Nitrofurantoin

Macrobid is indicated only for acute uncomplicated cystitis caused by susceptible E. coli or S. saprophyticus. Selected macrocrystal capsules and suspension label UTIs caused by susceptible E. coli, enterococci, S. aureus and certain Klebsiella/Enterobacter strains; suspension includes adults and children from 1 month. None is indicated for pyelonephritis or perinephric abscess. Use susceptibility/local resistance information; an in-vitro organism list does not establish every clinical indication.

The 2026 IDSA AMR guidance includes nitrofurantoin among preferred options for susceptible ESBL-producing Enterobacterales uncomplicated UTI. This is a specific resistant-organism/lower-tract context, not a universal first-line recommendation, bloodstream-infection regimen or replacement for product age/renal restrictions.

Macrocrystal and suspension adult labels describe 50–100 mg at bedtime for long-term suppression after weighing risks. The macrocrystal label describes pediatric suppression as low as 1 mg/kg per 24 hours in 1 or 2 doses; this is not a routine acute-UTI regimen or an inferred suspension pediatric suppression instruction. AGS criteria advise avoiding long-term suppression in older adults because of toxicity. IDSA 2026 adult Table 1 lists Macrobid 100 mg every 12 hours or suspension 50 mg every 6 hours for its specified AMR context with normal renal/hepatic function. Its discussion cites 5-day nitrofurantoin trials; the selected Macrobid label still specifies 7 days. The prescriber determines the indication-specific course; no blanket 5-day substitution is provided.

Macrobid’s dose section says over 12 years while its pediatric section says below 12 is unestablished; verify exact-product use at age 12 instead of inferring a regimen. Suspension is 25 mg/5 mL (5 mg/mL): shake vigorously and use an oral syringe. For the labeled pediatric daily mg/kg dose, divide by 4 to obtain each mg dose, then divide by 5 mg/mL for mL. A pharmacist must select and round the measurable dose. The selected printed weight-bucket table has a ≤4 kg row without a lower-weight bound; it is not copied as a universally safe infant volume chart.

Selected U.S. labels contraindicate anuria, oliguria or significant renal impairment, explicitly including CrCl under 60 mL/min or clinically significant elevated serum creatinine; prior nitrofurantoin-related cholestatic jaundice/hepatic dysfunction; and hypersensitivity. Also contraindicated: pregnancy at term (38–42 weeks), labor/delivery or imminent labor, and infants under 1 month. The professional older-adult renal threshold is discussed separately; it does not silently change this labeled threshold.

These selected labels have no boxed warning. Capitalized pulmonary warnings do not create a boxed warning; serious lung, liver, neuropathy, hemolysis and allergy risks still require action.

Common effects include nausea, vomiting or appetite loss; Macrobid trials also reported headache and flatulence. Serious reports include pulmonary/liver injury, neuropathy, blood-count abnormalities, hemolysis, severe skin reactions and allergy; voluntary reports cannot establish a reliable incidence. Overdose often produces vomiting; no specific antidote is described and nitrofurantoin is dialyzable. Obtain immediate medical/Poison Help advice and individualized supportive care. Legacy label emesis instructions are not provided as home treatment; fluid decisions require assessment of renal/cardiac status.

Magnesium-trisilicate antacids reduce absorption. Capsule counseling advises avoiding them; suspension labeling advises monitoring effectiveness if coadministration cannot be avoided. Probenecid or sulfinpyrazone can reduce tubular secretion, increasing serum toxicity while lowering urinary antibacterial exposure; review alternatives or monitor response/adverse effects with the prescriber.

Copper-reduction urine-glucose tests such as Benedict/Fehling can be falsely positive; enzymatic glucose testing is not affected in the cited labels. Nitrofurantoin/quinolone antagonism was demonstrated in vitro, with unknown clinical significance, so no blanket clinical combination contraindication is inferred. Suspension PK studies found altered excretion with propantheline, but clinical significance was unknown and no dose-adjustment formula is supplied.

All selected U.S. labels retain the CrCl <60 mL/min renal contraindication. Separately, 2023 AGS criteria for adults ≥65 advise avoiding nitrofurantoin below CrCl 30 mL/min and for long-term suppression. These sources differ; prescribing in the 30–<60 range requires clinician review of the exact label and applicable guidance rather than an automatic dose reduction. No hepatic adjustment formula is established; previous nitrofurantoin-related hepatic dysfunction is contraindicated and liver toxicity needs monitoring. Older adults need attention to renal function and long-term lung/liver toxicity.

Term pregnancy at 38–42 weeks, labor/delivery or imminent labor is contraindicated. Earlier pregnancy requires individualized assessment: the current suspension label describes inconsistent observational findings that cannot establish absence or presence of birth-defect risk. Nitrofurantoin enters milk. The current suspension label does not recommend breastfeeding an infant under 1 month or with G6PD deficiency at any age. For an infant older than 1 month with normal G6PD, weigh maternal need/feeding benefits and monitor vomiting, diarrhea and rash; capsule labels also emphasize the under-1-month risk.

Macrocrystal/suspension treatment has a labeled weight-based regimen from 1 month; neonates younger than this are contraindicated. Macrobid pediatric age wording has the dose-section boundary noted above. Capsule sizes are not a reason to invent a capsule-opening or homemade liquid procedure. Label studies describe reversible sperm-count suppression at high doses (≥10 mg/kg/day in some human observations); they do not establish infertility at every standard therapeutic dose.

Bacterial flavoproteins reduce nitrofurantoin to intermediates that damage multiple macromolecular targets, disrupting protein synthesis, metabolism and nucleic-acid/cell-wall processes. Urinary concentrations are antibacterial. Susceptibility is organism/strain-dependent; in-vitro activity is not a guarantee of clinical efficacy or resistance absence.

Macrobid release

25 mg macrocrystals plus 75 mg monohydrate; monohydrate forms a gel matrix releasing drug over time. Food increases bioavailability by approximately 40%.

Macrocrystals / suspension

Food improves exposure; macrocrystals absorb more slowly than the smaller-crystal form. Do not exchange every-12-hour and 4-times-daily schedules automatically.

Distribution / elimination

Routine blood concentrations are low and tissue distribution is limited. Drug is excreted in urine and may turn it brown; renal function influences urinary recovery.

Data limits

Published urinary recovery values differ by formulation/study. No universal half-life, recovery percentage or hepatic/pediatric PK adjustment is extrapolated.

Confirm lower-tract bacterial indication, renal function/urine output, allergy, previous nitrofurantoin liver injury, pregnancy stage and infant/G6PD considerations. Review culture/susceptibility and symptoms; capsule labels call for before/after cultures, with persistence/reappearance requiring reevaluation. For ongoing therapy reassess benefit versus harm and monitor pulmonary status, liver biochemistry and renal function; no universal monthly testing schedule is invented. Watch for neuropathy, hemolysis and severe diarrhea.

Take with food and verify the exact formulation/schedule; complete the prescribed course without independently shortening or prolonging it. Shake suspension vigorously and measure with the supplied appropriate oral syringe. Brown urine can reflect the drug, but breathing difficulty/new cough, jaundice, numbness/weakness, allergic swelling or watery/bloody diarrhea need prompt assessment. Avoid magnesium-trisilicate antacids and disclose gout medicines. Fever/flank pain, worsening symptoms or recurrence needs reassessment for infection beyond simple cystitis.

Ingredient / route

Nitrofurantoin 100 mg: 25 mg macrocrystals + 75 mg monohydrate · oral capsule.

Appearance / imprint

Opaque black/yellow capsule; banded Macrobid and 52427-285.

Labeler / example NDC

Almatica Pharma · 52427-285-01, bottle of 100.

U.S. status

Prescription NDA020064 product; no DEA schedule. Current source records do not prove local stock.

Macrobid

100 mg monohydrate/macrocrystal capsule with twice-daily labeled regimen.

Selected Amneal macrocrystals

50 mg pink/white (Zenith 50 mg / 2130); 100 mg pink (Zenith 100 mg / 2131), manufacturer-specific markings. Example NDCs 0115-1643-01 and 0115-1645-01, 100-count bottles.

Selected Somerset suspension

25 mg/5 mL = 5 mg/mL, yellow flavored oral suspension; NDC 70069-829-01, amber PET bottle of 230 mL.

Scope

Other manufacturers/strengths, including historical Macrodantin 25 mg records, need their own exact label/status check. No injectable formulation, automatic interchange or exhaustive present-stock claim is made.

Selected Macrobid: 15–30°C. Selected Amneal macrocrystals: 20–25°C, tight light-resistant container with child-resistant closure. Selected suspension: 20–25°C (excursions 15–30°C), protect from strong light and freezing, shake vigorously, dispense in tight light-resistant PET/glass. Its label says use within 30 days without defining the clock here; have the dispensing pharmacist specify the start/discard date. Keep all medicines away from children.