Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE 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
Cephalothin is a first-generation cephalosporin that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), thereby inhibiting transpeptidase activity and disrupting peptidoglycan cross-linking. This leads to cell lysis and death, primarily in Gram-positive bacteria.
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.
FDA-approved: Treatment of respiratory tract infections, skin and soft tissue infections, bone and joint infections, septicemia, and urinary tract infections caused by susceptible organisms,Off-label: Prophylaxis in surgery, treatment of endocarditis
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 4-6 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.
0.5-1 hour; prolonged in renal impairment (up to 8-12 hours in anuria)
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.
Cephalothin is metabolized in the liver by deacetylation to desacetylcephalothin, which has less antimicrobial activity. The enzyme responsible is not specifically identified but involves hepatic esterases.
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 excretion (60-70% unchanged); biliary excretion (20-30%); fecal elimination (<1%)
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%).
65-80% bound to serum albumin
9-33% bound to plasma proteins; binding is concentration-independent and predominantly to albumin.
0.2-0.3 L/kg; primarily 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).
Intravenous: 100%; intramuscular: approximately 50-60%
Intravenous administration yields 100% bioavailability. Oral bioavailability is 15-30% (not applicable to IV formulation).
Cr Cl 50-80 m L/min: no adjustment; Cr Cl 25-50 m L/min: 1-2 g every 6-8 hours; Cr Cl 10-25 m L/min: 1-2 g every 8-12 hours; Cr Cl <10 m L/min: 1-2 g every 12-24 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 specific dose adjustment recommended; use caution in severe hepatic impairment.
No dose adjustment required for hepatic impairment; acyclovir is minimally metabolized by the liver.
100-150 mg/kg/day IV divided every 6 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.
No specific adjustment; consider renal function and reduce dose if Cr Cl <50 m L/min.
Elderly patients may have reduced renal function; adjust dose based on Cr Cl and monitor for neurotoxicity (e.g., confusion, hallucinations).
None
None.
Hypersensitivity reactions: Cross-allergenicity with other beta-lactams, including penicillins; anaphylaxis may occur,Pseudomembranous colitis: Clostridium difficile-associated diarrhea can develop,Renal impairment: Dosage adjustment required due to renal excretion; monitor renal function,Bleeding risk: May potentiate anticoagulants; monitor prothrombin time,False-positive urine glucose test: With Clinitest or Benedict's solution, but not with glucose oxidase methods
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 cephalothin, any cephalosporin, or other beta-lactam antibiotics,Absolute: Known anaphylactic reaction to penicillins due to cross-sensitivity
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. Absorption is not affected by food. Avoid alcohol during treatment and for 72 hours after completion to prevent disulfiram-like reaction (reported with some cephalosporins, though rare with cephalothin).
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.
Cephalothin is a first-generation cephalosporin classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated fetal risk, and there are no adequate and well-controlled studies in pregnant women. However, systemic absorption is expected to be low with intraperitoneal administration. First trimester: No evidence of teratogenicity, but data limited. Second/third trimesters: Generally considered safe; cross the placenta with therapeutic concentrations achieved in fetal serum and amniotic fluid. No known association with congenital malformations.
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.
Cephalothin is excreted into human breast milk in low concentrations. The milk-to-plasma ratio is approximately 0.02–0.05. For a maternal dose of 1 g intravenously, the estimated infant dose is <1% of the therapeutic dose. Considered compatible with breastfeeding but monitor infant for potential gastrointestinal effects (e.g., diarrhea, candidiasis) or allergic reactions.
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-induced physiological changes (increased plasma volume, enhanced renal clearance) may reduce serum cephalothin concentrations. However, no formal dosing adjustments are recommended; standard adult dosing is used. For severe infections, monitor clinical response and consider higher doses if needed.
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.
Cephalothin is a first-generation cephalosporin with activity against gram-positive cocci (excluding MRSA and enterococci) and some gram-negative rods. It is often used perioperatively for surgical prophylaxis. Note that cephalothin is not active against Pseudomonas aeruginosa, Bacteroides fragilis, or Enterobacter species. Cross-allergenicity with penicillins occurs in approximately 5-10% of patients. Administer before meals if GI upset occurs. Monitor renal function in elderly or those with preexisting renal impairment, as cephalothin may accumulate and cause nephrotoxicity. Pain at injection site and phlebitis are common with IV administration.
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.
Take this medication exactly as prescribed, even if you feel well.,Complete the full course of therapy to prevent resistance.,Report any signs of allergic reaction such as rash, itching, swelling, or difficulty breathing immediately.,Inform your healthcare provider if you have a history of penicillin allergy.,If you experience severe diarrhea, especially with blood or mucus, contact your doctor (possible C. difficile colitis).,Use effective contraception during treatment, as cephalothin may reduce efficacy of oral contraceptives.
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 CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE IN PLASTIC CONTAINER vs ACYCLOVIR IN SODIUM CHLORIDE 0.9% PRESERVATIVE FREE, answered by our medical review team.
CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE IN PLASTIC CONTAINER is a Electrolyte that works by Cephalothin is a first-generation cephalosporin that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), thereby inhibiting transpeptidase activity and disrupting peptidoglycan cross-linking. This leads to cell lysis and death, primarily in Gram-positive bacteria.. 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 CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE 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 CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE IN PLASTIC CONTAINER is: 1-2 g IV every 4-6 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 CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE 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. CEPHALOTHIN SODIUM W/ SODIUM CHLORIDE IN PLASTIC CONTAINER is classified as Category A/B. Cephalothin is a first-generation cephalosporin classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated fetal risk, and there are no adequate and . 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.