Ceclor is the brand name for cefaclor, an oral antibiotic belonging to the cephalosporin family. It works by disrupting bacterial cell wall synthesis, and it has been prescribed since the late 1970s primarily for ear infections, upper and lower respiratory tract infections, urinary tract infections, and skin infections. While newer antibiotics have taken over many of its traditional roles, cefaclor remains in use worldwide, and its profile of effectiveness, side effects, and quirks around food and allergy cross-reactivity is worth understanding if you or your child has been prescribed it.
What Ceclor Treats and Which Bacteria It Covers
Cefaclor is classified as a second-generation cephalosporin, which places it a step above first-generation drugs like cephalexin in terms of the range of bacteria it can handle. In laboratory testing, cefaclor performed about as well as cephalexin against common gram-positive bacteria like staphylococci and streptococci but showed a clear advantage against several gram-negative organisms. It was more active against Escherichia coli, Salmonella, and Shigella, and it could inhibit Haemophilus strains, including those that produce beta-lactamase enzymes that typically break down older antibiotics.1PubMed Central. Cefaclor: in vitro spectrum of activity and beta-lactamase stability That potency advantage over cephalexin against Haemophilus species and Streptococcus pneumoniae made cefaclor particularly useful for respiratory and ear infections.2PubMed. Laboratory aspects of cefaclor, a new orally-effective cephalosporin antibiotic, are summarized
There are limits. Cefaclor does not cover Serratia, Acinetobacter, indole-positive Proteus, or Bacteroides fragilis.3PubMed Central. Cefaclor: in vitro spectrum of activity and beta-lactamase stability In testing against anaerobic bacteria, it performed reasonably well against gram-positive anaerobic cocci and some Bacteroides species other than B. fragilis, but Clostridia were resistant.4PubMed Central. In vitro activity of cefaclor against aerobic and anaerobic bacteria In practical terms, cefaclor is a reasonable choice when a doctor suspects common community-acquired pathogens, not when hospital-acquired or highly resistant organisms are involved.
The most common clinical use has been in children with acute otitis media and other respiratory infections.5PubMed. Therapy of acute bacterial infections with cefaclor in a pediatric population: an open assessment It also sees use for urinary tract infections caused by susceptible E. coli and for mild skin infections.
How Food Affects Absorption
One of the practical details that matters if you are taking Ceclor is whether to take it with or without food. The answer is more nuanced than the label might suggest. Several studies have consistently found that eating does not reduce the total amount of cefaclor your body absorbs. The area under the concentration-time curve, which reflects total drug exposure, stays about the same whether you eat or fast.6PubMed Central. Pharmacokinetic analysis of the effects of different foods on absorption of cefaclor However, food slows down how quickly the drug gets into your bloodstream and lowers the peak concentration it reaches. One study found that the peak blood level dropped from roughly 8.7 micrograms per milliliter when fasting to about 4.3 micrograms per milliliter after breakfast.7PubMed Central. Comparison of the effects of food on the pharmacokinetics of cefprozil and cefaclor
The type of meal matters too. Rice-based meals slowed absorption more than bread-based meals, and high-fat non-vegetarian meals produced the largest drop in peak levels, while low-fat vegetarian meals had the smallest effect.8PubMed. The effect of four different types of food on the bioavailability of cefaclor Because cefaclor kills bacteria most effectively when its concentration stays above a certain threshold for as long as possible, a lower peak can reduce how well the drug works against borderline-susceptible bugs. If your doctor tells you to take it on an empty stomach, this is why. That said, for the extended-release tablet formulation, the instructions are actually the opposite: it is meant to be taken with food.
Immediate-Release Versus Extended-Release Formulations
Ceclor originally came as a capsule (or liquid suspension for children) taken three times a day. An extended-release tablet was developed later, dosed at 500 mg twice a day. When taken with food, the extended-release version reaches its peak blood concentration about two and a half hours after the dose, compared with about one hour for the standard capsule. Despite the different timing, total drug absorption is equivalent between the two forms.9PubMed. Pharmacologic and clinical comparison of cefaclor in immediate-release capsule and extended-release tablet forms
The practical advantage of the extended-release tablet is that the drug stays above effective concentrations at the actual site of infection for a longer period. In a crossover study of healthy volunteers, the time the drug spent at meaningful levels in tissue fluid was significantly longer with the modified-release formulation than with the standard capsule.10PubMed. Comparative target site pharmacokinetics of immediate- and modified-release formulations of cefaclor in humans For conditions like acute flare-ups of chronic bronchitis, clinical trials showed similar cure rates between the two versions, but the extended-release formulation could be used for seven days instead of ten, and the simpler twice-daily schedule can make it easier to stick with the full course.11PubMed. Pharmacologic and clinical comparison of cefaclor in immediate-release capsule and extended-release tablet forms
Common Side Effects
Cefaclor’s most frequently reported side effects are the same ones you see with most oral antibiotics: nausea and diarrhea. In a controlled trial comparing it with another antibiotic for bronchitis exacerbations, about five percent of patients on cefaclor reported treatment-related adverse events, with nausea and diarrhea topping the list.12The American Journal of Medicine. Safety and efficacy of lomefloxacin versus cefaclor in the treatment of acute exacerbations of chronic bronchitis A broader review of the drug found that side effects are usually minor and short-lived, and drug interactions involving cefaclor are rare.13Clinical Therapeutics. Cefaclor revisited Oral cephalosporins as a class are considered one of the safer groups of antibiotics, though more serious reactions like antibiotic-associated colitis can occur infrequently with any member of this family.
Serum Sickness-Like Reactions in Children
There is one side effect that stands out for Ceclor specifically and that parents should be aware of. Cefaclor has a well-documented association with serum sickness-like reactions, particularly in children. This is not a true serum sickness caused by immune complexes the way the classic form is. Instead, it is thought to involve a reaction to drug metabolites. Symptoms typically include a hive-like rash, itching, joint pain, and sometimes swelling and fever, usually appearing several days into a course of treatment or shortly after finishing one.14PubMed. Serum sickness-like reactions from cefaclor in children
A study of 150 children who experienced adverse skin or joint reactions after antibiotics found that cefaclor was responsible for a disproportionate share. Of 44 children who met the criteria for a serum sickness-like reaction, 32 had received cefaclor alone and another five had received it in combination with other antibiotics. Otitis media was the most common reason the drug had been prescribed. Prolonged symptoms occurred in four children, though all ultimately recovered after the drug was stopped.15PubMed. Adverse skin and joint reactions associated with oral antibiotics in children: the role of cefaclor in serum sickness-like reactions
Research into why this happens points to the gut lining. In a study of children taking cefaclor for upper respiratory infections, those who developed serum sickness-like reactions showed significantly increased intestinal permeability compared with children who took the same drug without problems. Markers of gut barrier damage peaked around day thirteen of treatment and then gradually declined. The finding suggests that cefaclor may trigger these reactions by disrupting the integrity of the intestinal lining, allowing drug metabolites or other molecules to cross into the bloodstream in unusual quantities.16PubMed. Intestinal mucosal permeability of children with cefaclor-associated serum sickness-like reactions If your child develops a rash with joint pain while on Ceclor, stopping the drug is the standard step, and symptoms usually resolve without lasting harm.
Penicillin Allergy and Cross-Reactivity
A question that comes up frequently is whether someone with a penicillin allergy can safely take cefaclor. The old rule of thumb that all cephalosporins should be avoided if you are allergic to penicillin has been largely replaced by a more targeted understanding based on side-chain chemistry. Cefaclor shares an identical side chain with ampicillin, which means that people with a confirmed allergy to ampicillin or amoxicillin face a higher risk of cross-reacting with cefaclor specifically.17The Journal of Allergy and Clinical Immunology: In Practice. Ask the Expert
A study of over 250 patients with confirmed penicillin allergy found that about 38 percent tested positive to aminocephalosporins (the subgroup that includes cefaclor) or cefamandole, all of which share similar or identical side chains with penicillins. When the same patients were challenged with cephalosporins that have different side chains, like cefuroxime or ceftriaxone, all 244 who underwent those challenges tolerated them without problems. Among those specifically challenged with cefaclor, three patients reacted.18PubMed. Cross-Reactivity and Tolerability of Cephalosporins in Patients with IgE-Mediated Hypersensitivity to Penicillins The takeaway is that cross-reactivity is about side-chain similarity, not about the cephalosporin class as a whole. If you have a documented allergy to ampicillin or amoxicillin, your doctor will likely steer you toward a cephalosporin with a different side chain rather than prescribe cefaclor.
How Ceclor Compares to Amoxicillin-Clavulanate for Ear Infections
Because otitis media is one of the most common reasons Ceclor gets prescribed, parents often wonder how it stacks up against amoxicillin-clavulanate, the combination antibiotic widely considered a go-to for ear infections. The picture here is mixed, and the answer may depend on where the study was conducted and which bacterial strains were circulating.
An early randomized trial found that amoxicillin-clavulanate cleared bacteria from the middle ear in about 97 percent of cases after three to six days, compared with 75 percent for cefaclor. The organisms responsible for cefaclor failures included Streptococcus pneumoniae, non-beta-lactamase-producing Haemophilus influenzae, and beta-lactamase-producing Branhamella catarrhalis.19PubMed. A randomized controlled trial of amoxicillin plus clavulanate compared with cefaclor for treatment of acute otitis media A later trial of over 200 children found clinical success rates of about 91 percent for amoxicillin-clavulanate versus 79 percent for cefaclor at the end of the study period.20PubMed. A randomized, observer-blind trial of amoxycillin/clavulanate versus cefaclor in the treatment of children with acute otitis media
However, a separate controlled trial from India reported the opposite result: clinical success was 98 percent with cefaclor versus 85 percent with amoxicillin-clavulanate, and bacterial eradication was also higher in the cefaclor group.21PubMed. Comparative efficacy and safety evaluation of cefaclor VS amoxycillin + calvulanate in children with Acute Otitis Media (AOM) This discrepancy likely reflects differences in the local bacterial populations, resistance patterns, and possibly study design. The balance of evidence from multiple trials leans toward amoxicillin-clavulanate being more consistently effective for otitis media, which is one reason treatment guidelines in many countries prefer it. But Ceclor remains a reasonable second-line option, especially when amoxicillin-based drugs cannot be used.
Resistance and Whether Ceclor Still Works
A large surveillance study that tested cefaclor against thousands of clinical isolates from around the world found that over 90 percent of Haemophilus influenzae (including beta-lactamase producers), Moraxella catarrhalis, and methicillin-susceptible Staphylococcus aureus remained susceptible. About 85 percent of E. coli isolates were also susceptible. For Streptococcus pneumoniae strains that were penicillin-susceptible, there had been no erosion of cefaclor activity since the drug was introduced two decades earlier.22PubMed. Cefaclor: a contemporary look at susceptibility of key pathogens from around the globe That study is now itself over two decades old, and resistance patterns have continued to shift.
The growing threat comes from extended-spectrum beta-lactamase (ESBL)-producing bacteria, which are able to break down cefaclor and many other beta-lactam antibiotics. Recent laboratory work has explored combining cefaclor with beta-lactamase inhibitors like clavulanic acid or sulbactam to rescue its activity against ESBL-producing E. coli. The combinations restored susceptibility in over half of tested isolates and showed bactericidal effects in time-kill assays.23PubMed Central. In Vitro Activity of Cefaclor/Beta-Lactamases Inhibitors (Clavulanic Acid and Sulbactam) Combination Against Extended-Spectrum Beta-Lactamase Producing Uropathogenic E. coli These combinations are not yet approved for clinical use, but they show that there is interest in extending cefaclor’s useful life rather than simply replacing it.
Kidney Impairment and Dose Adjustments
Like most cephalosporins, cefaclor is primarily eliminated through the kidneys. In people with normal kidney function, it has a short half-life of about 40 minutes after a 500 mg dose. As kidney function declines, the drug hangs around longer. In patients with essentially no kidney function, the half-life stretches to roughly 2.3 hours.24PubMed Central. Pharmacokinetics of cefaclor and cephalexin: dosage nomograms for impaired renal function A systematic review confirmed that patients with renal impairment can reach peak blood levels more than twice as high as those with normal kidneys.25PubMed. Exploring the pharmacokinetics of second-generation cephalosporin, cefaclor: a systematic review in healthy and diseased populations While cefaclor is a relatively forgiving drug in terms of toxicity, doctors will typically adjust the dose or extend the interval between doses for patients with significant kidney disease to prevent unnecessarily high drug levels.
Cefaclor Absorption in Children Versus Adults
Parents giving Ceclor suspension to a young child should know that children tend to absorb the drug somewhat differently than adults. In the fed state, total drug exposure in pediatric patients was found to be significantly higher than in adults receiving equivalent weight-adjusted doses.26PubMed. Exploring the pharmacokinetics of second-generation cephalosporin, cefaclor: a systematic review in healthy and diseased populations This is a common pattern with many oral drugs in young children, driven by differences in gut motility, body composition, and how quickly the liver processes the drug. In practice, pediatric dosing is already weight-based and calibrated for these differences, so this is not something parents need to manually account for. But it does mean that the dosing your pediatrician calculates matters, and guessing at a dose based on adult guidelines would be a bad idea.
Where Ceclor Fits in Modern Prescribing
Cefaclor occupies an interesting niche. It is old enough that many clinicians think of it as a relic, yet it continues to see genuine use. A hospital-level antibiotic stewardship study noted that cefaclor was among the oral antibiotics whose relative use actually increased during a period of tighter prescribing controls, suggesting that it filled a specific gap in outpatient therapy where broader-spectrum agents were being pulled back.27PubMed Central. An outpatient antibacterial stewardship intervention during the journey to JCI accreditation Its oral formulation, decent tolerability, and coverage of common respiratory and urinary tract pathogens give it a role when first-line drugs like amoxicillin cannot be used due to allergy concerns (provided the allergy is not to a side-chain-sharing penicillin), resistance, or patient intolerance.
The flip side is that for the infections where Ceclor is most often prescribed, there are frequently better-studied and more effective alternatives available. For pediatric otitis media, amoxicillin or amoxicillin-clavulanate remain preferred in most guidelines. For urinary tract infections, resistance among E. coli to cefaclor has been creeping up in many regions. And the concern about serum sickness-like reactions in children, while uncommon, adds a wrinkle that newer drugs do not carry. If your doctor has chosen cefaclor for you or your child, it likely means the first-choice options were not suitable for your particular situation, and in that role, it remains a well-characterized and workable antibiotic with decades of clinical experience behind it.