Finish the antibiotic exactly as prescribed, even if you feel completely fine after two days. Feeling better means the treatment is working, not that the infection is over.
That’s the short answer. The longer one has a nuance worth understanding, because the way the length of a course is decided has changed in recent years.
Feeling better doesn’t mean the infection is cleared
Antibiotics start reducing the bacterial population from the first doses. The fever drops, the pain eases and you feel much better long before your body has eliminated the bacteria that remain.
That gap is precisely the problem. When you abandon the treatment at the moment you feel well, you are withdrawing the drug at the point where the surviving bacteria are the ones responding to it worst. They are the ones most likely to multiply again, and to do so with less sensitivity to the antibiotic you have just stopped.
The World Health Organization sums it up as one instruction for the general public: always follow your healthcare professional’s advice on using antibiotics, and never take them on your own initiative.
The nuance that has genuinely changed: duration
For decades, long courses were prescribed out of habit rather than evidence. That is being corrected. Spain’s national antimicrobial therapy guide, developed within the National Plan against Antibiotic Resistance (PRAN), exists precisely to bring prescribing into line with what the evidence supports, and for several common infections that means shorter courses than the classic ones.
The conclusion that matters to you is counterintuitive but simple:
- The correct duration is decided by whoever prescribes, based on the specific infection, not by a general “always ten days” rule.
- The existence of shorter courses does not authorise you to shorten yours. If you were prescribed five days, five days is the complete treatment; if you were prescribed seven, the treatment is seven.
- There are situations where shortening is not an option at all, such as serious infections, patients with compromised immunity, or infections associated with prostheses.
Put another way: the “shorter is better” debate happens in the consulting room, before the prescription is handed to you. Not in your kitchen on day three.
The most common mistakes
| What people do | Why it’s a problem |
|---|---|
| Stopping once they feel well | The bacteria least sensitive to the drug are the ones that survive |
| Keeping the leftover tablets | The pack is now incomplete and carries no guarantees for later use |
| Reusing it for a similar episode | There is no way to know whether this infection is bacterial, or whether that antibiotic is the right one |
| Giving it to a family member | The diagnosis, the drug and the dose are not transferable |
| Skipping doses and making them up later | You lose the sustained concentration the effect depends on |
| Asking for an antibiotic for a cold | It does nothing against viruses and exposes you to side effects with no benefit |
On that last point it’s worth being blunt: antibiotics treat bacterial infections. A cold, flu or most sore throats are viral in origin, and an antibiotic shortens nothing there. The WHO lists “only use antibiotics when prescribed by a certified health professional” among the actions the general public can take.
Why this isn’t only your business
Antibiotic resistance is not developed by the person: it is developed by the bacteria. And those bacteria circulate. According to the WHO, resistance lengthens hospital stays, raises the cost of care and increases mortality, and it threatens procedures we take for granted today, such as surgery, transplants and chemotherapy, all of which depend on being able to prevent and treat infection.
The WHO also notes that where antibiotics can be bought without a prescription, the emergence and spread of resistance gets worse. In Spain, dispensing antibiotics requires a medical prescription, and doing so without one is a punishable offence. That is not bureaucracy: it is the barrier that stops every common cold from ending in an antibiotic.
How to take them so they work
Three things that depend only on you:
Respect the intervals. If the course is every eight hours, it’s eight hours, not “three times a day when I remember”. The effect depends on maintaining a stable concentration of the drug.
Read the leaflet before the first dose. That’s where you’ll find whether it should be taken with food or on an empty stomach, and the specific interactions of that active substance. Some antibiotics have their absorption reduced by dairy, iron or antacids; your medicine’s technical data sheet spells it out.
Say what you already take. Contraceptives, anticoagulants, antacids, supplements and herbal remedies can all interact. Mention them when you collect the treatment, even if nobody asks.
If you miss a dose, the general rule is to take it as soon as you remember, unless the next one is already close: in that case skip the missed dose and carry on with the schedule. Never double up to compensate.
What to do with anything left over
Ideally nothing should be left over: pack sizes have gradually been adjusted to the real length of treatments, precisely to reduce the leftovers that end up stored in a drawer.
If you do have medication left, take it to the SIGRE point at any pharmacy, with its packaging and leaflet. Don’t keep it “just in case”, and don’t put it in the bin or down the toilet. An antibiotic stored at home is the most common route into self-medication during the next episode.
When to seek advice
Contact your doctor during treatment if any of these appear:
- No improvement at all after 48 to 72 hours, or symptoms getting worse
- The fever returns after having settled
- Skin rash, generalised itching, swelling of the lips, tongue or face, or difficulty breathing — seek urgent care, this may be an allergic reaction
- Severe, watery or bloody diarrhoea, particularly if it appears during or after the treatment
- Vomiting that stops you keeping the doses down
- Yellowing of the skin or eyes, very dark urine, or severe abdominal pain
- You are pregnant, breastfeeding, have kidney or liver disease or take several medicines: ask before starting
And if the course has finished and the symptoms are still there, go back to your doctor rather than restarting the pack on your own.
If anything about your specific antibiotic is unclear, the pharmacists at Farmàcia Arqué in Salou can talk it through with you, no appointment needed — see how to find us. Outside our regular hours, Salou’s duty pharmacy is still open.
This information is general guidance only. It does not replace a consultation with your doctor or pharmacist. Sources: WHO — Antibiotic resistance, WHO — Antimicrobial resistance, PRAN — National Health System antimicrobial therapy guide, National Plan against Antibiotic Resistance, AEMPS and the technical data sheets at CIMA.