McKenna's Pharmacology for Nursing, 2e

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P A R T 2  Chemotherapeutic agents

human cells, these drugs can be toxic to humans at high concentrations. Tetracyclines are indicated for treatment of infec- tions caused by Rickettsiae , M. pneumoniae , Borrelia recurrentis , H. influenzae , Haemophilus ducreyi , Pasteurella pestis , Pasteurella tularensis , Bartonella bacilliformis , Bacteroides species, Vibrio comma , Vibrio fetus , Brucella species, E. coli , E. aerogenes , Shigella species, Acinetobacter calcoaceticus , Klebsiella species, Diplococcus pneumoniae and S. aureus; against agents that cause psittacosis, ornithosis, lymphogranuloma venereum and granuloma inguinale; when penicillin is contraindicated in susceptible infections; and for treat- ment of acne and uncomplicated GU infections caused by C. trachomatis. Some of the tetracyclines are also used as adjuncts in the treatment of certain protozoal infections. See Table 9.7 for usual indications for each agent. Pharmacokinetics Tetracyclines are absorbed adequately, but not com- pletely, from the GI tract. Their absorption is affected by food, iron, calcium and other drugs in the stomach. Tetracyclines are concentrated in the liver and excreted unchanged in the urine, with half-lives ranging from 12 to 25 hours. These drugs cross the placenta and pass into breast milk (see contraindications and cautions). Tetracycline is available in oral and topical forms, in addition to being available as an ophthalmic agent. Doxycycline and minocycline are available in IV and oral forms. Contraindications and cautions Tetracyclines are contraindicated in people with known allergy to tetracyclines or to tartrazine (e.g. in specific oral preparations that contain tartrazine) and during pregnancy and breastfeeding because of effects on devel- oping bones and teeth. The ophthalmic preparation is contraindicated in people who have fungal, mycobac- terial or viral ocular infections because the drug kills

Evaluation

KEY POINTS ■■ Sulfonamides are older drugs; many strains have developed resistance to the sulfonamides, so they are no longer widely used. ■■ Monitor the person for CNS toxicity, nausea, vomiting, diarrhoea, liver injury, renal toxicity and bone marrow depression. TETRACYCLINES The tetracyclines (Table 9.7) were developed as semi­ synthetic antibiotics based on the structure of a common soil mould. They are composed of four rings, which is how they got their name. Researchers have developed newer tetracyclines to increase absorption and tissue penetration. Widespread resistance to the tetracyclines has limited their use in recent years. Tetracyclines include doxycycline ( Doryx , Frakas ), tigecycline ( Tygacil ) and minocycline ( Akamin ). Therapeutic actions and indications The tetracyclines work by inhibiting protein synthe- sis in a wide range of bacteria, leading to the inability of the bacteria to multiply (see Figure 9.2). Because the affected protein is similar to a protein found in ■ ■ Monitor person’s response to the drug (resolution of bacterial infection). ■ ■ Monitor for adverse effects (GI effects, CNS effects, rash and crystalluria). ■ ■ Evaluate the effectiveness of the teaching plan (person can name the drug, dosage, possible adverse effects to expect and specific measures to help avoid adverse effects). ■ ■ Monitor the effectiveness of comfort and safety measures and compliance with the regimen. KEY POINTS

TABLE 9.7

DRUGS IN FOCUS Tetracyclines

Drug name

Dosage/route

Usual indications

Adult and paediatric >8 years: Initially 200 mg/day PO followed by 100 mg/day PO

Treatment of a wide variety of infections, including traveller’s diarrhoea and sexually transmitted diseases; periodontal disease Treatment of meningococcal carriers and of various uncomplicated genitourinary and gynaecological infections

doxycycline (Doryx, Doxsig, Frakas)

minocycline (Akamin, Minomycin)

Adult: 200 mg PO initially, followed by 100 mg/day PO

tetracycline (Optycin Eye Ointment)

Applied to lower conjunctival sac q 2 hours

Ocular infection

tigecycline (Tygacil)

Adult: Initially, 100 mg IV followed by 50 mg IV q 12 hours

Complicated skin and intra-abdominal infections, including those with MRSA