can reduce the serum concentration of plicamycin, an antineoplastic antibiotic, when co-administered. This interaction likely occurs due to ampicillin-induced alterations in gut microbiota, which may decrease the enterohepatic recirculation of plicamycin, leading to reduced systemic exposure. The resulting subtherapeutic plicamycin levels may compromise its antitumor efficacy and increase the risk of treatment failure."
"Amoxicillin may reduce the metabolism of Indinavir via inhibition of CYP3A4, leading to increased plasma concentrations of Indinavir. This can elevate the risk of Indinavir-related toxicities such as nephrolithiasis, hepatotoxicity, and gastrointestinal intolerance. Patients may experience exacerbated adverse effects without a corresponding increase in antiviral efficacy."
"Amoxicillin may inhibit the CYP3A4-mediated metabolism of nicardipine, a calcium channel blocker, leading to increased plasma concentrations of nicardipine. This can potentiate vasodilation and negative chronotropic effects, resulting in an increased risk of hypotension, bradycardia, and peripheral edema. Patients, especially those with pre-existing cardiovascular conditions, should be monitored for enhanced antihypertensive effects and adverse reactions when these drugs are coadministered."
"Amoxicillin may inhibit the metabolism of bortezomib through competitive inhibition of cytochrome P450 enzymes, particularly CYP3A4 and CYP2C19, potentially leading to increased bortezomib exposure. This interaction could result in enhanced toxicity of bortezomib, including peripheral neuropathy, myelosuppression, and gastrointestinal adverse effects. Clinicians should monitor for signs of bortezomib toxicity when amoxicillin is coadministered, especially in patients with pre-existing hepatic impairment or other risk factors."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about Ampicillin vs AMOXICILLIN PEDIATRIC, answered by our medical review team.
Ampicillin is a Penicillin Antibiotic that works by Ampicillin is a penicillin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity, and disrupting peptidoglycan cross-linking.. AMOXICILLIN PEDIATRIC is a Penicillin Antibiotic that works by Amoxicillin is a semisynthetic penicillin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs). It blocks the transpeptidation step in peptidoglycan cross-linking, leading to cell lysis and death.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between Ampicillin and AMOXICILLIN PEDIATRIC depend on the specific clinical indication. These are both Penicillin Antibiotic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of Ampicillin is: 250-500 mg orally every 6 hours; 1-2 g IV/IM every 4-6 hours.. The standard adult dose of AMOXICILLIN PEDIATRIC is: 250-500 mg orally every 8 hours or 500-875 mg orally every 12 hours for adults.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between Ampicillin and AMOXICILLIN PEDIATRIC in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. Ampicillin is classified as Category A/B. Ampicillin is FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects. In humans, ample data across all trimesters indicate no increased risk of major bi. AMOXICILLIN PEDIATRIC is classified as Category A/B. Amoxicillin is classified as FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. Human data from pregnant women indicate no increased risk of major birth def. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.