Cephalexin

1st Gen Cephalosporin·Infectious Diseases - Cephalosporins

Staphylococcal/Streptococcal skin infections, cystitis in pregnancy

PBSCEPHALOSPORINKeflex, Rilexine250 mgS4+1

Max Dose

4 g/day

Half-life

1 h

Cross-Allergy

CAUTION

Renal Adj.

DOSE RED.

Rapid Summary

Overview

First-generation oral cephalosporin. Outstanding coverage against MSSA and basic Strep. The workhorse for mild-to-moderate skin infections and simple UTIs.

Maximum Dose

Max 4 g/day.

Clinical Focus

Approximately 1-5% of patients with a true penicillin allergy will cross-react with cephalosporins.

Bottom Line

Cephalexin is a safe, well-tolerated first-generation cephalosporin for skin and simple UTIs, but has limited gram-negative coverage and ~2% cross-reactivity in penicillin allergy.

Formulation & Access

Brand Names

Keflex, Rilexine

Oral Routes

Capsules (250 mg, 500 mg). Oral liquid (125 mg/5mL, 250 mg/5mL).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Staphylococcal/Streptococcal skin infections, cystitis in pregnancy.

Clinical Place

Oral step-down from IV Cefazolin. Excellent safe choice for UTIs during pregnancy.

Quick reference

Class & Role

1st Gen Cephalosporin — First-generation oral cephalosporin.

Route / Formulation

Capsules (250 mg, 500 mg). Oral liquid (125 mg/5mL, 250 mg/5mL). (Keflex, Rilexine)

Usual Dose & Max

PO 500 mg QID. Max 4 g/day.

Key Indication Doses

Cellulitis / Skin Infection: PO 500 mg QID. Uncomplicated UTI: PO 500 mg BD for 5 days. Renal Impairment: Max 500 mg BD if eGFR < 30.

Best Uses

Cephalexin is a safe, well-tolerated first-generation cephalosporin for skin and simple UTIs, but has limited gram-negative coverage and ~2% cross-reactivity in penicillin allergy.

Avoid / Cautions

Cephalosporin anaphylaxis. Avoid in severe immediate (IgE) Penicillin allergy (e.g., hives/anaphylaxis). Safe to use if penicillin allergy is just a mild childhood rash. Pregnancy Category A.

Key Risks

Gastrointestinal: Nausea, diarrhea, mild C. diff risk. Immunological: Hypersensitivity rash, rare anaphylaxis. Renal: Interstitial nephritis.

Key Interactions

Generally free of major liver/CYP interactions.

Monitoring

Check eGFR if using high doses (QID) in the elderly.

Clinical Pearl

Cephalexin has a very short half-life (1 hour). For a tissue infection like cellulitis, dosing it QID (every 6 hours) is mandatory to maintain blood levels. Dosing it BD for skin guarantees clinical failure.

Access

Keflex, Rilexine250 mg

Brand: Keflex, Rilexine
Formulation: Capsules (250 mg, 500 mg)

Cephalexin

1st Gen Cephalosporin·Infectious Diseases - Cephalosporins

Staphylococcal/Streptococcal skin infections, cystitis in pregnancy

PBSCEPHALOSPORINKeflex, Rilexine250 mgS4+1

Max Dose

4 g/day

Half-life

1 h

Cross-Allergy

CAUTION

Renal Adj.

DOSE RED.

Rapid Summary

Overview

First-generation oral cephalosporin. Outstanding coverage against MSSA and basic Strep. The workhorse for mild-to-moderate skin infections and simple UTIs.

Maximum Dose

Max 4 g/day.

Clinical Focus

Approximately 1-5% of patients with a true penicillin allergy will cross-react with cephalosporins.

Bottom Line

Cephalexin is a safe, well-tolerated first-generation cephalosporin for skin and simple UTIs, but has limited gram-negative coverage and ~2% cross-reactivity in penicillin allergy.

Formulation & Access

Brand Names

Keflex, Rilexine

Oral Routes

Capsules (250 mg, 500 mg). Oral liquid (125 mg/5mL, 250 mg/5mL).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Staphylococcal/Streptococcal skin infections, cystitis in pregnancy.

Clinical Place

Oral step-down from IV Cefazolin. Excellent safe choice for UTIs during pregnancy.

Quick reference

Class & Role

1st Gen Cephalosporin — First-generation oral cephalosporin.

Route / Formulation

Capsules (250 mg, 500 mg). Oral liquid (125 mg/5mL, 250 mg/5mL). (Keflex, Rilexine)

Usual Dose & Max

PO 500 mg QID. Max 4 g/day.

Key Indication Doses

Cellulitis / Skin Infection: PO 500 mg QID. Uncomplicated UTI: PO 500 mg BD for 5 days. Renal Impairment: Max 500 mg BD if eGFR < 30.

Best Uses

Cephalexin is a safe, well-tolerated first-generation cephalosporin for skin and simple UTIs, but has limited gram-negative coverage and ~2% cross-reactivity in penicillin allergy.

Avoid / Cautions

Cephalosporin anaphylaxis. Avoid in severe immediate (IgE) Penicillin allergy (e.g., hives/anaphylaxis). Safe to use if penicillin allergy is just a mild childhood rash. Pregnancy Category A.

Key Risks

Gastrointestinal: Nausea, diarrhea, mild C. diff risk. Immunological: Hypersensitivity rash, rare anaphylaxis. Renal: Interstitial nephritis.

Key Interactions

Generally free of major liver/CYP interactions.

Monitoring

Check eGFR if using high doses (QID) in the elderly.

Clinical Pearl

Access

Keflex, Rilexine250 mg

Brand: Keflex, Rilexine
Formulation: Capsules (250 mg, 500 mg)