Sulfamethoxazole and Trimethoprim (Page 2 of 5)

Quality Control

Standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay and the techniques of the individuals performing the test . Standard trimethoprim/sulfamethoxazole powder should provide the following range of MIC values noted in Table 2. For the diffusion technique using the 1.25/23.75 µg trimethoprim/sulfamethoxazole disk the criteria in Table 2 should be achieved. 4,14,15

Table 2: Acceptable Quality Control Ranges for Susceptibility Testing for Trimethoprim/Sulfamethoxazole
QC Strain Minimal Inhibitory Concentration (mcg/mL)
Zone Diameter (mm)
ATCC 25922 Escherichia coli ≤ 0.5/9.5 23–29
ATCC 49247 Haemophilus influenzae 0.03/0.59 – 0.25/4.75 24–32
ATCC 49619 Streptococcus pneumoniae 0.12/2.4 – 1/19 20–28


To reduce the development of drug-resistant bacteria and maintain the effectiveness of sulfamethoxazole and trimethoprim tablets and other antibacterial drugs, sulfamethoxazole and trimethoprim tablets should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to empiric selection of therapy.

For the treatment of urinary tract infections due to susceptible strains of the following organisms: species, species, and . It is recommended that initial episodes of uncomplicated urinary tract infections be treated with a single effective antibacterial agent rather than the combination. Urinary Tract Infections: Escherichia coli, Klebsiella Enterobacter Morganella morganii, Proteus mirabilis Proteus vulgaris

For the treatment of acute otitis media in pediatric patients due to susceptible strains of or when in the judgment of the physician sulfamethoxazole and trimethoprim offers some advantage over the use of other antimicrobial agents. To date, there are limited data on the safety of repeated use of sulfamethoxazole and trimethoprim in pediatric patients under two years of age. Sulfamethoxazole and trimethoprim is not indicated for prophylactic or prolonged administration in otitis media at any age. Acute Otitis Media: Streptococcus pneumoniae Haemophilus influenzae

For the treatment of acute exacerbations of chronic bronchitis due to susceptible strains of or when a physician deems that sulfamethoxazole and trimethoprim could offer some advantage over the use of a single antimicrobial agent. Acute Exacerbations of Chronic Bronchitis in Adults: Streptococcus pneumoniae Haemophilus influenzae

For the treatment of enteritis caused by susceptible strains of and when antibacterial therapy is indicated. Shigellosis: Shigella flexneri Shigella sonnei

For the treatment of documented pneumonia and for prophylaxis against pneumonia in individuals who are immunosuppressed and considered to be at an increased risk of developing pneumonia. Pneumocystis jiroveci Pneumonia: Pneumocystis jiroveci P. jiroveci P. jiroveci

For the treatment of traveler’s diarrhea due to susceptible strains of enterotoxigenic Traveler’s Diarrhea in Adults: E. coli.


Sulfamethoxazole and trimethoprim is contraindicated in patients with a known hypersensitivity to trimethoprim or sulfonamides, in patients with a history of drug-induced immune thrombocytopenia with use of trimethoprim and/or sulfonamides, and in patients with documented megaloblastic anemia due to folate deficiency.

Sulfamethoxazole and trimethoprim is contraindicated in pediatric patients less than 2 months of age. Sulfamethoxazole and trimethoprim is also contraindicated in patients with marked hepatic damage or with severe renal insufficiency when renal function status cannot be monitored.


Embryofetal Toxicity

Some epidemiologic studies suggest that exposure to sulfamethoxazole/trimethoprim during pregnancy may be associated with an increased risk of congenital malformations, particularly neural tube defects, cardiovascular malformations, urinary tract defects, oral clefts, and club foot. If sulfamethoxazole/trimethoprim is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be advised of the potential hazards to the fetus.

Hypersensitivity and Other Fatal Reactions

Fatalities associated with the administration of sulfonamides, although rare, have occurred due to severe reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia and other blood dyscrasias.

Sulfonamides, including sulfonamide-containing products such as sulfamethoxazole/trimethoprim, should be discontinued at the first appearance of skin rash or any sign of adverse reaction. In rare instances, a skin rash may be followed by a more severe reaction, such as Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic necrosis, and serious blood disorders (see ). Clinical signs, such as rash, sore throat, fever, arthralgia, pallor, purpura or jaundice may be early indications of serious reactions. PRECAUTIONS

Cough, shortness of breath, and pulmonary infiltrates are hypersensitivity reactions of the respiratory tract that have been reported in association with sulfonamide treatment.


Sulfamethoxazole/trimethoprim-induced thrombocytopenia may be an immune-mediated disorder. Severe cases of thrombocytopenia that are fatal or life threatening have been reported. Thrombocytopenia usually resolves within a week upon discontinuation of sulfamethoxazole/trimethoprim.

Streptococcal Infections and Rheumatic Fever

The sulfonamides should not be used for treatment of group A β-hemolytic streptococcal infections. In an established infection, they will not eradicate the streptococcus and, therefore, will not prevent sequelae such as rheumatic fever.

Clostridium difficile associated diarrhea

associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including sulfamethoxazole and trimethoprim, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of . Clostridium difficile C. difficile

produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents. C. difficile C. difficile

If CDAD is suspected or confirmed, ongoing antibiotic use not directed against may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of , and surgical evaluation should be instituted as clinically indicated. C. difficile C. difficile

Adjunctive treatment with Leucovorin for Pneumocystis jiroveci pneumonia

Treatment failure and excess mortality were observed when trimethoprim-sulfamethoxazole was used concomitantly with leucovorin for the treatment of HIV positive patients with pneumonia in a randomized placebo controlled trial. Co-administration of trimethoprim-sulfamethoxazole and leucovorin during treatment of pneumonia should be avoided. Pneumocystis jiroveci 6 Pneumocystis jiroveci

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