Trimethoprim

Description

DESCRIPTION Sulfamethoxazole and trimethoprim is a synthetic antibacterial combination product available in DS (double strength) tablets, each containing 800 mg sulfamethoxazole and 160 mg trimethoprim; in tablets, each containing 400 mg sulfamethoxazole and 80 mg trimethoprim for oral administration. Sulfamethoxazole is N 1 -(5-methyl-3-isoxazolyl)sulfanilamide; the molecular formula is C 10 H 11 N 3 O 3 S. It is a white to off-white, practically odorless, crystalline powder, tasteless compound with a molecular weight of 253.28 and the following structural formula: Trimethoprim is 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine; the molecular formula is C 14 H 18 N 4 O 3 . It is a white or cream-colored crystals or crystalline powder with a molecular weight of 290.3 and the following structural formula: Inactive Ingredients: Docusate sodium, magnesium stearate, pregelatinized starch (maize), sodium benzoate, and sodium starch glycolate. Sulfamethoxazole Chemical Structure Trimethoprim Chemical Structure

What Is Trimethoprim Used For?

INDICATIONS AND USAGE To reduce the development of drug-resistant bacteria and maintain the effectiveness of sulfamethoxazole and trimethoprim tablets, USP and other antibacterial drugs, sulfamethoxazole and trimethoprim tablets, USP 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. Urinary Tract Infections For the treatment of urinary tract infections due to susceptible strains of the following organisms: Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis and Proteus vulgaris. It is recommended that initial episodes of uncomplicated urinary tract infections be treated with a single effective antibacterial agent rather than the combination. Acute Otitis Media For the treatment of acute otitis media in pediatric patients due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae when in the judgment of the physician sulfamethoxazole and trimethoprim tablets offer 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 tablets, USP in pediatric patients under two years of age. Sulfamethoxazole and trimethoprim tablets, USP are not indicated for prophylactic or prolonged administration in otitis media at any age. Acute Exacerbations of Chronic Bronchitis in Adults For the treatment of acute exacerbations of chronic bronchitis due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae when a physician deems that sulfamethoxazole and trimethoprim tablets, USP could offer some advantage over the use of a single antimicrobial agent. Shigellosis For the treatment of enteritis caused by susceptible strains of Shigella flexneri and Shigella sonnei when antibacterial therapy is indicated. Pneumocystis jiroveci Pneumonia For the treatment of documented Pneumocystis jiroveci pneumonia and for prophylaxis against P. jiroveci pneumonia in individuals who are immunosuppressed and considered to be at an increased risk of developing P. jiroveci pneumonia. Traveler's Diarrhea in Adults For the treatment of traveler's diarrhea due to susceptible strains of enterotoxigenic E. coli.

Dosage and Administration

DOSAGE AND ADMINISTRATION Sulfamethoxazole and trimethoprim tablets are contraindicated in pediatric patients less than 2 months of age. Urinary Tract Infections and Shigellosis in Adults and Pediatric Patients, and Acute Otitis Media in Children Adults The usual adult dosage in the treatment of urinary tract infections is 1 sulfamethoxazole and trimethoprim DS (double strength) tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours for 10 to 14 days. An identical daily dosage is used for 5 days in the treatment of shigellosis. Children The recommended dose for children with urinary tract infections or acute otitis media is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days. An identical daily dosage is used for 5 days in the treatment of shigellosis. The following table is a guideline for the attainment of this dosage: Children 2 months of age or older: Weight Dose–every 12 hours lb kg Tablets 22 44 66 88 10 20 30 40 – 1 1½ 2 or 1 DS tablet For Patients with Impaired Renal Function When renal function is impaired, a reduced dosage should be employed using the following table: Creatinine Clearance (mL/min) Recommended Dosage Regimen Above 30 15–30 Below 15 Usual standard regimen ½ the usual regimen Use not recommended Acute Exacerbations of Chronic Bronchitis in Adults The usual adult dosage in the treatment of acute exacerbations of chronic bronchitis is 1 sulfamethoxazole and trimethoprim DS (double strength) tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours for 14 days. Pneumocystis Jiroveci Pneumonia Treatment Adults and Children The recommended dosage for treatment of patients with documented Pneumocystis jiroveci pneumonia is 75 to 100 mg/kg sulfamethoxazole and 15 to 20 mg/kg trimethoprim per 24 hours given in equally divided doses every 6 hours for 14 to 21 days. 11 The following table is a guideline for the upper limit of this dosage: Weight Dose–every 6 hours lb kg Tablets 18 35 53 70 88 106 141 176 8 16 24 32 40 48 64 80 – 1 1½ 2 or 1 DS tablet 2½ 3 or 1½ DS tablets 4 or 2 DS tablets 5 or 2½ DS tablets For the lower limit dose (75 mg/kg sulfamethoxazole and 15 mg/kg trimethoprim per 24 hours) administer 75% of the dose in the above table. Prophylaxis Adults The recommended dosage for prophylaxis in adults is 1 sulfamethoxazole and trimethoprim DS (double strength) tablet daily. 12 Children For children, the recommended dose is 750 mg/m 2 /day sulfamethoxazole with 150 mg/m 2 /day trimethoprim given orally in equally divided doses twice a day, on 3 consecutive days per week. The total daily dose should not exceed 1600 mg sulfamethoxazole and 320 mg trimethoprim. 13 The following table is a guideline for the attainment of this dosage in children: Body Surface Area Dose–every 12 hours (m 2 ) Tablets 0.26 0.53 1.06 – ½ 1 Traveler's Diarrhea in Adults For the treatment of traveler’s diarrhea, the usual adult dosage is 1 sulfamethoxazole and...

Side Effects (Adverse Reactions)

ADVERSE REACTIONS The most common adverse effects are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions (such as rash and urticaria). 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 (SEE WARNINGS SECTION). Hematologic Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrombinemia, methemoglobinemia, eosinophilia. Allergic Reactions Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis, allergic myocarditis, erythema multiforme, exfoliative dermatitis, angioedema, drug fever, chills, Henoch-Schoenlein purpura, serum sickness-like syndrome, generalized allergic reactions, generalized skin eruptions, photosensitivity, conjunctival and scleral injection, pruritus, urticaria and rash. In addition, periarteritis nodosa and systemic lupus erythematosus have been reported. Gastrointestinal Hepatitis (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, pseudomembranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, anorexia. Genitourinary Renal failure, interstitial nephritis, BUN and serum creatinine elevation, toxic nephrosis with oliguria and anuria, crystalluria and nephrotoxicity in association with cyclosporine. Metabolic and Nutritional Hyperkalemia, hyponatremia ( see PRECAUTIONS: Electrolyte Abnormalities ). Neurologic Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache. Psychiatric Hallucinations, depression, apathy, nervousness. Endocrine The sulfonamides bear certain chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides) and oral hypoglycemic agents. Cross-sensitivity may exist with these agents. Diuresis and hypoglycemia have occurred rarely in patients receiving sulfonamides. Musculoskeletal Arthralgia and myalgia. Isolated cases of rhabdomyolysis have been reported with sulfamethoxazole and trimethoprim, mainly in AIDS patients. Respiratory Cough, shortness of breath and pulmonary infiltrates (see WARNINGS ). Miscellaneous Weakness, fatigue, insomnia. Postmarketing Experience The following adverse reactions have been identified during post-approval use of trimethoprim-sulfamethoxazole. Because these reactions were reported voluntarily from a population of uncertain size, it is not possible to reliably estimate their frequency or establish a causal relationship to drug exposure: Thrombotic thrombocytopenia purpura Idiopathic thrombocytopenic purpura QT prolongation resulting in ventricular tachycardia and torsade de pointes

Drug Interactions

Drug Interactions Potential for Sulfamethoxazole and Trimethoprim to Affect Other Drugs Trimethoprim is an inhibitor of CYP2C8 as well as OCT2 transporter. Sulfamethoxazole is an inhibitor of CYP2C9. Caution is recommended when sulfamethoxazole and trimethoprim is co-administered with drugs that are substrates of CYP2C8 and 2C9 or OCT2. In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported. It has been reported that sulfamethoxazole and trimethoprim may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin (a CYP2C9 substrate). This interaction should be kept in mind when sulfamethoxazole and trimethoprim is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed. Sulfamethoxazole and trimethoprim may inhibit the hepatic metabolism of phenytoin (a CYP2C9 substrate). Sulfamethoxazole and trimethoprim, given at a common clinical dosage, increased the phenytoin half-life by 39% and decreased the phenytoin metabolic clearance rate by 27%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect. Sulfonamides can also displace methotrexate from plasma protein binding sites and can compete with the renal transport of methotrexate, thus increasing free methotrexate concentrations. There have been reports of marked but reversible nephrotoxicity with coadministration of sulfamethoxazole and trimethoprim and cyclosporine in renal transplant recipients. Increased digoxin blood levels can occur with concomitant sulfamethoxazole and trimethoprim therapy, especially in elderly patients. Serum digoxin levels should be monitored. Increased sulfamethoxazole blood levels may occur in patients who are also receiving indomethacin. Occasional reports suggest that patients receiving pyrimethamine as malaria prophylaxis in doses exceeding 25 mg weekly may develop megaloblastic anemia if sulfamethoxazole and trimethoprim is prescribed. The efficacy of tricyclic antidepressants can decrease when coadministered with sulfamethoxazole and trimethoprim. Sulfamethoxazole and trimethoprim potentiates the effect of oral hypoglycemics that are metabolized by CYP2C8 (e.g., pioglitazone, repaglinide, and rosiglitazone) or CYP2C9 (e.g., glipizide and glyburide) or eliminated renally via OCT2 (e.g., metformin). Additional monitoring of blood glucose may be warranted. In the literature, a single case of toxic delirium has been reported after concomitant intake of sulfamethoxazole and trimethoprim and amantadine (an OCT2 substrate). Cases of interactions with other OCT2 substrates, memantine and metformin, have also been reported. In the literature, three cases of hyperkalemia in elderly patients have been reported after concomitant intake of sulfamethoxazole and trimethoprim and an angiotensin converting enzyme inhibitor. 8,9

Contraindications

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

Pregnancy and Breastfeeding

Pregnancy While there are no large, well-controlled studies on the use of sulfamethoxazole and trimethoprim in pregnant women, Brumfitt and Pursell, 10 in a retrospective study, reported the outcome of 186 pregnancies during which the mother received either placebo or sulfamethoxazole and trimethoprim. The incidence of congenital abnormalities was 4.5% (3 of 66) in those who received placebo and 3.3% (4 of 120) in those receiving sulfamethoxazole and trimethoprim. There were no abnormalities in the 10 children whose mothers received the drug during the first trimester. In a separate survey, Brumfitt and Pursell also found no congenital abnormalities in 35 children whose mothers had received oral sulfamethoxazole and trimethoprim at the time of conception or shortly thereafter. Because sulfamethoxazole and trimethoprim may interfere with folic acid metabolism, sulfamethoxazole and trimethoprim should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Teratogenic Effects Pregnancy Category D Human Data While there are no large prospective, well controlled studies in pregnant women and their babies, some retrospective epidemiologic studies suggest an association between first trimester exposure to sulfamethoxazole and trimethoprim with an increased risk of congenital malformations, particularly neural tube defects, cardiovascular abnormalities, urinary tract defects, oral clefts, and club foot. These studies, however, were limited by the small number of exposed cases and the lack of adjustment for multiple statistical comparisons and confounders. These studies are further limited by recall, selection, and information biases, and by limited generalizability of their findings. Lastly, outcome measures varied between studies, limiting cross-study comparisons. Alternatively, other epidemiologic studies did not detect statistically significant associations between sulfamethoxazole and trimethoprim exposure and specific...

Nursing Mothers Levels of trimethoprim and sulfamethoxazole in breast milk are approximately 2 to 5% of the recommended daily dose for infants over 2 months of age. Caution should be exercised when sulfamethoxazole and trimethoprim is administered to a nursing woman, especially when breastfeeding, jaundiced, ill, stressed, or premature infants because of the potential risk of bilirubin displacement and kernicterus.

Overdosage

OVERDOSAGE Acute The amount of a single dose of sulfamethoxazole and trimethoprim that is either associated with symptoms of overdosage or is likely to be life-threatening has not been reported. Signs and symptoms of overdosage reported with sulfonamides include anorexia, colic, nausea, vomiting, dizziness, headache, drowsiness and unconsciousness. Pyrexia, hematuria and crystalluria may be noted. Blood dyscrasias and jaundice are potential late manifestations of overdosage. Signs of acute overdosage with trimethoprim include nausea, vomiting, dizziness, headache, mental depression, confusion and bone marrow depression. General principles of treatment include the institution of gastric lavage or emesis, forcing oral fluids, and the administration of intravenous fluids if urine output is low and renal function is normal. Acidification of the urine will increase renal elimination of trimethoprim. The patient should be monitored with blood counts and appropriate blood chemistries, including electrolytes. If a significant blood dyscrasia or jaundice occurs, specific therapy should be instituted for these complications. Peritoneal dialysis is not effective and hemodialysis is only moderately effective in eliminating sulfamethoxazole and trimethoprim. Chronic Use of sulfamethoxazole and trimethoprim at high doses and/or for extended periods of time may cause bone marrow depression manifested as thrombocytopenia, leukopenia and/or megaloblastic anemia. If signs of bone marrow depression occur, the patient should be given leucovorin 5 to 15 mg daily until normal hematopoiesis is restored.

How Supplied

HOW SUPPLIED Sulfamethoxazole and Trimethoprim Tablets USP, 400 mg/80 mg are white to off-white circular, beveled edge uncoated tablets, debossed with “H 48” on one side and deep break line on the other side. Sulfamethoxazole and Trimethoprim Tablets USP, 800 mg/160 mg are white to off-white oval, beveled edge uncoated tablets, debossed with “H 49” on one side and deep break line on other side. 55700-611-10 55700-611-14 55700-611-20 55700-611-28 Store at 20º to 25ºC (68º to 77ºF); excursions permitted to 15º to 30ºC (59° to 86°F) [see USP Controlled Room Temperature]. DISPENSE IN TIGHT, LIGHT-RESISTANT CONTAINER.