UTI, treatment

UTI, treatment

Question: we traditionally think of 1st generation cephalosporins as effective against gram-positive organisms only. Why do we use it in the treatment of UTI when E.coli is the main organism we are treating? Answer is below, in green highlight.

Duration of therapy. 10-14 days of age. Infants < 2-3 mos of age should be hospitalized on parenteral antibiotics until afebrile for at least 24-36 hours, then discharge home on 10 more days of oral antibiotics. If blood culture is positive, parenteral antibiotics are recommended for the duration of treatment.

For inpatient treatment of complicated acute pyelonephritis, use a 3rd generation cephalosporin (ceftriaxone or cefotaxime). Add ampicillin if gram+cocci seen on gram stain or if no organisms are observed. Gentamicin is an alternative for term infants older than 7 days, older children, and teens allergic to cephalosporins.

Causes of UTI:

In early childhood, enterobacteria and enterococci are part of the normal periurethral flora.
Escherichia coli is the dominant gram-negative species in young girls, while E coli and Proteus species predominate in boys.
Children up to about age 5 years are predisposed to UTIs partly because of periurethral colonization by E coli, enterococci, and Proteus species. Usually, these potential uropathogens diminish in the first year of life and are rarely found in children older than 5 years.
E coli usually causes initial infection, but other gram-negative bacilli and enterococci may also cause infection. (note that 1st gen cephalosporins don't cover enterococci)
Staphylococcal, especially S saprophyticus, infections are common among adolescent females.

Some Antimicrobials for Parenteral Treatment of UTI

Antimicrobial	Daily Dosage

Ceftriaxone	75 mg/kg every 24 h
Cefotaxime	150 mg/kg/d divided every 6 h
Ceftazidime	150 mg/kg/d divided every 6 h
Cefazolin	50 mg/kg/d divided every 8 h
Gentamicin	7.5 mg/kg/d divided every 8 h
Tobramycin	5 mg/kg/d divided every 8 h
Ticarcillin	300 mg/kg/d divided every 6 h
Ampicillin1	100 mg/kg/d divided every 6 h

Some Antimicrobials for Oral Treatment of UTI

Antimicrobial	Dosage

Amoxicillin (but increasing resistance)1	20-40 mg/kg/d in 3 doses
Sulfonamide: 3
- TMP in combination with SMX	6-12 mg TMP, 30-60 mg SMX per kg per d in 2 doses
- Sulfisoxazole	120-150 mg/kg/d in 4 doses
Cephalosporin 2 (% renal excretion)
Cefixime (41)	8 mg/kg/d in 2 doses
Cefpodixime, 3rd gen (81)	10 mg/kg/d in 2 doses
Cefprozil, (73)	30 mg/kg/d in 2 doses
Cephalexin (91)	50-100 mg/kg/d in 4 doses
Loracarbef 2nd gen. (94)	15-30 mg/kg/d in 2 doses

1.In many communities, a large percentage of E coli strains are resistant to amoxicillin. Ampicillin or amoxicillin are not recommended because of the high incidence of resistant E coli.

2.Cephalosporins, in particular cephalexin (with 91% excreted unchanged in the urine), have the required spectrum of activity and resistance levels are low, but they are somewhat more likely than trimethoprim to disturb the gastrointestinal flora.

"The first generation cephalosporins... have good activity against gram-positive bacteria and relatively modest activity against gram-negative micro-organisms. Most gram-positive cocci are susceptible (with the exception of enterococci, MRSA and Staph epidermidis). Most oral cavity anaerobes are susceptible, but the B. fragilis group is resistant. Activity against Moraxella catarrhalis, E. coli, K. pneumoniae, and Pr mirabilis is good." Goodman and Gilman's: The Pharmacological basis of therapeutics. Ninth edition.

3.Do not use nitrofurantoin and sulfa drugs in infants younger than 6 weeks. Reduced doses of an oral first-generation cephalosporin, such as cephalexin at 10 mg/kg, may be used until the child reaches age 6 weeks.

Sources include, but not limited to:

http://www.emedicine.com/ped/topic2366.htm