Lehne 9th Edition Chapter 84: Drugs That Weaken the Bacterial Cell Wall I: Penicillins

5. A child with an ear infection is not responding to treatment with amoxicillin [Amoxil]. The nurse will expect the provider to order: a. amoxicillin-clavulanic acid [Augmentin]. b. ampicillin. c. nafcillin. d. penicillin G [Benzylpenicillin].

ANS: A Beta-lactamase inhibitors are drugs that inhibit bacterial beta-lactamases. These drugs are always given in combination with a penicillinase-sensitive penicillin. Augmentin contains amoxicillin and clavulanic acid and is often used when patients fail to respond to amoxicillin alone. Ampicillin is similar to amoxicillin, but amoxicillin is preferred and, if drug resistance occurs, ampicillin is equally ineffective. Pharmaceutical chemists have developed a group of penicillins that are resistant to inactivation by beta-lactamases (eg, nafcillin), but these drugs are indicated only for penicillinase-producing strains of staphylococci. Penicillin G would be as ineffective as amoxicillin if beta-lactamase is present.

1. A nurse transcribes a new prescription for potassium penicillin G given intravenously (IV) every 8 hours and gentamicin given IV every 12 hours. Which is the best schedule for administering these drugs? a. Give the penicillin at 0800, 1600, and 2400; give the gentamicin [Garamycin] at 1800 and 0600. b. Give the penicillin at 0800, 1600, and 2400; give the gentamicin [Garamycin] at 1200 and 2400. c. Give the penicillin at 0600, 1400, and 2200; give the gentamicin [Garamycin] at 0600 and 1800. d. Give the penicillin every 8 hours; give the gentamicin [Garamycin] simultaneously with two of the penicillin doses.

ANS: A Gentamicin should never be administered concurrently with penicillin, because they will interact, and the penicillin may inactivate the aminoglycoside. All the other options show concurrent administration.

12. A nurse is discussing methicillin-resistant Staphylococcus aureus (MRSA) with a group of nursing students. Which statement by a student correctly identifies the basis for MRSA resistance? a. "MRSA bacteria have developed PBPs with a low affinity for penicillins." b. "MRSA bacteria produce penicillinases that render penicillin ineffective." c. "MRSA occurs because of host resistance to penicillins." d. "MRSA strains replicate faster than other Staphylococcus aureus strains."

ANS: A MRSA strains have a unique mechanism of resistance, which is the production of PBPs with a low affinity for penicillins and all other beta-lactam antibiotics. MRSA resistance is not related to beta-lactamase production. MRSA resistance refers to bacterial and not host resistance. The resistance of MRSA strains is not related to speed of replication.

8. A patient with no known drug allergies is receiving amoxicillin [Amoxil] PO twice daily. Twenty minutes after being given a dose, the patient complains of shortness of breath. The patient's blood pressure is 100/58 mm Hg. What will the nurse do? a. Contact the provider and prepare to administer epinephrine. b. Notify the provider if the patient develops a rash. c. Request an order for a skin test to evaluate possible PCN allergy. d. Withhold the next dose until symptoms subside.

ANS: A This patient is showing signs of an immediate penicillin allergy, that is, one that occurs within 2 to 30 minutes after administration of the drug. The patient is showing signs of anaphylaxis, which include laryngeal edema, bronchoconstriction, and hypotension; these must be treated with epinephrine. This is an emergency, and the provider must be notified immediately, not when other symptoms develop. It is not necessary to order skin testing. The patient must be treated immediately, and subsequent doses should not be given.

2. A patient has an infection caused by Pseudomonas aeruginosa. The prescriber has ordered piperacillin and amikacin, both to be given intravenously. What will the nurse do? a. Make sure to administer the drugs at different times using different IV tubing. b. Suggest giving larger doses of piperacillin and discontinuing the amikacin. c. Suggest that a fixed-dose combination of piperacillin and tazobactam [Zosyn] be used. d. Watch the patient closely for allergic reactions, because this risk is increased with this combination.

ANS: A When penicillins are present in high concentrations, they interact with aminoglycosides and inactivate the aminoglycoside; therefore, these two drugs should never be mixed in the same IV solution. The drugs should be given at different times with different tubing. In the treatment of Pseudomonas infections, extended-spectrum penicillins, such as piperacillin, usually are given in conjunction with an antipseudomonal aminoglycoside, such as amikacin; therefore, suggesting a larger dose of piperacillin and discontinuation of the amikacin is incorrect. Zosyn is not recommended. The risk of allergic reactions does not increase with this combination of drugs.

A nursing student wants to know the differences between hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). Which statements about CA-MRSA are true? (Select all that apply.) a. 20% to 30% of the general population are colonized with CA-MRSA. b. Boils caused by CA-MRSA can be treated without antibiotics. c. CA-MRSA is less dangerous than HA-MRSA. d. CA-MRSA does not cause necrotizing fasciitis. e. CA-MRSA is transmitted by airborne droplets.

ANS: A, B, C CA-MRSA is thought to be present in 20% to 30% of the population, and many of these individuals are asymptomatic carriers. Boils caused by CA-MRSA can often be treated by surgical drainage alone. CA-MRSA is less dangerous than HA-MRSA but more dangerous than methicillin-sensitive Staphylococcus aureus (MSSA). CA-MRSA generally causes mild skin infections but can cause more serious infections, such as necrotizing fasciitis. CA-MRSA is transmitted by skin-to-skin contact and by contact with contaminated objects.

3. A nurse assisting a nursing student with medications asks the student to describe how penicillins (PCNs) work to treat bacterial infections. The student is correct in responding that penicillins: a. disinhibit transpeptidases. b. disrupt bacterial cell wall synthesis. c. inhibit autolysins. d. inhibit host cell wall function.

ANS: B PCNs weaken the cell wall, causing bacteria to take up excessive amounts of water and subsequently rupture. PCNs inhibit transpeptidases and disinhibit autolysins. PCNs do not affect the cell walls of the host.

Which organisms can be treated with penicillin G (Benzylpenicillin)? (Select all that apply.) a. Methicillin-resistant Staphylococcus aureus b. Neisseria meningitidis c. Pseudomonas aeruginosa d. Streptococcus pyogenes e. Treponema pallidum

ANS: B, D, E Penicillin G is the first drug of choice for N. meningitidis. It is a drug of first choice for infections caused by sensitive gram-positive cocci, including S. pyogenes. It is a drug of choice for T. pallidum. It is not effective against methicillin-resistant S. aureus or P. aeruginosa.

7. A patient is about to receive penicillin G for an infection that is highly sensitive to this drug. While obtaining the patient's medication history, the nurse learns that the patient experienced a rash when given amoxicillin [Amoxil] as a child 20 years earlier. What will the nurse do? a. Ask the provider to order a cephalosporin. b. Reassure the patient that allergic responses diminish over time. c. Request an order for a skin test to assess the current risk. d. Suggest using a desensitization schedule to administer the drug.

ANS: C Allergy to penicillin can decrease over time; therefore, in patients with a previous allergic reaction who need to take penicillin, skin tests can be performed to assess the current risk. Until this risk is known, changing to a cephalosporin is not necessary. Reassuring the patient that allergic responses will diminish is not correct, because this is not always the case; the occurrence of a reaction must be confirmed with skin tests. Desensitizing schedules are used when patients are known to be allergic and the drug is required

6. A patient is receiving intravenous potassium penicillin G, 2 million units to be administered over 1 hour. At 1900, the nurse notes that the dose hung at 1830 has infused completely. What will the nurse do? a. Assess the skin at the infusion site for signs of tissue necrosis. b. Observe the patient closely for confusion and other neurotoxic effects. c. Request an order for serum electrolytes and cardiac monitoring. d. Watch the patient's actions and report any bizarre behaviors.

ANS: C Although penicillin G is the least toxic of all antibiotics, certain adverse effects may be caused by compounds coadministered with penicillin. When large doses of potassium penicillin G are administered rapidly, hyperkalemia can occur, which can cause fatal dysrhythmias. When penicillin G is administered IM, tissue necrosis occurs with inadvertent intra-arterial injection. Confusion, seizures, and hallucinations can occur if blood levels of the drug are too high. Bizarre behaviors result with large IV doses of procaine penicillin G.

11. A patient with an infection caused by Pseudomonas aeruginosa is being treated with piperacillin. The nurse providing care reviews the patient's laboratory reports and notes that the patient's blood urea nitrogen and serum creatinine levels are elevated. The nurse will contact the provider to discuss: a. adding an aminoglycoside. b. changing to penicillin G. c. reducing the dose of piperacillin. d. ordering nafcillin.

ANS: C Patients with renal impairment should receive lower doses of piperacillin than patients with normal renal function. Aminoglycosides are nephrotoxic. Penicillin G and nafcillin are not effective against Pseudomonas infections.

9. A patient has an infection caused by Streptococcus pyogenes. The prescriber has ordered dicloxacillin PO. What will the nurse do? a. Administer the medication as ordered. b. Contact the provider to suggest giving the drug IV. c. Question the need for a penicillinase-resistant penicillin. d. Suggest ordering vancomycin to treat this infection.

ANS: C Penicillinase-resistant penicillins have been developed for use against penicillinase-producing strains of staphylococci. These drugs have a very narrow antimicrobial spectrum and should be used only for such infections. S. pyogenes can be treated with penicillin G. The nurse should question the order. It is incorrect to contact the provider to ask for IV dosing. This infection can be treated with penicillin G and not with vancomycin.

13. A nurse is preparing to administer intramuscular penicillin to a patient who is infected with T. pallidum and notes that the order is for sodium penicillin G. Which action is correct? a. Administer the drug as prescribed. b. Contact the provider to discuss administering the drug intravenously. c. Contact the provider to discuss changing the drug to benzathine penicillin G. d. Request an order for piperacillin instead of penicillin G.

ANS: C The procaine and benzathine penicillin salts are absorbed slowly and are considered repository preparations. When benzathine penicillin G is injected IM, penicillin G is absorbed for weeks and is useful only against highly sensitive organisms such as T. pallidum. Sodium penicillin G is absorbed rapidly, with peak effects in 15 minutes. Administering the drug IV will not yield repository effects. Piperacillin is not used for T. pallidum IC.

10. The parent of an infant with otitis media asks the nurse why the prescriber has ordered amoxicillin [Amoxil] and not ampicillin [Unasyn]. What will the nurse tell the parent? a. Amoxicillin is a broader spectrum antibiotic than ampicillin. b. Amoxicillin is not inactivated by beta-lactamases. c. Ampicillin is associated with more allergic reactions. d. Ampicillin is not as acid stable as amoxicillin.

ANS: D Amoxicillin and ampicillin are similar in structure and actions but differ primarily in acid stability. Amoxicillin is more acid stable and, when administered orally, results in higher blood levels than can be obtained with equivalent doses of ampicillin. The two drugs have the same spectrum, both are inactivated by beta-lactamases, and both can cause allergic reactions.

4. A child with otitis media has had three ear infections in the past year. The child has just completed a 10-day course of amoxicillin [Amoxil] with no improvement. The parent asks the nurse why this drug is not working, because it has worked in the past. What will the nurse tell the patient? a. "Amoxicillin is too narrow in spectrum." b. "The bacteria have developed a three-layer cell envelope." c. "The bacteria have developed penicillin-binding proteins (PBPs) that have a low affinity for penicillins." d. "The bacteria have synthesized penicillinase."

ANS: D Beta-lactamases are enzymes that cleave the beta-lactam ring and render the PCN inactive. This resistance is common with organisms that cause ear infections. Amoxicillin is a broad-spectrum antibiotic. A three-layer cell envelope occurs in gram-negative bacteria. Some bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA), develop PBPs with a low affinity for penicillins. MRSA is not a common cause of otitis media.