The standard adult dose of amoxicillin for a bacterial sinus infection is 500 mg taken three times a day, or 875 mg taken twice a day, for a total daily intake of roughly 1,500 to 1,750 mg. Children are dosed by weight, starting at 45 mg per kilogram of body weight per day and sometimes going as high as 90 mg/kg/day depending on the severity and risk of resistant bacteria. But the right dose for any individual depends on several factors, including whether you actually have a bacterial infection, how severe it is, and your local patterns of antibiotic resistance.
The Standard Adult Dose
Most clinical guidelines and trials use one of two regimens for adults with uncomplicated acute bacterial sinusitis: 500 mg three times daily or 875 mg twice daily. A well-known randomized trial published in JAMA used a 10-day course of 500 mg three times daily, totaling 1,500 mg per day.1PubMed Central. Amoxicillin for acute rhinosinusitis: A randomized controlled trial The twice-daily option at 875 mg per dose is equally common in practice and may be easier to remember. Both approaches deliver enough amoxicillin to reach concentrations in sinus tissue that exceed what’s needed to kill the bacteria most commonly responsible for sinus infections.2PubMed. Amoxicillin concentrations in nasal secretions of patients with acute uncomplicated sinusitis and in paranasal sinus mucosa of patients with chronic sinusitis
A study measuring amoxicillin levels in sinus tissue found that 1,000 mg given twice daily produced concentrations high enough to be clinically effective against the usual culprits.2PubMed. Amoxicillin concentrations in nasal secretions of patients with acute uncomplicated sinusitis and in paranasal sinus mucosa of patients with chronic sinusitis That matters because amoxicillin’s effectiveness depends on spending enough time above a certain concentration threshold. As long as you take the doses at roughly even intervals throughout the day, either regimen keeps the drug above that threshold for the pathogens involved.
When Higher Doses Are Prescribed
Some doctors prescribe what’s called “high-dose” amoxicillin, around 2,000 mg twice daily for adults or 80 to 90 mg/kg/day for children. This isn’t about a more severe infection in the Hollywood sense; it’s about resistance. The main bacteria behind sinus infections are Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pyogenes.3PubMed. Microbiology of sinusitis In some communities, a sizable fraction of pneumococcal strains have reduced susceptibility to standard-dose amoxicillin. Pumping up the dose raises the drug concentration in sinus tissue enough to overwhelm these partially resistant bacteria.
For children, the American Academy of Pediatrics spells out when to go high-dose: kids younger than two, those in child care, those recently treated with another antibiotic, or those in communities where resistant pneumococcus exceeds about 10% of isolates. In those situations the guideline calls for 80 to 90 mg/kg/day, with a maximum of 2 g per dose.4Pediatrics. Clinical Practice Guideline for the Diagnosis and Management of Acute Bacterial Sinusitis in Children Aged 1 to 18 Years For adults, a similar logic applies, though the decision often rests on your doctor’s judgment of local resistance patterns and your recent antibiotic history.
Interestingly, a randomized trial comparing high-dose and standard-dose amoxicillin-clavulanate in adults with acute sinusitis found no meaningful difference in improvement. By day three, roughly 44% of the standard-dose group and 36% of the high-dose group reported feeling substantially better or symptom-free, a gap that was not statistically significant.5JAMA Network Open. High-Dose vs Standard-Dose Amoxicillin Plus Clavulanate for Adults With Acute Sinusitis: A Randomized Clinical Trial Diarrhea rates were similar in both groups, hovering around 40 to 43%. The takeaway: for most adults, standard dosing works, and jumping to high-dose may not buy you much unless resistant bacteria are a real concern.
Dosing for Children
Children’s doses are calculated by body weight, not by a fixed number of milligrams. The standard pediatric dose for uncomplicated bacterial sinusitis is 45 mg/kg/day, split into two doses taken twelve hours apart. For a child weighing 20 kilograms (about 44 pounds), that works out to 900 mg per day, or 450 mg per dose.4Pediatrics. Clinical Practice Guideline for the Diagnosis and Management of Acute Bacterial Sinusitis in Children Aged 1 to 18 Years
When the infection is moderate to severe, or when the child has risk factors for resistant organisms, guidelines recommend bumping up to 90 mg/kg/day.6PubMed Central. Acute bacterial sinusitis in children: an updated review At that higher dose, the same 20 kg child would receive 900 mg per dose twice daily, capped at 2 g per dose for larger children. Liquid suspensions come in various concentrations, so parents should pay close attention to the specific product their pharmacy dispenses and use the measuring syringe provided rather than a kitchen spoon.
How Long the Course Should Last
Traditionally, sinus infection antibiotics have been prescribed for 10 to 14 days. But a growing body of evidence questions whether all that time is necessary. A meta-analysis of 12 randomized trials involving over 4,400 patients found that shorter courses of three to seven days had similar clinical success rates compared to longer courses of six to ten days.7PubMed Central. Effectiveness and safety of short vs. long duration of antibiotic therapy for acute bacterial sinusitis: a meta-analysis of randomized trials When the analysis narrowed to five-day versus ten-day regimens specifically, outcomes remained similar, and the shorter group had fewer side effects.
A separate review echoed these findings, concluding that five-day antibiotic therapy can match the effectiveness of a traditional ten-day course for uncomplicated acute maxillary sinusitis in adults.8PubMed. Short-course therapy for acute sinusitis: how long is enough? Despite this, real-world prescribing data in the United States show that most adults still receive courses longer than seven days.9JAMA Internal Medicine. Antibiotic Therapy Duration in US Adults With Sinusitis That gap between evidence and practice matters because every extra day of antibiotics adds side-effect risk and can contribute to resistance.
If your doctor prescribes a 10-day course, follow through on it. But if you have an uncomplicated infection and your clinician suggests five to seven days, the evidence supports that shorter duration. The key is not to stop early on your own because you feel better after two or three days. Feeling better is not the same as clearing the bacteria.
Plain Amoxicillin or Amoxicillin-Clavulanate
You may see amoxicillin-clavulanate (brand name Augmentin) prescribed instead of plain amoxicillin. Clavulanate is a compound that blocks an enzyme called beta-lactamase, which some bacteria produce to neutralize amoxicillin. In theory, adding clavulanate should make the drug effective against a broader range of bugs. In practice, for routine acute sinusitis, the advantage is slim.
A large retrospective study of adults treated in emergency departments and urgent care settings found no significant difference in sinusitis-related return visits between those given plain amoxicillin and those given amoxicillin-clavulanate. What did differ was side effects: the amoxicillin-only group had about a third fewer gastrointestinal complaints.10PubMed Central. Comparative effectiveness of amoxicillin versus amoxicillin‐clavulanate among adults with acute sinusitis in emergency department and urgent care settings The AAP guideline for children allows either drug as first-line therapy, reserving amoxicillin-clavulanate for situations where H. influenzae resistance is likely or the infection is more severe.4Pediatrics. Clinical Practice Guideline for the Diagnosis and Management of Acute Bacterial Sinusitis in Children Aged 1 to 18 Years
If your pharmacy fills a prescription for amoxicillin-clavulanate, note that the dosing is described in terms of the amoxicillin component. A “875/125” tablet means 875 mg of amoxicillin and 125 mg of clavulanate. The clavulanate portion stays relatively constant regardless of whether you’re on standard or high-dose amoxicillin. Too much clavulanate relative to amoxicillin is one of the main culprits behind the diarrhea that comes with Augmentin.
Side Effects to Expect
Amoxicillin is generally well tolerated, but gastrointestinal symptoms are the most common complaint. In large observational data on amoxicillin-clavulanate, diarrhea was the leading side effect, followed by nausea and, less commonly, vomiting. Skin reactions like rash and itching occurred in a small percentage of patients.11PubMed Central. Clinical Outcomes and Real-World Effectiveness of Amoxicillin-Clavulanic Acid Across Indian Healthcare Settings: A Retrospective Multicenter Study These reactions were overwhelmingly mild and resolved on their own.
Taking amoxicillin with food can reduce stomach upset. If diarrhea becomes bothersome, a probiotic taken a few hours apart from the antibiotic may help, though the evidence on that is mixed. More concerning reactions such as severe rash, difficulty breathing, or facial swelling warrant immediate medical attention, as they may indicate an allergic reaction.
Longer antibiotic courses carry a greater toll on your gut microbiome. An animal study found that while bacterial diversity largely recovered after amoxicillin treatment ended, mice that received the drug for 14 days took longer to bounce back than those treated for shorter periods, and certain bacterial groups did not fully recover even three weeks later.12PubMed Central. Effects of different amoxicillin treatment durations on microbiome diversity and composition in the gut This is another reason not to take antibiotics longer than clinically necessary.
What If You’re Allergic to Penicillin
Amoxicillin belongs to the penicillin family, so a penicillin allergy takes it off the table. For mild allergies (say, a childhood rash that wasn’t clearly anaphylaxis), some clinicians will cautiously prescribe certain cephalosporins like cefuroxime, cefpodoxime, or cefdinir, because the actual cross-reactivity rate between penicillins and modern cephalosporins is low. For people with a history of serious allergic reactions, macrolides like clarithromycin or azithromycin are options, as are respiratory fluoroquinolones in adults, though those carry their own side-effect baggage.13PubMed. Beginning antibiotics for acute rhinosinusitis and choosing the right treatment
It’s worth noting that many people who were told they have a penicillin allergy as children actually aren’t allergic. An allergy evaluation or skin test can clarify the situation and potentially restore amoxicillin as an option, which matters because it’s cheap, effective, narrow-spectrum, and well-studied for sinusitis.
Do You Actually Need an Antibiotic
This is the question that gets skipped too often. The vast majority of sinus infections start as viral upper respiratory infections, and most resolve without antibiotics. Even among patients whose sinuses show clear signs of inflammation, only about half have bacteria growing on culture.14PubMed Central. The prevalence of bacterial infection in acute rhinosinusitis: A systematic review and meta-analysis That means roughly half of people with sinus symptoms who might assume they need an antibiotic have a viral infection that amoxicillin won’t touch.
Clinical guidelines generally recommend antibiotics only when symptoms have lasted at least 10 days without improvement, when symptoms are severe (high fever above 39°C with purulent nasal discharge for at least three consecutive days), or when symptoms initially improve and then worsen (“double sickening”). Certain signs, like tooth pain or a foul smell on the breath, are among the better predictors that a sinus infection is bacterial rather than viral.15PubMed Central. Accuracy of Signs and Symptoms for the Diagnosis of Acute Rhinosinusitis and Acute Bacterial Rhinosinusitis
A Cochrane review of delayed prescribing strategies for respiratory infections, including sinusitis, found that when patients were given a prescription but told to wait and fill it only if symptoms didn’t improve, antibiotic use dropped from about 93% to 31% compared to immediate prescribing.16PubMed Central. Delayed antibiotic prescriptions for respiratory infections Patient satisfaction stayed high, and safety was not compromised. If your doctor hands you a “just in case” prescription, that’s what’s happening, and the evidence suggests it’s a reasonable approach.
Nasal Irrigation as a Partner Treatment
Saline nasal irrigation isn’t glamorous, but it’s one of the few adjunctive treatments with real evidence behind it for sinusitis. In a study of children with acute sinusitis, those treated with high-dose amoxicillin plus nasal irrigation recovered faster early on than those using irrigation alone, with 85% cured by day three versus 38% in the irrigation-only group. By day 14, though, cure rates were essentially identical at about 95 to 97%.17PubMed Central. A comparison of the efficacy of amoxicillin and nasal irrigation in treatment of acute sinusitis in children
What this suggests is that irrigation can be a useful complement to antibiotics for quicker early relief, and in milder cases, it may be a reasonable standalone approach if you’re trying to avoid antibiotics. A squeeze bottle or neti pot with isotonic or hypertonic saline washes mucus and inflammatory debris out of the sinuses mechanically. It doesn’t kill bacteria, but it reduces the load and opens drainage pathways. If you’re taking amoxicillin, adding nasal rinses is unlikely to cause harm and may help you feel better sooner.
Chronic Sinusitis Is a Different Problem
Everything discussed so far applies to acute bacterial sinusitis, meaning an infection that’s been going on for less than four weeks. Chronic sinusitis, where inflammation persists for twelve weeks or longer, is a fundamentally different condition with different causes, and the role of antibiotics there is much less clear. A review noted that rigorous studies of antibiotic efficacy for chronic sinusitis are surprisingly few, and the results are conflicting.18PubMed Central. Is there a role for antibiotics in the treatment of chronic rhinosinusitis? Chronic sinusitis is driven more by persistent inflammation, nasal polyps, immune dysfunction, or structural issues than by a single bacterial culprit you can kill with amoxicillin. If your sinus problems have been dragging on for months, the treatment plan will look very different from a 5-to-10-day course of amoxicillin.
Why the Drug Still Reaches Your Sinuses
A reasonable worry is whether a pill you swallow can actually reach infected sinus tissue trapped behind swollen mucous membranes. The answer is yes. After oral amoxicillin is absorbed into the bloodstream, it distributes into sinus mucosa and nasal secretions at concentrations that exceed the minimum needed to kill the common pathogens.19PubMed. Sinus tissue pharmacokinetics after oral administration of amoxicillin/clavulanic acid One pharmacokinetic study comparing 1 g taken twice daily versus 500 mg three times daily found that the larger, less frequent dose actually achieved higher peak concentrations in sinus tissue, while both regimens stayed above the effective threshold for key organisms.20PubMed. Sinusal penetration of amoxicillin-clavulanic acid. Formulation 1 g./125 mg., twice daily versus formulation 500 mg./125 mg., three times daily This is partly why the twice-daily dosing option works: you’re giving a bigger bolus that penetrates well, even if you’re taking fewer doses.
Amoxicillin’s ability to reach the sinuses is one of the reasons it has remained the go-to drug for decades despite the availability of newer antibiotics. Broad-spectrum options like fluoroquinolones can also reach sinus tissue, but they carry more side effects and contribute more to resistance. Amoxicillin’s narrow spectrum, meaning it targets a limited range of bacteria rather than carpet-bombing everything, is actually an advantage. It gets the job done while doing less collateral damage to the beneficial bacteria in your body.