BACTIFENIN ORAL SUSPENSION

Indications

• Urinary tract infections
• Respiratory tract infections
• Gastrointestinal infections
• Pneumocystis pneumonia
• Toxoplasmosis

Dosage

Children: Refer to the BNF for Children for specific dosing information appropriate for paediatric patients, as doses are typically weight-based and vary by age and condition.

Adults: Refer to the BNF for specific dosing information based on the clinical condition being treated, as dosing may vary depending on the severity of the infection and patient characteristics.

Mechanism of action

Sulfamethoxazole inhibits bacterial dihydrofolic acid synthesis due to its structural similarity to para-aminobenzoic acid (PABA). It competitively inhibits dihydropteroate synthase, the enzyme responsible for converting PABA to dihydrofolic acid. This action prevents the synthesis of tetrahydrofolate, leading to the inhibition of bacterial purine and DNA synthesis, resulting in a bacteriostatic effect.

Pharmacodynamics

Sulfamethoxazole is generally bacteriostatic, inhibiting a crucial step in bacterial folate synthesis. It is typically used in combination with trimethoprim, which inhibits the reduction of dihydrofolic acid to tetrahydrofolate. This combination allows for a synergistic effect, reducing the rate of bacterial resistance development compared to using either drug alone. Care should be taken as sulfamethoxazole can cause hypersensitivity reactions, and it may contribute to folate deficiency, particularly in at-risk populations.

Pharmacokinetics

Sulfamethoxazole is well absorbed following oral administration and is widely distributed in body tissues. It has a moderate half-life, necessitating multiple daily doses for sustained therapeutic effect. The drug is metabolized in the liver and excreted primarily via the kidneys, with some metabolites being active. Its excretion can be influenced by renal function, necessitating dose adjustments in patients with compromised kidney function.

Contra-indications

• Hypersensitivity to sulfamethoxazole or other sulfonamides
• Severe liver impairment
• Severe renal impairment
• History of severe adverse reactions to sulfonamides (e.g., Stevens-Johnson syndrome)

Adverse effects

• Rash
• Nausea
• Vomiting
• Diarrhea
• Hematological reactions (e.g., leukopenia, thrombocytopenia)
• Liver toxicity
• Renal toxicity
• Hemolytic anemia in patients with G6PD deficiency
• Stevens-Johnson syndrome
• Toxic epidermal necrolysis

Interactions

• Sulfamethoxazole may increase the anticoagulant effect of coumarins
• Concurrent use with other folate antagonists may enhance toxicity
• May interact with methotrexate, increasing the risk of toxicity

Precautions

• Use with caution in patients with a history of hypersensitivity reactions
• Monitor for signs of folate deficiency
• Assess renal and liver function prior to and during treatment
• Discontinue immediately at the first sign of rash or skin reaction

Pregnancy

Sulfamethoxazole is generally not recommended during pregnancy, especially in the first trimester and near term, due to potential risks of teratogenic effects and kernicterus in the newborn.

Breast-feeding

Sulfamethoxazole is excreted in breast milk; caution is advised when administering to nursing mothers due to potential effects on the nursing infant.

Storage

Store at room temperature, away from moisture and heat. Protect from light.

Formulations

• Oral tablets
• Oral suspension
• Injection

Indications

• Bacterial infections
• Urinary tract infections
• Respiratory tract infections
• Prophylaxis of recurrent urinary tract infections

Dosage

Children: For children aged 6 weeks to 5 months: 4 mg/kg twice daily (max. 200 mg). For children 6 months to 5 years: 4 mg/kg twice daily (max. 200 mg). For children 6–11 years: 4 mg/kg twice daily (max. 200 mg). For children

Adults: 200 mg twice daily.

Mechanism of action

Trimethoprim is a reversible inhibitor of dihydrofolate reductase, an enzyme that catalyzes the formation of tetrahydrofolic acid from dihydrofolic acid. By inhibiting this enzyme, trimethoprim disrupts the biosynthesis of nucleic acids and proteins in bacteria, leading to their growth inhibition. The drug has a significantly higher affinity for bacterial dihydrofolate reductase compared to the mammalian enzyme, ensuring selective antibacterial activity.

Pharmacodynamics

Trimethoprim exerts its antimicrobial effects by disrupting bacterial nucleic acid synthesis. It is effective against various gram-negative bacteria and some coagulase-negative Staphylococcus species. Resistance can develop through mechanisms such as alterations to the bacterial cell wall or overproduction of the target enzyme. Monitoring for potential blood disorders is important during therapy, as rare adverse effects can occur.

Pharmacokinetics

Trimethoprim is well absorbed from the gastrointestinal tract and reaches peak plasma concentrations within 1-4 hours post-administration. It has a volume of distribution that suggests extensive tissue penetration, including into the lungs and kidneys, and is primarily excreted unchanged in the urine. The elimination half-life is approximately 8-10 hours, and dosing adjustments may be necessary in cases of renal impairment.

Contra-indications

• Severe renal impairment
• Known hypersensitivity to trimethoprim or any component of the formulation

Adverse effects

• Diarrhoea
• Nausea
• Headache
• Dizziness
• Fatigue
• Skin reactions
• Vomiting
• Anxiety
• Agranulocytosis
• Eosinophilia
• Photosensitivity reactions
• Thrombocytopenia
• Leukopenia
• Pseudomembranous colitis

Interactions

• Increases exposure to pramipexole
• Increases exposure to treprostinil
• Increases exposure to dopaminergic receptor agonists
• Increases concentration of antiepileptics
• Increases concentration of fosphenytoin
• Increases concentration of phenytoin
• Increases risk of haematological toxicity with azathioprine in renal transplant patients
• Increases concentration of digoxin
• Increases exposure to repaglinide

Precautions

• Caution in patients with renal impairment
• Caution in elderly patients (75 years and over)
• Monitor for signs of blood disorders such as sore throat, fever, and pallor
• Consider local antimicrobial susceptibility patterns before use

Pregnancy

Manufacturer advises avoidance due to potential fetal developmental toxicity observed in animal studies.

Breast-feeding

Manufacturer advises avoidance as trimethoprim is present in milk in animal studies.

Storage

Store in a cool, dry place, away from direct sunlight. Keep out of reach of children.

Formulations

• Tablets
• Oral suspension
• Injection solution

Mechanism of action

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. Sulfonamides are usually bacteriostatic in action. Sulfonamides interfere with the utilization of p-aminobenzoic acid (PABA) in the biosynthesis of tetrahydrofolic acid (the reduced form of folic acid) cofactors in susceptible bacteria. Sulfonamides are structural analogs of PABA and appear to interfere with PABA utilization by competitively inhibiting the enzyme dihydropteroate synthase, which catalyzes the formation of dihydropteroic acid (a precursor of tetrahydrofolic acid) from PABA and pteridine; however, other mechanism(s) affecting the biosynthetic pathway also may be involved. Compounds such as pyrimethamine and trimethoprim, which block later stages in the synthesis of folic acid, act synergistically with sulfonamides. Only microorganisms that synthesize their own folic acid are inhibited by sulfonamides; animal cells and bacteria which are capable of utilizing folic acid precursors or preformed folic acid are not affected by these drugs. The antibacterial activity of the sulfonamides is reportedly decreased in the presence of blood or purulent body exudates. /Sulfonamides/ /Sulfonamides inhibit bacterial growth by preventing para-aminobenzoic acid (PABA) from being incorporated/ into dihydropteroic acid, the immediate precursor of folic acid. Sensitive microorganisms are those that must synthesize their own folic acid; bacteria that can utilize preformed folate are not affected. Bacteriostasis induced by sulfonamides is counteracted by PABA competitively. Sulfonamides do not affect mammalian cells by this mechanism, since they require preformed folic acid and cannot synthesize it. /Sulfonamides/ Sulfonamides are broad-spectrum, bacteriostatic anti-infectives. They are structural analogs of para-aminobenzoic acid and competively inhibit a bacterial enzyme, dihydropteroate synthetase, that is responsible for incorporation of para-aminobenzoic acid into dihydrofolic acid. This blocks the synthesis of dihydrofolic acid and decreases the amount of metabolically active tetrahydrofolic acid, a cofactor for the synthesis of purines, thymidine, and DNA. /Sulfonamides/ The hydroxylamine and nitroso metabolites formed by N4-oxidation of sulfonamides are thought to be involved in the pathogenesis of idiosyncratic reactions to this class of drugs. Idiosyncratic reactions to sulfonamides are characterized by multisystemic toxicity, including hepatitis, nephritis, dermatitis, and blood dyscrasias (aplastic anemia, agranulocytosis). Previously it has been shown that cytochrome p-450 in the liver metabolizes sulfamethoxazole to its hydroxylamine metabolite. In this paper the N4-oxidation of sulfamethoxazole by activated monocytes and neutrophils (human and canine) to form sulfamethoxazole hydroxylamine and nitrosulfamethoxazole is reported. The presumed nitroso intermediate was not detected. Purified myeloperoxidase and prostaglandin H synthase were also capable of mediating the oxidation of sulfamethoxazole. The present studies suggest that myeloperoxidase is responsible for the observed oxidation by phagocytic cells. Oxidation by neutrophils may play a role in agranulocytosis, and oxidation by monocytes may facilitate antigen presentation. Extrahepatic bioactivation of sulfonamides by peroxidases in phagocytic cells and other tissues may be important in determining the range of adverse reactions to sulfonamides

Pharmacodynamics

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.

Mechanism of action

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. Trimethoprim is a bacteriostatic lipophilic weak base structurally related to pyrimethamine. It binds to and reversibly inhibits the bacterial enzyme dihydrofolate reductase, selectively blocking conversion of dihydrofolic acid to its functional form, tetrahydrofolic acid. This depletes folate, an essential cofactor in the biosynthesis of nucleic acids, resulting in interference with bacterial nucleic acid and protein production. Bacterial dihydrofolate reductase is approximately 50,000 to 60,000 times more tightly bound by trimethoprim than is the corresponding mammalian enzyme. To determine the incidence & severity of hyperkalemia during trimethoprim therapy, 30 consecutive patients with acquired immunodeficiency syndrome receiving high-dose (20 mg/kg/day) trimethoprim were studied; in addition, the mechanism of trimethoprim-induced hyperkalemia was investigated in rats. Trimethoprim increased serum potassium concn by 0.6 mmol/l despite normal adrenocortical function & glomerular filtration rate. Serum potassium levels >5 mmol/l were observed during trimethoprim treatment in 15 of 30 patients. In rats, iv trimethoprim inhibited renal potassium excretion by 40% & increased sodium excretion by 46%. It was concluded that trimethoprim blocks apical membrane sodium channels in the mammalian distal nephron. As a consequence, the transepithelial voltage is reduced & potassium secretion is inhibited. Decreased renal potassium excretion secondary to these direct effects on kidney tubules leads to hyperkalemia in a substantial number of patients being treated with trimethoprim-containing drugs.

Pharmacodynamics

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.