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Using antibacterial drugs

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VOL: 98, ISSUE: 49, PAGE NO: 50

Michele Butler, MmedSci, BSc, RGN, RNT, CertED (FE), senior lecturer in clinical science, School of Biological and Molecular Science, Oxford Brookes University

Molly Courtenay, PHD, MSc, Cert Ed, RNT, RGN, lecturer, Southampton University

Michele Butler, MmedSci, BSc, RGN, RNT, CertED (FE), senior lecturer in clinical science, School of Biological and Molecular Science, Oxford Brookes University

Antibacterial drugs can be classified in several ways - bacteriostatic or bacteriocidal, by chemical structure, according to their mode of action, or according to their spectrum of activity.

Mode of action There are five major mechanisms by which antibacterial drugs have their effect:

- Inhibition of synthesis and damage to the bacterial cell wall - penicillins, penicillinase-resistant penicillins, broad-spectrum penicillins and cephalosporins all disrupt formation of the peptidoglycan layer of the cell wall. The bacterial cell is then unable to maintain its osmotic gradient and begins to swell. Eventually the cell ruptures and dies;

- Inhibition of synthesis and damage to the bacterial cell membrane - polymyxins bind to membrane phospholipids and alter permeability to sodium and potassium ions. Holes are generated in the cell membrane and this disrupts the cell's osmotic gradient. The cell eventually ruptures;

- Modification of bacterial nucleic acid synthesis - quinolones inhibit replication of bacterial deoxyribonucleic acid (DNA). They block the activity of DNA gyrase, an enzyme essential for DNA replication and repair. Metronidazole acts via an intermediate which inhibits the synthesis of bacterial DNA and breaks down existing DNA. The precise action of nitrofurantoin is not established. It is thought that the drug is reduced to an unstable metabolite which causes DNA strand breakage and bacterial damage;

- Inhibition or modification of bacterial protein synthesis. Several groups of antibacterials prevent the production of essential bacterial cell proteins. Tetracyclines, aminoglycosides, macrolides, clindamycin and chloramphenicol all act by binding to one of the subunits of the bacterial ribosomes where proteins are actually manufactured and hence prevent protein synthesis. Fusidic acid prevents transfer ribonucleic acid (tRNA) binding to the ribosomes. Protein synthesis inhibitors tend to have bacteriostatic properties;

- Modification of bacterial energy metabolism - trimethoprim acts by inhibition of the folate pathway in bacteria. Bacteria have to synthesise their own folate derivatives, which are important in intracellular reactions. Trimethoprim interrupts the conversion of dihydrofolic acid to tetrahydrofolic acid, by inhibiting the enzyme dihydrofolate reductase.

Prescribing points Before prescribing an antibacterial the nurse prescriber must consider the following factors related to the client: is an antibiotic indicated, previous history of antibacterial therapy, previous history of allergy, present hepatic and renal function, and contraindications and side-effects. The dose of drug to be prescribed will depend on several factors, including age, weight and renal function.

Viral infections should not be treated with antibacterials. The nurse prescriber should not prescribe antibacterials as prophylaxis.

Specimens should be obtained from the affected site for culture and sensitivity so the causative organism can be identified. When the organism has been isolated, treatment may be changed to another drug, if deemed more appropriate.

The client should receive education about timing and spacing of medication, side-effects and the importance of completing the prescribed course. If allergic reactions occur, the drug should be discontinued and a physician notified immediately.

Examples of prescribing

Conjunctivitis is one of the most common causes of 'red eye'. Infective conjunctivitis may be due to bacterial or viral infection. In both cases, the eye appears red, with engorged conjunctival vessels.

Bacterial infection is most commonly due to infection by Staphylococcus species, followed by infection from Streptococcus pneumoniae and Haemophilus influenzae. The client has a purulent exudate in one eye and sticky lids on waking. The infection usually starts in one eye and is spread to the other via the hand. It may be spread from person to person.

Viral conjunctivitis is more common than bacterial conjunctivitis and usually due to highly infectious adenoviruses. This type of conjunctivitis often occurs in epidemics. Clients will complain of gritty eyes with a watery discharge. They may also have a sore throat and fever associated with upper respiratory tract infection.

Management involves preventing spread of infection to the other eye and to other individuals. In addition, topical antibiotics are usually prescribed empirically. They will hasten clinical improvement in bacterial conjunctivitis (Chung and Cohen, 2000) and provide symptomatic relief and prevent secondary bacterial infection for those with viral conjunctivitis (Khaw and Elkington, 1999).

Antibiotic preparations for the treatment of infective conjunctivitis are chloramphenicol eye drops and eye ointment and fusidic acid eye drops.

Chloramphenicol should be avoided in pregnancy and while breast-feeding, and in clients with porphyria. Fusidic acid should be avoided in clients with hypersensitivity. Topical chloramphenicol may cause transient stinging. Fusidic acid has been reported to cause hypersensitivity.

Topical chloramphenicol has a broad spectrum of activity and is the drug of choice for superficial infections. It is the only topical antibiotic possibly associated with serious systemic adverse effects (aplastic anaemia). However, Chung and Cohen (2000) report no good evidence about the magnitude of this risk for chloramphenicol versus other topical antibiotics.

Strict hygiene measures are of utmost importance in preventing spread of infection. Clients should be advised to use their own flannel, towel and pillow case. Where possible, they should administer their own treatment, washing their hands before and after touching the eye. Blurring of vision may follow application of the eye drops/ointment, together with possible burning or stinging sensation. Contact lenses should not be worn while treatment is undertaken, and eye make-up should be avoided. Lack of response to treatment requires medical assessment.

Uncomplicated lower urinary tract infection (UTI) An uncomplicated urinary tract infection is one where the individual has an anatomically and physiologically normal urinary tract, normal renal function and there is no associated disorder which impairs defence mechanisms (Davison et al, 1999).

In women, the urethra is short and in close proximity to the vagina and rectum. This offers little protection against the entry of microorganisms into the bladder from these areas. The main risk factors for uncomplicated UTIs are sexual intercourse, personal or family history of urinary tract infection, and use of the contraceptive diaphragm plus spermicide (Drugs and Therapeutics Bulletin, 1998). UTIs are also more common during pregnancy. Normal changes in the functioning of the urinary tract that occur during pregnancy predispose to these infections. In 70% of cases, Escherichia coli is the causative organism (Gruneberg, 1994), with the remaining 30% being caused by Proteus mirabilis, Klebsiella pneumoniae and Staphylococcus saprophyticus.

Symptoms of lower UTI include lower abdominal discomfort, dysuria and frequency and urgency of micturition. Cloudy or foul-smelling urine, haematuria and confusion (especially in the elderly) may also occur.

Diagnosis can be made based on the client's history and clinical signs and without the need for urine culture. Dipstick urine tests are good indicators of the presence of UTI. The leucocyte esterase test detects pus cells in urine, while bacteria in the urine that reduce nitrate to nitrite can be detected by the nitrate reductase test.

Children and men with suspected or confirmed UTI and people with suspected upper UTI (pyelonephritis), require medical assessment by a physician. The Department of Health (2000) also indicates medical assessment for clients with frank haematuria, or those over 50 with microscopic haematuria.

Antibiotic preparations for the treatment of UTI in the Nurse Prescriber's Extended Formulary are amoxicillin, nitrofurantoin and trimethoprim. The first-line antibiotics for treatment of cystitis are trimethoprim or nitrofutantoin. Winstanley et al (1997) indicate that trimethoprim is effective against 70% of urinary pathogens.

A three-day course of an oral antibiotic is usually used to treat uncomplicated cystitis. If symptoms do not respond to empirical antibiotics within two to three days, a urine sample should be obtained for culture and sensitivity testing (Drugs and Therapeutics Bulletin, 1998).

In pregnancy, all UTIs should be treated, and successful treatment of the infection should be confirmed by a urine culture test. Nitrofurantoin is recommended for blind treatment while waiting for the results of a urine culture and sensitivity test. Urine culture is essential in pregnant women with UTI. Co-amoxiclav, trimethoprim, tetracyclines, and quinolones are not recommended for use in pregnancy.

Clients should be encouraged to drink three litres of fluid a day in order to keep the urine dilute. Making the urine alkaline by giving sodium bicarbonate or potassium citrate may make urination less painful (Blandy, 1998). Cranberry juice and other cranberry products have also been suggested to inhibit the adherence of bacteria to mucosal cells (Beachy, 1981). Busuttil Leaver (1996) identifies some of the potential effects of cranberry juice, but more research appears to be required regarding its effectiveness and role in prevention of UTI (Cooper and Jepson, 2001).

In addition to increasing fluid intake and the use of alkalising agents, mild analgesia may be required, and local pain relief using a heat pad may be beneficial.

Advice about preventing future infection includes maintaining an adequate fluid intake, not allowing the bladder to get overfull, ensuring that the bladder is completely emptied when voiding, and emptying the bladder after sexual intercourse.

This article is based on a book by Courtney, M. and Butler, M. (2002) Essentials of Nurse Prescribing, Greenwich Medical Media, London.

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