Combination-product calculations
Augmentin substitution: add both ingredients, not just amoxicillin
Two smaller tablets may match one ingredient while doubling another. Augmentin strength substitution requires checking amoxicillin and clavulanate separately, as well as whether the product is a standard tablet or a chewable formulation.
Sources checked October 12, 2026. Independent educational content, not NABP exam questions or individual treatment advice.
Read the slash as two ingredient amounts
A 250/125 mg tablet contains 250 mg amoxicillin and 125 mg clavulanic acid. Taking two supplies 500 mg amoxicillin but 250 mg clavulanate. One 500/125 mg tablet supplies 500 mg amoxicillin and only 125 mg clavulanate.
The label explicitly says two 250 mg standard tablets should not be substituted for one 500 mg standard tablet because the clavulanate amount differs. Matching amoxicillin alone is not a complete equivalence check.
Check formulation as well as nominal strength
The label distinguishes the 250/125 mg standard tablet from the 250/62.5 mg chewable tablet. Both may be described casually as 250 mg, but they do not have the same amoxicillin-to-clavulanate ratio.
A patient weight or pediatric instruction can change which formulation is appropriate. The standard tablet information says the 250 mg tablet should not be used until the pediatric patient weighs at least 40 kg because of the different ratio. Use the exact label for the intended pediatric product.
Do not solve a stock problem by silent substitution
If the prescribed strength is unavailable, verify a suitable product and regimen with the prescriber and dispensing process. Tablet count, frequency and both active ingredients must remain consistent with the actual order.
The arithmetic can identify why a proposed substitute is wrong without identifying the best replacement. That replacement also needs infection indication, age or weight, renal function and product availability.
Use an ingredient table in the explanation
Write amoxicillin and clavulanate as separate columns before comparing total dose. This prevents a familiar tablet-equivalence shortcut from hiding the second ingredient. The same reasoning applies to other fixed-dose combinations, but their actual substitution rules must be checked separately.
The worked example concerns ingredient amounts, not a recommendation for any particular infection regimen. A correct calculation must still be connected to the exact supplied formulation and prescribed directions.
A worked case
One Augmentin 500/125 mg tablet is prescribed. A proposed substitute is two standard 250/125 mg tablets because both give 500 mg amoxicillin. Calculate the second ingredient and decide whether the substitution is equivalent.
- Two standard 250/125 tablets give 500 mg amoxicillin.
- They also give 250 mg clavulanate, compared with 125 mg in the prescribed tablet.
- The label specifically rejects that substitution.
Answer: It is not equivalent: the clavulanate amount doubles. Resolve the correct product rather than matching only the amoxicillin.
Try it before reading the answer
Write the key fact, decision and safety check first. These are original practice exercises, not recalled exam items.
1. How much clavulanate is in two 250/125 tablets?
250 mg.
2. Does the 250 mg chewable have the same ratio as the standard tablet?
No. The cited chewable is 250/62.5, not 250/125.
3. Does matching one active ingredient establish equivalence?
No.
Continue learning
Put the topic into a study planSources and scope
Source dates and limits matter. Follow the current official source for clinical or regulatory decisions. Examples are simplified teaching cases, not prescribing, diagnostic or compounding instructions. Check the full current guidance and individual clinical context.