There are numerous drugs on the market that can cause confusion, both among medical professionals or non-medical professionals alike.
This confusion can occur for a multitude of reasons, including similarities in drug name (The Institute for Safe Medication Practices has a comprehensive list of commonly confused drugs) and variations in dosage form or composition.
Two such drugs are Macrobid and Macrodantin. Both contain the same active ingredient, nitrofurantoin (although in different forms), and are used for the treatment of urinary tract infections.
There are two main differences between them:
- Macrodantin contains one form of nitrofurantoin (macrocrystalline) while Macrobid comprises of two types of nitrofurantoin (macrocrystalline and monohydrate)
- Macrobid is dosed twice daily while Macrodantin is dosed four times daily.
I discuss these differences and more in detail in the below sections.
Macrocrystals Vs. Monohydrate
Over time, there has been quite an evolution in nitrofurantoin products. Nitrofurantoin as a drug was approved by the FDA in 1953 as the brand name drug 'Furdantin'.
Furdantin actually contained nitrofurantoin microcrystals and while effective in treating urinary tract infections, it tended to cause significant gastrointestinal side effects, such as nausea and vomiting. It no longer available on the market.
Moving on to the available drugs, as stated above, Macrobid (nitrofurantoin monohydrate/macrocrystals) has two forms of nitrofurantoin while Macrodantin (macrocrystals) has one.
We'll start with nitrofurantoin macrocrystals since both Macrobid and Macrodantin contain it.
The nitrofurantoin macrocrystalline form was approved by the FDA in 1970 as Macrodantin and was far better tolerated regarding side effects than the microcrystal form as it absorbs slower.
Nevertheless, although it absorbs more slowly, it is still metabolized and excreted from our system quickly and requires four times a day dosing to be effective.
The monohydrate form of nitrofurantoin was approved by the FDA in 1991 and is even more slowly absorbed than the macrocrystals due to how it reacts when it reaches our stomach.
Once nitrofurantoin monohydrate comes into contact with the gastric juices in the stomach, it forms 'a gel-like' matrix. This gel-like matrix significantly slows the absorption of nitrofurantoin and it is released slowly over time.
The prescribing information for Macrobid states this property of nitrofurantoin monohydrate as follows:
"...nitrofurantoin monohydrate contained in a powder blend which, upon exposure to gastric and intestinal fluids, forms a gel matrix that releases nitrofurantoin over time."
Macrobid Vs. Macrodantin
Macrodantin contains only nitrofurantoin macrocrystals. It is available in three different strengths:
- 25 mg
- 50 mg
- 100 mg
Macrobid contains 25% percent of the macrocrystalline form and 75% of the monohydrate form.
As Macrobid capsules are 100mg, this equates to each capsule containing 25 mg nitrofurantoin macrocrystals and 75 mg nitrofurantoin monohydrate.
The big advantage of Macrobid, since it contains nitrofurantoin monohydrate, is that it can be dosed less often than Macrodantin and is equally effective in treating urinary tract infections.
Macrobid is dosed:
- One capsule (100 mg) twice daily (every 12 hours) for seven days. Courses of 5 days are becoming more common as they seem to be equally effective and that is the duration the Infectious Diseases Society of America (IDSA) suggests.
Macrodantin is dosed:
- 50 to 100 mg four times daily (every 6 hours) for seven days.
For nitrofurantoin to be effective, it needs to be found in high concentrations in the urine. Therefore, dosing frequency is critical to maintain high concentrations for an extended period.
Since nitrofurantoin monohydrate (which is in Macrobid) gets released slowly over time, it has a longer duration of action. Nitrofurantoin macrocrystals are absorbed far quicker and have a short duration of action.
Is One Better?
Studies indicate that Macrobid and Macrodantin are equally effective in treating uncomplicated urinary tract infections. One isn't considered 'stronger' than the other.
However, Macrobid is often the drug of choice since it is easier to take (twice daily vs. four times daily). Twice daily dosing for Macrobid is easy to remember since 'b.i.d.' in a medical sense means twice a day.
Additionally, the slower absorption of Macrobid results in it having fewer stomach side effects such as nausea, cramping, and vomiting. In other words, it's better tolerated than Macrodantin.
Are There Any Other Differences?
Macrodantin is FDA-approved for the prophylaxis (i.e. prevention) of UTIs while Macrobid is not, although there is no reason that Macrobid couldn't be used.
The prescribing information for Macrodantin lists prophylaxis dosing as:
- 50 to 100 mg by mouth as a single dose at bedtime
Taking Macrobid and Macrodantin with food isn't necessary but may help reduce gastrointestinal side effects. Food also increases the bioavailability of the drugs (i.e. the rate and extent of absorption), but this isn't thought to alter the effectiveness one way or the other.
Article SummaryMacrodantin contains nitrofurantoin in the macrocrystalline form. Macrobid contains nitrofurantoin in two forms, macrocrystalline and monohydrate.
Macrobid is generally considered the drug of choice since it can be dosed twice daily (instead of four times daily for Macrodantin) and causes less gastrointestinal side effects.
- Elsevier ClinicalKey: Nitrofurantoin (Accessed 1/28/19)
- Drugs@FDA (Accessed 1/28/19)
- Macrodantin Prescribing Information (Accessed 1/28/19)
- Macrobid Prescribing Information (Accessed 1/28/19)
- International clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women: A 2010 update by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases. PubMed (Accessed 1/28/19)