No, you should take the recommended dosage as described on the package, add it to the water and wait for 14 days before doing the first water change.
If you do a water change within those 14 days then you need to top off the medicine dosage again in relation to the volume of water you changed.
After 14 days you can do a big 80% water change to take the no longer needed medication out and alternatively filter over active carbon to filter out the remaining medication.
Depending on the type of infection this is the most effective term treatment with fluke solve for external parasites such as Trichodina which are a tad harder to kill than flukes and other worms. Flukes are also a type of flatworm, worms are usually killed within 24 hours. That's why with short term treatments a second dose a week later is recommended to kill the newborns from latently present eggs.
This was once advised to me personally by the developer of this medicine Dr Fiona Mcdonald.
If you are not sure what you are dealing with I advise you to contact
Specialists Fish Treatments & Medicines | Fish Treatment Ltd
They will ask you some more questions, such as tank volume, type of fish, symptoms, maybe some pictures and advise you accordingly.
That was a few years ago, so I do not know what and how today but back then she did send me the Fluke-Solve® Aquarium 10 gram sachet and charged no P&P. And as you can see I'm not from the UK but at the other side of the pond.