Antimicrobial therapy

Antimicrobial questions are less about memorizing every bug and more about the safety move before the first dose, the toxicity organ for that class, and the teaching line that keeps clients on therapy.

Universal antibiotic safety

Systemic antibiotics fail in three predictable ways on the exam: you give a beta-lactam to someone with a known allergy, the client stops early when symptoms ease, or you freeze while waiting on a culture as perfusion collapses. The first dose is an allergy decision before it is a microbiology decision.

• Allergy check before penicillin and related beta-lactams. A listed allergy means hold and clarify, not a quiet test dose.
• Finish the course as prescribed to reduce resistance and incomplete kill.
• Culture when ordered, but do not use “waiting on culture” as an excuse to ignore a crashing septic client (see the sepsis chapter).

A listed penicillin or beta-lactam allergy is a hard stop until you clarify what happened (rash versus anaphylaxis) and get a safe plan. Quiet “test doses” or “they probably outgrew it” are how stems turn into airway emergencies. Cross-reactivity details vary in real practice; on the exam, a documented severe allergy means you do not push through the related drug without clarification.

Finishing the prescribed course is about incomplete kill and resistance pressure when clients self-stop because they feel better. That is different from a provider revising duration or stopping for toxicity. Teach the plan on the label and the order, not the client’s symptom calendar. Cultures guide later narrowing when ordered, but a crashing septic picture needs the sepsis pathway now. Waiting on the lab report is not a reason to withhold urgent resuscitation and ordered empiric therapy. Details of shock escalation live in Shock and sepsis.

The distractor that looks thorough is delaying the first dose for “one more allergy question later,” stopping antibiotics the day fever breaks without an order, or refusing to treat sepsis until every culture result posts. Edge case: if the stem already names a confirmed allergy to the drug in hand, the first action is hold and clarify, not give-and-watch.

Class traps the exam recycles

Vancomycin flushing vs anaphylaxis

Red man pattern is often infusion-rate related: face and neck flush while the drug runs fast. Slow or stop the infusion per protocol and assess the airway. True anaphylaxis (wheeze, shock, progressive airway swelling) is a different emergency pathway after the drug is stopped.

TB drugs: keep clients on therapy

• INH neuropathy prevention is why pyridoxine (B6) appears in the order set.
• Rifampin’s orange fluids are expected. Teach contact-lens staining so clients do not abandon therapy.
• Report jaundice, severe fatigue, or dark urine as hepatotoxicity cues for several TB agents.

More class traps worth a line

Metronidazole plus alcohol can trigger a disulfiram-like reaction (flushing, nausea, tachycardia) - teach zero alcohol during therapy and for the post-course window the label or order names. Sulfonamides need hydration so crystals do not form in the urine; sun sensitivity and rash (including severe cutaneous reactions) are report-now. Macrolides (azithromycin/erythromycin patterns) add QT-prolongation and interaction awareness when stems stack cardiac drugs. Aminoglycosides and vancomycin often use peak and trough levels - draw at the times protocol names so the number means something; rising creatinine or tinnitus still pauses the drug conversation even before the lab returns.

Antibiotics that wipe normal flora raise *C. difficile* risk later - new watery diarrhea on or after antibiotics is not “expected GI upset” to ignore. Isolation and soap-and-water teaching connect to Transmission-based precautions.

Topicals and antiparasitics that still show up

These agents are not obscure trivia. Burn cream, scabies lotion, and oral nail-fungus therapy show up because technique and organ watch matter as much as the drug name. Wrong application wastes the course; missed sulfa or liver cues turn a “simple” med into harm.

Silver sulfadiazine is a topical sulfa product used on burn wounds. Clean the wound and apply a thin layer as ordered so the cream contacts the burned surface rather than sitting on debris. Watch the site for infection cues, and remember sulfa-related concerns in teaching: known sulfa allergy usually means hold and clarify, and protocols often watch white blood cell trends because leukopenia is a recognized risk with this agent.

Permethrin for scabies only works if enough skin is covered for long enough. Apply to clean, cool, dry skin over the body areas the order or product instructions name, leave it on for the instructed time, then wash off. Treating only the itchy patch leaves mites elsewhere. Household contacts and linen or clothing guidance are part of the plan so reinfestation does not erase a correct application.

Oral terbinafine for onychomycosis is a long course that can injure the liver. Teach clients to report jaundice, dark urine, pale stools, severe fatigue, or right-upper-quadrant pain promptly, and that baseline or follow-up liver tests may be part of the plan. Feeling better about the nail does not cancel hepatotoxicity teaching.

The distractor that looks efficient is a quick dab of burn cream on dirty eschar, washing permethrin off early because itching worsens briefly, or shrugging off dark urine on terbinafine as “just dehydration.” Edge case: a client with a documented sulfa allergy and an SSD order is a clarify-before-apply problem, not a routine dressing change.

1. Confirm the allergy history before the first systemic dose.
2. Match the toxicity organ to the class (ears/kidneys, tendons, liver).
3. Teach the expected nuisance (orange fluids) separately from the report-now harm.
4. For topicals, application technique and contact treatment matter as much as the drug name.

Priority map