Infectrin

Quick links to important sections

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 Infectrin

Quick Facts

Property Description
Active Ingredients Sulphamethoxazole, Trimethoprim
Form Tablet, Oral Suspension, IV Solution
Pharmacological Class Combination Antibacterial / Antimicrobial
General Purpose Systemic anti-infective agent
Origin Synthetic, Fixed-Dose Combination

What is the General Identity of Infectrin (Co-trimoxazole)?

Infectrin is a synthetic, prescription-only medicine, widely recognized as one of the established trade names for the dual-agent antibacterial Co-trimoxazole (also designated TMP-SMX). It is a systemic antimicrobial agent whose unique design is clinically recognized for its reliable efficacy against a broad range of susceptible pathogens. Pharmacologically, this medication is categorized as a Sulfonamide Antibacterial combined with a Dihydrofolate Reductase Inhibitor. The fundamental purpose of this compound is to act as a powerful anti-infective agent across patient groups, including children (over two months of age) and adults.

Composition and Available Forms of the Fixed Combination

The therapeutic effectiveness of Infectrin hinges upon its two distinct active ingredients: Sulphamethoxazole and Trimethoprim. It is manufactured as a fixed-dose combination product, ensuring these substances are consistently delivered in a specific 1:5 ratio (Trimethoprim to Sulphamethoxazole). This formulation is available in multiple dosage forms, providing options for various needs, specifically tablets (often in standard and double-strength preparations) and oral suspensions for oral consumption, as well as an intravenous solution used in hospital settings. Other well-known trade names containing the same Co-trimoxazole formulation include Septra and Bactrim.

How Does the Synergistic Action Define Its Purpose?

The combination of the two active ingredients is designed to produce a profound synergistic effect, which is substantially more potent than the activity of either single component alone. This mechanism, known as sequential blockade, prevents bacteria from synthesizing and utilizing folic acid, a nutrient essential for their growth. By targeting two separate steps in the microbial process, the drug achieves a potent, bactericidal effect. This specialized dual action defines its essential role as an effective treatment for systemic bacterial infections and specific protozoan infections.

Regulatory References

  1. Folic acid in diet: MedlinePlus Medical Encyclopedia

What side effects are possible with Infectrin?

Infectrin (Co-trimoxazole) Safety Profile

The possible side effects and safety characteristics of Co-trimoxazole are officially documented and classified by regulatory authorities. The adverse reaction profile is organized by frequency and the body system affected (System-Organ Class).

Documented Adverse Reactions

Classification Examples of Documented Reactions
Very Common Hyperkalemia (elevated potassium levels)
Common Nausea, Diarrhea, Headache, Fungal overgrowth
Uncommon Vomiting

Adverse reactions are also noted across several system classes, including Gastrointestinal Disorders, Skin and Subcutaneous Tissue Disorders, Metabolism and Nutrition Disorders, and Blood and Lymphatic System Disorders.

Serious Adverse Reactions and Safety Constraints

Serious adverse reactions, though classified as Very Rare, are explicitly documented and include potentially life-threatening conditions such as Stevens-Johnson syndrome (SJS), Toxic epidermal necrolysis (TEN), Agranulocytosis, and Aplastic anaemia. The highest risk for severe skin reactions is generally noted to be within the initial weeks of treatment. For patients on prolonged therapy, the label advises for regular monitoring of blood counts.

Specific safety considerations are documented for certain populations. The medicine is contraindicated in infants under two months of age and in individuals with severe hepatic damage or severe renal insufficiency where close monitoring is not possible. Regulatory safety notes also address the increased susceptibility to adverse effects in older adults, particularly the risk of thrombocytopenia and hyperkalemia. Adequate fluid intake must be maintained to mitigate the risk of crystalluria.

Overdose and Emergency Response

Overdose and When to Seek Help

The regulatory documentation for Infectrin (Co-trimoxazole) strictly mandates that immediate medical attention must be sought for any suspected or confirmed overdose, given the potential for severe or life-threatening outcomes.

Documented Overdose Manifestations

Element Regulatory Statement
Acute Presentations Acute overdose may present with nausea, vomiting, and Central Nervous System (CNS) effects such as dizziness and confusion (FDA/EMA).
Chronic/Severe Risks Bone marrow depression and megaloblastic anemia are documented manifestations of chronic overexposure due to folate antagonism, along with severe blood dyscrasias (e.g., leukopenia).
Physiological Systems The drug affects the Hematologic system, Renal system (crystalluria and renal toxicity), and can cause dangerous hyperkalemia (elevated potassium levels) (FDA/EMA).

Official Emergency Actions and Management

Regulatory texts explicitly state that no specific antidote is known for Co-trimoxazole overdose; therefore, management is defined as symptomatic and supportive treatment. Interventions such as gastric lavage and the administration of activated charcoal are officially described procedures to reduce drug absorption.

Hospital monitoring is required after an overdose to observe blood counts, serum electrolytes, and renal function. For chronic overdose effects, the administration of leucovorin (folinic acid) is officially advised to counteract severe toxicity on the bone marrow.

Population-Specific Overdose Notes

Official labeling notes that elderly patients are at an increased risk of severe toxicity and mortality in overdose situations. Individuals with pre-existing severe renal insufficiency are also at a heightened risk of drug accumulation and subsequent adverse effects due to impaired clearance.

Therapeutic Uses of Infectrin

What Infectrin Treats: Main Uses and Benefits

Infectrin (Co-trimoxazole) is a systemic anti-infective agent generally used to address symptoms related to physical discomfort and functional disruption caused by susceptible bacterial and specific protozoal pathogens. The combination is considered relevant for infections of the lungs, kidneys, and urinary tract, among others. It generally contributes to easing the overall symptom load associated with acute infections.

This medication is applied across domains where additional symptomatic support is needed, primarily focusing on acute symptomatic episodes. It is commonly used to help manage: Urinary Tract Infections (UTIs), severe Pneumocystis Pneumonia (PJP) in vulnerable patients, acute exacerbations of chronic bronchitis, and specific gastrointestinal infections like Shigellosis. It assists with maintaining functional stability by relieving symptoms that interfere with daily functioning, such as painful urination (dysuria) and severe shortness of breath in lung infections. It is applied in clinical settings that involve acute or unstable symptom patterns, supporting patients during difficult episodes by easing distress.

Quick Fact Relief for Symptom
Domain Focus Acute Bacterial & Opportunistic Infections
Primary Benefit Support for easing the overall symptom burden

Regulatory References

  1. NIH's MedlinePlus Drug Information

Eligibility and Restrictions for Use

Official Regulatory Eligibility for Infectrin (Co-trimoxazole)

Official prescribing information establishes strict constraints on patient eligibility based on age, organ function, and specific medical history.

Eligibility Status Population / Condition
Allowed Adults and pediatric patients two months of age and older (standard use profile).
Contraindicated Infants less than two months of age; patients with known hypersensitivity to trimethoprim or sulfonamides; patients with marked hepatic damage; patients with severe renal insufficiency (CrCl < 15 mL/min); and patients with documented megaloblastic anemia due to folate deficiency.
Restricted Use Patients with renal impairment (CrCl 15 to 30 mL/min) are eligible only under a mandated dose reduction. Caution is required for patients with G6PD deficiency or folate deficiency states.

The medicine is contraindicated at term for pregnant patients and is not recommended in the first trimester. Breastfeeding is generally avoided, particularly if the infant is premature or jaundiced, due to the regulatory risk of kernicterus. For older adults, use is permitted but often requires close monitoring due to an increased likelihood of age-related organ impairment.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Infectrin (Co-trimoxazole) is subject to several officially documented interactions that are based on specific pharmacokinetic and pharmacodynamic effects, as outlined in regulatory prescribing information. The co-administration of certain substances is formally restricted or contraindicated due to the risk of altering drug exposure or causing additive toxicity.


Formal Regulatory Prohibitions

Substance Official Restriction Interaction Outcome
Dofetilide Contraindicated Increases plasma concentration, posing risk of Torsades de Pointes (ventricular arrhythmia).
Clozapine Contraindicated Documented increased risk of neutropenia.

Documented Pharmacokinetic and Pharmacodynamic Interactions

The components of Infectrin affect the metabolism and renal transport of several other medicines. Co-administration potentiates the anticoagulant activity of Warfarin via metabolic inhibition and may prolong the half-life of Phenytoin, leading to increased exposure. The use of Trimethoprim interferes with the assay for serum creatinine and decreases its renal tubular secretion.

Pharmacodynamic reinforcement is observed with ACE Inhibitors, ARBs, or Potassium-sparing Diuretics, which carry an officially documented risk of hyperkalaemia. Additionally, the combination with Digoxin has been shown to increase plasma digoxin levels, particularly in elderly patients. The regulatory profile notes that the co-use of Ethanol (Alcohol) may result in documented unpleasant side effects.

Mechanism of Action

The Sequential Blockade of Bacterial Folic Acid Synthesis

The drug's primary action is the sequential blockade of the bacterial folate synthesis pathway in susceptible organisms. The two active agents target two separate steps: Sulphamethoxazole competitively inhibits the enzyme dihydropteroate synthase (DHPS), and Trimethoprim inhibits dihydrofolate reductase (DHFR). This folate pathway generates cofactors required for microbial growth.


Synergistic Disruption of DNA and RNA Production

The combined, dual-step inhibition achieves a synergistic effect. By preventing the formation of active tetrahydrofolate (THF), the entire downstream process of creating purines and pyrimidines (the building blocks of DNA and RNA) is halted. This metabolic failure stops DNA replication, leading to the direct killing of the microbe (a bactericidal physiological effect).


Mechanistic Limitations and Microbial Resistance

The effectiveness of this DHPS/DHFR dual block is constrained when bacteria adapt by developing genetic mutations in the target enzymes, which lowers the drug's binding affinity. Additionally, the mechanism is bypassed entirely if the pathogen can acquire pre-formed folates or related precursors from the host environment, limiting the drug's capacity to halt folate-dependent biosynthesis.

Dosage and Administration Information

How Infectrin is Used (Co-trimoxazole)

Infectrin is administered as a fixed-dose combination of Sulphamethoxazole and Trimethoprim following structured regimens. The method of administration, dosage, and duration are based on the specific condition being addressed.

Routes of Administration and Dosage Forms

The medicine is available for two primary routes: oral and intravenous (IV) infusion. For oral consumption, Infectrin is available as a Regular-Strength tablet (80 mg Trimethoprim/400 mg Sulphamethoxazole) and a Double-Strength (DS) tablet (160 mg Trimethoprim/800 mg Sulphamethoxazole), in addition to an oral suspension. The IV solution is used in hospital settings for systemic therapy and requires specialized dilution before use.

Standard Dosing, Frequency, and Duration

The standard adult regimen for general acute infections is one Double-Strength tablet every 12 hours. Treatment duration for acute infections often continues for 10 to 14 days, but may be as short as five days for certain gastrointestinal infections. Treatment for complex infections like Pneumocystis pneumonia (PJP) involves higher doses of 15 - 20 mg/kg/day of the Trimethoprim component, divided into three to four doses per day for up to three weeks.

Usage Principles and Adjustments

Oral preparations should be taken with a full glass of water to ensure adequate fluid intake is maintained. For patients with reduced kidney function, dosage must be adjusted based on creatinine clearance (CrCl). For example, patients with a CrCl between 15 and 30 mL/min typically receive half the usual dose. The medicine is not recommended for use in infants younger than two months of age.

Recent Clinical Evidence

Infectrin: Recent Clinical Evidence

The following overview describes the types of research and the study patterns reported for Infectrin (Co-trimoxazole), focusing on official scientific literature. This information summarizes what has been studied and what is known about the evidence landscape, but it does not provide clinical guidance or recommendations.


Research Evidence for Urinary Tract Infections (UTIs)

Research examined the compound in contexts related to both uncomplicated and complicated Urinary Tract Infections (UTIs). The research landscape for this indication utilizes Randomized Controlled Trials (RCTs) and Systematic Reviews. These studies focused on adult patient cohorts, primarily measuring the resolution of acute symptoms (like painful urination) and the microbiological eradication (clearing) of bacteria.

Research so far describes patterns of measured symptom changes and bacterial clearance that were observed over the typically short-term treatment course. What remains uncertain is that the continued evolution of bacterial resistance in common urinary pathogens, such as E. coli, means that the results apply only to the populations studied in the historical trials.


Research Evidence for Pneumocystis Jirovecii Pneumonia (PJP)

Studies were evaluated in immunocompromised individuals, most notably those with HIV/AIDS, for both acute treatment and its role in prophylaxis. The research monitored outcomes reflecting physiological strain, such as death rates observed and the need for mechanical ventilation.

Comparative trials described measurements related to death rates observed and the frequency of PJP occurrence. What remains uncertain is that much of the established evidence for prophylaxis was observed in some studies with limited comparative evidence against newer agents, and evidence quality varies across some older studies.


Research Evidence for Acute Bronchitis and Other Infections

Research examined the compound in contexts related to the treatment of acute flare-ups of chronic bronchitis (ABECB) in adults and specific gastrointestinal infections. Study data described patterns of measured patient changes across definitions of symptom clearance. For ABECB, findings were mixed regarding the statistical magnitude of symptom clearance measurements in some trials. Limited evidence details the drug's use in pregnancy-related populations, and comparative evidence is lacking for many specific comorbidity groups.

Key Studies & References

  1. Pneumocystis Pneumonia: Adult and Adolescent OIs | NIH - Clinical Info .HIV.gov (Guidelines on PJP Prophylaxis and Treatment)
  2. Short-course versus conventional length antimicrobial therapy for uncomplicated lower urinary tract infections in children: a meta-analysis of 1279 patients
  3. Chronic obstructive pulmonary disease (acute exacerbation): antimicrobial prescribing | NICE Guidance (Evidence Summary)

Frequently Asked Questions (FAQ)

Common questions about Infectrin (FAQ)


Q: Is a metallic taste in my mouth a common side effect of Infectrin?

Official product information notes that certain gastrointestinal issues are documented side effects. These reactions, such as Glossitis (inflammation of the tongue) and Stomatitis (inflammation of the mouth), may be associated with changes in taste, but are reported as infrequent or very rare.

Q: Does Infectrin make you tired or dizzy?

Regulatory documents list common side effects that affect the nervous system, including Headache. Other reactions such as Dizziness, Vertigo (a sensation of spinning), and general Weakness or fatigue are also documented, but are generally reported as infrequent.

Q: Is it normal to have mild nausea when starting Infectrin?

Yes, regulatory documents classify Nausea as a Common side effect associated with the use of Infectrin. If any side effect, including nausea, becomes persistent or severe, individuals are generally advised to contact a healthcare professional.

Q: Does taking Infectrin affect your gut flora (probiotics)?

As with many antibacterials, Infectrin can impact the balance of microorganisms in your body. Concerns about maintaining gut balance are a common topic, and the label documents the risk of Fungal overgrowth and a severe bowel condition called Pseudomembranous colitis which can result from flora disruption.

Q: Is Infectrin used for traveler's diarrhea?

Yes, Infectrin is indicated in official prescribing information for the treatment of Traveler's Diarrhea. Specifically, it is used when the infection is caused by susceptible strains of enterotoxigenic Escherichia coli.

Q: Can Infectrin cause changes in mood or anxiety?

Regulatory safety documents include information on psychiatric disorders that have been reported with the use of Infectrin. Depression and Hallucinations are listed as very rare or infrequent adverse reactions.

Q: Is it possible for Infectrin to cause yeast infections?

Official information lists Fungal overgrowth (sometimes referred to as Monilial overgrowth or Candidiasis) as a common side effect of the medicine. This is often linked to the way antibacterials can disrupt the balance of the body's natural microorganisms.

Q: Does Infectrin make you feel 'foggy' or have trouble concentrating?

Adverse reactions related to the nervous system, such as Confusion, Apathy, and reports of Trouble Concentrating, are documented in regulatory sources. These effects are classified as very rare or infrequent.

Q: Is Infectrin effective against staph infections?

Official microbiological data indicates that certain species of Staphylococcus, including some strains of Community-Acquired Methicillin-Resistant Staphylococcus aureus, are susceptible to Infectrin. Whether it is appropriate for a specific Staph infection must be determined by a healthcare provider.

Q: How is Infectrin eliminated from the body?

The active ingredients are eliminated primarily through the urine. Regulatory pharmacokinetic information states that one component, Trimethoprim, is mostly excreted unchanged, while the other component, Sulfamethoxazole, is first metabolized by the liver before being eliminated.

Q: What are the signs of a non-serious versus a serious allergic reaction to Infectrin?

Official documents describe a range of skin reactions. Less severe reactions include common side effects like Rash and Urticaria (hives). More serious, though very rare, reactions can include the potentially life-threatening conditions like Stevens-Johnson syndrome (SJS). Any sign of a severe skin reaction requires immediate medical attention.

Q: Does Infectrin work against viral infections?

No. The official indications state that Infectrin is an antibacterial and is intended to treat infections caused by susceptible bacteria (and some protozoa). It is not indicated for the treatment of viral infections.

Q: What's the typical duration before an Infectrin side effect appears?

The timing of side effects can vary widely. For example, regulatory warnings note that the highest risk for developing serious skin reactions, like SJS, is generally within the initial weeks of treatment.

Q: Can Infectrin cause sensitivity to the sun?

Yes, official safety information documents that a Photosensitivity reaction is a possible skin side effect of Infectrin. Because photosensitivity is documented, individuals should discuss sun exposure precautions with their prescribing healthcare provider.

Q: Can Infectrin be crushed or chewed if someone has trouble swallowing pills?

The tablets often feature a scoreline which is intended to facilitate breaking the tablet only for ease of swallowing of the pill form, not for dividing it into precise, equal doses. An oral suspension formulation is available for those who cannot swallow tablets.

Q: Why are people often told to drink a lot of water with Infectrin?

Official safety warnings emphasize that adequate fluid intake must be maintained during therapy. This is specifically to help prevent a condition called crystalluria (the formation of tiny crystals in the urine), which is a documented safety concern.

How should Infectrin be stored and disposed of?

Storage and Disposal of Infectrin (Co-trimoxazole)

Infectrin must be stored at Controlled Room Temperature, typically 20 C to 25 C (68 F to 77 F), protected from moisture and excessive heat. It is mandatory to keep the medicine out of the sight and reach of children.

Storage Restriction Requirement
Freezing Do not freeze any formulation.
IV Solution Do not refrigerate the concentrated injection solution.
Oral Suspension Protect from light and discard after a defined period (e.g., 14 days) once opened.

All forms must be kept in the original container and tightly closed. Unused or expired medication must be discarded according to local regulations, ideally through a medicine take-back program. Do not flush the product down the toilet or pour it down a drain.

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

Available in countries:

Equivalent of Infectrin found in:

A-Z Index: