9.1 Anti-Infectives & Infection Management

9.1 Anti-Infectives & Infection Management

Quick Answer: For community infection scenarios, confirm a bacterial indication (or other clear anti-infective need), check allergy quality and cross-reactivity risk, match an appropriate spectrum and duration, screen renal function and interactions, counsel adherence and red flags, and practise stewardship — especially avoiding antibiotics for typical viral upper respiratory illness. Use AMH for dosing, cautions, and duration; use APF for counselling standards.

Anti-infectives appear across APC Intern Written competencies 3.1–3.3: assess the clinical situation, implement a medication plan, and monitor for efficacy, adverse effects, and resistance-related harm. This section focuses on community-facing agents and syndromes you will see at the counter and in primary-care prescriptions — not full hospital ID specialty practice.

Stewardship first — then drug selection

Australian quality use of medicines expects judicious antimicrobial use: right patient, right drug, right dose, right duration, and no drug when none is needed. Stewardship in community pharmacy includes:

• Explaining that many colds, flu-like illnesses, and acute bronchitis are viral and do not improve with antibiotics
• Supporting symptomatic care and safety-netting (worsening dyspnoea, dehydration, high fever, confusion, chest pain)
• Checking that prescribed courses have a plausible indication and duration
• Flagging duplicate anti-infectives, unnecessary prolonged courses, and interactions
• Encouraging return if diarrhoea is severe or persistent (possible Clostridioides difficile)

Intern exam answers that automatically “start an antibiotic” for a self-limiting viral picture are usually wrong. Answers that match spectrum to syndrome and define stop rules are usually right.

Common community antibiotic classes

Penicillins

Phenoxymethylpenicillin (penicillin V) and amoxicillin remain first-line for many streptococcal and susceptible respiratory or ENT pathogens when allergy does not preclude them. Amoxicillin with clavulanic acid broadens coverage against beta-lactamase-producing organisms (e.g. some skin/soft-tissue or mixed infections) but increases gastrointestinal adverse effects and C. difficile risk relative to narrower agents.

Counselling priorities: complete the prescribed course unless advised to stop for toxicity; take with or without food as product-specific (clavulanate combinations often better tolerated with food); report rash, swelling, or breathing difficulty promptly.

Cephalosporins

Oral cefalexin is widely used for skin and soft-tissue infection and selected urinary tract infection (UTI) contexts per guidelines. Spectrum and generation matter: broader cephalosporins are not automatically “stronger and better” for community syndromes and may worsen resistance and C. difficile ecology.

Macrolides

Azithromycin, clarithromycin, and erythromycin are alternatives in penicillin allergy for some indications, and cover atypical respiratory pathogens in selected pneumonia pathways. Watch QT prolongation risk (especially with interacting drugs), CYP3A4 interactions (clarithromycin is a notable inhibitor), and gastrointestinal intolerance. Clarithromycin–statin interactions can precipitate myopathy — check before supply.

Tetracyclines

Doxycycline is common for selected respiratory, skin, and other community indications. Counsel: photosensitivity, oesophagitis risk (take with adequate water, remain upright), and avoid concurrent antacids/iron/calcium that chelate absorption. Not for pregnancy or young children when alternatives exist (tooth staining / developmental concerns — follow AMH age rules).

Trimethoprim and nitrofurantoin

Trimethoprim is a classic short-course agent for uncomplicated lower UTI in many Australian primary-care pathways when resistance patterns allow. Nitrofurantoin is highly concentrated in urine and used for lower UTI; it is not appropriate for pyelonephritis or systemic infection because tissue levels are inadequate. Check renal function for nitrofurantoin — efficacy falls and toxicity risk rises when eGFR is low (confirm current AMH cut-offs). Counsel brown urine with nitrofurantoin and complete short courses as directed.

Allergy and cross-reactivity principles

“Penicillin allergy” on the record is often intolerance (nausea, thrush, mild delayed rash decades ago) rather than IgE-mediated anaphylaxis. Poor documentation drives unnecessary broad-spectrum use.

Exam-ready principles:

1. Clarify the reaction — timing, severity, organ involvement, treatment needed, and whether the patient later tolerated related drugs.
2. True immediate allergy (urticaria, angioedema, anaphylaxis soon after a dose) is high risk for re-exposure to the same drug and close relatives.
3. Severe delayed reactions (e.g. severe cutaneous adverse reactions, organ involvement) generally mean avoid related beta-lactams pending specialist advice.
4. Cross-reactivity between penicillins and cephalosporins is not automatic. Risk is higher with similar R1 side-chains; many non-severe histories allow carefully selected cephalosporins. Do not invent “always cross-reacts” or “never cross-reacts” absolute rules — use history quality + AMH/specialist guidance.
5. If the history is unclear and the indication is non-urgent, defer and clarify rather than default to an unnecessarily broad second-line agent without reason.

Document what you clarified. Intern scenarios often reward reclassifying a vague childhood rash before cascading to last-line options.

Syndrome duration concepts (high-level)

Exact durations change with guidelines and local resistance — always verify AMH/therapeutic guidelines for the exam open-book context. Master duration logic, not memorised trivia alone:

Do not extend antibiotics “just in case” without clinical reason. Do counsel that improvement should begin within a few days for many bacterial infections — lack of improvement needs medical review, not automatic second scripts at the counter without assessment.

Clostridioides difficile risk

Almost any antibiotic can precipitate C. difficile infection (CDI), but risk is higher with broad-spectrum agents, prolonged or repeated courses, hospital exposure, advanced age, and proton pump inhibitor co-use. Community pharmacists should:

• Prefer narrower effective agents when prescribed choices allow stewardship discussion with the prescriber
• Counsel patients to seek urgent review for profuse watery diarrhoea, severe abdominal pain, fever, or blood in stool during or after antibiotics
• Avoid antidiarrhoeal self-medication that masks severe colitis when CDI is possible
• Support hand hygiene and careful antibiotic indication review in recurrent CDI history

CDI is a stewardship and safety outcome, not merely an inconvenience.

Select antifungals and antivirals — counselling high points

Fluconazole

Oral fluconazole is used for selected candida infections (e.g. vaginal candidiasis single-dose pathways when appropriate). Interaction check is mandatory: fluconazole inhibits CYP pathways and can potentiate warfarin (INR rise), interact with some statins, and affect other narrow-therapeutic-index drugs. Confirm concurrent medicines before supply, including OTC and complementary products. Counsel expected response time and when thrush-like symptoms need medical review (recurrent, pregnancy, diabetes, immunosuppression).

Oseltamivir

Oseltamivir for influenza is time-critical. Benefit is greatest when started as early as possible, ideally within 48 hours of symptom onset, in people for whom treatment is indicated (high-risk groups, severe disease pathways — follow current national guidance). Late initiation still occurs in some severe or high-risk settings under clinician direction, but “start anytime for mild illness days later” is not a general community rule. Counsel: full course as directed, gastrointestinal adverse effects, and that antivirals are not a substitute for influenza vaccination. Check renal dosing adjustments in AMH.

Other antifungals (high-level)

Topical azoles for skin/vaginal use need correct duration and site counselling. Oral terbinafine (when prescribed for nail/skin infection) requires interaction and hepatic caution awareness. Systemic antifungals beyond community single-dose candidiasis usually need more structured monitoring — escalate uncertainty.

Monitoring and when to escalate

During and after anti-infective supply:

• Efficacy — symptom trajectory matches expected infection course
• Toxicity — rash, anaphylaxis symptoms, severe diarrhoea, tendon symptoms with fluoroquinolones if used, photosensitivity with doxycycline
• Interactions — macrolides, fluconazole, rifamycins (when present) with chronic medicines
• Adherence barriers — taste, cost, complex multi-daily dosing, side effects leading to early stop

Red flags requiring urgent medical care: sepsis features (fever with rigors, confusion, hypotension symptoms), rapidly progressive cellulitis, suspected pyelonephritis, respiratory distress, or anaphylaxis.

Exam mindset

Intern Written anti-infective items rarely reward “strongest antibiotic available.” They reward indication clarity, allergy quality, spectrum matching, duration discipline, interaction checks, and stewardship communication. When AMH is open, use it for the exact dose and caution — your clinical reasoning still chooses the safe pathway.