Fisat

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Medically reviewed

Rosario Oropesa

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Fisat

Property Description
Active Ingredients Sulphamethoxazole, Trimethoprim
Form Tablets, Oral Suspension, IV Solution
Pharmacological Class Antibacterial Combination Product
Common Use Treating bacterial and protozoal infections
Origin Synthetic (Chemically manufactured)

What Type of Medicine is Fisat?

Fisat is the trade name for the generic medicine Co-trimoxazole, which is classified as a prescription-only synthetic antibacterial combination product. It is fundamentally an antibiotic and potent antimicrobial agent, with its overall purpose being to treat and prevent infections caused by susceptible bacteria and certain protozoa. This medicine is used for fighting infections where microbial growth needs to be stopped quickly.

This compound belongs to a specialized pharmacological grouping that includes the sulfonamide antibiotic and antifolate agent classes. The primary purpose of this dual classification is to combat infections by effectively stopping the growth and replication of susceptible infectious organisms.


Composition and Form: A Fixed-Dose Combination

Fisat is a fixed-dose combination of the two active ingredients: Sulphamethoxazole (a sulfonamide) and Trimethoprim (an antifolate). This specific pairing is used to achieve a powerful synergistic effect against target microbes. The combined action improves the overall potency of the medication compared to single agents.

The medicine is a chemically manufactured, synthetic compound and is supplied in various pharmaceutical preparations for both oral and parenteral routes of administration. These forms include the standard and Double Strength (DS) tablets, an oral suspension for liquid dosing, and an intravenous solution for infusion, particularly for severe infections. This range of forms allows for broad use across different patient groups, including pediatric subjects.


Understanding the Synergistic Purpose of Co-trimoxazole

The therapeutic effectiveness of this medication is derived from its dual-action blockade, which ensures a high degree of potency against infectious organisms. This principle is utilized for treating various systemic microbial challenges.

This synergistic mechanism works by preventing the infectious agent from synthesizing folic acid, a critical substance required for the production of DNA and essential proteins. This systemic action allows the medicine to achieve a broad and deep antimicrobial effect necessary to help clear established infections, such as those that may occur in the urinary tract or respiratory system.

Regulatory References

  1. Trimethoprim Sulfamethoxazole - StatPearls - NCBI Bookshelf

What side effects are possible with Fisat?

Possible side effects and safety information

The official safety profile of Fisat (Co-trimoxazole) is categorized according to the frequency and body system affected, consistent with regulatory standards set by bodies like the FDA and EMA. Adverse reactions are grouped into categories ranging from Very Common to Very Rare.

Commonly Documented Adverse Reactions

The most frequent reactions are officially classified as Common or Very Common, typically affecting the gastrointestinal system and skin. These include headache, nausea, diarrhea, and rash. Effects on metabolism are also noted, most commonly hyperkalemia (high blood potassium).

System-Organ Classes and Serious Reactions

Adverse effects are documented across various physiological systems, including Blood and Lymphatic, Hepatobiliary, Renal and Urinary, and Skin disorders. Rare but severe reactions that have been associated with this medicine and are highlighted in official labeling include Severe Cutaneous Adverse Reactions (SCARs) such as Stevens-Johnson syndrome (SJS) and Toxic Epidermal Necrolysis (TEN). Other serious, rare effects include severe blood dyscrasias like aplastic anemia and fulminant hepatic necrosis.

Population-Specific and Time-Related Safety Constraints

Safety constraints are explicitly documented for specific groups. Fisat is contraindicated in children less than two months of age due to the risk of kernicterus. Older adults are noted as being more susceptible to adverse effects. The highest risk for the occurrence of severe skin reactions (SJS/TEN) is documented as being within the first weeks of treatment. Maintaining adequate fluid intake is officially noted as advisable to help prevent crystalluria.

Overdose and Emergency Response

Fisat (Co-trimoxazole) overdose is defined by distinct acute and chronic clinical manifestations officially documented in regulatory labeling. Acute overdosage may present with gastrointestinal symptoms such as severe nausea, vomiting, and diarrhea, alongside central nervous system effects including headache, confusion, dizziness, and mental depression. Documented effects on the renal system include crystalluria and hematuria.

The most severe documented outcomes arise from chronic overdosage, which can lead to life-threatening complications, including severe bone marrow depression (e.g., leukopenia, megaloblastic anemia) and signs of acute folic acid deficiency, potentially resulting in coma or fatal outcomes. Elderly patients and individuals with pre-existing hepatic or renal impairment are noted to have an increased risk for severe adverse effects following overdose.

Immediate medical attention must be sought for any suspected overdose. While no specific antidote is known, regulatory guidance mandates prompt symptomatic and supportive treatment. Interventions described include gastric lavage and activated charcoal for recent ingestion, and the specific use of leucovorin (folinic acid) to counteract the severe antifolate effects of chronic toxicity. Close hospital monitoring, particularly of blood counts and renal function, is officially required.

Therapeutic Uses of Fisat

Fisat (Co-trimoxazole) is applied across domains where additional symptomatic support is needed, and is used for managing symptom clusters that may become intense or disruptive. The therapeutic focus is on managing conditions associated with urinary, respiratory, and certain enteric infections.

The medicine is commonly used across conditions presenting with acute episodes, including urinary tract infections, acute bronchitis exacerbations, middle ear infections, and specific severe conditions like Pneumocystis jirovecii Pneumonia (PJP) and Shigellosis. It is relevant for easing symptoms that interfere with daily comfort, such as painful urination, fever, severe cough, and acute diarrhea. It generally provides supportive relief when symptoms interfere with routine activities.

This medication is applied in scenarios where additional management of discomfort is required, and helps improve day-to-day comfort during symptomatic periods. “Fisat may assist with maintaining functional stability in situations where symptoms become temporarily overwhelming.”


Quick Fact: Supportive Management for Acute Symptom Clusters Fisat is considered relevant when symptoms of increased physiological stress cluster into patterns where supportive symptom management is appropriate, such as in cases of Traveler’s Diarrhea or recurrent UTIs.

Eligibility and Restrictions for Use

Who can and cannot use Fisat?

The population eligibility for Fisat (Co-trimoxazole) is strictly defined by regulatory authorities based on contraindications, age limits, and coexisting health conditions.

Contraindicated Populations

Use of this medicine is formally contraindicated in patients with a known hypersensitivity to sulfonamides or trimethoprim or a history of drug-induced immune thrombocytopenia. It is also prohibited for individuals with documented marked hepatic damage, severe renal insufficiency (if function cannot be monitored), megaloblastic anemia due to folate deficiency, or acute porphyria. The medicine is strictly contraindicated in infants under two months of age and for women who are pregnant at term.

Age and Condition Restrictions

The medicine is generally approved for adults, adolescents, and pediatric patients two months of age and older. However, it is not recommended for nursing mothers of infants under eight weeks and requires caution for older adults. Use requires explicit caution and monitoring in patients with conditions such as G6PD deficiency, folate deficiency, or hyperkalemia. Dose reduction is mandated for patients with moderate renal impairment (Creatinine Clearance 15-30 mL/minute).

What should I know about interactions with other medicines?

Fisat is known to interact with various medications and other substances. Before starting treatment, it is essential to inform your healthcare provider of all prescription and over-the-counter drugs, vitamins, and herbal supplements you are currently taking.

Medication-Specific Interactions

Concomitant Drug Class/Product Potential Interaction/Risk
Anticoagulants (e.g., Warfarin) and Antiplatelets (e.g., low-dose Aspirin, Clopidogrel) Increased risk of serious bleeding events, particularly gastrointestinal bleeding. Close monitoring is required.
Other NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) Greatly increased risk of serious gastrointestinal side effects, including ulcers and bleeding. This combination should be avoided.
Antihypertensives (e.g., ACE Inhibitors, ARBs, Diuretics, Beta-Blockers) Fisat may reduce the blood pressure-lowering effect of these medications. The combination with Diuretics or ACE Inhibitors/ARBs also increases the risk of kidney function impairment (renal toxicity).
Lithium Fisat can increase serum lithium levels, potentially leading to toxicity.
Methotrexate Fisat can increase blood concentrations of methotrexate, raising the risk of toxicity.
Selective Serotonin Reuptake Inhibitors (SSRIs) Increased risk of gastrointestinal bleeding.
Cyclosporine Increased risk of kidney damage (nephrotoxicity).

Other Notable Interactions

Alcohol consumption while taking Fisat can increase the risk of gastrointestinal irritation and bleeding and should be limited or avoided. Herbal supplements, such as Ginkgo Biloba or Garlic, may also increase the risk of bleeding when taken concurrently with Fisat.

Mechanism of Action

How Fisat Works: The Sequential Mechanism

Fisat (Co-trimoxazole) exerts its effect through a sequential double blockade of the folate synthesis pathway within susceptible microorganisms. The first component, Sulphamethoxazole, acts as a structural analog of PABA and competitively inhibits the enzyme Dihydropteroate Synthase (DHPS). The second component, Trimethoprim, then inhibits the subsequent enzyme, Dihydrofolate Reductase (DHFR).

This synergistic mechanism, achieved by blocking two consecutive, vital steps, results in a greater degree of biochemical inhibition than either component alone. The dual-action strategy prevents the infectious agent from producing active tetrahydrofolic acid (THF), a necessary cofactor for single-carbon transfer reactions required for the synthesis of DNA and proteins. The physiological consequence of this blockade is the cessation of metabolic activity required for the organism's growth and replication, leading to a physiological decrease in the capacity for microbial proliferation. The mechanism exhibits high selectivity because its targets are structurally distinct from human enzymes; however, it is constrained by acquired resistance that diminishes the sequential blockade.

Dosage and Administration Information

Fisat, the trade name for Co-trimoxazole, is utilized via specific routes, dosage schedules, and required administration conditions.

Administration Routes and Forms

Fisat is administered via the oral route (tablets or suspension) or by intravenous (IV) infusion. Administration by rapid IV injection or intramuscularly must be avoided. The IV solution must be diluted, typically in 5% dextrose in water, and administered over a period of 60 to 90 minutes. Oral forms should be taken with a full glass of water and may be taken with food to minimize gastrointestinal disturbances.


Official Dosing and Frequency

Usage Pattern Standard Adult Regimen Frequency and Duration
Standard Acute Dose One Double Strength (DS) tablet (800 mg SMX / 160 mg TMP) is common. Generally every 12 hours for 5 to 14 days.
High Dose (Severe) Dose is calculated based on body weight (mg/kg) using the trimethoprim component. Administered every 6 to 8 hours for 14 to 21 days.

Population and Procedural Rules

Age-Group and Renal Adjustment: Dosing for pediatric patients (two months and older) is based on body weight. For adults with moderate renal impairment (15 to 30 mL/min Creatinine Clearance), the usual dose should be reduced by half. Use is not recommended for patients with Creatinine Clearance below 15 mL/min.

Missed Dose: If a dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose is skipped, and the regular schedule is continued; do not take a double dose.

Recent Clinical Evidence

Research Evidence Overview: Understanding the Clinical Trials for Fisat

This section summarizes the structure of the official research used by regulatory bodies to evaluate Fisat (Co-trimoxazole). It focuses on the types of studies conducted, the groups of people examined, and the clinical outcomes measured across its main approved uses. Research provides context but not individual predictions; the findings describe group patterns, not personal outcomes.

Evidence for Use in Urinary Tract Infections (UTIs) and Other Common Acute Bacterial Infections

Research for Fisat's role in infections like UTIs was studied for its association with various outcomes through numerous Randomized Controlled Trials (RCTs) and Systematic Reviews. These studies focused on measuring outcomes related to physical discomfort and systemic or functional imbalance. Studies have monitored responses over defined time intervals, particularly investigating patients with acute, uncomplicated UTIs.

Findings describe patterns observed in the studies related to the short-term resolution of symptoms and clearance of the infection. The evidence contributes to understanding symptom patterns within the broader evidence landscape for specific acute infections, reflecting a documented history of research.

What remains uncertain is the full impact of current, evolving antimicrobial resistance on the medicine's utility across all populations; current use may be guided by local susceptibility patterns. Furthermore, follow-up durations were limited to the immediate post-treatment period, meaning there is limited information for long-term outcomes beyond preventing early relapse.

Evidence for Use in Severe and Opportunistic Infections (PJP)

Fisat was evaluated in research contexts involving outcomes reflecting daily functioning related to Pneumocystis jirovecii Pneumonia (PJP), both for acute treatment and long-term prevention. These studies often used large-scale Observational Cohort Studies alongside RCTs due to the critical nature of the disease.

Research for prevention explored outcomes related to systemic or functional imbalance over months or years. Findings indicate patterns where the medicine was studied for its association with patient survival and infection outcomes related to systemic or functional imbalance in these specific, high-risk groups, and the data show patterns related to prevention.

Research Gaps and What Remains Uncertain

While Fisat has been studied for many indications, certain research limitations and gaps exist. A key area of research is ongoing regarding the effect of global antimicrobial resistance trends on the reliability of past findings and its comparative utility against newer agents.

Furthermore, comparative evidence is lacking or data are still emerging when evaluating its performance against other current standard treatment options for specific acute infections. The findings were mixed across studies for secondary indications, and data for certain groups of patients with complicated underlying health conditions remain insufficient compared to that for acute, uncomplicated cases.

Key Studies & References Effectiveness of different treatment regimens for acute uncomplicated cystitis in women: A systematic review and meta-analysis

Frequently Asked Questions (FAQ)

Common questions about Fisat (FAQ)

Q: Does Fisat cause weight gain or loss?

A: Official regulatory documents list adverse effects across various body systems, including some metabolism disorders. However, official product information does not specifically list weight gain or weight loss as a common or known adverse reaction of Fisat (Co-trimoxazole).

Q: Are there any long-term effects of taking Fisat?

A: For patients receiving Fisat over long periods, official information indicates that the need for regular monitoring of blood counts is noted. Furthermore, caution is advised for prolonged use in patients who are known to have folate deficiency.

Q: Does Fisat affect blood pressure or heart rate?

A: Fisat is officially associated with hyperkalemia (high blood potassium) as a very common side effect. High potassium levels can potentially lead to abnormal heart rhythms, known as palpitations. Official documents also describe that Fisat can interact with certain medications used to manage blood pressure.

Q: Can I take Fisat if I'm taking a blood thinner?

A: Official documentation states that Fisat may increase the effect of certain blood thinning medications known as anticoagulants, such as warfarin. This combination can increase the risk of bleeding. Regulatory warnings indicate that close monitoring is required when these medicines are used concomitantly (together).

Q: Can Fisat be crushed or split if it's hard to swallow?

A: Some regulatory administration guidance for the tablet forms of Fisat describes that they may be crushed and mixed with a small amount of water or soft food before administration. This is described as an administration option for patients.

Q: Do I need to stop Fisat gradually, or can I stop all at once?

A: Official patient information often clarifies that the full prescribed course is intended to be completed, even if symptoms improve quickly. Treatment duration is defined in days, but specific instructions for cessation (such as tapering) are not generally provided in public-facing literature for acute treatment.

Q: Is Fisat used for any other conditions besides the main one?

A: Fisat is officially indicated for several uses. This includes the treatment and prevention of serious infections like Pneumocystis jiroveci pneumonitis (PJP) and toxoplasmosis. It is also approved for certain urinary tract infections, acute otitis media (ear infection), and acute exacerbation of chronic bronchitis.

Q: Does Fisat interact with common supplements like multivitamins?

A: Fisat works by disrupting a process that requires folic acid in infectious organisms. The documentation notes that folic acid supplementation, when needed, may be administered concomitantly (at the same time) without interfering with the antibacterial action of Fisat.

Q: Can Fisat be used by people with a history of kidney stones?

A: Official warnings state that maintaining an adequate urinary output is advised while using Fisat to help prevent crystalluria, which is the formation of crystals in the urine. The medicine is contraindicated in patients with severe, unmonitored renal insufficiency.

Q: Is Fisat the same kind of drug as [Similar Drug Name]?

A: Fisat is the trade name for Co-trimoxazole, which is classified as a synthetic antibacterial combination product. This means it is a mixture of two antimicrobial agents: a sulfonamide antibiotic (Sulphamethoxazole) and an antifolate agent (Trimethoprim).

Q: How long does it typically take for Fisat to start working?

A: Patient information indicates that a person should typically begin to feel better during the first few days of taking Fisat. Pharmacokinetic studies describe that the average peak concentration of the drug components in the blood is usually reached within one to four hours after administration.

Q: Will taking Fisat make me feel tired or drowsy?

A: Official adverse reaction lists describe that experiencing unusual weakness or tiredness is a known side effect reported with Fisat. Other reported effects affecting the nervous system include dizziness and headache.

Q: Is Fisat a new drug or has it been around for a while?

A: The combination of the two active ingredients in Fisat, Co-trimoxazole, has a long history. It was introduced into clinical practice in the late 1960s, making it a well-established medication.

Q: What does the research say about Fisat's effectiveness?

A: Research reviewed by regulatory bodies indicates that Fisat is effective in inhibiting the growth of susceptible bacteria and certain protozoa. This is achieved by blocking two vital steps in the organism's DNA synthesis pathway, making it useful in the treatment and prevention of specific infections.

Q: Does Fisat affect sleep quality?

A: Official documentation lists insomnia (difficulty sleeping) as an adverse effect that may occur while taking Fisat. This is categorized alongside other reported effects that influence the nervous system.

Q: Is it true that Fisat can cause mood changes?

A: Official adverse effect lists for Fisat include reports of psychiatric disorders. These reported effects may include depression and hallucinations, among others.

Q: How long does the effect of one dose of Fisat last?

A: The length of time the drug components stay active in the body is measured by the elimination half-life. For Fisat, this is generally described as being between 8 and 12 hours in people with normal kidney function, which influences the frequency of dosing.

Q: Can Fisat interact with common cold or flu medicines?

A: Because cold and flu products often contain multiple ingredients, there is a large number of potential interactions to consider. Official warnings note the potential for interactions with various components found in cold and flu medicines, such as certain decongestants. Regulatory information highlights the need to consider all concomitant use.

Q: Does taking Fisat affect lab test results?

A: Yes, Fisat can affect certain laboratory results. It may interfere with some methods used to measure serum creatinine and can lead to elevated potassium levels (hyperkalemia). This means laboratory monitoring may be needed during use.

Q: What happens when the drug leaves the body?

A: The components of Fisat are primarily eliminated via the kidneys (renal excretion) and leave the body mainly through the urine. This process is directly related to the drug's half-life and is why proper kidney function is important when using the medicine.

Q: What were the main reasons Fisat was approved by regulators?

A: Fisat was approved by regulatory agencies based on evidence demonstrating its therapeutic efficacy in clinical trials. The approval covers its use in treating a range of infections caused by susceptible organisms, including specific types of urinary tract, respiratory, and enteric infections, and severe opportunistic infections like PJP.

Q: Is Fisat described as a cure or a management tool?

A: Fisat is officially described as an antibacterial agent and is used for the treatment and prophylaxis (prevention) of infections caused by susceptible microbes. It is generally categorized as a treatment tool for infectious diseases.

Q: What is the evidence level for Fisat's benefits?

A: Evidence supporting the use of Fisat in acute infections often comes from Randomized Controlled Trials (RCTs) and Systematic Reviews. Evidence for its use in severe opportunistic infections, like PJP, includes large-scale Observational Cohort Studies alongside RCTs.

Q: Does the efficacy of Fisat depend on diet or lifestyle?

A: Official documentation notes that caution is advised for patients who have suspected folate depletion, which can be associated with certain factors such as malnutrition or alcoholism. This suggests that certain dietary and nutritional statuses may influence its use.

How should Fisat be stored and disposed of?

Official Storage and Disposal Requirements

Fisat (Co-trimoxazole) must be stored strictly according to official regulatory conditions to ensure stability. All forms should be stored at controlled room temperature, generally between 20 C and 25 C (68 F and 77 F), in a tightly closed container and protected from heat, moisture, and direct light.

Storage Restriction Requirement
Temperature Do not freeze oral forms; do not refrigerate tablets or IV concentrate.
Safety Keep the medicine out of the sight and reach of children.
Stability (IV) Use the diluted intravenous solution within 24 hours of preparation.

Do not use the medicine after the expiry date. Unused or expired product must be disposed of by following established FDA and local waste guidelines; the injectable form requires specific handling to avoid release to the environment.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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