Antibiotics: When You Need Them, and How Resistance Happens
Antibiotics kill bacteria. They have no effect at all on viruses, which cause the common cold, influenza, dengue, most sore throats, most coughs and most watery diarrhoea, so taking one for those illnesses gives you the side effects without any of the benefit. They are genuinely necessary and sometimes life-saving for bacterial infections such as pneumonia, typhoid, most kidney and many bladder infections, serious skin infections and sepsis, and in those situations they should be started promptly. Resistance happens because every course kills the susceptible bacteria and leaves the resistant ones behind to multiply — it is the bacteria that become resistant, not your body, and you can acquire a resistant organism from someone else without ever having taken an antibiotic yourself. Pakistan is one of the countries where this has already caused real harm: extensively drug-resistant typhoid, first identified here in 2016, no longer responds to most of the drugs that used to cure it, leaving very few options. The single most useful thing an individual can do is stop buying antibiotics without a prescription, which is both illegal and the main engine of the problem here. Take a prescribed course exactly as directed, do not shorten or extend it on your own judgement, do not save leftovers, and do not use someone else's. Modern guidance sets shorter courses than it used to, so the length written on your prescription is a deliberate decision rather than a habit. Get emergency help for a rash with swelling of the face or difficulty breathing after a dose, a severe blistering rash, severe watery diarrhoea during or after a course, or the signs of sepsis.
Health writers · Aslam Clinic
What antibiotics can and cannot treat
An antibiotic works by attacking something that have and human cells do not — a cell wall, a particular enzyme, their way of making protein. A has none of those things and reproduces inside your own cells, so there is nothing for the drug to attack. This is not a matter of the antibiotic being weak or the wrong one; it is a category error, like using a key on a wall.
| Illness | Usual cause | Does an antibiotic help? |
|---|---|---|
| Common cold, blocked nose, sneezing | No. Green mucus does not change this — it is a normal stage of a cold. | |
| Influenza | Virus | No, unless a bacterial chest infection develops on top of it. |
| Dengue | Virus | No. Fluids, paracetamol and monitoring are the treatment. |
| Most sore throats | Virus in most cases | Usually not. Streptococcal throat does need one, and here the threshold for testing or treating is deliberately lower because of rheumatic fever. |
| Cough and bronchitis lasting under three weeks | Virus in most cases | Usually not, even when the cough sounds dramatic. |
| Pneumonia | Often | Yes, and promptly. This is one of the diagnoses antibiotics exist for. |
| Typhoid | Bacterial | Yes, and the choice now depends entirely on local resistance patterns. |
| Most watery diarrhoea | Virus, or self-limiting | No. and fluids are the treatment. Antibiotics often make it worse. |
| Bloody diarrhoea with high fever | May be bacterial or amoebic | Sometimes, after assessment. Not something to self-treat. |
| Urine infection with burning and frequency | Bacterial | Usually yes, guided by symptoms and a . See our article on . |
| Boil or skin abscess | Bacterial | Drainage is the main treatment; an antibiotic is added in some cases. |
| Tuberculosis | Bacterial | Yes, but with a specific multi-drug regimen over months, never a short general course. |
How resistance actually happens
Bacteria multiply in minutes and make copying errors as they go. A few of those errors happen, by chance, to make the bacterium survive a particular drug. When an antibiotic is taken, it kills off the susceptible bacteria — including the harmless ones living in your gut, mouth and skin — and the few resistant ones are left with the space and food to multiply. That is the whole mechanism. Nothing about your immune system changes.
Two consequences follow that people usually get wrong. First, you do not become resistant; the bacteria do. Second, because bacteria are exchanged constantly between people, water and food, a resistant organism selected in one person can infect anyone. A child who has never taken an antibiotic can catch a resistant infection. Resistance is a shared problem in the most literal sense, and this is why an individual's decision to buy a course from a shop is not a private one.
The pressure comes from volume. Unnecessary courses for viral illness, courses bought without a diagnosis, doses too low to clear the organism, courses abandoned halfway and restarted, injections given for ordinary fevers, and heavy antibiotic use in poultry and livestock all add to the same total. A global analysis published in 2022 estimated that more than a million deaths a year are directly attributable to bacterial resistance, with South Asia among the worst-affected regions.
What this has already cost Pakistan
The clearest local example is typhoid. An extensively drug-resistant strain of the typhoid bacterium emerged in Sindh from 2016 and has since spread. It resists the older first-line drugs, the fluoroquinolones and the third-generation cephalosporins that had replaced them — leaving azithromycin and intravenous carbapenems as the main remaining options, one of which requires hospital admission. A disease that a general practitioner could treat with a cheap tablet a generation ago now sometimes needs a drip and a ward.
Pakistan also has one of the world's highest rates of over-the-counter antibiotic sale. Selling them without a prescription is prohibited under the country's drug laws, and it happens anyway, in every bazaar. The result is predictable: many people receive an antibiotic for an illness that never needed one, at a dose or duration nobody supervised, chosen without a diagnosis.
The classes, and what they are for
This is here so a prescription makes sense to you, not so that you can choose one. No doses appear below, and none should: the right drug, dose and duration depend on the infection, your kidney and liver function, your allergies, your other medicines, pregnancy, and what is resistant locally.
| Class | Typically used for | Common problems to know about |
|---|---|---|
| Penicillins — amoxicillin, co-amoxiclav | Chest, throat, dental and some urine infections | Diarrhoea, rash. True penicillin allergy is far rarer than the number of people labelled with it. |
| Cephalosporins — cefixime, ceftriaxone | Urine and chest infections, and formerly typhoid | Diarrhoea; overuse selects strongly for resistance, and typhoid resistance to these is now widespread here. |
| Macrolides — azithromycin, clarithromycin | Chest infections, throat where penicillin cannot be used, and resistant typhoid | Nausea, and effects on heart rhythm that matter for anyone with an or on certain other drugs. |
| Fluoroquinolones — ciprofloxacin, levofloxacin | Some urine, gut and chest infections | Tendon and nerve problems, and restricted in children and pregnancy. Not a first choice for simple infections. |
| Nitrofurantoin | Simple bladder infection | Nausea; not suitable when function is poor or at the very end of pregnancy. |
| Metronidazole | Dental and gut infections, amoebiasis, giardiasis | Metallic taste, nausea. Alcohol should be avoided during and shortly after the course. |
| Carbapenems — meropenem | Serious hospital infections and extensively resistant typhoid | Given by injection in hospital. A last-line option that must be protected. |
The truth about finishing the course
The instruction to always finish the course was taught for decades on the reasoning that stopping early leaves the hardier bacteria alive. For some infections — tuberculosis above all, and streptococcal throat where the aim is preventing rheumatic fever — that reasoning still holds absolutely. For many ordinary infections the evidence now points the other way: longer exposure to an antibiotic creates more selection pressure, not less, and modern guidelines have shortened many standard courses accordingly.
What that means for you is narrower than it sounds, and it is important not to over-read it. The length written on your prescription is a considered decision for your particular infection. Take exactly that. Do not stop early because you feel better on day two, and do not carry on for extra days because you are anxious. If you feel completely well before the course ends and wonder whether you still need it, ask the prescriber — that is a reasonable question with a real answer, and it is a different thing from deciding for yourself.
What you can do
- Do not buy an antibiotic without a prescription, and do not ask a chemist to recommend one. This is the single highest-impact thing on the list.
- Do not press your doctor for one. A good consultation that ends without a prescription is a good consultation. Ask instead what would need to change for you to need one.
- Take it as prescribed — right times, right number of days, and with or without food as directed.
- Do not keep leftovers, do not use an old course for a new illness, and do not share with family. Return unused medicine to a pharmacy.
- Tell the prescriber about allergies and every other medicine you take, including herbal ones.
- Ask what the plan is if you are not better. Knowing when to return is more useful than the tablet itself.
- Prevent infections in the first place: hand washing, safe water, food hygiene, and keeping vaccinations up to date for the whole family.
- Do not accept an injection for an ordinary fever without an explanation. Injectable antibiotics for viral illness are common here, and they add cost, resistance and risk without benefit.
Side effects and allergy
Every antibiotic has a cost. Diarrhoea is the commonest, because the drug kills useful gut bacteria along with the target; thrush in the mouth or vagina is common for the same reason. Nausea, rash and headache are frequent. Some interact with other medicines — warfarin and heart-rhythm drugs in particular. In a small number of people, a course clears the way for a severe gut infection that causes profuse watery diarrhoea, which is why that always deserves a call.
It is worth separating a side effect from an allergy, because being labelled penicillin-allergic on the strength of childhood diarrhoea narrows your options for life and pushes you towards broader, more resistance-driving alternatives. Nausea and loose stools are side effects. Hives, swelling of the face or throat, wheeze and collapse are allergy, and they matter enormously. If you have been told you are allergic, ask your doctor whether it can be properly assessed rather than assumed.
When to see a doctor
- Any of the emergency signs listed near the top of this article, immediately.
- A fever lasting more than three days, or one that settles and returns.
- Breathlessness, chest pain, or a cough bringing up blood.
- A cough lasting more than three weeks, which needs tuberculosis excluded in this country.
- Burning on passing urine with fever, back or flank pain, or vomiting — a possible kidney infection.
- A wound, boil or area of skin that is spreading, hot and increasingly painful, or red streaks tracking away from it.
- No improvement after two to three days on a prescribed antibiotic. That is information the prescriber needs.
- If you have already taken something bought without a prescription, say so honestly at the appointment. It changes what the tests will show and what will work. See also our articles on typhoid fever and sore throat.
Common questions
Still not sure what to do?
Reading about a symptom only goes so far. A doctor who can ask you questions and examine you will get further in ten minutes than any article can.
