Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
Ampicillin vs AMOXICILLIN AND CLAVULANATE POTASSIUM
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 inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins. Clavulanate potassium is a beta-lactamase inhibitor that irreversibly inactivates beta-lactamase enzymes, preventing degradation of amoxicillin.
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
Lower respiratory tract infections,Acute bacterial sinusitis,Otitis media,Urinary tract infections,Skin and skin structure infections,Bone and joint infections,Intra-abdominal infections,Dental infections
250-500 mg orally every 6 hours; 1-2 g IV/IM every 4-6 hours.
500 mg amoxicillin/125 mg clavulanate orally every 8 hours or 875 mg amoxicillin/125 mg clavulanate orally every 12 hours. For severe infections: 875 mg amoxicillin/125 mg clavulanate orally every 8 hours or 1000 mg amoxicillin/62.5 mg clavulanate extended-release orally every 12 hours.
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).
Amoxicillin: ~1-1.5 hours; Clavulanate: ~1 hour. Prolonged in renal impairment.
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 undergoes partial hepatic metabolism via hydrolysis. Clavulanate is extensively metabolized in the liver, primarily by hydrolysis and conjugation.
Renal: 90% unchanged via glomerular filtration and tubular secretion; biliary: 10% (small amount).
Renal: ~50-70% amoxicillin unchanged; ~25-40% clavulanate as metabolites. Fecal: minimal. Biliary: minor.
17-20% bound to serum albumin.
Amoxicillin: ~20% (mainly albumin); Clavulanate: ~25% (albumin).
0.28-0.31 L/kg (higher in neonates and critically ill patients).
Amoxicillin: ~0.3-0.4 L/kg; Clavulanate: ~0.3 L/kg. Distributes into tissues, not CSF unless inflamed.
Oral: 50% (fasting); reduced by 25-50% with food. IM: ~100% (complete absorption).
Oral: ~80-90% for amoxicillin; ~60-75% for clavulanate. Enhanced with food.
Cr Cl 10-50 m L/min: administer every 6-12 hours; Cr Cl <10 m L/min: administer every 12-24 hours.
For Cr Cl 10-30 m L/min: 250-500 mg amoxicillin component every 12 hours. For Cr Cl <10 m L/min: 250-500 mg amoxicillin component every 24 hours. Hemodialysis: 250-500 mg every 24 hours, give additional dose during and after dialysis.
No adjustment needed for hepatic impairment; dose as in normal hepatic function.
No specific dose adjustment recommended for mild to moderate hepatic impairment. Use with caution in severe hepatic impairment (Child-Pugh C); consider alternative therapy or reduced dosing, but no formal guidelines.
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.
For children >3 months: 25-45 mg/kg/day of amoxicillin component divided every 12 hours (based on 200 mg/28.5 mg per 5 m L suspension) or 20-40 mg/kg/day divided every 8 hours (based on 125 mg/31.25 mg per 5 m L suspension). For severe infections, up to 90 mg/kg/day of amoxicillin component divided every 12 hours (using 400 mg/57 mg per 5 m L suspension).
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.
Initiate at lower end of dosing range due to increased risk of renal impairment. Monitor renal function and adjust dose based on creatinine clearance as per renal adjustment guidelines.
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 boxed 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
Hypersensitivity reactions (anaphylaxis, Stevens-Johnson syndrome) in patients with penicillin allergy,Clostridioides difficile-associated diarrhea,Hepatic toxicity (elevated liver enzymes, hepatitis, cholestatic jaundice) more common in elderly and with prolonged use,Renal impairment requires dose adjustment,Risk of superinfection with prolonged therapy,Skin rash can occur in patients with mononucleosis
Hypersensitivity to ampicillin or any penicillin,Hypersensitivity to cephalosporins (cross-allergenicity possible),Infections caused by penicillinase-producing bacteria (including methicillin-resistant Staphylococci)
History of anaphylactic reaction to penicillins or cephalosporins,Previous cholestatic jaundice or hepatic dysfunction associated with amoxicillin-clavulanate,Concurrent use with disulfiram or probenecid (relative)
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.
May be taken with or without food; food enhances absorption; avoid ingestion with high-dose clavulanate? (no significant interaction); no specific food restrictions; milk-containing products do not interact significantly.
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-clavulanate is pregnancy category B. No evidence of teratogenicity in animal studies; human data do not demonstrate increased risk of major congenital malformations. Use during first trimester is considered safe if clinically indicated. During second and third trimesters, no known fetal risks. However, avoid use near term due to potential for neonatal kernicterus (theoretical risk from high doses, but not confirmed).
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 and clavulanate are excreted into breast milk in low concentrations. M/P ratio not established. Considered compatible with breastfeeding by AAP; risk of infant sensitization, diarrhea, or thrush. Use with caution in infants with history of penicillin allergy.
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.
Pharmacokinetic changes in pregnancy (increased renal clearance, expanded plasma volume) may require dose adjustments: total daily dose typically remains same but dosing interval may need to be shortened (e.g., every 6-8 hours instead of every 12 hours) for severe infections; monitor clinical response. No standard recommendation for routine adjustment; base on severity and renal function.
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.
Use weight-based dosing for pediatric patients; reconstitute oral suspension with appropriate amount of water; administer at start of meal to reduce GI upset; check renal function before dosing; avoid in patients with mononucleosis due to risk of maculopapular rash; higher doses of clavulanate may cause diarrhea; intravenous infusion over 30-40 minutes; consider penicillin allergy cross-reactivity; not effective against MRSA; requires dose adjustment in Cr Cl <30 m L/min.
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, usually every 12 hours.,Take with food to reduce stomach upset and improve absorption.,Complete the full course even if you feel better.,Shake the oral suspension well before each use.,Store oral suspension in refrigerator, discard after 10 days.,Report severe diarrhea, rash, or signs of allergy immediately.,May cause diarrhea; do not treat without consulting doctor.,Inform your doctor if you are pregnant, breastfeeding, or have liver disease.
"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 AND CLAVULANATE POTASSIUM, 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 AND CLAVULANATE POTASSIUM is a Penicillin Antibiotic that works by Amoxicillin inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins. Clavulanate potassium is a beta-lactamase inhibitor that irreversibly inactivates beta-lactamase enzymes, preventing degradation of amoxicillin.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between Ampicillin and AMOXICILLIN AND CLAVULANATE POTASSIUM 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 AND CLAVULANATE POTASSIUM is: 500 mg amoxicillin/125 mg clavulanate orally every 8 hours or 875 mg amoxicillin/125 mg clavulanate orally every 12 hours. For severe infections: 875 mg amoxicillin/125 mg clavulanate orally every 8 hours or 1000 mg amoxicillin/62.5 mg clavulanate extended-release orally every 12 hours.. 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 AND CLAVULANATE POTASSIUM 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 AND CLAVULANATE POTASSIUM is classified as Category A/B. Amoxicillin-clavulanate is pregnancy category B. No evidence of teratogenicity in animal studies; human data do not demonstrate increased risk of major congenital malformations. Us. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.