Anti-infectives: antibiotics, antivirals and antifungals

What Are Anti-infectives?

Anti-infectives are drugs that kill or slow the growth of microorganisms that cause infection. Pharmacy technicians encounter three major categories every day: antibiotics (bacteria), antivirals (viruses), and antifungals (fungi). Understanding how each class works, why patients must finish the full course, and which agents carry common allergy risks will help you catch errors before they reach the patient.

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Antibiotics

Antibiotics target structures or processes that bacterial cells have but human cells do not, such as the cell wall, the ribosome, or DNA-replication enzymes. The major classes you will see on the Top 200 list include:

• Penicillins – amoxicillin, amoxicillin-clavulanate (Augmentin), ampicillin. They block cell-wall synthesis. Penicillin allergy is the most commonly reported drug allergy in the United States. Patients who report a penicillin allergy may also react to cephalosporins (cross-reactivity), so always flag both classes when a penicillin allergy is on file.
• Cephalosporins – cephalexin (Keflex), cefdinir, ceftriaxone. Also block cell-wall synthesis; structurally similar to penicillins.
• Macrolides – azithromycin (Z-Pak), clarithromycin. Inhibit bacterial protein synthesis. A common alternative when penicillin allergy is documented.
• Fluoroquinolones – ciprofloxacin, levofloxacin. Inhibit bacterial DNA gyrase. Carry FDA black-box warnings for tendon damage and peripheral neuropathy.
• Tetracyclines – doxycycline, minocycline. Inhibit protein synthesis. Should not be taken with dairy, antacids, or iron supplements that can bind the drug.
• Sulfonamides – sulfamethoxazole-trimethoprim (Bactrim, Septra). Disrupt folate synthesis. Sulfa allergy is the second most commonly reported antibiotic allergy; patients with sulfa allergy must be flagged because the allergen appears in other drug classes (some diuretics, certain diabetes medications) as well.
• Nitroimidazoles – metronidazole (Flagyl). Disrupts DNA in anaerobic bacteria and certain parasites. Patients must avoid alcohol during therapy and for at least 48 hours after the last dose.
• Lincosamides – clindamycin. Inhibits protein synthesis; used for skin and anaerobic infections.

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Antivirals

Viruses replicate inside human cells, so antiviral drugs must target viral-specific enzymes without harming the host cell. Common Top-200 antivirals include:

• Acyclovir, valacyclovir – treat herpes simplex and varicella-zoster infections by inhibiting viral DNA polymerase.
• Oseltamivir (Tamiflu) – inhibits influenza neuraminidase; most effective when started within 48 hours of symptom onset.
• HIV antiretrovirals – combinations such as emtricitabine-tenofovir and dolutegravir suppress viral replication; patients must take them consistently every day to prevent resistance.

There are no true antibiotics effective against viruses. A key patient-education point—and a common counseling topic for pharmacy staff—is that taking an antibiotic for a viral illness (such as a cold) does not help and contributes to antibiotic resistance.

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Antifungals

Fungal infections range from superficial (athlete's foot, oral thrush) to life-threatening systemic infections. Common agents include:

• Fluconazole – oral or IV azole used for yeast infections and candidiasis; significant drug-interaction profile (inhibits CYP2C9 and CYP3A4).
• Clotrimazole, miconazole – topical azoles for skin and vaginal fungal infections, available OTC.
• Nystatin – topical or oral suspension used for oral thrush; not absorbed systemically when taken by mouth.

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Why the Full Course Matters

One of the most important concepts in anti-infective therapy is adherence to the full prescribed course. When a patient feels better and stops early, a small number of surviving bacteria remain. These may be the hardiest organisms in the infection—the ones least susceptible to the drug. If they reproduce, the result can be a relapse or the emergence of antibiotic-resistant organisms. Resistance is a public-health crisis, and the pharmacy counter is a frontline defense. Technicians can reinforce this message and alert the pharmacist when a patient says they are stopping early or sharing leftover medication.

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Allergy Flags Every Technician Must Know

| Allergy on File | Flag These Drug Classes |

|---|---|

| Penicillin | All penicillins, cephalosporins (possible cross-reactivity), carbapenems |

| Sulfa | Sulfonamide antibiotics, thiazide diuretics, loop diuretics, some oral hypoglycemics |

When entering a new prescription, the pharmacy dispensing software performs an allergy check automatically, but the technician must ensure allergy information is current and complete before processing any order.

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Reconstitution at the Counter

Many oral antibiotics—especially those prescribed for children—are dispensed as a powder for oral suspension. The powder must be mixed with a measured amount of purified water before dispensing. Common examples include amoxicillin oral suspension, amoxicillin-clavulanate oral suspension, and cephalexin oral suspension. The reconstituted product is stored in the refrigerator and carries a short beyond-use date (typically 10–14 days). You will practice reconstitution technique in the activities that follow.

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Summary

Anti-infectives fight infections caused by bacteria, viruses, and fungi, each class targeting a pathogen-specific weakness. Completing the full course prevents relapse and resistance. Penicillin and sulfa allergies are the most clinically significant to flag, and cross-reactivity patterns mean a single allergy can affect multiple drug classes. Recognizing which antibiotics need reconstitution at the counter is an essential dispensing skill.