Types of Antibiotics and Their Uses: Broad Spectrum, Narrow Spectrum and the Common Ones

A broad spectrum antibiotic would cover both of these major bacterial families, the Gram-positive and the Gram-negative. Amoxicillin with clavulanic acid, doxycycline and the fluoroquinolones like ciprofloxacin are examples in this group. They are useful when the doctor does not yet know which bacterium is causing the infection, or if multiple ones are in play at once.

The cost of that coverage is collateral damage. A broad-spectrum drug also removes bacteria in the gut and on the skin that help keep parts of the body in balance, which is why diarrhoea and thrush are common after a course. It also pushes resistance harder. The World Health Organization divides antibiotics into three groups, Access, Watch and Reserve, and recommends that a country should prescribe at least 60 percent of their antibiotics from the Access group. Both amoxicillin and doxycycline are Access medicines. Azithromycin and ciprofloxacin are Watch drugs: these are reserved for cases where the narrower option will not be effective.

A narrow spectrum antibiotic like phenoxymethylpenicillin (penicillin V) or flucloxacillin takes out one family while leaving the others unharmed. When the bacterium is known, narrow is better.

Penicillins are the oldest group and the most frequently prescribed group of antibiotics in Europe even now. Amoxicillin, penicillin V and flucloxacillin are best classified here. Cefuroxime is a close relative of the penicillins and it, too, is often used for infections when a penicillin has failed. Macrolides are among the standard alternatives for penicillin allergy, with azithromycin and clarithromycin being the most common. Doxycycline is one of a class of drugs called tetracyclines, which have an atypically broad-spectrum activity that includes the tick-borne and sexually transmitted infections. Ciprofloxacin belongs to a powerful group of broad-spectrum antibiotics called fluoroquinolones, but following rare cases of disabling side effects on tendons, nerves and joints the European Medicines Agency restricted their use in 2019. Nitrofurantoin is a specialised antibiotic that concentrates in the urine and is used only for bladder infections. Metronidazole targets the anaerobic bacteria, those that live without air, thus its involvement in dental and gut infections.

Amoxicillin is the workhorse. Its uses range from chest infections and pneumonia to middle ear infections in children, sinus infections that have gone on too long, dental abscesses and combination treatment for Helicobacter pylori. It is administered 3 times daily for a course of five to seven days. Please see our amoxicillin 500mg page for dosing info.

Azithromycin is a macrolide that has an extremely long half-life (68 hours), which is why a course is only 3 days of 500 mg once daily. Its primary uses are for chlamydia (a single 1 g dose is usual), community-acquired pneumonia caused by atypical bacteria such as Mycoplasma, and chest or ear infections in patients who cannot take penicillin. See the azithromycin 500mg page for the course lengths.

Doxycycline is the tetracycline of choice for Europe. Indications include early Lyme disease following a tick bite, chlamydia at 100 mg twice daily for seven days, acne, malaria prophylaxis in travellers, and some chest infections. It is not used in children under eight or during pregnancy, because it stains developing teeth, and it makes the skin burn faster in the sun. See the full list on our doxycycline 100mg page.

For uncomplicated cystitis in a woman, the first-line treatment across much of Europe is a five-day course of nitrofurantoin with a single dose fosfomycin as an alternative. Amoxicillin is not a first choice because too many strains of E. coli are now resistant to it. But in men, pregnant women and others with a fever or back pain treatment is longer and uses another medicine as the infection may have reached the kidneys.

The majority of sinus infections are viral and resolve on their own within ten days. Antibiotics are only recommended if your symptoms are severe or persistent beyond that time, in which case amoxicillin would be first line.

A dentist treats a tooth infection much more than a tablet because an abscess needs to be drained. Amoxicillin is the standard where an antibiotic is given, with metronidazole added for anaerobic species if the swelling is spreading.

Penicillin V and amoxicillin are in the same family and share the same allergy. Amoxicillin has better absorption from the gut, and it covers more Gram-negative bacteria. Penicillin V is narrower spectrum and is the drug of choice for confirmed streptococcal sore throat, exactly because it does less collateral damage.

Amoxicillin and azithromycin are two different classes of drugs that treat bacterial infections. Amoxicillin is the first-line treatment for most ear, chest and sinus infections. Azithromycin fills in when penicillin is not tolerated, where the infection is chlamydia or an atypical pneumonia, and where duration matters. Resistance to macrolides is increasing among the pneumonia bugs in many EU countries, so it is not the stronger drug, only a different one.

Doxycycline and amoxicillin overlap on chest infections but then diverge elsewhere. Doxycycline, the winner for Lyme disease in adults, chlamydia, acne and malaria prophylaxis. Amoxicillin wins for children under eight, for pregnancy and for streptococcal infections.