In Brief
| Diclofenac in acute pain | |
|---|---|
| Potassium salt 50 mg | NNT 2.1 (1.9–2.5), 7 studies, high certainty |
| Sodium salt 50 mg | NNT 6.6 (4.1–17), small number of studies |
| Authors on the sodium salt | «limited efficacy, should probably not be used in acute pain» |
| Direct comparison of salts | None — both compared with placebo |
| Germany and Italy | Over the counter up to 25 mg, prescription from 50 mg |
| France | No potassium salt; sodium only, prescription |
Someone walks into a pharmacy for diclofenac and gets diclofenac. That the box says «potassium» or «sodium» after the name looks like chemical bookkeeping.
In acute pain it is not bookkeeping. It is a threefold difference.
Where the Difference Comes From
The active molecule is identical. What differs is how quickly it reaches the blood.
The potassium salt dissolves faster and produces a higher, earlier peak concentration. The sodium salt is usually supplied in enteric-coated and modified-release forms, designed for sustained treatment rather than for rapid relief.
In chronic use that distinction largely fades. In acute pain, where the first hours decide everything, it becomes the whole story.
What the Numbers Showed
The 2015 Cochrane review: 18 studies, 3,714 participants.
| Form | NNT | Data |
|---|---|---|
| Diclofenac potassium 50 mg | 2.1 (1.9–2.5) | 7 studies, high certainty |
| Diclofenac sodium 50 mg | 6.6 (4.1–17) | small number of studies |
Look at the interval on the sodium salt: 4.1 to 17. That spread by itself says the data are sparse and unstable.
The authors put their conclusion about the sodium salt plainly, without hedging: it «has limited efficacy and should probably not be used in acute pain». For a Cochrane review that is unusually definite language.
What Follows in Practice
- For acute pain — dental, after injury, after surgery — the potassium salt or another fast form is the one that makes sense.
- For chronic pain, taken as a course, the distinction between salts loses much of its weight, and the choice turns on tolerability and dosing schedule.
- The salt is printed in small type next to the active substance. If a pharmacist offers «just diclofenac» for acute pain, it is worth asking which salt it is.
Where It Is Sold
- Germany. The rules treat salts as the substance itself, so one line covers both: over the counter up to 25 mg per dose unit, 25–75 mg a day, no longer than three days for fever or four for pain. Anything above that is prescription-only.
- Italy. The potassium salt is registered. Only 25 mg is over the counter (Itamifast, Muscadvance); all 50 mg forms (Voltfast and others) are prescription-only. The line falls at exactly the same 25 mg as in Germany.
- France. No potassium salt at all — the database holds only the sodium salt, and all of it is prescription-only. A fast diclofenac form simply cannot be bought in France.
Safety
Diclofenac is a non-selective NSAID with all the risks of its class. The essentials:
- Stomach. Risk of erosions and bleeding; with a history of peptic ulcer, only with gastroprotection and on a doctor's decision.
- Heart. Diclofenac carries a higher cardiovascular risk than some other NSAIDs; caution in coronary disease, heart failure and after stroke.
- Kidneys and blood pressure. It reduces renal blood flow and can raise blood pressure.
- Never two NSAIDs at once. The effect does not add up; the risk does.
- The day limits are not paperwork. German over-the-counter forms are designed for three to four days at most. Prolonged self-treatment is the main source of complications.
The Bottom Line
Diclofenac is a good example of how a detail on the box changes the result. In acute pain the potassium salt performs reliably and has plenty of data behind it. The sodium salt performed poorly in the same setting, and the review authors advise directly against using it there.
The practical conclusion is simple: in acute pain, read not only the word «diclofenac» but what stands next to it.
About buying
The drug is in the catalogue: Voltfast (diclofenac potassium) 50 mg. No price is shown — prescription medicines are ordered through the chat, and the administrator confirms availability and cost. The prescribing stays with a doctor: this guide explains what is known about the drug, it does not replace a consultation.
Key facts
- Diclofenac POTASSIUM 50 mg: NNT 2.1 (95% CI 1.9–2.5), seven studies, high certainty of evidence.
- Diclofenac SODIUM 50 mg: NNT 6.6 (95% CI 4.1–17), assessed in only a small number of studies.
- The review authors' conclusion about the sodium salt, verbatim: it «has limited efficacy and should probably not be used in acute pain».
- Both salts were compared with placebo, not with each other — the comparison is indirect, though the intervals do not overlap.
- Germany and Italy drew the same line: over the counter only up to 25 mg, everything from 50 mg by prescription.
- France has no potassium salt at all: only the sodium salt is registered, and only on prescription.
