PTCB Guide to Cephalosporins

Also called cef- and ceph- beta-lactam antibiotics · suffix cef- or ceph- · updated August 4, 2026

What gets tested

• Recognizing the cef- and ceph- stem, which sits at the front of the name rather than the end (Keflex is cephalexin, Rocephin is ceftriaxone)
• The generation each common drug belongs to, especially cephalexin (first) and ceftriaxone (third)
• The shared beta-lactam mechanism and the relationship to penicillins
• The cross-reactivity question with penicillin allergy, and that it is escalated rather than decided by a technician
• Route: several important cephalosporins such as ceftriaxone are injectable only
• Reconstitution and storage of the oral suspensions

What is not tested

You are not expected to recite which organisms each generation covers, to know breakpoints, or to choose an agent for an infection. Focus instead on name recognition, brand to generic pairs, the generation of the common agents, the route, and the allergy and counseling points. Strengths, dosage forms, routes, special handling, and duration of therapy are all inside PTCE knowledge area 1.4, so the suspension concentrations and storage rules remain fair game.

Why cephalosporins matter

Cephalexin is one of the most dispensed antibiotics in the United States, and ceftriaxone is a workhorse injectable in hospitals and clinics. Because the stem sits at the front of the name rather than the end, cephalosporins are a favourite way for the exam to test whether you actually recognize drug stems or have only memorized suffixes.

Cephalosporins at a glance

Mechanism of action

Cephalosporins share the beta-lactam ring with penicillins and work the same way: they bind penicillin-binding proteins in the bacterial membrane and block the transpeptidation step that cross-links peptidoglycan, so the cell wall fails and the bacterium dies. What separates cephalosporins from penicillins is the side chains attached to the core, and those side chains are the basis of the generation system. First generation agents such as cephalexin have strong activity against gram-positive organisms including staph and strep, which is why they are so common for skin infections. Moving up the generations, chemists progressively traded gram-positive potency for the ability to cross the outer membrane of gram-negative bacteria and to resist more beta-lactamase enzymes, which is why third generation ceftriaxone reaches organisms cephalexin cannot and can penetrate the central nervous system well enough to treat meningitis. The fourth generation returns some gram-positive coverage while keeping the broad gram-negative reach, and the fifth generation, ceftaroline, is notable for being the cephalosporin that covers MRSA, which the others do not. Because the beta-lactam ring is common to both families, cephalosporins can be attacked by some of the same bacterial enzymes, and can also be recognized by the immune system of a patient sensitized to penicillin.

Common and important side effects

• Diarrhea, nausea, and abdominal discomfort
• Rash and other hypersensitivity reactions, including anaphylaxis in rare cases
• Clostridioides difficile associated diarrhea, a well-recognized risk with this class
• Injection site pain with intramuscular administration, notably ceftriaxone
• Yeast infections from disruption of normal flora
• Rarely, blood count changes or elevated liver enzymes with prolonged therapy

Key interactions

• A documented penicillin allergy is the key profile-level flag, because both classes share the beta-lactam ring
• Probenecid slows the renal excretion of many cephalosporins and raises their levels
• Warfarin's effect may be increased, so INR monitoring is tightened
• Ceftriaxone must not be mixed or co-administered with calcium-containing intravenous solutions in neonates, because a precipitate can form
• Some cephalosporins can cause a disulfiram-like reaction with alcohol (flushing, nausea, palpitations), which is why avoiding alcohol during and shortly after therapy is standard counseling

Patient counseling notes

• Complete the full course even after symptoms resolve
• Shake oral suspensions thoroughly before each dose and use a proper measuring device
• Check the label for whether the reconstituted suspension is refrigerated or kept at room temperature, because this varies by product within the class
• Avoid alcohol during therapy and for several days afterward with the agents that carry a disulfiram-like warning
• Report any rash, swelling, or difficulty breathing immediately
• Report severe or watery diarrhea, which can indicate C. difficile

Practice questions

Work the Cephalosporins questions below first, then widen out. Two skills carry most of the Medications domain, and each has its own quiz. The first is drug class identification: recognising which class a drug belongs to from its name or its stem, which is what the drug class identification quiz drills across every class. The second is brand and generic recall, because the exam switches between the two names freely and expects you to follow. Pair this guide with the brand and generic quiz until the brand and generic pairs in the table above come back without effort.

Related drug-class guides

Official sources

• MedlinePlus: Cephalexin
• MedlinePlus: Cefuroxime
• MedlinePlus: Ceftriaxone Injection
• MedlinePlus: Antibiotics (topic overview)
• ClinCalc DrugStats: Cephalexin (dispensing data)

PTCB Quiz Prep is an independent study resource, not affiliated with the Pharmacy Technician Certification Board. This guide is for exam preparation, not medical advice. Part of the PTCB Medications domain.