Cephalexin Monohydrate

(cephalexin monohydrate)


Keflex, Biocef


  • Capsules: 250 mg, 500 mg
  • Suspension: 125 mg/5mL, 250 mg/5mL
  • Injectable: 180 mg/mL (may not be available in the USA)


A first generation cephalosporin, cephalexin is a broad-spectrum, bactericidal antibiotic. It is effective against most Gram-positive organisms such as beta-hemolytic streptococci, Staphylococcus intermedius and aureus, Proteus mirabilis, some E. coli, klebsiella, Actinobacillis, pasteurella, and salmonella. It, however, does not directly attack mycoplasma, but is useful in secondary infections.

The drug is well absorbed orally, and widely distributed throughout the body. While cephalexin crosses both placental and fetal serum studies have shown no adverse effects on embryofetal development. It also does not show significant levels in breast milk and may be given to lactating females. Cephalexin does not enter cerebral spinal fluid in appreciable levels.

The drug is excreted by the kidneys via tubular and or glomerulo secretion.


Used for treating deep skin (pyodermas), soft tissue, and urinary tract infections. Also good for use prophylactically following surgery to prevent infection.

Drug Interactions or Contraindications

  • Should not be used orally in cases of septicemia or shock as absorption may be delayed significantly in grave illness.
  • May have synergistic effect against certain bacteria, when used with the aminoglycosides, penicillin’s, and chloramphenicol. Use in combination cautiously.
  • Concomitant use of Probenecid may decrease the ability of the kidneys to remove some antibiotics (e.g., cephalexin) thereby increasing their plasma level.

Adverse Reactions

Blood: neutopenia, hemolytic anemia

GI: anorexia(poor or no appetite), diarrhea, anal pruritus (itching)

Other: potential for nephrotoxicity minimal in animals

Dosage Recommendations

15 mg/kg, SQ, q12hr  31, 34,  35


15 mg/kg, SQ, IM, q24hr   34,  41,  44


20 mg/kg, PO, q8hr   41, 44


60 mg/kg, PO   7


60 mg/kg, PO, q12hr, or 15 mg/kg, SQ, q12hr  8, 19


  • Can be used simultaneously with Gentocin.
  • Give yogurt, Lactobacillus capsules/granules, or Bene-Bac to help maintain normal gut flora.
  • In treating suspected polymicrobial infections, where a broader coverage may be needed, synergistic or combination drugs may be used. The following drugs may be seen used simultaneously with cephalexin: aminoglycosides (e.g., amikacin or gentamicin), or clindamycin, or fluoroquinolones (e.g., enrofloxacin or orbifloxicin), or metronidazole, or ampicillin. 1
  • Please note that it is imperative to discuss the changing or adding of any medications during your rat’s treatment with your veterinarian to prevent future resistance of microbes to the drugs prescribed.
  • May store tablets and capsules at room temperature.
  • Reconstituted suspensions kept refrigerated are good for 14 days.
  • Considered safe for long term use.


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