McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 9  Antibiotics

When methoxyflurane is combined with tetra- cycline, the risk of nephrotoxicity increases. If at all possible, this combination should be avoided. In addition, digoxin toxicity rises when tetracyclines are taken concurrently. Digoxin levels should be moni- tored and dose adjusted appropriately during treatment and after tetracycline therapy is discontinued. Finally, decreased absorption of tetracyclines results from oral combinations with calcium salts, magnesium salts, zinc salts, aluminium salts, bismuth salts, iron, urinary alka- linisers and charcoal. Clinically important drug–food interactions Because oral tetracyclines are not absorbed effectively if taken with food or dairy products, they should be administered on an empty stomach 1 hour before or 2 to 3 hours after any meal or other medication. by susceptible strains of bacteria; acne; when penicillin is contraindicated for eradication of susceptible organisms. Actions: Inhibits protein synthesis in susceptible bacteria, preventing cell replication. Pharmacokinetics: Route Onset Peak Oral Varies 2–4 hours Topical Minimal absorption occurs T 1/2 : 6 to 12 hours; excreted unchanged in the urine. Adverse effects: Nausea, vomiting, diarrhoea, glossitis, discolouring and inadequate calcification of primary teeth of fetus when used in pregnant women or of secondary teeth when Prototype summary: Doxycycline Indications: Treatment of various infections caused

not only the undesired bacteria, but also bacteria of the normal flora, which increases the risk for exacerbation of the ocular infection that is being treated. Tetracyclines should be used with caution in children younger than 8 years of age because they can potentially damage developing bones and teeth ; and in people with hepatic or renal dysfunction because they are concen- trated in the bile and excreted in the urine. Adverse effects The major adverse effects of tetracycline therapy involve direct irritation of the GI tract and include nausea, vomiting, diarrhoea, abdominal pain, glossitis and dysphagia. Fatal hepatotoxicity related to the drug’s irri- tating effect on the liver has also been reported. Skeletal effects involve damage to the teeth and bones. Because tetracyclines have an affinity for teeth and bones, they accumulate there, weakening the structure and causing staining and pitting of teeth and bones. Dermatological effects include photosensitivity and rash. Superinfec- tions, including yeast infections, occur when bacteria of the normal flora are destroyed. Local effects, such as pain and stinging with topical or ocular application, are fairly common. Haematological effects are less frequent, such as haemolytic anaemia and bone marrow depres- sion secondary to the effects on bone marrow cells that turn over rapidly. Hypersensitivity reactions reportedly range from urticaria to anaphylaxis and also include intracranial hypertension. Clinically important drug–drug interactions When penicillin G and tetracyclines are taken concur- rently, the effectiveness of penicillin G decreases. If this combination is used, the penicillin dose should be increased. When oral contraceptives are taken with tetra­ cyclines, the effectiveness of the contraceptives decreases, and women who take oral contraceptives should be advised to use an additional form of birth control while receiving the tetracycline. (See Critical thinking scenario.)

used in children, bone marrow suppression, photosensitivity, superinfections, rash, local irritation with topical forms.

CRITICAL THINKING SCENARIO Antibiotics and oral contraceptives

THE SITUATION G.S., a 27-year-old married female postgraduate student, is seen in the student health clinic a few weeks into the autumn semester. She has developed a severe sinusitis and complains of head pressure, difficulty sleeping, fever, and muscle aches and pains. A culture is done, and the next day the culture and sensitivity report identifies the

infecting organism as a strain of Klebsiella that is sensitive to doxycycline. G.S. returns to the clinic to get the prescription for doxycycline. In talking with you, G.S. tells you that she began university with plans to start a family in 2 years, after completing her program. She is a very organised person and has carefully planned her rigorous course work and her non-academic activities so that almost every hour