Septrin Tablets

Septrin Tablets Uses, Dosage, Side Effects, Food Interaction and all others data.

Sulfamethoxazole is a bacteriostatic sulfonamide antibiotic that interferes with folic acid synthesis in susceptible bacteria. It is generally given in combination with trimethoprim, which inhibits a sequential step in bacterial folic acid synthesis - these agents work synergistically to block two consecutive steps in the biosynthesis of nucleic acids and proteins which are necessary for bacterial growth and division, and using them in conjunction helps to slow the development of bacterial resistance. In this combination, sulfamethoxazole is useful for the treatment of a variety of bacterial infections, including those of the urinary, respiratory, and gastrointestinal tracts.

Sulfamethoxazole is a bacteriostatic sulfonamide antibiotic that inhibits a critical step in bacterial folate synthesis. It is generally given in combination with trimethoprim, a dihydrofolate reductase inhibitor, which inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid. Studies have shown that bacterial resistance develops more slowly with the combination of the two drugs than with either trimethoprim or sulfamethoxazole alone, as together they inhibit sequential steps in the bacterial folate synthesis pathway.

Sulfonamides, including sulfamethoxazole, have been implicated in hypersensitivity reactions - these agents should be discontinued at the first sign of a developing rash, as this may signal the start of a more severe reaction such as Stevens-Johnson syndrome or toxic epidermal necrolysis. Sulfamethoxazole treatment may contribute to folate deficiency and should therefore be used with caution in patients at a higher risk of developing a deficiency. Hemolysis has been observed in patients with glucose-6-phosphate dehydrogenase deficiency who are using sulfamethoxazole/trimethoprim.

Trimethoprim, a diaminopyrimidine, is a reversible inhibitor of dihydrofolate reductase. It inhibits the conversion of bacterial dihydrofolic acid to tetrahydrofolic acid necessary for the synthesis of nucleic acids and proteins. It is either bacteriostatic or bacteriocidal, acting on the same metabolic pathway as sulfonamides.

Trimethoprim exerts its antimicrobial effects by inhibiting an essential step in the synthesis of bacterial nucleic acids and proteins. It has shown activity against several species of gram-negative bacteria, as well as coagulase-negative Staphylococcus species. Resistance to trimethoprim may arise via a variety of mechanisms, including alterations to the bacterial cell wall, overproduction of dihydrofolate reductase, or production of resistant dihydrofolate reductase. Rarely, trimethoprim can precipitate the development of blood disorders (e.g. thrombocytopenia, leukopenia, etc.) which may be preceded by symptoms such as sore throat, fever, pallor, and or purpura - patients should be monitored closely for the development of these symptoms throught the course of therapy.

As antimicrobial susceptibility patterns are geographically distinct, local antibiograms should be consulted to ensure adequate coverage of relevant pathogens prior to use.

Septrin Tablets
Uses
Dosage
Side Effect
Precautions
Interactions
Uses during Pregnancy
Uses during Breastfeeding
Accute Overdose
Food Interaction
Half Life
Volume of Distribution
Clearance
Interaction With other Medicine
Contradiction
Storage

Trade Name	Septrin Tablets
Generic	Sulfamethoxazole + Trimethoprim
Type
Therapeutic Class
Manufacturer
Available Country
Last Updated:	September 19, 2023 at 7:00 am

Uses

Sulfamethoxazole is an oral sulfonamide antibiotic, given in combination with trimethoprim, used to treat a variety of infections of the urinary tract, respiratory system, and gastrointestinal tract.

Sulfamethoxazole is indicated in combination with trimethoprim, in various formulations, for the following infections caused by bacteria with documented susceptibility: urinary tract infections, acute otitis media in pediatric patients (when clinically indicated), acute exacerbations of chronic bronchitis in adults, enteritis caused by susceptible Shigella, prophylaxis and treatment of Pneumocystis jiroveci pneumonia, and travelers' diarrhea caused by enterotoxigenic E. coli.

In Canada, additional indications include the adjunctive treatment of cholera, treatment of bacillary dysentery, nocardiosis, and second-line treatment of brucellosis in combination with gentamicin or rifampicin.

For the treatment of initial episodes of uncomplicated urinary tract infections due to susceptible strains of the following organisms: Escherichiacoli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species and coagulase-negative Staphylococcus species, including S. saprophyticus.

Cultures and susceptibility tests should be performed to determine the susceptibility of the bacteria to trimethoprim. Therapy may be initiated prior to obtaining the results of these tests.

How Septrin Tablets works

Sulfamethoxazole is a sulfonamide that inhibits bacterial dihydrofolic acid synthesis due to its structural similarity to an endogenous substrate, para-aminobenzoic acid (PABA). Most bacteria meet their need for folic acid by synthesizing it from PABA, as opposed to Animalia that require exogenous folic acid sources. Sulfamethoxazole competitively inhibits dihydropteroate synthase, the enzyme responsible for bacterial conversion of PABA to dihydrofolic acid. Inhibition of this pathway prevents the synthesis of tetrahydrofolate and, ultimately, the synthesis of bacterial purines and DNA, resulting in a bacteriostatic effect.

Trimethoprim is a reversible inhibitor of dihydrofolate reductase, one of the principal enzymes catalyzing the formation of tetrahydrofolic acid (THF) from dihydrofolic acid (DHF). Tetrahydrofolic acid is necessary for the biosynthesis of bacterial nucleic acids and proteins and ultimately for continued bacterial survival - inhibiting its synthesis, then, results in bactericidal activity. Trimethoprim binds with a much stronger affinity to bacterial dihydrofolate reductase as compared to its mammalian counterpart, allowing trimethoprim to selectively interfere with bacterial biosynthetic processes.

Trimethoprim is often given in combination with sulfamethoxazole, which inhibits the preceding step in bacterial protein synthesis - given together, sulfamethoxazole and trimethoprim inhibit two consecutive steps in the biosynthesis of bacterial nucleic acids and proteins. As a monotherapy trimethoprim is considered bacteriostatic, but in combination with sulfamethoxazole is thought to exert bactericidal activity.

Dosage

Septrin Tablets dosage

The usual oral adult dosage is 100 mg of trimethoprim every 12 hours or 200 mg trimethoprim every 24 hours, each for 10 days.

The use of trimethoprim in patients with acreatinineclearance of less than 15 ml/min is not recommended.

For patients with a creatinine clearance of 15 to 30 ml/min, the dose should be 50 mg every 12 hours

Side Effects

Pruritus, rash, urticaria, mild GI disturbance (e.g. nausea, vomiting, glossitis, sore mouth); disturbance of liver enzymes, photosensitivity, angioedema, myalgia, headache; hyperkalaemia, hyponatraemia; agranulocytosis. Rarely, fever, cholestatic jaundice, exfoliative dermatitis, anaphylaxis, aseptic meningitis, megaloblastic anaemia, thrombocytopenia, leucopenia, neutropenia, methaemoglobinaemia.

Toxicity

The oral LD₅₀ of sulfamethoxazole in mice and rats is 2300 mg/kg and 6200 mg/kg, respectively.

Signs or symptoms of sulfonamide overdose include anorexia, colic, nausea, vomiting, dizziness, headache, drowsiness, and unconsciousness. Less common symptoms may include pyrexia, hematuria, and crystalluria. Later manifestations of overdose may include blood dyscrasias and jaundice. Treatment should be symptomatic and supportive, and may include gastric lavage or forced emesis if applicable. Monitor patient lab work for evidence of blood dyscrasias or electrolyte imbalances.

The oral LD₅₀ in mice and rats is 2764 mg/kg and >5300 mg/kg, respectively.

Prescribing information for trimethoprim states that signs of overdose may be evident following ingestion of doses >1 gram, and may include nausea, vomiting, dizziness, headaches, mental depression, confusion, and bone marrow depression. Treatment should consist of general supportive measures and gastric lavage, if applicable. Urinary acidification may increase renal elimination of trimethoprim. Hemodialysis is only moderately effective in eliminating trimethoprim and peritoneal dialysis is of no benefit.

Precaution

Patient with actual or potential folate deficiency (e.g. malnourished, chronic anticonvulsant therapy, elderly). Hepatic and renal impairment. Childn (esp those with fragile X chromosome associated with mental retardation). Pregnancy and lactation.

Interaction

May increase concentration of dapsone. Increased elimination and shortened elimination half-life with rifampicin. Increases concentration of phenytoin, digoxin, procainamide, rosiglitazone, repaglinide, zidovudine, zalcitabine, lamivudine. Increased risk of nephrotoxicity with ciclosporin. Potentiates anticoagulant effect of warfarin. May cause hyponatraemia with diuretics. May cause megaloblastic anaemia with other folate inhibitors (e.g. pyrimethamine, methotrexate). May increase potential for bone marrow aplasia with bone barrow depressants. Increased risk of hyperkalaemia with ACE inhibitors.

Volume of Distribution

The volume of distribution sulfamethoxazole following a single oral dose was found to be 13 L. Sulfamethoxazole distributes into sputum, vaginal fluid, middle ear fluid, breast milk, and the placenta.

Trimethoprim is extensively distributed into various tissues following oral administration. It distributes well into sputum, middle ear fluid, and bronchial secretions. Trimethoprim distributes efficiently into vaginal fluids, with observed concentrations approximately 1.6-fold higher than those seen in the serum. It may pass the placental barrier and into breast milk. Trimethoprim is also sufficiently excreted in the feces to markedly reduce and/or eliminate trimethoprim-susceptible fecal flora.

Elimination Route

Sulfamethoxazole is rapidly absorbed following oral administration and has a bioavailability of 85-90%. The T_max is approximately 1-4 hours following oral administration, and the C_max at steady-state is 57.4 - 68.0 μg/mL.

Steady-state concentrations are achieved after approximately 3 days of repeat administration. Average peak serum concentrations of approximately 1 µg/mL (C_max) are achieved within 1 to 4 hours (T_max) following the administration of a single 100mg dose. Trimethoprim appears to follow first-order pharmacokinetics, as a single 200mg dose results in serum concentrations approximately double that of a 100mg dose. The steady-state AUC of orally administered trimethoprim is approximately 30 mg/L·h.

Half Life

The average serum half-life of sulfamethoxazole is 10 hours and may be increased in patients with severely impaired renal function.

Trimethoprim half-life ranges from 8-10 hours, but may be prolonged in patients with renal dysfunction.

Clearance

The oral and renal clearance of sulfamethoxazole have been estimated as 1.2 ± 0.2 and 0.22 ± 0.05 L/h, respectively.

Following oral administration, the renal clearance of trimethoprim has been variably reported between 51.7 - 91.3 mL/min.

Elimination Route

Elimination occurs primarily via glomerular filtration and tubular secretion in the kidneys, with urine concentrations generally considerably higher than plasma concentrations. Approximately 84.5% of a single oral dose of sulfamethoxazole is recovered in the urine within 72 hours, of which ~30% is free sulfamethoxazole and the remainder is the N4-acetylated metabolite.

Approximately 10-20% of an ingested trimethoprim dose is metabolized, primarily in the liver, while a large portion of the remainder is excreted unchanged in the urine. Following oral administration, 50% to 60% of trimethoprim is excreted in the urine within 24 hours, approximately 80% of which is unchanged parent drug.

Pregnancy & Breastfeeding use

Pregnancy Category C. Trimethoprim has been shown to be teratogenic in the rat when given in doses 40 times the human dose. In some rabbit studies, the overall increase in fetal loss (dead and resorbed and malformed conceptuses) was associated with doses six times the human therapeutic dose.

Nursing Mothers: Trimethoprim is excreted in human milk. Because trimethoprim may interfere with folic acid metabolism, caution should be exercised when trimethoprim is administered to a nursing woman.

Contraindication

Hypersensitivity. Blood dyscrasias (e.g. megaloblastic anaemia).

Special Warning

Pediatric Use: Safety and effectiveness in pediatric patients below the age of 2 months have not been established. The effectiveness of Trimethoprim as a single agent has not been established in pediatric patients under 12 years of age.

Geriatric Use: Clinical studies of Trimethoprim tablets did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in response between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy.

Case reports of hyperkalemia in elderly patients receiving trimethoprim-sulfamethoxazole have been published. Trimethoprim is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor potassium concentrations and to monitor renal function by calculating creatinine clearance.

Acute Overdose

Symptoms: Nausea, vomiting, dizziness, headache, mental depression, confusion, bone marrow depression (e.g. thrombocytopenia, leucopenia, megaloblastic anaemia).

Management: Symptomatic and supportive treatment. May employ gastric lavage and forced diuresis. Enhance elimination through urine acidification. May administer Ca folinate (5-15 mg daily) if bone marrow depression occurs.