Antimicrobials – antibiotics
- • Overview
- • Choice of antibiotic
- • Mechanism of action of antibiotics
- • Pharmacokinetics
- • Antibiotic prophylaxis
- • To be aware of the importance of the correct choice of antibiotic in different circumstances
- • To understand the issues around antibiotic prophylaxis in dentistry
An antibiotic is defined as a substance produced by, or derived from, a microorganism that destroys or inhibits the growth of other microorganisms. Antibiotics aim to be selectively toxic to the invading bacteria while having minimal effect on the host.
The discovery of antibiotics transformed the management and outcomes of bacterial infections and facilitated the ability to safely perform surgical procedures. This pivotal advance in therapeutics was quickly eroded by the emergence of antibiotic resistance, especially by staphylococci, and antimicrobial resistance to antibiotics threatens to become the major global health challenge of the century. Antibiotic prescribing stewardship is now of utmost importance to good clinical practice among prescribers of whom dental practitioners form a significant part.
Dentists are the second largest group of prescribers of antibiotics to patients after medical practitioners and antibiotics are by far the largest group of drugs prescribed by dentists who prescribe antibiotics on almost a daily basis. A proper understanding of the rationale underpinning the appropriate prescription of antibiotics in dental practice is therefore of paramount importance not only to provide optimal clinical care but also to protect society from the devastating consequences of increasing antimicrobial resistance to drugs.
Antibiotics may be appropriately prescribed to treat uncontrolled infection or may be used prophylactically to prevent infection. These uses of antibiotics will now be considered in turn followed by a discussion of both patient and microbial factors, which are important when prescribing antibiotics. Finally, there will be a consideration of the individual groups of available antibiotics.
Bacterial infections of the mouth may arise from dental infection causing apical abscess formation or from infection of the periodontium or gingivae including pericoronitis. Less commonly, bacterial mucosal infections or sinusitis may occur.
Antibiotics are indicated to treat infections where there is evidence of spreading infection such as cellulitis, lymph node involvement, local swelling or evidence of systemic involvement such as pyrexia, malaise or leucocytosis.
Specifically, there is no evidence to support the use of antibiotics in alveolar osteitis (dry socket) or pulpitis which do not meet the criteria for prescribing antibiotics.
Dental abscesses are usually infected with viridans Streptococci spp. or Gram negative organisms or both. These organisms are usually susceptible to penicillin antibiotics. Although best practice suggests antibiotics should be prescribed with knowledge of the sensitivities of the infecting organism, in primary-care dental practice, antibiotics are usually prescribed empirically and, for the above reasons, penicillins are usually appropriate and effective.
The use of broad spectrum antibiotics encourages the emergence of Clostridium difficile-associated disease, especially in vulnerable groups and those on proton pump inhibitors and so should be avoided. Similarly, broad spectrum drugs encourage the emergence of resistant forms of Staphylococci spp. which has negative public health implications and should be avoided as first line drugs.
Patients who have received an antibiotic within the last six weeks are at risk of harbouring resistant organisms, however, and so a different antibiotic should be prescribed on the second occasion.
Antibiotics are not appropriate for the management of localized periapical infection even in the presence of localized swelling. Treatment, in the first instance, should be by drainage of the abscess either by extraction or through the root canal. Fluctuant swellings should be incised to allow drainage although this should not be performed if there is evidence of cellulitis. Antibiotics should only be prescribed if there is evidence of spreading infection as outlined above.
Floor of mouth swelling, difficulty breathing or trismus suggests infection of tissue spaces and is an emergency requiring admission to hospital.
Patients given antibiotics should be reviewed after 24 to 48 hours to assess any improvement. A lack of clinical response may indicate microbial resistance and the need for alternative antibiotic medication.
Antibiotic therapy should continue until a clinical response indicates that the immune system is, once again, coping with the infection, usually five days. Antibiotic courses should not be prolonged since this encourages the development of antibiotic resistance.
Necrotizing ulcerative gingivitis and pericoronitis
Necrotizing ulcerative gingivitis is an anaerobic fuso-spirocaetal bacterial infection of the gingival margins which is usually localized and can be managed by local measures. More severe cases or those with evidence of spreading infection should also be given antibiotics.
Pericoronitis is also an anaerobic infection around an erupting tooth and can usually be managed by local measures. Again, evidence of spreading infection is an indication for antibiotics.
For both necrotizing ulcerative gingivitis and pericoronitis, which are anaerobic infections, metronidazole is the drug of first choice although amoxicillin is also effective.
Oral mucosal infections
Bacterial infections affecting the oral mucosa are rare and should be treated either with topical antiseptics or with antibiotics with appropriate knowledge of the infecting organism and its sensitivities.
Sinusitis is usually self-limiting and responds to steam inhalations. Persistent or purulent sinusitis should respond to a penicillin antibiotic such as amoxicillin.
Antibiotics may be used in specialist periodontal practice as an adjunct in periodontal therapy to control acute episodes of periodontitis. Therapy usually uses metronidazole or a tetracycline or amoxicillin.
Antibiotic prophylaxis may be used for surgical prophylaxis such as before colonic or prostatic surgery or it may be prescribed to prevent infective endocarditis after dental procedures.
Surgical prophylaxis is not required for oral surgical procedures and there is no evidence it confers any advantages.
Historically, antibiotic prophylaxis for infective endocarditis was recommended for patients at increased risk of developing endocarditis as a result of bacteraemias arising from dental procedures. In 2008, the National Institute for Health and Clinical Excellence (NICE) issued Clinical Guidance 64 (www.nice.org.uk/guidance/cg64). This stated that antibiotic prophylaxis was not recommended before dental procedures. This was concluded in light of a lack of evidence for the efficacy of antibiotics used prophylactically for prevention. Also there was evidence that everyday activities such as tooth brushing gave rise to bacteraemias without dental procedures. Furthermore, oral hygiene was felt to be importance in the prevention of endocarditis and that antibiotic prophylaxis regimes may act as a barrier to best oral hygiene regimes. Finally, the risks of antibiotic prophylaxis may outweigh the benefits.
Such a paradigm shift in thinking around accepted prophylactic regimes has caused a significant dichotomy of opinion especially between cardiologists and the dental profession and is perpetuated by opposite advice from Europe and the United States. NICE guidance remains extant, however, and advice within the current British National Formulary reflects this.
Notwithstanding the considerations above regarding the specific management of oral infections there are a number of overarching factors that influence the choice of antibiotic. Before choosing an antibiotic the clinician must consider two factors – the patient and the known or causative organism.
Several patient-orientated factors should be taken into account before prescribing antibiotics. The patient’s age, sex, weight and general state of health must be considered when choosing both the drug and its dose.
Documentation of infection:
Whenever possible, clinical suspicion of infection should be supported by laboratory diagnosis. Relevant samples, for example sputum, urine, pus, blood should be obtained before treatment is commenced.
Drug kinetics are influenced by age-dependent changes in the path of elimination.
Renal and hepatic function:
Many commonly used antimicrobials are eliminated by the kidney while a few undergo hepatic metabolism. Dose modification is likely to be necessary if renal function is moderately or severely impaired. Drug monitoring is mandatory for antimicrobials with concentration-related toxicity (see Table 5.1).
Table 5.1 Antimicrobials for which dose modification is required in mild, moderate or severe renal failure and in liver disease