Pediatric Examination and Board Review (173 page)

(A)
Stenotrophomonas maltophilia

(B) MRSA

(C) penicillin-resistant
Streptococcus pneumoniae

(D)
Serratia marcescens

(E) A and C

ANSWERS

1.
(A)
There is a difference in the susceptibility break points for ceftriaxone and cefotaxime for meningeal versus nonmeningeal infections. For meningeal isolates, the MIC of ceftriaxone must be 0.5 μg/mL or less to be considered susceptible. For nonmeningeal isolates, the susceptibility break point is 1.0 μg/mL or less. Thus the meningeal isolate is susceptible to ceftriaxone.

2.
(A)
There are a number of formulations of penicillin. Benzathine penicillin by IM injection can be used for the treatment of group A streptococcal pharyngitis. Actinomycosis is best treated initially with IV penicillin G.
E faecalis
causing a urinary tract infection is usually treated with oral amoxicillin or IV ampicillin. Procaine penicillin G is sometimes used to treat congenital syphilis.

3.
(C)
The penicillinase-resistant penicillin oxacillin is active against MSSA. Enterococci and gramnegative bacilli (including
Pasteurella
species) and methicillin-resistant coagulase-negative staphylococcal infections cannot be treated with semisynthetic penicillins.

4.
(E)
Ampicillin is considered a preferred antimicrobial agent for treatment of
Listeria
infections. Bacteria that produce beta-lactamase are resistant to ampicillin because the enzyme hydrolyzes the beta-lactam antibiotic. Staphylococcal resistance to ampicillin is also mediated through production of penicillinase.
C difficile
pseudomembranous colitis can occur after treatment with ampicillin, as it can after most antibiotics.

5.
(A)
In this clinical situation infection with
Pseudomonas aeruginosa
is a major concern. Ceftazidime, a third-generation cephalosporin, is active against most pseudomonas strains. Its low toxicity makes it an appealing choice for this situation. Tobramycin- or gentamicin-containing regimens are also generally active against pseudomonas. But they have the disadvantage of greater toxicity as well as the need to monitor blood levels.

6.
(B)
The most common adverse effect of erythromycin is GI discomfort and nausea. A rare association between oral erythromycin and infantile hypertrophic pyloric stenosis has been reported in infants younger than 6 weeks of age. Azithromycin also is a recommended antimicrobial agent for the treatment of chlamydia pneumonia.

7.
(D)
Azithromycin can be used for treatment of uncomplicated Chlamydia cervicitis (single 1-g oral dose). MRSA strains are almost always resistant to macrolides like azithromycin. A high percentage (>75%) of penicillin-resistant
S pneumoniae
isolates are also resistant to azithromycin.

8.
(E)
The MRSA isolate is erythromycin resistant and clindamycin susceptible, so the D-test was performed. The D-test is used to screen for the presence of the erythromycin ribosomal methylase (erm) gene. If the D-test is positive, it suggests the presence of the
erm
gene in the
S aureus
isolate. In this instance, treatment of the
S aureus
infection with clindamycin can select for mutants during therapy that are also clindamycin resistant. Because the D-test is negative this risk does not exist.

9.
(A)
Linezolid is an oxazolidinone antibiotic that binds the 50S ribosomal subunit and inhibits protein synthesis. Linezolid is active against MRSA, vancomycin-resistant enterococci (VRE), and penicillin-resistant
S pneumoniae
. The other choices are inactive against this isolate.

10.
(D)
The most common adverse events are GI (nausea and vomiting) and skin reactions. Adverse reactions to TMP-SMX occur infrequently in non-AIDS patients (<5%) but frequently (15%) in children with AIDS. The most common adverse event in children with AIDS is an erythematous maculopapular rash that is often transient and can clear without stopping the drug.

11.
(D)
Sulfonamides are not recommended for treatment of meningococcal meningitis but were once used to successfully treat meningitis caused by
Salmonella
and
Listeria
. Sulfonamides are useful for the treatment of urinary tract infections and pyelonephritis, gastroenteritis when caused by susceptible strains of
Shigella,
and in the treatment of infections caused by
Nocardia
.

12.
(C)
The Centers for Disease Control and Prevention (CDC) has established guidelines for situations in which the use of vancomycin is appropriate as well as situations in which the use of vancomycin is discouraged (
Table 98-1
). Vancomycin is not recommended for initial empiric therapy of a patient with fever and neutropenia.

13.
(C)
Tetracyclines can combine with newly formed bone to produce a tetracycline-calcium orthophosphate complex that can inhibit bone growth in neonates and cause staining of the enamel of the teeth in children younger than 8 years. For this 5-year-old child the treatment of choice for Lyme arthritis would be amoxicillin for a 28-day course (compared with amoxicillin for 14-21 days for early localized disease). For persistent or recurrent arthritis, the treatment of choice would be ceftriaxone.

TABLE 98-1
Situations in Which Vancomycin Use Should be Discouraged

Abbreviation: MRSA, methicillin-resistant
Staphylococcus aureus
.

14.
(B)
Gentamicin nephrotoxicity is characterized by proximal tubular necrosis in the kidneys. Risk factors for nephrotoxicity from aminoglycosides include high dose, prolonged course, liver disease, concomitant use of other nephrotoxic drugs such as cyclosporine, and salt and water depletion (such as dehydration or sepsis).

15.
(E)
Bone marrow suppression can occur with chloramphenicol in two ways. The first is related to the duration of the dose and is reversible. It is usually seen after 7 days of therapy and manifests as anemia with a low reticulocyte count. It is associated with peak and trough serum chloramphenicol concentrations greater than 25 and 10 μg/mL, respectively. Chloramphenicol can also cause idiosyncratic aplastic anemia that is irreversible and occurs in about 1 in 40,000 patients treated. This is similar to the rate of fatal anaphylaxis with beta-lactams such as penicillins and cephalosporins.

16.
(B)
Use of the fluoroquinolones is still generally contraindicated in children and adolescents younger than 18 years of age. There are certain situations in which fluoroquinolones may be useful including when no other oral agent is available or the infection is caused by a multidrug-resistant gramnegative enteric bacterium such as
Pseudomonas aeruginosa
. MRSA are often fluoroquinolone resistant; resistance to them may develop rapidly. For community-associated MRSA infections in children, there are alternative antibiotics.

17.
(C)
Rifampin has been used alone for the treatment of latent tuberculosis infection in infants, children and adolescents when isoniazid (INH) could not be tolerated, or the index case was infected with an INH-resistant, rifampin-susceptible organism. In this clinical situation rifampin should be given for at least 6 months. Patients should be informed that rifampin can cause orange urine, sweat, and tears and discoloration of soft contact lenses. Sexually active women on oral contraception should be informed that rifampin can make oral contraceptives ineffective.

18.
(D)
Meropenem is a carbapenem antibiotic that has a broad spectrum of activity against many grampositive aerobic cocci, gram-negative enteric bacteria, and anaerobes. In this example, meropenem would likely be active against
Serratia marcescens
but not against MRSA.
Stenotrophomonas maltophilia
is commonly resistant to the carbapenems. Another carbapenem antibiotic, imipenem-cilastin, has been associated with an increased risk of seizures. This risk appears to be related to high dose, age (elderly), and impaired renal function.

S
UGGESTED
R
EADING

Bradley JS, Sauberan J. Antimicrobial agents. In: Long SS, Pickering LK, Prober CG, eds.
Principles and Practices of Infectious Diseases.
3rd ed. Philadelphia, PA: Churchill Livingstone; 2008: 1420.

Jacob RF. Judicious use of antibiotics for common pediatric respiratory infections.
Pediatr Infect Dis J.
2000;19:938-943.

CASE 99: AN 18-MONTH-OLD WITH FEVER AFTER RENAL TRANSPLANT

An 18-month-old boy whom you have followed in your practice since birth was diagnosed with renal failure secondary to posterior urethral valves. As a result he underwent a renal transplant with success. Renal function post-transplant has been normal, and he is receiving a number of immunosuppressive medications to prevent rejection of the transplanted kidney. One month after the kidney transplant, he develops fever associated with cough and rhinorrhea.

On physical examination the child is sitting up in his mother’s lap. He is alert and active. The temperature is 101.4°F (38.6°C). There is clear rhinorrhea but no abnormalities of the oropharynx. Lungs and heart examinations are normal. Examination of the abdomen reveals a palpable kidney in the right lower quadrant but no abdominal tenderness. The leukocyte count is 8900/mm
³
(S-20, L-65, M-15), the hemoglobin concentration is 8.0 g/dL, and the platelet count is 120,000/mm
³
. A chest radiograph reveals no evidence of pneumonia.