Cefaclor for Strep Throat: Uses, Dosing, Safety, and Alternatives (2025 Guide)

Penicillin and amoxicillin are still the stars for strep throat. So why do some people end up on cefaclor? Short answer: it can work, but it’s a second-line option with a few caveats. If you (or your child) were prescribed cefaclor, this guide shows where it fits, how to take it safely, what side effects to watch for, and which alternatives are usually better in 2025-especially here in New Zealand.

• TL;DR: Cefaclor kills Group A Strep, but penicillin or amoxicillin are first choice; cephalexin is preferred if you can’t take penicillin.
• Typical course is 10 days; most people feel better within 24-48 hours and aren’t contagious after 24 hours on antibiotics.
• Watch for rash, diarrhea, and rare “serum sickness-like” reactions (fever + rash + sore joints about a week in-see a doctor fast).
• Warfarin, probenecid, and severe penicillin allergy change the plan; check with your prescriber.
• NZ guidance (NZF/bpacnz) backs penicillin or amoxicillin first; cephalexin is usually the go-to if penicillin isn’t an option.

Where cefaclor fits for strep throat (and when it doesn’t)

Group A Streptococcus (GAS) causes classic strep throat-sudden sore throat, fever, swollen tonsils, and no cough. Antibiotics shorten illness a bit, stop spread, and in high-risk groups help prevent rheumatic fever. Global guidance (CDC 2024, IDSA pharyngitis guideline) and New Zealand advice (NZ Formulary 2025, bpacnz 2023) still recommend penicillin V or amoxicillin as first choice for confirmed strep throat.

Where does cefaclor come in? It’s a second-generation cephalosporin that covers GAS well. It’s considered when:

• You can’t tolerate penicillin or amoxicillin due to a mild, non-immediate allergy (for example, a delayed rash as a child).
• You had stomach upset on first-line options and your clinician thinks a cephalosporin might be better tolerated.
• Local supply issues mean your pharmacy doesn’t have the ideal first-line choices.

Even then, many clinicians pick cephalexin over cefaclor because cefaclor has a higher chance of a “serum sickness-like” reaction in children. That reaction is uncommon, but it’s well described. NZ prescribers and pharmacists see enough of it that cephalexin tends to be preferred when a cephalosporin is needed.

When not to use cefaclor:

• History of immediate, severe penicillin allergy (hives, throat swelling, anaphylaxis). Cross-reactivity with cephalosporins is low but not zero; if you’ve had anaphylaxis to penicillin, macrolides (like azithromycin) or clindamycin are safer picks.
• Past serum sickness-like reaction to cefaclor. Avoid it in future.
• Suspected viral sore throat (runny nose, cough, hoarse voice) without strep features-antibiotics don’t help.

How soon should you feel better? Symptoms often ease within 24-48 hours of starting any effective antibiotic, and you’re usually not contagious after 24 hours of therapy and no fever. If you’re not improving by day 3, message your clinic-resistant strep is rare, but non-adherence, wrong diagnosis, or another infection can mimic strep.

NZ context matters. In Aotearoa New Zealand, Māori and Pacific peoples and some communities have a higher risk of rheumatic fever. In those settings, clinicians may be quicker to test and treat confirmed strep. First-line still means penicillin or amoxicillin for 10 days; cephalexin is preferred if there’s a non-severe penicillin allergy. Cefaclor is an option, but not the top one.

Evidence corner (no links, just the sources): CDC 2024 group A strep guidance; IDSA pharyngitis guideline (2012 with updates); New Zealand Formulary (2025) antibiotic choices; bpacnz primary care antibiotic advice (2023). These consistently keep penicillin and amoxicillin at the top.

How to take cefaclor safely: dosing, timing, and practical steps

If your clinician chose cefaclor, here’s the practical how-to. Stick to your prescribed dose, but these are common reference ranges used by prescribers.

Standard dosing (typical references)

• Adults and adolescents: 250 mg every 8 hours for 10 days. Some use 500 mg every 12 hours if using an extended-release brand (availability varies by country).
• Children: 20 mg/kg/day divided every 8 hours for 10 days (max often 1 g/day for routine infections). Your prescription label should show both the mg and the mL per dose.

Note: Doses can differ based on your exact product (immediate vs. extended release), body weight, and kidney function. Double-check your bottle’s instructions and ask your pharmacist if anything looks off.

Food, timing, and measuring

• With or without food? Either is fine; a snack can help if you feel nauseated.
• Spread doses evenly (for example, breakfast-mid-afternoon-bedtime for “every 8 hours”). Set alarms-consistency matters.
• Liquid? Use a proper oral syringe/spoon from the pharmacy. Teaspoons at home are inaccurate.
• Refrigeration: Some cefaclor suspensions should be kept in the fridge. Check your label.

Course length and missed doses

• Finish the full 10-day course even if your throat feels normal by day 3. Shorter courses increase the chance of relapse and-here in NZ-undercut rheumatic fever prevention in at-risk groups.
• Missed dose? Take it when you remember if it’s within a few hours. If it’s close to the next dose, skip the missed one. Don’t double.

What to combine (and what to avoid)

• Pain/fever: Paracetamol or ibuprofen help a lot. Sip warm fluids, try honey (over age 1), and consider salt-water gargles.
• Avoid codeine in children and teens. It’s not needed for strep throat.
• Probiotics are optional. If you’re prone to antibiotic diarrhea or thrush, they can help; separate from antibiotics by a few hours.

When to contact your clinician

• No improvement by 48-72 hours, or symptoms worsen.
• New fever after initially getting better.
• Rash, hives, breathing trouble, facial swelling, severe diarrhea, or joint pains with rash and fever.

Back-to-school/work rule of thumb: 24 hours on antibiotics, no fever, and you feel up to it. Keep up hand hygiene and don’t share utensils or water bottles.

Safety, side effects, and interactions you should know

Common side effects

• Upset stomach, loose stools, mild nausea.
• Headache, tiredness.
• Skin rash. Stop and check in if it spreads or you’re also unwell.

Serious or notable reactions

• Allergic reaction: Hives, wheeze, throat tightness, swelling-call emergency services.
• Serum sickness-like reaction: Classically 7-10 days after starting cefaclor-fever, itchy or bruise-like rash (often on the legs), and sore, swollen joints. Stop the medicine and get assessed the same day. This is uncommon but more linked to cefaclor than many other antibiotics, especially in kids.
• Severe diarrhea or abdominal cramps: Think about Clostridioides difficile. Seek care if diarrhea is watery and frequent, especially with fever or blood.
• Yeast infections: Oral thrush or vaginal thrush can pop up after any antibiotic. Over-the-counter treatments help; see your GP if recurrent.

Allergy and cross-reactivity

If you once had a mild, delayed rash to penicillin, your doctor may still choose a cephalosporin. But if you’ve had an immediate, severe reaction (hives within hours, facial swelling, wheeze, anaphylaxis), avoid cephalosporins like cefaclor unless an allergy specialist says otherwise. In that case, azithromycin or clindamycin are the usual picks.

Interactions and special situations

• Warfarin: Antibiotics can raise INR. If you’re on warfarin, arrange an extra INR check a few days into therapy and after finishing.
• Probenecid: Increases cefaclor levels. Your prescriber will adjust if needed.
• Oral contraceptive pill: No direct interaction, but vomiting/diarrhea can reduce absorption. Use backup if you’re unwell.
• Live oral typhoid vaccine: Antibiotics can blunt the vaccine’s effect. Space them apart.
• Kidney issues: Dose adjustment may be needed in significant renal impairment. Tell your clinician if you have kidney disease.
• Alcohol: No specific interaction. Light-to-moderate alcohol is fine if you’re otherwise well.

Pregnancy and breastfeeding

• Pregnancy: Cephalosporins are generally considered safe in pregnancy when needed. Penicillin or amoxicillin are still first choice for strep. If you’ve been prescribed cefaclor, your clinician weighed risks and benefits.
• Breastfeeding: Small amounts pass into milk. Usually safe; watch baby for loose stools or thrush.

If you’ve ever had a bad reaction to cefaclor, make sure it’s listed on your medical record and pharmacy profile. That saves you from repeat exposure.

Alternatives, comparisons, and quick answers

Quick comparison: where cefaclor sits

Decision tips you can use

• No penicillin allergy? Choose penicillin V or amoxicillin for 10 days.
• Mild, non-severe penicillin allergy? Cephalexin is usually preferred. Cefaclor is a backup if cephalexin isn’t suitable or available.
• Immediate penicillin anaphylaxis? Azithromycin (5 days) or clindamycin (10 days).
• High risk for rheumatic fever (common in some NZ communities)? Prioritize testing and a full 10-day course of a recommended antibiotic.
• Recurrent strep? Check adherence, household carriers, and timing. Don’t bounce between antibiotics without a plan-ask about culture and follow-up.

Checklist: make your course count

• Confirm it’s actually strep (swab or clear clinical reasoning).
• Start the antibiotic early and take it on time.
• Finish all 10 days, even if you feel better fast.
• Stay home for the first 24 hours after starting antibiotics and until fever-free.
• Replace your toothbrush on day 3-4 to cut reinfection risk.
• Hydrate, rest, and use pain relief if you need it.

Mini‑FAQ

• Does cefaclor work for tonsillitis? If the tonsillitis is caused by Group A Strep, yes. Viral tonsillitis won’t respond.
• Is 5 days enough? Not for penicillins and most cephalosporins. Ten days is standard for strep throat. Some macrolides (like azithromycin) are 5 days, but that’s a different class.
• How fast will I feel better? Usually within 24-48 hours. If not, check in.
• Can I drink alcohol? In moderation, yes. Focus on hydration and rest.
• I’m allergic to amoxicillin. Can I take cefaclor? If your reaction was mild and delayed, your clinician may consider a cephalosporin. If you’ve had anaphylaxis to penicillin, avoid cefaclor and use a different class.
• Do I need a throat swab? Many clinics swab before antibiotics. In higher-risk NZ settings, clinicians may treat confirmed cases promptly to protect against rheumatic fever.
• Is cefaclor readily available in NZ? Availability can vary by brand and region. Pharmacies commonly stock penicillin, amoxicillin, and cephalexin; cefaclor may not be first on the shelf. Your pharmacist can advise.
• Can I stop once I feel better? Don’t. Finish the 10 days to prevent relapse and reduce complications.
• What if I keep getting strep? Ask about adherence, close contacts, and timing. A culture, different antibiotic class, or checking for carriers in the household can help.

Next steps and troubleshooting

• Parent of a child on cefaclor: Use an oral syringe. Keep liquid in the fridge if the label says so. Watch for rash, diarrhea, or joint pains plus fever after a week-seek care if you see that pattern.
• Adult with a history of penicillin rash: If your prescriber chose a cephalosporin, that’s common practice. If you’re anxious about it, ask whether cephalexin would be a safer swap than cefaclor.
• Taking warfarin: Book an INR check within a few days of starting and again near the end. Tell your anticoagulation clinic you’re on an antibiotic.
• Can’t swallow capsules: Ask for a liquid. If your pharmacy can’t source cefaclor suspension, they may dispense an alternative (often amoxicillin or cephalexin liquids are easier to get).
• Missed multiple doses: Don’t double up. Extend the course only if your clinician advises it. If you missed more than a day early on, let them know.
• Worsening symptoms or new fever after improvement: Recheck. You may have a new infection, non-adherence, or (rarely) a complication.
• Pregnant or breastfeeding: Safe options exist. If you were started on cefaclor and have questions, ask whether penicillin or amoxicillin is a better fit.

Why this advice? It lines up with CDC 2024 guidance, IDSA recommendations on pharyngitis, and New Zealand’s 2025 Formulary and bpacnz updates-sources that keep penicillin/amoxicillin first, prefer cephalexin for non-severe penicillin allergy, and place cefaclor behind those because of tolerability concerns, especially the serum sickness-like reaction signal in kids.

If you already have a cefaclor script, you’re not doing anything wrong-just use it correctly, watch for the warning signs we covered, and check in if things don’t improve on schedule. If you haven’t started yet and you have options, ask whether penicillin, amoxicillin, or cephalexin is the better pick for you or your child.