Penicillins: Mechanism and Clinical Use

• Antibiotics that affect the cell wall are bactericidal.
• These include penicillins, cephalosporins, carbapenems, and monobactams.

Penicillins

• Penicillins destroy bacteria by weakening the bacterial cell wall and are considered beta-lactam antibiotics that affect protein synthesis.
• Penicillin G potassium is a narrow-spectrum medication used for IM or IV administration.
• Other narrow-spectrum penicillins include: Penicillin G benzathine (IM) and Penicillin V (PO).
• Broad-spectrum penicillins include: amoxicillin, amoxicillin-clavulanate (both PO), and ampicillin (PO or IV).
• Nafcillin (IM or IV) is used as an antistaphylococcal penicillin.
• Piperacillin tazobactam (IV) is an antipseudomonal penicillin.
• Penicillins treat gram-positive cocci infections like Streptococcus pneumoniae (pneumonia, meningitis), Streptococcus viridans (infectious endocarditis), and Streptococcus pyogenes (pharyngitis, strep throat).
• They are effective against gram-positive bacteria.
• Penicillins treat meningitis from gram-negative cocci (Neisseria meningitides).
• Penicillins kill spirochetes (Treponema pallidum), which cause syphilis.
• Extended-spectrum penicillins (piperacillin, ticarcillin) are effective against Pseudomonas aeruginosa and other organisms causing urinary tract, lung, and abdominal infections.
• Stronger penicillins (extended-spectrum) target more bacteria types.
• Medications like piperacillin and ticarcillin can treat "tough" infections.
• Penicillins are also used prophylactically against bacterial endocarditis in at-risk clients before dental/medical procedures to prevent bloodstream infections.

Complications of Penicillins

• Allergies/anaphylaxis are a severe, rapid allergic reaction.
• Always interview clients for allergies before administration.
• Observe for allergic reactions for 30 minutes after parenteral administration.
• Immediate reactions occur 2-30 minutes post-administration, accelerated within 1-72 hours, and delayed reactions occur within days to weeks.
• Ensure epinephrine and respiratory support are accessible.
• Clients should wear an allergy identification bracelet.
• Cross-sensitivity means allergy to one penicillin may indicate allergy to all.
• Renal impairment can occur.
• Monitor kidney function and I&O.
• Hyperkalemia, dysrhythmias, and hypernatremia are possible.
• High doses of penicillin G potassium can cause hyperkalemia/dysrhythmias.
• High doses of penicillin G sodium can cause hypernatremia.
• Monitor cardiac status and electrolyte levels.

Contraindications/Precautions for Penicillins

• Use during pregnancy requires caution, although it has been used safely, safety is not fully established
• Lactation safety isn't established.
• Contraindicated in clients with a history of severe allergic reactions to penicillin, cephalosporins, or impenem.
• Use cautiously for clients at risk for kidney dysfunction (acutely ill, older adults, young children).
• Clients allergic to one penicillin are cross-allergic to others and may be cross-sensitive to cephalosporins.

Interactions with Penicillins

• Penicillin inactivates aminoglycosides when mixed in the same IV solution.
• Probenecid delays penicillin excretion.
• Instruct clients to report allergic responses (dyspnea, rash, itching, hives).
• Administer IM injections cautiously to avoid nerve/artery injection to prevent sensory/motor dysfunction or neurotoxicity.
• Penicillin V, amoxicillin, and amoxicillin-clavulanate can be taken with meals, while others must be taken with 8 oz of water 1 hr before or 2 hr after meals.
• Complete therapy course even if manifestations resolve.
• Use non-hormonal contraception, as penicillins can decrease contraceptive effectiveness.

Cephalosporins

• Cephalosporins are similar to penicillins, and destroy bacterial cell walls, affecting protein synthesis.
• The prototype medication is cephalexin, a first-generation cephalosporin.
• Most are administered IV or IM due to decreased GI absorption.
• Later generations are more likely to reach cerebrospinal fluid and are more effective against gram-negative organisms and anaerobes
• They are broad-spectrum bactericidal medications with a high therapeutic index for treating diverse infections.

Cephalosporin Generations and Examples:

• First generation: cefazolin (IM or IV)
• Second generation: cefaclor (PO), cefotetan (IM or IV)
• Third generation: ceftriaxone, cefotaxime (IM or IV)
• Fourth generation: cefepime (IM or IV)
• Fifth generation: ceftaroline (IV), effective against MRSA

Complications of Cephalosporins

• Hypersensitivity, anaphylaxis and possible cross-sensitivity to penicillin can happen
• Stop cephalosporin for allergy indications (urticaria, rash, hypotension, dyspnea) and notify the provider
• Question clients carefully about penicillin/cephalosporin allergies and notify the provider if present, but cephalosporins may be used on clients with mild penicillin allergies.
• Cefotetan and ceftriaxone can cause bleeding tendencies.
• Avoid in clients with bleeding disorders or on anticoagulants; monitor for bleeding and prothrombin/bleeding times. Administer parenteral vitamin K if delays in clotting
• Thrombophlebitis (vein inflammation from a blood clot) with IV infusion.
• Observe injection site for phlebitis, rotate sites, and administer as a dilute intermittent infusion slowly over 3-5 minutes for bolus dosing.
• Renal insufficiency can occur, give lower doses of most cephalosporins to prevent toxic accumulation and cephalosporins are mainly eliminated in the kidneys.
• Ceftriaxone is eliminated largely by the liver, so dosage reduction isn't necessary for clients with renal impairment.
• IM injections can cause pain.
• Administer IM injections deep into a large muscle mass and educate the client about the possibility of injection site pain.
• Antibiotic-associated pseudomembranous colitis can occur.

Nursing actions for pseudomembranous colitis

• Nursing actions include observing for diarrhea, notifying the provider, and stopping the medication
• There is a risk for developing C. difficile by consuming broad-spectrum antibiotics.

Contraindications/Precautions for Cephalosporins

• Pregnancy: Has been used safely
• Lactation: Has been used safely
• Do not give cephalosporins to clients with a history of severe allergic reactions to penicillins or cephalosporins.
• use cautiously with clients who have renal impairment or bleeding tendencies

Interactions with Cephalosporins

• Disulfiram reaction (alcohol intolerance) occurs with alcohol and cefotetan or cefazolin.
• Clients should avoid alcohol while taking these cephalosporins.
• Probenecid delays renal excretion.
• Calcium and ceftriaxone interaction, avoid administering together due to precipitation risks.
• Complete therapy course, even if manifestations resolve.
• Take oral cephalosporins with food.
• Store oral cephalosporin suspensions in a refrigerator.

Explore the mechanisms of action, clinical uses, and considerations for penicillin antibiotics. The quiz covers penicillin's bactericidal effects, resistance mechanisms, appropriate use, and alternatives for patients with penicillin allergies.