Natrilix SR is indapamide 1.5 mg in a sustained-release tablet, taken once daily for high blood pressure. It is a thiazide-like diuretic, and the sustained-release form exists specifically to deliver the blood-pressure benefit with less of the salt disturbance that higher doses cause.
What is Natrilix Sr?
The South African Medicine Price Registry lists Natrilix SR as a Schedule 3 sustained-release tablet containing indapamide 1.5 mg.
“SR” means sustained release. The tablet releases indapamide gradually over the day rather than all at once. The tablet must be swallowed whole — crushing or chewing it releases the whole dose immediately and defeats the design.
Indapamide is a thiazide-like diuretic. It is not chemically a thiazide, but it acts at the same place in the kidney tubule, reducing sodium reabsorption so that more sodium and water leave in the urine.
But the diuretic effect is not how it mainly lowers blood pressure long term. Indapamide also relaxes the smooth muscle of blood vessel walls directly, and after the first weeks that vascular effect provides most of the benefit.
Two consequences follow, and both surprise people.
You may notice little or no extra urination, particularly after the first week or two. The tablet is still working. At 1.5 mg the diuretic effect is deliberately modest.
1.5 mg is a low dose on purpose. Older indapamide tablets were 2.5 mg. Research established that the lower sustained-release dose lowers blood pressure essentially as well while causing considerably less disturbance of potassium, sodium, uric acid and blood sugar. The 1.5 mg SR formulation is refined prescribing, not a token dose.
Indapamide is also in combination tablets — with amlodipine as Natrixam, and with perindopril in others. If you take a combination, check you are not also taking indapamide separately.
Compared with hydrochlorothiazide — see Ridaq — indapamide works longer, has somewhat less effect on blood sugar and cholesterol, and has good outcome evidence behind it, including in older people.
What is Natrilix Sr commonly used for?
- High blood pressure (hypertension) — its principal use, alone or with other blood pressure medicines.
- Reducing the risk of stroke, heart attack, heart failure and kidney damage, which is the actual purpose of treating blood pressure.
- High blood pressure in older people, where thiazide-like diuretics have strong evidence, including for stroke prevention.
- Fluid retention in some heart failure, though a loop diuretic is usually preferred.
- Preventing recurrent calcium kidney stones, since thiazide-type diuretics reduce calcium in the urine.
Two points about treating blood pressure:
It is preventive, not symptomatic. High blood pressure causes no symptoms until it causes a stroke, heart attack or kidney failure. Nobody feels better on treatment — which is precisely why people stop, and why stopping is so costly.
It is usually lifelong. Blood pressure rises again within weeks of stopping. A normal reading on treatment means the medicine is working, not that it is no longer needed.
Lifestyle change makes this specific tablet work better. Indapamide acts by removing sodium, so reducing dietary salt directly amplifies its effect. Losing excess weight, regular activity, moderating alcohol and stopping smoking all lower blood pressure genuinely, and can reduce how much medicine is needed.
How Natrilix Sr fits into this medicine category
| Group | Examples | How it works |
|---|---|---|
| Thiazide-like diuretics | Indapamide (Natrilix SR), chlorthalidone | Remove sodium; relax vessels; long-acting |
| Thiazide diuretics | Hydrochlorothiazide (Ridaq) | Similar; shorter acting |
| Loop diuretics | Furosemide | Stronger diuresis; for fluid overload |
| Potassium-sparing | Spironolactone, amiloride | Retain potassium; often combined |
| Calcium channel blockers | Amlodipine (Ciplavasc) | Relax arteries |
| ACE inhibitors | Perindopril, enalapril | Block a vessel-narrowing hormone |
| ARBs | Losartan, telmisartan | Similar, without the cough |
| Combinations | Natrixam (indapamide + amlodipine) | Two mechanisms, one tablet |
Diuretics combine particularly well with ACE inhibitors and ARBs — the diuretic tends to lower potassium and those tend to raise it, so together the effect is more balanced than either alone.
See the heart and blood pressure medicines hub.
What to check before using Natrilix Sr
Tell your doctor or pharmacist if you:
- Have gout, or have had it. Indapamide raises uric acid and can trigger an attack.
- Have kidney disease or liver disease, particularly cirrhosis.
- Have diabetes. Blood sugar can rise slightly, though less at 1.5 mg than at higher doses.
- Have low potassium or sodium, or a condition causing them.
- Have a heart rhythm problem or a long QT interval, or take medicines affecting heart rhythm.
- Take lithium. Indapamide raises lithium levels, and this needs careful monitoring.
- Take digoxin, other diuretics, ACE inhibitors or ARBs, steroids, or regular anti-inflammatories. NSAIDs reduce the blood-pressure benefit and, with a diuretic, can affect the kidneys.
- Have a sulfonamide allergy.
- Are pregnant, planning pregnancy or breastfeeding — diuretics are generally avoided.
- Are elderly, where low sodium, dehydration and falls are more likely.
Practical points:
- Take it once daily in the morning, so any diuretic effect falls during the day.
- Swallow the tablet whole. Do not crush or chew it.
- Keep your blood tests. Kidney function, sodium, potassium and sometimes uric acid and glucose are checked periodically — routine monitoring, not a sign of a problem.
- Get up slowly from sitting or lying, especially at first.
- Use sun protection. Indapamide increases sensitivity to sunlight.
- Take care in hot weather and during vomiting or diarrhoea illness, when dehydration develops quickly.
- Do not stop because your reading is normal.
Possible cautions and when to ask a pharmacist or doctor
Common effects: increased urination (often mild), dizziness on standing, muscle cramps, tiredness, sensitivity to sunlight and a rash.
Seek prompt medical advice for:
- Confusion, marked drowsiness, headache with nausea, or unusual unsteadiness — possible low sodium. This is the commonest serious effect in older people, develops gradually, and is easily mistaken for ageing or a virus.
- Muscle weakness, cramps, palpitations or an irregular heartbeat — possible low potassium.
- Fainting, or persistent dizziness on standing.
- A sudden painful, hot, swollen joint — often the big toe — which may be gout.
- Marked reduction in urine output.
- A rash, particularly in sun-exposed areas, or a widespread or blistering rash.
- Sudden loss of vision or eye pain, which is rare but needs same-day attention.
Get emergency help for chest pain, severe breathlessness, signs of a stroke, or swelling of the face, lips or tongue with difficulty breathing.
Contact your doctor if readings stay high, if you develop a vomiting or diarrhoea illness and cannot drink normally, if another prescriber starts you on a new medicine, or if side effects are making you consider stopping. There are many blood pressure medicines, and almost every side effect here has an alternative — stopping altogether is the one option with a real cost.
Related medicine guides
Frequently asked questions
What is Natrilix SR used for? Lowering high blood pressure. It contains indapamide 1.5 mg, a thiazide-like diuretic, in a sustained-release tablet.
What does SR mean? Sustained release — the tablet releases the medicine gradually over the day. It must be swallowed whole.
Is 1.5 mg a low dose? Deliberately so. It lowers blood pressure essentially as well as the older 2.5 mg tablet while causing considerably less disturbance of potassium, sodium, uric acid and blood sugar.
Why am I not urinating more? After the first week or two the diuretic effect settles, and the benefit comes mainly from relaxation of the blood vessels. The tablet is still working.
When should I take it? Once daily in the morning, so any diuretic effect falls during the day rather than at night.
Can I stop when my blood pressure is normal? No. A normal reading means the medicine is working. Blood pressure rises again within weeks of stopping.
Does it affect gout? It can. Indapamide raises uric acid and can trigger an attack. Tell your doctor if you have had gout.
How is it different from hydrochlorothiazide? Both act at the same place in the kidney. Indapamide works longer, affects blood sugar and cholesterol somewhat less, and has good outcome evidence including in older people.
Do I need blood tests? Yes, periodically — kidney function, sodium and potassium, and sometimes uric acid and glucose.