Yes, Macrobid (nitrofurantoin) can be safely taken with Lamictal (lamotrigine)
There are no clinically significant drug interactions between nitrofurantoin and lamotrigine, and these medications can be co-administered without dose adjustments.
Evidence Base
Drug Label Information
The FDA-approved prescribing information for Lamictal 1 does not list nitrofurantoin as a contraindicated medication or one requiring special monitoring. The label specifically identifies drugs that interact with lamotrigine (such as valproate, carbamazepine, oral contraceptives, and phenytoin), but nitrofurantoin is notably absent from these lists.
Research Evidence on Drug Interactions
A comprehensive therapeutic drug monitoring study evaluated lamotrigine interactions with 35 different comedications, including 25 psychiatric drugs 2. Nitrofurantoin was not among the medications that altered lamotrigine serum concentration-to-dose ratios, suggesting no pharmacokinetic interaction exists.
The only documented interaction between nitrofurantoin and an antiepileptic drug involves phenytoin (not lamotrigine), where nitrofurantoin decreased phenytoin levels, possibly through hepatic enzyme induction 3. This mechanism does not apply to lamotrigine, which has a different metabolic profile.
Clinical Considerations
When This Combination Is Relevant
This combination is most commonly encountered when treating urinary tract infections in patients taking lamotrigine for:
- Epilepsy
- Bipolar disorder
- Other psychiatric conditions
Nitrofurantoin Dosing for UTI
For acute uncomplicated cystitis, the standard regimen is nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days 4, 5, 6. This remains the first-line recommendation with 88-93% clinical cure rates 4.
No Monitoring Required
Unlike some drug combinations with lamotrigine (such as valproate or oral contraceptives that require dose adjustments), no special monitoring of lamotrigine levels or seizure control is needed when adding nitrofurantoin for a short course of UTI treatment.
Important Caveats
Monitor for lamotrigine-specific adverse effects as you normally would (rash, CNS effects, cardiac symptoms) 1, but these are not increased by nitrofurantoin co-administration.
Complete the full nitrofurantoin course as prescribed—typically 5 days for cystitis 4, 5—without interrupting lamotrigine therapy.