Bactrim
In brief
- Co-trimoxazole (Bactrim) is a prescription-only medicine (POM) in the UK.
- Bactrim (sulfamethoxazole + trimethoprim) is used to treat bacterial infections such as urinary tract infections, bronchitis, shigellosis and Pneumocystis jirovecii pneumonia; it works by combining two agents that inhibit sequential steps in bacterial folate synthesis (sulfamethoxazole inhibits dihydropteroate synthase and trimethoprim inhibits dihydrofolate reductase), producing a synergistic antibacterial effect.
- The usual adult dose for common infections is one double‑strength tablet (800 mg sulfamethoxazole/160 mg trimethoprim) every 12 hours; paediatric doses are weight‑based (for example 8 mg/kg TMP + 40 mg/kg SMX divided every 12 hours) and PCP treatment uses higher, weight‑based dosing (approximately 15–20 mg/kg TMP per day divided q6–8h); treatment duration varies by indication (UTI 3–14 days, PCP 14–21 days, etc.).
- Administration forms include oral tablets (400/80 mg and 800/160 mg DS), oral suspension (typically 200 mg SMX/40 mg TMP per 5 mL) and, in some settings, intravenous formulations for hospital use.
- Symptom relief is often noticed within 24–72 hours for common bacterial infections, although some conditions (for example PCP) may take several days to show improvement; seek medical advice if no improvement within 48–72 hours.
- The drug is usually dosed twice daily (roughly 12 hours of clinical activity per dose for standard DS tablets); total course length depends on the infection (commonly 3–14 days, up to 21 days for PCP).
- Avoid excessive alcohol while taking Bactrim; alcohol can worsen side effects such as nausea and may impair recovery — it is safest to limit or abstain from alcohol during treatment.
- The most common side effect is nausea (other frequent reactions include vomiting, diarrhoea, and rash; more serious effects such as hyperkalaemia or blood dyscrasias can occur and should be monitored).
- Would you like to try Bactrim without a prescription?
Legal status and availability in the UK
Bactrim (co-trimoxazole) is a prescription-only medicine (POM) in the UK.
In our online pharmacy, Bactrim is available without a prescription, with discreet delivery to the United Kingdom in 9–21 days.
Basic Bactrim information
- INN (international nonproprietary name): Sulfamethoxazole and Trimethoprim
- Brand names available in the United Kingdom: Bactrim; generic co-trimoxazole
- ATC code: J01EE01
- Forms and dosages: Tablets 400mg SMX/80mg TMP and 800mg SMX/160mg TMP (DS); Oral suspension 200mg SMX/40mg TMP per 5mL; IV injection 80mg TMP/400mg SMX per 5mL vial
- OTC / Rx classification: Prescription-only medicine (POM)
Bactrim is a prescription antibiotic (co-trimoxazole) used mainly for urinary and respiratory infections.
Common patient complaints include rash, gastrointestinal upset, the size of DS tablets and the unpleasant taste of the paediatric suspension.
Adherence can be challenged by twice‑daily dosing and by suspension taste for children, leading to missed doses or early discontinuation.
What Bactrim contains and how it works
INN and drug class
Sulfamethoxazole and Trimethoprim is the International Nonproprietary Name, often shortened to co‑trimoxazole in clinical guidance.
The ATC classification is J01EE01, which groups combinations of sulfonamides and trimethoprim for systemic antibacterial use.
Mechanism of action (simple summary)
Co‑trimoxazole combines a sulfonamide (sulfamethoxazole) with trimethoprim to block bacterial folate synthesis at two sequential steps.
This sequential blockade reduces bacterial DNA and protein production, giving broad‑spectrum activity against many urinary and respiratory pathogens.
Brand names and packaging
Brand names include Bactrim and Bactrim DS, with generic co‑trimoxazole supplied by manufacturers such as Sun Pharma, Teva and Sandoz.
Typical packaging includes tablets in blister packs or bottles and oral suspensions in 50–100 mL bottles; IV vials are used in hospitals in some markets.
| Item | Detail |
|---|---|
| INN | Sulfamethoxazole and Trimethoprim |
| ATC code | J01EE01 |
| Common strengths | 400mg/80mg; 800mg/160mg (DS); Suspension 200mg/40mg per 5mL |
| Formulations | Tablets, oral suspension, IV injection |
Licensed indications and common use cases
Most frequent community indications (UTI, bronchitis)
Primary care commonly prescribes co‑trimoxazole for uncomplicated urinary tract infection and for certain respiratory infections when appropriate.
Traveller’s diarrhoea and shigellosis are also community uses where the drug may be chosen based on clinical judgement and sensitivity patterns.
Specialist indications (PCP prophylaxis/treatment)
Co‑trimoxazole is the standard oral agent for Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment in immunocompromised patients under specialist care.
High‑dose regimens for PCP require specialist supervision and often intravenous preparations in hospital settings.
| Condition | Adult dose | Typical duration |
|---|---|---|
| Uncomplicated UTI | 1 DS tab (800/160 mg) every 12 hours | 3–14 days |
| Bronchitis / traveller’s diarrhoea | 1 DS tab every 12 hours | 5–14 days |
| Shigellosis | 1 DS tab every 12 hours | 5 days |
| PCP prophylaxis | 1 DS tab once daily or three times weekly | As long as risk persists |
| PCP treatment | 15–20 mg/kg TMP daily divided q6–8h | 14–21 days |
Specialist review is needed for severe sepsis, suspected resistant organisms or when high‑dose IV therapy is being considered.
Dosage forms, strengths and paediatric formulations
Tablets and DS (double‑strength) details
Tablets are available as 400mg sulfamethoxazole / 80mg trimethoprim and 800mg/160mg double‑strength (DS) formulations.
Packs are commonly supplied in blister packs or bottles suitable for community dispensing.
Oral suspension: measuring and reconstitution
Oral suspension strength is typically 200mg SMX / 40mg TMP per 5mL in 50–100 mL bottles.
Paediatric dosing is weight‑based and only the suspension should be used for young children; an accurate measuring spoon or oral syringe should be used.
IV formulation (where used)
IV injection strength is 80mg TMP / 400mg SMX per 5mL vial, reserved for hospital use and severe infections.
| Form | Common strength | Typical use |
|---|---|---|
| Tablet | 400/80 mg; 800/160 mg (DS) | Adults, adolescents able to swallow |
| Oral suspension | 200/40 mg per 5mL | Paediatric dosing by weight |
| IV injection | 80 mg TMP / 400 mg SMX per 5mL | Hospital treatment for severe infection |
Practical dosing, renal/hepatic adjustments and elderly use
Renal impairment dosing rules
Dose reduction is required in renal impairment and co‑trimoxazole should be avoided if creatinine clearance is less than 15 mL/min.
Trimethoprim and sulfamethoxazole are partly renally excreted and accumulation increases risk of toxicity, including hyperkalaemia.
Hepatic impairment and monitoring
Use with caution in hepatic impairment and monitor liver function tests on prolonged courses or if baseline abnormalities exist.
Where hepatic disease is significant, specialist review is advised before supply.
Older adults: risks and dose considerations
Older patients are more prone to adverse effects such as hyperkalaemia, hyponatraemia and renal toxicity, especially when renal function is reduced.
Practical checks: estimated creatinine clearance, review concomitant medicines that raise potassium, measure baseline renal function and electrolytes, and arrange follow‑up bloods for prolonged treatment.
- Creatinine clearance: Avoid if <15 mL/min.
- Moderate impairment: Reduce dose and monitor electrolytes.
- Monitoring: Baseline renal function and potassium; FBC for prolonged courses.
Contraindications, cautions and special populations
Absolute contraindications
- Known allergy to sulfonamides, trimethoprim or any excipient.
- Severe renal impairment (avoid if creatinine clearance <15 mL/min).
- Severe hepatic impairment.
- Megaloblastic anaemia due to folate deficiency.
- Infants under 2 months old.
- Pregnancy and breastfeeding (refer to prescriber).
Relative cautions (G6PD, haematology)
Use caution in patients with G6PD deficiency due to the risk of haemolysis, and in patients with known haematological disorders or porphyria.
Longer courses require blood count monitoring because of rare but serious haematological effects.
Children under 2 months and infants
Co‑trimoxazole is contraindicated in infants under two months and the suspension should be used cautiously in older infants with specialist advice.
Known drug allergy, pregnancy or breastfeeding status, the age of the child, and current medicines such as ACE inhibitors or methotrexate should be checked before use.
Common adverse effects, severe reactions and reporting
Mild‑to‑moderate side effects (patient‑facing)
Most patients experience mild effects such as nausea, vomiting, diarrhoea, rash and headache.
Hyperkalaemia is a recognised effect, particularly in the elderly or those with renal impairment, so monitoring is important for at‑risk patients.
Serious reactions needing immediate care (SJS/TEN)
Stop the drug and seek urgent medical attention for widespread blistering rash, mucosal involvement, unexplained fever or yellowing of the skin, as these may indicate Stevens‑Johnson syndrome or toxic epidermal necrolysis.
Prolonged therapy can rarely cause agranulocytosis or aplastic anaemia, so new onset sore throat, fever or unusual bruising should prompt immediate review and blood tests.
Reporting side effects
Suspected adverse reactions can be reported to the MHRA Yellow Card scheme.
- When to stop and seek help: severe rash or blisters, difficulty breathing, high fever, yellow eyes or unexplained bleeding.
- Blood concerns: unexplained sore throat, fever or bruising—get urgent blood tests.
Significant drug interactions and monitoring
High‑risk interactions (warfarin, methotrexate, ACEi/ARBs)
Co‑trimoxazole potentiates warfarin anticoagulation and patients may need INR monitoring when therapy starts or stops.
Concomitant methotrexate can increase haematological toxicity due to additive folate antagonism and requires specialist oversight.
ACE inhibitors, ARBs and potassium‑sparing diuretics increase the risk of hyperkalaemia when used with co‑trimoxazole.
Antimicrobials and resistance considerations
Antibiotic stewardship should guide prescribing: confirm the indication, use the shortest effective duration and consider local E. coli resistance rates when choosing therapy for UTI.
| Interacting drug class | Clinical risk | Recommended action |
|---|---|---|
| Warfarin | Increased INR, bleeding risk | Check INR, liaise with prescriber, arrange closer monitoring |
| Methotrexate | Increased haematological toxicity | Avoid co‑administration or arrange specialist monitoring |
| ACEi/ARBs/Potassium‑sparing diuretics | Additive hyperkalaemia | Check potassium; consider alternative or stop interacting drug |
Pregnancy, breastfeeding and contraception considerations
Pregnancy risks and trimester guidance
Co‑trimoxazole is generally contraindicated in pregnancy, particularly near term, because of neonatal jaundice risk and folate antagonism.
Avoid use in the first trimester where possible and discuss alternative antibiotics with the prescriber if pregnancy is confirmed or suspected.
Breastfeeding safety and alternatives
Sulfamethoxazole may displace bilirubin in the neonate and breastfeeding should be reviewed by a prescriber or specialist before supply.
Consider alternative agents if the infant is a neonate or has risk factors for hyperbilirubinaemia.
Contraception counselling while on therapy
Women of childbearing potential should be advised to use effective contraception while taking co‑trimoxazole and to have a pregnancy test where appropriate before starting treatment.
- Q: Can I take Bactrim if pregnant?
- A: It is generally avoided in pregnancy; consult your prescriber for safer alternatives.
- Q: Can I breastfeed on Bactrim?
- A: Specialist review is advised as the drug can affect newborn bilirubin; alternatives may be preferable.
Administration advice and patient counselling points
How and when to take (food, dosing)
Take tablets with a full glass of water; food may reduce gastrointestinal upset though absorption is not substantially affected.
Most regimens use twice‑daily dosing; doses should be evenly spaced for consistent blood levels.
Missed dose and completing the course
If a dose is missed, take it as soon as remembered unless the next dose is near, in which case skip the missed dose and do not double up.
Complete the prescribed course unless an adverse reaction develops or a prescriber instructs otherwise.
Managing common side effects at home
Mild nausea or diarrhoea can be managed with simple measures like taking with food and staying hydrated; stop and seek advice for severe rash or jaundice.
- Top counselling points: take with water; use supplied measuring device for suspension; do not double missed doses; finish the course; seek help for severe rash, breathlessness or jaundice.
Storage and disposal
Storage conditions for tablets and suspensions
Store tablets and bottles at room temperature, typically 20–25°C, and keep suspensions protected from light.
Do not freeze reconstituted suspensions and follow the product SmPC for exact storage guidance.
Reconstitution and stability of suspension
After reconstitution, stability commonly ranges between 7 and 14 days depending on formulation; check the product leaflet or SmPC for the exact shelf life.
Safe disposal of unused antibiotics
Unused or expired antibiotics should be returned to the pharmacy for safe disposal rather than thrown away in household waste.
Alternatives and when to switch
First‑line alternatives for common infections
For uncomplicated cystitis consider nitrofurantoin, trimethoprim alone or pivmecillinam where available, bearing in mind local resistance patterns.
More complicated infections may require broader agents such as ciprofloxacin under specialist guidance.
When resistance or side effects prompt a change
Switch therapy for confirmed resistance, intolerable adverse effects such as severe rash, pregnancy or problematic drug interactions like unstable warfarin control.
Comparative tolerability
Tolerability can differ between agents; weigh side‑effect profiles and resistance data when choosing an alternative.
- Decision prompts to switch: culture shows resistance; severe adverse reaction; pregnancy; problematic interactions.
Delivery across the United Kingdom
| City | Region | Delivery time |
|---|---|---|
| London | England | 9–21 days |
| Birmingham | England | 9–21 days |
| Manchester | England | 9–21 days |
| Glasgow | Scotland | 9–21 days |
| Leeds | England | 9–21 days |
| Edinburgh | Scotland | 9–21 days |
| Bristol | England | 9–21 days |
| Liverpool | England | 9–21 days |
| Belfast | Northern Ireland | 9–21 days |
| Cardiff | Wales | 9–21 days |
| Sheffield | England | 9–21 days |
| Newcastle Upon Tyne | England | 9–21 days |
| Nottingham | England | 9–21 days |
