McKenna's Pharmacology for Nursing, 2e

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P A R T 2  Chemotherapeutic agents

be taken on an empty stomach to ensure adequate absorption. Penicillins are excreted unchanged in the urine, making renal function an important factor in safe use of the drug. Penicillins enter breast milk and can cause adverse reactions (see contraindications and cautions). Contraindications and cautions These drugs are contraindicated in people with aller- gies to penicillin or cephalosporins or other allergens. Penicillin sensitivity tests are available if the person’s history of allergy is unclear and a penicillin is the drug of choice. Use with caution in people with renal disease (lowered doses are necessary because excretion is reduced ). Although there are no adequate studies of use during pregnancy, use in women who are pregnant and in breastfeeding women should be limited to situa- tions in which the mother clearly would benefit from the drug, because diarrhoea and superinfections may occur in the infant . Perform culture and sensitivity tests to ensure that the causative organism is sensitive to the penicillin selected for use. With the emergence of many resist- ant strains of bacteria, this has become increasingly important. Adverse effects The major adverse effects of penicillin therapy involve the GI tract. Common adverse effects include nausea, vomiting, diarrhoea, abdominal pain, glossitis, sto- matitis, gastritis, sore mouth and furry tongue. These effects are primarily related to the loss of bacteria from the normal flora and the subsequent opportunistic infections that occur. Superinfections, including yeast infections, are also very common and are again associ- ated with the loss of bacteria from the normal flora. Pain and inflammation at the injection site can occur with injectable forms of the drugs. Hypersensitivity reactions may include rash, fever, wheezing and, with repeated exposure, anaphylaxis that can progress to anaphylactic shock and death. Clinically important drug–drug interactions If penicillins and penicillinase-resistant antibiotics are taken concurrently with tetracyclines, a decrease in the effectiveness of the penicillins results. This combina- tion should be avoided if at all possible, or the penicillin doses should be raised, which could increase the occur- rence of adverse effects. In addition, when the parenteral forms of penicil- lins and penicillinase-resistant drugs are administered in combination with any of the parenteral aminoglyco- sides, inactivation of the aminoglycosides occurs. These combinations should also be avoided.

Prototype summary: Amoxycillin Indications: Treatment of infections caused by susceptible strains of bacteria, postexposure prophylaxis for anthrax, treatment of Helicobacter infections as part of combination therapy. Actions: Inhibits synthesis of the cell wall in susceptible bacteria, causing cell death. Pharmacokinetics: Route Onset Peak Duration T 1/2 : 1 to 1.4 hours; excreted unchanged in the urine. Adverse effects: Nausea, vomiting, diarrhoea, glossitis, stomatitis, bone marrow suppression, rash, fever, superinfections, lethargy. Oral Varies 1 hours 6–8 hours

Care considerations for people receiving penicillins and penicillinase-resistant antibiotics

Assessment: History and examination

■ ■ Assess for possible contraindications or cautions : known allergy to any cephalosporins, penicillins or other allergens because cross-sensitivity often occurs (obtain specific information about the nature and occurrence of allergic reactions); history of renal disease that could interfere with excretion of the drug ; and current pregnancy or breastfeeding status. ■ ■ Perform a physical assessment to establish baseline data for evaluating the effectiveness of the drug and the occurrence of any adverse effects associated with drug therapy. ■ ■ Examine skin and mucous membranes for any rashes or lesions and injection sites for abscess formation to provide a baseline for possible adverse effects. ■ ■ Perform culture and sensitivity tests at the site of infection to ensure that this is the drug of choice for this person. ■ ■ Note respiratory status to provide a baseline for the occurrence of hypersensitivity reactions. ■ ■ Examine the abdomen to monitor for adverse effects. Evaluate renal function test findings, including BUN and creatinine clearance, to assess the status of renal functioning and to determine

any needed alteration in dose. Implementation with rationale

■ ■ Check culture and sensitivity reports to ensure that this is the drug of choice for this person.