Sulfamethoxazole and Trimethoprim
SULFAMETHOXAZOLE AND TRIMETHOPRIM — sulfamethoxazole and trimethoprim suspension
Lupin Pharmaceuticals, Inc.
To reduce the development of drug-resistant bacteria and maintain the effectiveness of sulfamethoxazole and trimethoprim oral suspension and other antibacterial drugs, sulfamethoxazole and trimethoprim oral suspension should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria.
Sulfamethoxazole and Trimethoprim Oral Suspension, USP is a synthetic antibacterial combination product available in a pediatric suspension for oral administration, with each teaspoonful (5 mL) containing 200 mg sulfamethoxazole and 40 mg trimethoprim.
Sulfamethoxazole is N1 -(5-methyl-3-isoxazolyl) sulfanilamide; the molecular formula is C10 H11 N3 O3 S. It is a white to off-white, practically odorless, crystalline powder with a molecular weight of 253.3 and the following structural formula:
Trimethoprim is 2,4-diamino-5-(3, 4, 5-trimethoxybenzyl) pyrimidine; the molecular formula is C14 H18 N4 O3 . It is a White to cream colored, odorless crystals or crystalline powder with a molecular weight of 290.32 and the following structural formula:
Inactive ingredients: dehydrated alcohol 0.26%, methyl paraben 0.1% and sodium benzoate 0.1% (added as preservatives), carboxymethylcellulose sodium, citric acid (anhydrous), colloidal silicon dioxide, glycerol anhydrous, microcrystalline cellulose and carboxy methyl cellulose sodium, non crystalizing sorbitol solution, polysorbate 80, purified water and saccharin sodium The pink, cherry flavored suspension contains the following inactive ingredient: FD&C Red No. 40, maltodextrin (corn) and natural cherry flavor.
Sulfamethoxazole and trimethoprim is rapidly absorbed following oral administration. Both sulfamethoxazole and trimethoprim exist in the blood as unbound, protein-bound and metabolized forms; sulfamethoxazole also exists as the conjugated form. Sulfamethoxazole is metabolized in humans to at least 5 metabolites: the N4 -acetyl-, N4 -hydroxy-, 5-methylhydroxy-, N4 -acetyl-5- methylhydroxy-sulfamethoxazole metabolites, and an N- glucuronide conjugate. The formation of N4 -hydroxy metabolite is mediated via CYP2C9.
Trimethoprim is metabolized in vitro to 11 different metabolites, of which, five are glutathione adducts and six are oxidative metabolites, including the major metabolites, 1- and 3-oxides and the 3- and 4-hydroxy derivatives.
The free forms of sulfamethoxazole and trimethoprim are considered to be the therapeutically active forms.
In vitro studies suggest that trimethoprim is a substrate of P-glycoprotein, OCT1 and OCT2, and that sulfamethoxazole is not a substrate of P-glycoprotein.
Approximately 70% of sulfamethoxazole and 44% of trimethoprim are bound to plasma proteins. The presence of 10 mg percent sulfamethoxazole in plasma decreases the protein binding of trimethoprim by an insignificant degree; trimethoprim does not influence the protein binding of sulfamethoxazole.
Peak blood levels for the individual components occur 1 to 4 hours after oral administration. The mean serum half-lives of sulfamethoxazole and trimethoprim are 10 and 8 to 10 hours, respectively. However, patients with severely impaired renal function exhibit an increase in the half-lives of both components, requiring dosage regimen adjustment (see DOSAGE AND ADMINISTRATION section). Detectable amounts of sulfamethoxazole and trimethoprim are present in the blood 24 hours after drug administration. During administration of 800 mg sulfamethoxazole and 160 mg trimethoprim b.i.d., the mean steady-state plasma concentration of trimethoprim was 1.72 mcg/mL. The steady-state mean plasma levels of free and total sulfamethoxazole were 57.4 mcg /mL and 68 mcg /mL, respectively. These steady-state levels were achieved after three days of drug administration.1 Excretion of sulfamethoxazole and trimethoprim is primarily by the kidneys through both glomerular filtration and tubular secretion. Urine concentrations of both sulfamethoxazole and trimethoprim are considerably higher than are the concentrations in the blood. The average percentage of the dose recovered in urine from 0 to 72 hours after a single oral dose of sulfamethoxazole and trimethoprim is 84.5% for total sulfonamide and 66.8% for free trimethoprim. Thirty percent of the total sulfonamide is excreted as free sulfamethoxazole, with the remaining as N4-acetylated metabolite2. When administered together as sulfamethoxazole and trimethoprim, neither sulfamethoxazole nor trimethoprim affects the urinary excretion pattern of the other.
Both sulfamethoxazole and trimethoprim distribute to sputum, vaginal fluid and middle ear fluid; trimethoprim also distributes to bronchial secretion, and both pass the placental barrier and are excreted in human milk.
Pharmacokinetics in Pediatric Patients
A simulation conducted with data from a pharmacokinetic study in 153 infants and children demonstrated that mean steady state AUC and maximum plasma concentration of trimethoprim and sulfamethoxazole would be comparable between pediatric patients 2 months to 18 years receiving 8/40 (trimethoprim/ sulfamethoxazole) mg/kg/day divided every 12 hours and adult patients receiving 320/1600 (trimethoprim/ sulfamethoxazole) mg/day.
Pharmacokinetics in Geriatric Patients
The pharmacokinetics of sulfamethoxazole 800 mg and trimethoprim 160 mg were studied in 6 geriatric subjects (mean age: 78.6 years) and 6 young healthy subjects (mean age: 29.3 years) using a non- US approved formulation.
Pharmacokinetic values for sulfamethoxazole in geriatric subjects were similar to those observed in young adult subjects. The mean renal clearance of trimethoprim was significantly lower in geriatric subjects compared with young adult subjects (19 mL/h/kg vs. 55 mL/h/kg). However, after normalizing by body weight, the apparent total body clearance of trimethoprim was on average 19% lower in geriatric subjects compared with young adult subjects.3
Mechanism of Action
Sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid (PABA). Trimethoprim blocks the production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the required enzyme, dihydrofolate reductase. Thus, sulfamethoxazole and trimethoprim blocks two consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria.
In vitro studies have shown that bacterial resistance develops more slowly with both sulfamethoxazole and trimethoprim in combination than with either sulfamethoxazole or trimethoprim alone.
Sulfamethoxazole and trimethoprim has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.
Aerobic gram-positive bacteria
Aerobic gram-negative bacteria
Escherichia coli (including susceptible enterotoxigenic strains implicated in traveler’s diarrhea)
For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.
INDICATIONS AND USAGE
To reduce the development of drug-resistant bacteria and maintain the effectiveness of sulfamethoxazole and trimethoprim oral suspension and other antibacterial drugs, sulfamethoxazole and trimethoprim oral suspension 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 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 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 could offer some advantage over the use of a single antimicrobial agent.
For the treatment of enteritis caused by susceptible strains of Shigella flexneri and Shigella sonnei when antibacterial therapy is indicated.
Pneumocystis jirovecii Pneumonia
For the treatment of documented Pneumocystis jirovecii pneumonia and for prophylaxis against P. jirovecii pneumonia in individuals who are immunosuppressed and considered to be at an increased risk of developing P. jirovecii pneumonia.
Traveler’s Diarrhea in Adults
For the treatment of traveler’s diarrhea due to susceptible strains of enterotoxigenic E. coli.
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