Macrobid and Macrodantin look alike and sound alike—down to having almost the same active ingredient. They’re both used to treat urinary tract infections, but there are a few key differences you may want to keep in mind.

Macrobid has its daily dosing schedule right in its name—it’s taken 2 times daily (sometimes abbreviated BID on a prescription: MacroBID). The active ingredient in Macrobid is nitrofurantoin monohydrate macrocrystals or nitrofurantoin mono/macro.

Macrodantin, on the other hand, is typically taken 4 times daily. The active ingredient in Macrodantin is nitrofurantion macrocrystalline (sometimes just referred to as nitrofurantoin)—which differs a little from the type of nitrofurantoin in Macrobid.

How is Macrobid (nitrofurantoin mono/macro) available?
Macrobid is available as a 100 mg capsule.

How is Macrodantin (nitrofurantoin macrocrystalline) available?

Macrodantin is available as a capsule in three strengths: 25 mg, 50 mg, and 100 mg.

What are macrocrystals?
Nitrofurantoin products were originally formulated as microcrystals, which came with the unwanted side effects of nausea and vomiting. Medications containing nitrofurantoin were later reformulated with macrocrystals to slow absorption and decrease the effect on your stomach. Only the macrocrystalline versions are still available.

Macrobid takes this a step further by using the monohydrate salt form—all you need to know about this is that it is supposed to further decrease the chance of stomach upset.

Is there an advantage to using Macrobid instead of Macrodantin?

Yes. Macrobid may be easier to take, since it’s given twice daily (while Macrodantin needs to be taken four times daily). Medications like Macrodantin that are taken more frequently throughout the day have a much smaller chance of you taking them as prescribed.

As mentioned above, you may also have a smaller chance of an upset stomach with Macrobid.

How do they compare in price?
Macrobid comes away with a clear advantage here too, at almost half the price of Macrodantin.

Both are available as generics, and the recommended course is usually one week to start with. This means you would take 28 capsules of Macrodantin (4 times daily) and only 14 capsules of Macrobid (2 times daily).

*Prices as of September 16, 2015.