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Blind Treatment of Bacterial Infection

This PatientPlus article is written for healthcare professionals so the language may be more technical than the condition leaflets. You may find the abbreviations list helpful.

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:1,2

  • 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 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, e.g. 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 cerebro-spinal fluid. Where clinically appropriate, consider FBC, ESR, C-reactive protein, urea and electrolytes, liver function tests, clotting, atypical serology, malaria film, serum for virology, chest X-ray, and arterial blood gas analysis. Stick test the urine.
  • 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.
    • Excessive dose may result in toxicity, particularly for antibiotics with a narrow margin between the toxic and therapeutic dose (e.g. 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, though some patients have difficulty swallowing tablets and may need liquid or dispersible preparations. Serious infections may require intravenous administration. Avoid intramuscular antibiotics in children as these are likely to be painful.
  • Duration depends on condition and severity. Chronic infections such as TB may require prolonged treatment. Upper respiratory infections usually require short courses. Follow local policy and national guidelines.3
  • Consider any other factors relating to the patient likely to be relevant, e.g. ethnicity, history of allergy, whether immunocompromised, severity of condition, and whether taking other medication.
  • If female:
  • 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 gastro-intestinal side-effects with erythromycin.
  • If blind treatment fails and test results are not available, check with a microbiologist.

Which anti-infective?3

Choosing the right drug in the absence of sensitivity results is an inexact science at the best of time but should be guided by the following principles:

  • History:
    • A detailed history may reveal the source of infection.
    • Ask about respiratory, gastro-intestinal or genito-urinary symptoms.
    • Ask about recent travel or treatment or conditions which could compromise the immune system.
  • Examination - check vital signs: temperature, pulse, BP, respiratory rate and capillary return, to assess the severity of illness and signs of septicaemia.
  • Treatment:
    • After 'best guessing' the source of infection, follow local guidelines.
    • If none exists, use the guidance from the Health Protection Agency (HPA).3
    • Be ready to change treatment once drug sensitivities are known.
    • Treatment of most infections should not exceed 7 days.
    • In a hospital or intermediate care setting, intravenous 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 Agency3

Blind treatment of infection

Infection

Treatment

Tonsillitis
  • Most sore throats viral, but if bacterial tonsillitis suspected:
    • Phenoxymethylpenicillin 500 mg QDS or 1g BD for 10 days
    • If allergic to penicillin, clarithromycin 250 mg-500 mg BD QDS for 10 days
Otitis media in childhood
  • Many viral, 80% resolve without antibiotics. If clinically appropriate:
    • Amoxicillin first-line - 40 mg/kg/day in 3 divided doses
      Maximum 1g TDS FOR 5 days
    • Co-amoxiclav second-line for resistant Haemophilus - 1-6 yrs 156 mg TDS; 6-12 yrs 312 mg TDS
    • If allergic to penicillin:
      • Erythromycin first-line - under 2 yrs 125 mg QDS; 2-8 yrs 250 mg QDS; other 250-500 mg QDS
      • Azithromycin second-line -15-25 kg: 200 mg OD; 26-35 kg: 300 mg OD
Rhinosinusitis
  • Reserve antibiotics for severe, or symptoms lasting more than 10 days. 69% resolve without antibiotics, and 84% resolve with antibiotics
  • First-line - amoxicillin 500 mg TDS 7 days or doxycycline or 200 mg stat/100 mg OD 7 days or clarithromycin 250 mg/500 mg BD or phenoxymethylpenicillin 250 mg QDS/500 mg BD
  • Second-line - co-amoxiclav 625 mg TDS or ciprofloxacin 250-500 mg BD plus metronidazole 400 mg TDS
Acute bronchitis/LRTIMarginal benefits in otherwise healthy adults. Patient leaflets can reduce antibiotic use.

  • Amoxicillin 500 mg TDS or or doxycycline 200 mg stat/100 mg OD for 5 days
  • If penicillin allergy and tetracycline contra-indicated, use erythromycin
Acute exacerbation COPD30% viral, 30-50% bacterial, rest undetermined.
Use antibiotics if increased dyspnoea and increased purulence of sputum volume. In penicillin allergy use clarithromycin if doxycycline contra-indicated.

  • First-line - amoxicillin 500 mg TDS or doxycycline 200 mg stat/100 mg OD for 5 days
  • If allergic to penicillin use clarithromycin 500 mg BD for 5 days
  • Second-line - co-amoxiclav 625 mg TDS
Community acquired pneumoniaStart antibiotics immediately.

  • First-line: amoxicillin 500 mg-1 g TDS or clarithromycin 500 mg BD for up to 10 days.
  • No response in 48 hours consider admission or add clarithromycin to amoxycillin to cover mycoplasma (rare over 65) or oxytetracycline 250-500 mg QDS or doxycycline 200 mg stat/100 mg OD for up to 10 days.
  • Severely ill, give parenteral benzylpenicillin prior to admission.
  • Consider risk factors for Staphylococcus aureus and Legionella spp.
Meningitis
  • Admit to hospital immediately.
  • Benzylpenicillin prior to admission, unless history of anaphylaxis, (NOT allergy). Ideally IV but IM if a vein cannot be found.
    • Adults and children 10 yr and over: 1200 mg
    • Children 1-9 yr: 600 mg
    • Children under 1 yr: 300 mg
Uncomplicated urinary tract infection (i.e. no fever or flank pain)
  • Amoxicillin resistance common; therefore ONLY use if culture confirms susceptibility.
  • In the elderly (>65 years), do not treat asymptomatic bacteriuria; it occurs in 25% of women and 10% of men and is not associated with increased morbidity.
  • In the presence of a catheter, antibiotics will not eradicate bacteriuria; only treat if systemically unwell or pyelonephritis likely.
  • Do MSU on all treatment failures - extended-spectrum B-lactamase enzyme-producing organisms increasing multiple resistance but still sensitive to nitrofurantoin.

Uncomplicated UTI (no fever or flank pain).
  • Use urine dipstick to exclude UTI -ve nitrite and leucocyte 95% negative predictive value
  • First-line - trimethoprim 200 mg BD PO or nitrofurantoin 50-100 mg QDS for 3 days in women, 7 days in men
  • Second-line - depends on susceptibility of organism isolated, e.g. nitrofurantoin, amoxicillin, cefalexin, co-amoxiclav, quinolone, pivmecillinam
  • Extended-spectrum beta-lactamase enzymes are increasing but often remain sensitive to nitrofurantoin or fosfomycin (on a named patient basis)

UTI in pregnancy:
  • Send MSU for culture. Short-term use of trimethoprim or nitrofurantoin in pregnancy is unlikely to cause problems to the fetus. Trimethoprim should, however, be avoided in folate deficiency or patients taking anti-folate drugs.
  • First-line - nitrofurantoin 50 mg–100 mg QDS or trimethoprim 200 mg BD for 7 days
  • Second-line - cefalexin 500 mg BD or amoxicillin 250 mg TDS for 7 days.

Children

  • Refer all children under 3 months to a paediatrician.
  • If three years or under use positive nitrite on stick testing to start antibiotics.
  • Do not refer to specialist if older than six months, unless imaging is abnormal.
  • Send MSU for culture and sensitivity - waiting is not detrimental if results available within 24 hours.
  • Trimethoprim or nitrofurantoin or cefalexin or co-amoxiclav or quinilone or pivmecillinam for 7 days (see BNF for details).
  • Upper UTI - use co-amoxiclav.

Acute pyelonephritis
  • Send MSU for culture. If no response within 24 hours admit.
  • Ciprofloxacin 500 mg BD for 7 days or co-amoxiclav 625 mg TDS for 14 days; if susceptible, trimethoprim 200 mg BD for 14 days.

Recurrent UTI in women for 3 years or more:
  • Postcoital prophylaxis is as effective as prophylaxis taken nightly.
  • For prophylaxis use nitrofurantoin 50 mg stat postcoital or trimethoprim 100 mg OD at night.
Skin/soft tissue InfectionsImpetigo
  • Topical/oral produce similar results - reserve topical for very localised lesions to obviate resistance
  • Reserve Muciprocin for MRSA
  • First-line oral medication - flucloxacillin 500 mg or clarithromycin 250-500 mg BD for 7 days
  • Topical - use fusidic acid TDS for 5 days

Eczema
  • Using antibiotics, or adding them to steroids, in eczema does not improve healing unless there are visible signs of infection.

Cellulitis
  • If patient afebrile and healthy other than cellulitis, flucloxacillin may be used as single drug treatment 500 mg QDS, or if penicillin allergic, clarithromycin 500 mg BD or clindamycin 450 mg QDS.
  • If febrile and ill, admit for IV treatment.
  • If water exposure, consult a microbiologist.
  • In facial cellulitis use co-amoxiclav 625 TDS 7-14 days.

Leg ulcers
  • Bacteria will always be present. Antibiotics do not improve healing. Culture swabs and antibiotics are only indicated if there is evidence of clinical infection such as inflammation/redness/cellulitis; increased pain; purulent exudate; rapid deterioration of ulcer or pyrexia.
  • Review antibiotics after culture results. Refer to specialist if severe infection.
  • Diabetic leg ulcers - co-amoxiclav 625 mg TDS for 7 days, review, refer to specialist in severe cases.

Animal bites
  • Surgical toilet most important
  • Assess tetanus and rabies risk
  • Antibiotics should be considered for:
    • Puncture wound
    • Bite involving hand, foot, face, joint, tendon, ligament
    • Iimmunocompromised, diabetics, elderly, asplenic
    • First-line is co-amoxiclav 375-625 mg TDS for 7 days
    • If penicillin-allergic use metronidazole 200 mg-400 mg TDS PLUS doxycycline 100 mg BD or oxytetracycline 150-500 mg QDS and review at 24&48 hrs

Human bites
  • Antibiotic prophylaxis is advised.
  • Assess HIV/hepatitis B&C risk.
  • Co-amoxiclav as for animal bites. If allergic to penicillin use metronidazole 200-400 mg TDS PLUS doxycycline 100 mg BD or clarithromycin 250-500 mg BD.
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 for the most up to date guidance and details of the management of specific conditions.3

Document references

  1. Wong SY, Lam MS; Pyrexia of unknown origin--approach to management.; Singapore Med J. 1995 Apr;36(2):204-8. [abstract]
  2. 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. [abstract]
  3. Management of Infection - Guidance for Primary Care; Management of Infection - Primary Care Guidance, Health Protection Agency (various dates); Guidelines for primary care (including diagnosis - quick reference guides)

Internet and further reading

Acknowledgements

EMIS is grateful to Dr Laurence Knott for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2010.
Document ID: 454
Document Version: 3
Document Reference: bgp328
Last Updated: 6 Feb 2010
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