If a bacterial infection is suspected, it is often impracticable to wait for test results before starting treatment. Selecting the 'best guess' antibiotic should be guided by the following principles:
- Use antibiotics responsibly, considering issues such as safety, resistance and cost.
- Check that an antibiotic is really needed - history and examination may yield clues as to whether a condition is bacterial or viral, but this is not always easy. Consider delayed antibiotics. Some viral conditions may need prophylaxis to prevent secondary bacterial overgrowth - eg, acute necrotising ulcerative gingivitis secondary to herpes simplex infection.
- Blind prescribing does not obviate the need to take samples for culture and sensitivity, before starting treatment, whenever appropriate. Depending on the clinical picture, this may include skin or wound swabs, high vaginal swabs, endocervical swabs, urine, faeces, sputum, blood, aspirate. In the hospital environment, consider cerebrospinal fluid. Where clinically appropriate, consider FBC, ESR, CRP, U&Es, LFTs, clotting, atypical serology, malaria film, serum for virology, CXR, and arterial blood gas analysis. Perform urinalysis.
- Blind antibiotic prescribing for pyrexia of unknown origin (PUO) in a relatively well and stable patient is rarely helpful.
- Calculating dosage is not an exact science but consider factors affecting absorption or bioavailability, such as age, weight, hepatic function, renal function, severity of infection and other medication:
- Underdosing may result in significant failure of treatment and bacterial resistance in serious infection.
- An excessive dose may result in toxicity, particularly for antibiotics with a narrow margin between the toxic and therapeutic dose (eg, an aminoglycoside).
- Consider drug plasma monitoring, although this is difficult in primary care and may be more appropriate in an intermediate care setting.
- Route of administration - most patients in primary care will cope with oral antibiotics, although some patients have difficulty swallowing tablets and may need liquid or dispersible preparations. Serious infections may require intravenous (IV) administration. Avoid intramuscular (IM) antibiotics in children, as these are likely to be painful.
- Duration depends on condition and severity. Chronic infections such as tuberculosis may require prolonged treatment.
- Follow local policy and national guidelines.
- Consider any other factors relating to the patient which are likely to be relevant - eg, ethnicity, history of allergy, whether immunocompromised, severity of condition, and whether taking other medication.
- If female:
- Check whether pregnant, breast-feeding or taking an oral contraceptive.
- In pregnancy avoid tetracyclines, aminoglycosides, quinolones, high-dose metronidazole.
- Short-term use of trimethoprim (there is a theoretical risk in the first trimester in patients with a poor diet, as it is a folate antagonist) or of nitrofurantoin (at term, there is a theoretical risk of neonatal haemolysis) is unlikely to cause problems.
- Prescribing antibiotics after a telephone consultation should be the exception rather than the rule.
- Choose simple generics first-line unless there is a very good case for using newer more expensive antibiotics.
- Avoid widespread use of topical antibiotics, especially those readily used in oral forms, as this may spread resistance.
- Clarithromycin is an acceptable alternative in patients who get gastrointestinal side-effects with erythromycin.
- If blind treatment fails and test results are not available, check with a microbiologist.
Choosing the right drug in the absence of sensitivity results is an inexact science at the best of times but should be guided by the following principles:
- A detailed history may reveal the source of infection.
- Ask about respiratory, gastrointestinal or genitourinary symptoms.
- Ask about recent travel or treatment or conditions which could compromise the immune system.
- Examination - check vital signs: temperature, pulse, blood pressure, respiratory rate and capillary return, to assess the severity of illness and signs of septicaemia.
- After 'best guessing' the source of infection, follow local guidelines.
- If there are none, use the guidance from the Health Protection Agency (HPA).
- Be ready to change treatment once drug sensitivities are known.
- Treatment of most infections should not exceed seven days.
- In a hospital or intermediate care setting, IV antibiotic therapy is usually reviewed after 48 hours and changed to oral preparations when possible.
- If in doubt, ask a microbiologist.
Management of infection guidance for primary care from the Health Protection Agency
Blind Treatment of Infection
|Tonsillitis||Most sore throats are viral, but if bacterial tonsillitis is suspected:
|Otitis media in childhood||Many are viral - 80% resolve without antibiotics. If clinically appropriate:
|Acute bronchitis/ lower respiratory tract infection||Marginal benefits in otherwise healthy adults. Patient leaflets can reduce antibiotic use.
|Acute exacerbation of chronic obstructive pulmonary disease||30% are viral, 30-50% bacterial, and the rest undetermined.
Use antibiotics if there is increased dyspnoea and increased purulence of sputum volume. In penicillin allergy use clarithromycin if doxycycline is contra-indicated.
First-line - amoxicillin 500 mg TDS or doxycycline 200 mg stat/100 mg OD for 5 days:
|Community-acquired pneumonia||Start antibiotics immediately.
|Meningitis||Admit to hospital immediately.
|Uncomplicated urinary tract infection (UTI) - ie no fever or flank pain||
|Skin/soft tissue infections||Impetigo:
NB: doses are for adults unless otherwise stated - for further details see the BNF.
The table is a brief summary. Guidance changes from time to time depending on prevailing antibiotic sensitivities. Check the HPA information for the most up-to-date guidance and details of the management of specific conditions.
Further reading & references
- Reducing Antibiotic Prescribing, Bandolier, 2000
- Sepsis following Pregnancy, Bacterial; Royal College of Obstetricians and Gynaecologists (April 2012)
- Cunha BA; Fever of unknown origin: focused diagnostic approach based on clinical clues from the history, physical examination, and laboratory tests. Infect Dis Clin North Am. 2007 Dec;21(4):1137-87, xi.
- British National Formulary; 64th Edition (Sep 2012) British Medical Association and Royal Pharmaceutical Society of Great Britain, London
- Management of Infection - Guidance for Primary Care, Health Protection Agency (various dates)
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Laurence Knott
Dr Colin Tidy
Dr Adrian Bonsall