Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER vs ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Cefoxitin is a cephamycin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis and death.
Acyclovir is a synthetic purine nucleoside analog with inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2), and varicella-zoster virus (VZV). After intracellular conversion to acyclovir triphosphate, it inhibits viral DNA polymerase, leading to chain termination and viral DNA replication inhibition.
Treatment of serious infections caused by susceptible Gram-positive and Gram-negative bacteria including intra-abdominal infections, pelvic inflammatory disease, diabetic foot infections, and prophylaxis in colorectal surgery,Off-label: Treatment of aspiration pneumonia, perioperative prophylaxis in cesarean section
Treatment of herpes simplex virus (HSV) infections (genital herpes, herpes labialis, herpes simplex encephalitis),Treatment of varicella-zoster virus (VZV) infections (chickenpox, herpes zoster),Neonatal herpes simplex virus infection,Off-label: Prevention of HSV reactivation in immunocompromised patients, treatment of eczema herpeticum
1-2 g IV every 6-8 hours. Maximum 12 g/day.
5 mg/kg IV every 8 hours (or 10 mg/kg IV every 8 hours for varicella-zoster or herpes simplex encephalitis) infused over 1 hour.
Terminal elimination half-life: 0.7–1.1 hours in normal renal function; prolonged to 5–10 hours in severe renal impairment (Cr Cl <10 m L/min).
Terminal elimination half-life in adults with normal renal function is 2.5-3.3 hours. In anuric patients, half-life extends to approximately 19.5 hours, necessitating dosage adjustment in renal impairment.
Cefoxitin is not significantly metabolized; primarily excreted unchanged in urine via glomerular filtration and tubular secretion.
Acyclovir is partially metabolized by aldehyde oxidase and alcohol dehydrogenase to 9-carboxymethoxymethylguanine and other minor metabolites. The majority (62-90%) is excreted unchanged in urine via glomerular filtration and tubular secretion.
Renal: ~85% unchanged; biliary/fecal: ~15% as active metabolite and unchanged drug.
Primarily renal excretion via glomerular filtration and tubular secretion; approximately 62-91% of an administered dose is recovered unchanged in urine. Fecal excretion is minimal (<2%).
73% (primarily albumin).
9-33% bound to plasma proteins; binding is concentration-independent and predominantly to albumin.
0.13–0.22 L/kg; indicates distribution mainly into extracellular fluid.
Approximately 0.7 L/kg, indicating distribution into total body water. Penetrates well into tissues, including cerebrospinal fluid (CSF concentrations ~50% of plasma).
IM: ~100%.
Intravenous administration yields 100% bioavailability. Oral bioavailability is 15-30% (not applicable to IV formulation).
Cr Cl 30-50 m L/min: 1-2 g every 8 hours; Cr Cl 10-29 m L/min: 1-2 g every 12 hours; Cr Cl <10 m L/min: 1-2 g every 24-48 hours.
Cr Cl >50 m L/min: no adjustment; Cr Cl 25-50 m L/min: 5-10 mg/kg every 12 hours; Cr Cl 10-25 m L/min: 5-10 mg/kg every 24 hours; Cr Cl <10 m L/min: 2.5-5 mg/kg every 24 hours; hemodialysis: give dose after dialysis.
No adjustment required for hepatic impairment.
No dose adjustment required for hepatic impairment; acyclovir is minimally metabolized by the liver.
3 months to 12 years: 80-160 mg/kg/day IV divided every 6-8 hours. Maximum 12 g/day.
Neonates (0-3 months): 10 mg/kg IV every 8 hours for HSV; Infants and children (3 months-12 years): 10 mg/kg IV every 8 hours for HSV, 20 mg/kg IV every 8 hours for VZV; maximum dose 500 mg/m² per dose.
Based on renal function; Cr Cl 30-50 m L/min: 1-2 g every 8 hours; Cr Cl 10-29 m L/min: 1-2 g every 12 hours; Cr Cl <10 m L/min: 1-2 g every 24-48 hours.
Elderly patients may have reduced renal function; adjust dose based on Cr Cl and monitor for neurotoxicity (e.g., confusion, hallucinations).
No FDA black box warning.
None.
Hypersensitivity reactions including anaphylaxis,Clostridium difficile-associated diarrhea (CDAD),Prolonged use may result in superinfection,Dose adjustment required in renal impairment,May cause false-positive urine glucose tests with copper reduction methods,Use with caution in patients with history of gastrointestinal disease
Renal impairment: Dose adjustment required; monitor renal function.,Neurotoxicity: May cause agitation, hallucinations, confusion, seizures (especially in elderly or renally impaired).,Crystalluria: Risk increased with rapid infusion or dehydration; ensure adequate hydration.,Hemolytic uremic syndrome/thrombotic thrombocytopenic purpura (HUS/TTP): Rare but serious, reported in immunocompromised patients.,Pregnancy: Use only if clearly needed (Category B).
Hypersensitivity to cefoxitin or other cephalosporins,Porphyria
Hypersensitivity to acyclovir, valacyclovir, or any component of the formulation.,Neonates: Use of bacteriostatic water-containing preparations (e.g., benzyl alcohol) is contraindicated.
No significant food interactions. However, alcohol should be avoided to prevent disulfiram-like reactions (rare). Maintain adequate hydration.
No specific food interactions. Adequate fluid intake is recommended to prevent renal toxicity. Avoid concurrent use of nephrotoxic substances (e.g., certain NSAIDs, aminoglycosides) without medical supervision.
Cefoxitin is a second-generation cephalosporin classified as FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. Inadequate human data; risk cannot be ruled out. First trimester: unlikely to cause major malformations based on limited data. Second and third trimesters: no documented fetal harm. However, use only if clearly needed.
FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. Limited human data: no increased risk of major birth defects or miscarriage. Risk cannot be ruled out; use only if clearly needed.
Cefoxitin is excreted into human breast milk in low concentrations (M/P ratio approximately 0.04-0.3). Likely compatible with breastfeeding due to poor oral bioavailability in infants. Caution with theoretical risk of diarrhea or allergic sensitization.
Acyclovir excreted in breast milk at low levels; M/P ratio unknown. Typical infant dose ~0.6 mg/kg/day (2-3% of maternal IV dose). No adverse effects reported in breastfeeding infants. Compatible with breastfeeding; caution with high maternal doses.
Pregnancy increases glomerular filtration rate (GFR) and volume of distribution, potentially reducing cefoxitin peak concentrations and elimination half-life. However, no specific dose adjustments recommended for pregnancy-induced pharmacokinetic changes. Standard dosing for adults is 1-2 g every 6-8 hours; use lower end if renal impairment.
Increased renal clearance and volume of distribution in pregnancy may reduce acyclovir exposure. No dose adjustment routinely recommended; however, higher doses or more frequent dosing may be considered for severe infections. Monitor therapeutic response.
MEFOXIN (cefoxitin) is a cephamycin antibiotic with activity against anaerobes, including Bacteroides fragilis. Use for surgical prophylaxis, intra-abdominal infections, and pelvic inflammatory disease. Note that it has poor activity against Pseudomonas and Enterococci. Administer 1-2 g IV every 6-8 hours; dose adjustment required in renal impairment (Cr Cl <50 m L/min). May cause false-positive urine glucose with Clinitest but not with glucose oxidase methods. Can prolong prothrombin time; monitor INR in patients on warfarin.
Acyclovir in sodium chloride 0.9% preservative-free is for IV administration only; do not administer IM or SC. Infuse over at least 1 hour to prevent renal tubular damage. Monitor renal function and adjust dose in renal impairment (Cr Cl <50 m L/min). Ensure adequate hydration (e.g., 500 m L IV fluids per gram acyclovir) to reduce risk of crystalluria. In obese patients, use ideal body weight for dosing. Phlebitis at infusion site is common; rotate sites.
Complete the full course of antibiotics even if you feel better.,Report any severe diarrhea, rash, or difficulty breathing to your healthcare provider.,This medication is given intravenously; do not mix with other drugs in the same IV line without consulting a pharmacist.,If you have a history of allergic reactions to penicillins or cephalosporins, inform your doctor.,Monitor for signs of bleeding (easy bruising, dark stools) if you are taking blood thinners.
This medication is given intravenously (into a vein) to treat viral infections.,Drink plenty of fluids before and during treatment to prevent kidney problems.,Report any pain, redness, or swelling at the injection site, or any lower back pain.,Tell your healthcare provider if you have kidney disease or are taking other medications that can affect the kidneys.,This drug does not cure herpes infections but helps reduce symptoms and recurrence.
"Lithium cation may increase the excretion rate of Sodium chloride which could result in a lower serum level and potentially a reduction in efficacy."
"The risk or severity of adverse effects can be increased when Sodium chloride is combined with Tolvaptan."
"Teriflunomide, the active metabolite of leflunomide, inhibits dihydroorotate dehydrogenase (DHODH), a key enzyme in de novo pyrimidine synthesis, exerting immunomodulatory effects. Acyclovir, an antiviral nucleoside analog, may inhibit organic anion transporter 3 (OAT3)-mediated renal tubular secretion of teriflunomide, leading to increased systemic exposure. Elevated teriflunomide concentrations can potentiate hepatotoxicity, myelosuppression, and immunosuppression, increasing the risk of infections and other adverse effects."
"The serum concentration of Acyclovir can be increased when it is combined with Tizanidine."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER vs ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE, answered by our medical review team.
MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER is a Electrolyte that works by Cefoxitin is a cephamycin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis and death.. ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE is a Electrolyte that works by Acyclovir is a synthetic purine nucleoside analog with inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2), and varicella-zoster virus (VZV). After intracellular conversion to acyclovir triphosphate, it inhibits viral DNA polymerase, leading to chain termination and viral DNA replication inhibition.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER and ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE depend on the specific clinical indication. These are both Electrolyte agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER is: 1-2 g IV every 6-8 hours. Maximum 12 g/day.. The standard adult dose of ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE is: 5 mg/kg IV every 8 hours (or 10 mg/kg IV every 8 hours for varicella-zoster or herpes simplex encephalitis) infused over 1 hour.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
A moderate-severity drug interaction has been identified when combining MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER and ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE. The risk or severity of adverse effects can be increased when Sodium chloride is combined with Tolvaptan. Consult your prescriber before combining these medications.
The maternal-fetal safety profiles differ. MEFOXIN IN SODIUM CHLORIDE 0.9% IN PLASTIC CONTAINER is classified as Category A/B. Cefoxitin is a second-generation cephalosporin classified as FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. Inadequate human data; risk cannot be ruled . ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE is classified as Category A/B. FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. Limited human data: no increased risk of major birth defects or miscarriage. Risk cannot be ruled out; us. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.