Ideally painkiller should not be the treatment for ankle sprain.
Try to get a plaster done so that the ankle gets proper rest and ligament heals in proper position.
Next Steps
Consult online.
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To answer your question zerodol sp can be taken for 4-6 weeks or even a month or 2 , once or twice a day.
But again as I said, avoid painkiller and seek alternative treatment options.