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Inappropriate choice and overuse of antibiotics may result in microbiological resistance in a community.
Many of the new antibiotics are strongly marketed and frequently have an easier dosage schedule and a broad spectrum of cover. However, they are not always the most appropriate first-line choice in treating an infec- tion. Thus a general approach to the prescribing of antibiotics and an understanding of the role of the newer antibiotics are necessary.
It is often very difficult for the treating clinician to know when antibiotic use is appropriate for the treat- ment of upper respiratory tract infections (URTIs).
These infections account for approximately two-thirds of antibiotics prescribed, although only 10 - 20% of these infections are bacterial. Six main bacteria are responsible for 90% of respiratory bacterial infections.
These are Streptococcus pneumoniae,Haemophilus influenzae, Staphylococcus aureus, Mycoplasma pneumoni- ae, Chlamydia pneumoniaeand Chlamydia trachomatis.
Approximately one-third of URTIs have a mixed viral and bacterial infection. Antibiotics are not usually required initially to treat these infections, but may be needed at a later stage if secondary bacterial complica- tions arise.
As 80 - 90% of URTIs are viral, it is suggested that antibiotics should only be recommended when a sec- ondary bacterial infection is suspected or if the patient is considered to be a high risk (e.g. patients immuno- compromised due to age or co-morbidity). Under these circumstances a delay in treatment could pose a risk to the patient. When treating an immunocompro- mised patient, a broad-spectrum antibiotic should be selected as it is important that the medication is imme- diately effective.
Factors to be considered when choosing an antibiotic to treat an URTI
Ideally a specific narrow-spectrum antibiotic should be used in the empirical treatment of URTIs. Amoxycillin remains an adequate and appropriate first-line antibi- otic. However, if antibiotic resistance levels in a com- munity are high, broader-spectrum agents may be required to be effective against beta-lactamase-produc- ing bacteria. The following factors should be taken into account when choosing an initial antibiotic:
• knowledge of the usual causative organism and the
local pattern of resistance for the area in which the patient lives
• the previous use of antibiotics for prophylaxis of infections
• the patient’s environment (e.g. hospital or child care facility)
• recurrent use of antibiotics
• the immune state, comorbidities and age of the patient
• antibiotic allergy.
If a patient has had a previous beta-lactam allergy the degree of allergic reaction would determine the subsequent choice of antibiotic. If the allergic reac- tion was mild (e.g. skin rash) cephalosporins could be used as an alternative as cross-reaction only occurs in 7 - 8% of cases. If the patient had a previ- ous anaphylactic reaction or an immediate reaction, then all beta-lactam antibiotics should be avoided and an alternative second-line treatment such as a macrolide, trimethoprim-sulphamethoxazole or a tetracycline should be selected. If the nature of a previous reaction is not known, it is advisable to select an alternative second-line treatment.
The risk of antimicrobial resistance increases if a patient:
• has had multiple previous antibiotic courses
• has previously been hospitalised
• is less than 2 years old
• has had prophylactic antibiotic therapy
• has been in a childcare facility, e.g. a crèche.
A clinical response to an antibiotic is expected within 48 hours. If there is no response within this time, treatment should be reviewed. Antibiotic ‘failure’ may indicate that no bacterial pathogen is involved. It could also be due to antimicrobial resistance, the incorrect choice of antibiotic or patient non-compliance. In some instances additional physical measures may be required (e.g. drainage of secretions or relief of an obstruction).
Role of the newer antibiotics
The range of antibiotics available for the treatment of URTIs has increased substantially. However, none of these has replaced the role of the traditional antibiotics in the treatment of bacterial URTIs.
An approach to the prescribing of antibiotics for the treatment of
upper respiratory tract infections
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C M E J a n u a r y 2 0 0 3 V o l . 2 1 N o . 1 51 New second- and third-generation cephalosporins have
been developed. The macrolide group of antibiotics now includes erythromycin, roxithromycin (Rulide), clarithromycin (Klacid) and azithromycin (Zithromax), all of which are broad-spectrum antibiotics. The macrolides are not as effective as the beta-lactam antibiotics in treating classic respiratory bacteria and resistance to these drugs develops rapidly.
Fluoroquinolones that may be used in the treatment of URTIs include ciprofloxacin (Ciprobay, Adco-Ciptin, Cifran, Cifloc) and ofloxacin (Taravid), which have potent bactericidal Gram-negative activity.
Levofloxacin (Tavanic) has Gram-positive and anaero- bic activity and is indicated for treatment of sinusitis, exacerbation of chronic bronchitis and community- acquired pneumonia. Lomefloxacin (Maxaquin, Uniquin) may also be used for acute exacerbations of chronic bronchitis. Gatifloxacin (Tequin) and moxi- floxacin (Avelon) are effective in the treatment of acute sinusitis, acute exacerbations of chronic bronchitis and community-acquired pneumonia as they are active against Gram-positive, Gram-negative, anaerobic and atypical pathogens.
The newer antibiotics should be reserved as second- or third-line treatment options. Traditional antibiotics should still form the basis of treatment. They must be used judiciously in order to preserve their efficacy for when they are truly needed.
Medifile is initially published as a supplement to the SA Pharmaceutical Journal.It is adapted and reprinted in CMEwith the kind permission of MediKredit. For further information about Medifile, contact MediKredit, tel (011) 770-6000, fax (011) 770-6325.
