Macrodantin is nitrofurantoin, in 50 mg and 100 mg capsules. It treats bladder infections — and essentially only bladder infections. That narrowness is why it is first-line: it concentrates in urine, works where it is needed, and leaves the rest of the body’s bacteria alone.
What is Macrodantin?
The South African Medicine Price Registry lists Macrodantin as Schedule 4 capsules containing nitrofurantoin macrocrystals, at 50 mg and 100 mg.
Nitrofurantoin works differently from most antibiotics. It is converted inside bacterial cells into reactive compounds that damage several targets at once — bacterial DNA, ribosomes and metabolic enzymes. Attacking multiple targets simultaneously makes resistance much harder to develop, which is why nitrofurantoin has stayed effective for over sixty years while resistance to other urinary antibiotics has climbed steadily.
The second unusual feature is where it goes. Nitrofurantoin is absorbed and then excreted rapidly into the urine, reaching high concentrations in the bladder while blood levels stay low.
That single fact explains everything about how it is used:
It works excellently for bladder infections, where the antibiotic sits at high concentration exactly where the bacteria are.
It does not work for kidney infections, or for any infection outside the urinary tract, because tissue levels never get high enough. A urinary infection with fever, back pain or feeling systemically unwell needs a different antibiotic.
“Macrocrystals” means larger crystals that dissolve more slowly, which reduces nausea — a common problem with earlier formulations.
What is Macrodantin commonly used for?
- Uncomplicated urinary tract infections — cystitis. This is its main use and, in most guidelines, the first-line choice.
- Recurrent urinary tract infections, as a low nightly dose taken long-term to prevent recurrence.
- Preventing infection around urinary procedures.
- Asymptomatic bacteriuria in pregnancy, where treatment is recommended — though not in the final weeks (see below).
What it does not treat:
- Kidney infection (pyelonephritis). Fever, chills, back or flank pain, nausea, or feeling generally unwell mean the infection has gone above the bladder, and nitrofurantoin will not reach it. This needs different treatment and prompt medical review.
- Prostatitis, for the same reason.
- Any infection outside the urinary tract — chest, skin, throat, gut. None.
Its narrowness is the point. A broad antibiotic used for a bladder infection kills a large amount of your normal bacteria and pushes resistance across the board. Nitrofurantoin does the job in the bladder and barely touches anything else — which is why keeping ciprofloxacin and co-amoxiclav in reserve, and using this first, is good practice rather than second best.
How Macrodantin fits into this medicine category
| Group | Examples | Role in urinary infection |
|---|---|---|
| Nitrofurans | Nitrofurantoin (Macrodantin) | First-line for uncomplicated cystitis |
| Fosfomycin | Fosfomycin | Single-dose alternative for cystitis |
| Sulfonamides | Co-trimoxazole | Alternative, where local resistance allows |
| Aminopenicillins | Amoxicillin | Only where sensitivity is confirmed |
| Fluoroquinolones | Ciprofloxacin | Reserved — kidney infection, complicated cases |
| Cephalosporins | Cefuroxime, cefixime | Alternative in pregnancy and complicated infection |
See the antibiotics and antimicrobials hub, and note that metronidazole and azithromycin treat entirely different organisms.
What to check before using Macrodantin
Kidney function is the critical check. Nitrofurantoin depends on healthy kidneys to concentrate it in the urine. If kidney function is reduced, two things happen at once: not enough reaches the bladder to work, and more stays in the body to cause harm. It is therefore avoided when kidney function falls below a defined threshold, and this is the commonest reason it is not prescribed.
Tell your doctor or pharmacist if you:
- Have kidney disease or reduced kidney function, or are elderly — kidney function declines with age even without a diagnosis.
- Have G6PD deficiency, an inherited condition that is not rare in some South African communities. Nitrofurantoin can trigger destruction of red blood cells in G6PD deficiency.
- Have lung disease, or have had a previous reaction to nitrofurantoin.
- Have liver disease, diabetes, anaemia, or a nerve condition.
- Are pregnant. Nitrofurantoin is used in pregnancy — but is avoided at term, from about 38 weeks and during labour, because of the risk of haemolysis in the newborn.
- Are breastfeeding a baby under one month, or one with G6PD deficiency.
- Take antacids containing magnesium trisilicate, which reduce absorption, or probenecid.
Practical points:
- Take it with food or milk. This improves absorption and greatly reduces nausea.
- Complete the course, usually three to seven days for cystitis.
- Expect your urine to turn dark yellow or brown. This is harmless and expected.
- Drink plenty of fluid.
Possible cautions and when to ask a pharmacist or doctor
Common effects are nausea, loss of appetite, headache, and dark urine. Nausea is the usual complaint and is largely solved by taking it with food.
Nitrofurantoin has three uncommon but important adverse effects, all more likely with long-term use — which matters because it is used long-term for recurrent infections:
Lung reactions. Acute reactions cause fever, cough, chest pain and breathlessness within days to weeks; chronic reactions cause gradually worsening breathlessness and a dry cough over months. Report any new breathlessness or persistent cough — this is reversible when caught, and not when it is not.
Peripheral neuropathy. Numbness, tingling, burning or weakness in the hands or feet. More likely with kidney impairment, diabetes, anaemia or B vitamin deficiency, and it can be irreversible if the medicine is continued.
Liver injury, which can appear months into long-term use.
Get emergency help for:
- Breathlessness, chest pain, wheezing or fever during treatment.
- Swelling of the face, lips or tongue, or a widespread blistering rash.
- Yellowing of the skin or eyes, dark urine with pale stools.
- Unusual tiredness, pallor or shortness of breath — possible haemolysis, especially with G6PD deficiency.
- Severe, watery or bloody diarrhoea with fever.
Contact your doctor if:
- Symptoms are not improving within two to three days.
- You develop fever, chills, back or flank pain, nausea or vomiting — the infection may have reached the kidneys and this antibiotic will not treat it.
- You notice numbness or tingling in the hands or feet.
- You are on long-term preventive treatment and have not been reviewed recently.
- Infections keep recurring, which deserves investigation rather than repeated courses.
Related medicine guides
Frequently asked questions
What is Macrodantin 100 mg used for? Uncomplicated bladder infections (cystitis), and preventing recurrent urinary infections at a lower nightly dose. It contains nitrofurantoin.
What is Macrodantin 50 mg used for? The same conditions — 50 mg is often the strength used for long-term prevention rather than treating an active infection.
Will it treat a kidney infection? No. Nitrofurantoin concentrates in urine but not in tissue. Fever, back pain or feeling unwell means a different antibiotic is needed — see a doctor.
Why is my urine dark? Nitrofurantoin colours urine dark yellow or brown. This is harmless and expected.
Should I take it with food? Yes. Food improves absorption and considerably reduces nausea.
Can I take it in pregnancy? It is used in pregnancy, but avoided from about 38 weeks and during labour because of the risk to the newborn. Follow your clinician’s advice.
Is it safe long term? It is used long term for recurrent infections, but lung, nerve and liver effects become more likely — which is why periodic review matters. Report any new breathlessness, cough or tingling.
Why this rather than a stronger antibiotic? Because it works where it is needed and spares everything else, which keeps stronger antibiotics effective for the infections that genuinely need them.