Macrobid: Indications, Dosage, Precautions, Adverse Effects
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Macrobid - Product Information

Manufacture: Actavis
Country: Canada
Condition: Bladder Infection, Prevention of Bladder infection (Cystitis Prophylaxis), Urinary Tract Infection
Class: Urinary anti-infectives
Form: Capsules
Ingredients: nitrofurantoin, carbomer 934P, corn starch, compressible sugar, D&C Yellow No. 10, edible gray ink, FD&C Blue No. 1, FD&C Red No. 40, gelatin, lactose, magnesium stearate, povidone, talc, and titanium dioxide

(nitrofurantoin monohydrate/macrocrystals)

capsules

USP Dissolution Test 2

Therapeutic Classification

Urinary Tract Antibacterial

Actions and Clinical Pharmacology

Nitrofurantoin is reduced by bacterial flavoproteins to reactive intermediates which inactivate or alter bacterial ribosomal proteins and other macromolecules. As a result of such inactivations, the vital biochemical processes of protein synthesis, aerobic energy metabolism, DNA synthesis, RNA synthesis, and cell wall synthesis are inhibited. The broad-based nature of this mode of action may explain the lack of acquired bacterial resistance to nitrofurantoin, as the necessary multiple and simultaneous mutations of the target macromolecules would likely be lethal to the bacteria.

Each MacroBID capsule contains two forms of nitrofurantoin. Twenty-five percent is macrocrystalline nitrofurantoin, which has slower dissolution and absorption than nitrofurantoin monohydrate. The remaining 75% is nitrofurantoin monohydrate contained in a powder blend which, upon exposure to gastric and intestinal fluids, forms a gel matrix that releases nitrofurantoin over time.

Following a single 100 mg dose, the extent and rate of nitrofurantoin excretion in the urine are similar for 100 mg capsules of MacroBID and 50 or 100 mg capsules of Macrodantin (nitrofurantoin macrocrystals). Nitrofurantoin bioavailability can be increased by as much as 40% when MacroBID is administered with food. Approximately 20-25% of a single dose of MacroBID is recovered in the urine unchanged over 24 hours and drug concentrations inhibitory of bacterial growth are reached or exceeded in the urine. Plasma levels attained with MacroBID usually do not exceed 1 μg/mL and are not considered systemically therapeutic.

Indications and Clinical Use

MacroBID is indicated for the treatment of acute uncomplicated urinary tract infections, e.g. cystitis, when due to susceptible strains of Escherichia coli, and Staphylococcus saprophyticus.

MacroBID is not indicated for the treatment of associated renal cortical or perinephric abscesses.

MacroBID is not indicated for therapy of any systemic infections or for use in prostatitis.

Contraindications

Anuria, oliguria, or significant impairment of renal function (creatinine clearance under 60 mL per minute or clinically significant elevated serum creatinine) are contraindications to therapy with this drug. Treatment of this type of patient carries an increased risk of toxicity because of impaired excretion of the drug. For the same reason, this drug is much less effective under these circumstances.

The drug is contraindicated in pregnant patients during labour and delivery, or when the onset of labour is imminent, and in infants under one month of age because of the possibility of hemolytic anemia in the fetus or the newborn infant due to their immature erythrocyte enzyme systems (glutathione instability).

MacroBID capsule therapy is also contraindicated in those patients with known hypersensitivity to nitrofurantoin.

Warnings

Acute, subacute or chronic pulmonary reactions have been observed in patients treated with nitrofurantoin products (SEE ADVERSE REACTIONS). If these reactions occur, the drug should be withdrawn and appropriate measures taken. Reports have cited pulmonary reactions as a contributing cause of death.

Chronic pulmonary reactions (diffuse interstitial pneumonitis or pulmonary fibrosis, or both) can develop insidiously. These reactions occur rarely and generally in patients receiving therapy for six months or longer. Close monitoring of the pulmonary condition of patients receiving long-term therapy is warranted and requires that the benefits of therapy be weighed against potential risks (SEE ADVERSE REACTIONS).

Hepatic reactions, including hepatitis, hepatic necrosis, cholestatic jaundice and chronic active hepatitis, occur rarely. Fatalities have been reported. The onset of chronic active hepatitis may be insidious, and patients should be monitored periodically for changes in liver function. If hepatitis occurs, the drug should be withdrawn immediately and appropriate measures taken.

Peripheral neuropathy (including optic neuritis) may occur with nitrofurantoin therapy; this may become severe or irreversible. Fatalities have been reported. Predisposing conditions such as renal impairment (creatinine clearance under 60 mL per minute or clinically significant elevated serum creatinine), anemia, diabetes mellitus, electrolyte imbalance, vitamin B deficiency, and debilitating disease may enhance such occurrence. Patients receiving long-term therapy should be monitored periodically for changes in renal function. If numbness or tingling occurs, discontinue use.

Cases of hemolytic anemia of the primaquine-sensitivity type have been induced by nitrofurantoin. The hemolysis appears to be linked to a glucose-6-phosphate dehydrogenase deficiency in the red blood cells of the affected patients. This deficiency is found in 10 percent of Blacks and a small percentage of ethnic groups of Mediterranean and Near-Eastern origin. Any sign of hemolysis is an indication to discontinue the drug. Hemolysis ceases when the drug is withdrawn.

Pseudomonas is the organism most commonly implicated in superinfections in patients with nitrofurantoin preparations.

Carcinogenesis, Mutagenesis and Impairment of Fertility

Nitrofurantoin presented evidence of carcinogenic activity in female B6C3F1 mice as shown by increased incidences of tubular adenomas, benign mixed tumours, and granulosa cell tumours of the ovary. In male F344/N rats, there were increased incidences of uncommon kidney tubular cell neoplasms, osteosarcomas of the bone, and neoplasms of the subcutaneous tissue. In one study involving three subcutaneous injections of 75 mg/kg nitrofurantoin to pregnant female mice, lung papillary adenomas were observed in the F1 generation.

Nitrofurantoin was not carcinogenic when fed to female Holtzman rats for 44.5 weeks or to female Sprague-Dawley rats for 75 weeks. Two chronic rodent bioassays utilizing male and female Sprague-Dawley rats and two chronic bioassays in Swiss mice and BDF1 mice revealed no evidence of carcinogenicity.

Nitrofurantoin has demonstrated mutagenic potential in a variety of laboratory assays conducted in vitro with mammalian and non-mammalian cells exposed to therapeutically attainable and higher concentrations. Point and possibly other types of mutations were observed in bacteria, yeast and fungi. Damage to DNA or inhibition of DNA synthesis were produced in human fibroblasts and lymphocytes, and Chinese hamster ovaries and lung fibroblasts.

In vivo tests on rodents utilizing a wide range of doses demonstrated similar potential. DNA damage to liver, lung, spleen and kidney were observed in rat (alkaline elution test), immature red blood cells (rat micronucleus test) and sperm (H-test in mouse). Some test results were negative such as the sex-linked recessive lethal assay in Drosophila where nitrofurantoin was administered by feeding or injection.

The significance of the carcinogenicity and mutagenicity findings relative to the therapeutic use of nitrofurantoin in humans is unknown. Because of the potential toxicity of nitrofurantoin when used for long-term therapy, the benefits of long-term therapy should be weighed against potential risks (See DOSAGE AND ADMINISTRATION section for prescribing information).

The administration of high doses of nitrofurantoin to rats causes temporary spermatogenic arrest, which is reversible on discontinuing the drug. Doses of 10 mg/kg/day or greater in healthy human males may, in certain unpredictable instances, produce slight to moderate spermatogenic arrest with a decrease in sperm count.

Precautions

Drug Interactions

Antacids containing magnesium trisilicate, when administered concomitantly with nitrofurantoin, reduce both the rate and extent of absorption. The mechanism for this interaction probably is adsorption of drug onto the surface of magnesium trisilicate. Nitrofurantoin should not be given along with drugs which may produce impaired renal function. Uricosuric drugs, such as probenecid and sulfinpyrazone, may inhibit renal tubular secretion of nitrofurantoin. The resulting increase in serum levels may increase toxicity and the decreased urinary levels could lessen its efficacy as a urinary tract antibacterial.

Drug/Laboratory Test Interactions

As a result of administration of nitrofurantoin, a false-positive reaction for glucose in the urine may occur. This has been observed with Benedict's and Fehling's solution but not with the glucose enzymatic test.

Antimicrobial Antagonism

Antagonism has been demonstrated in vitro between nitrofurantoin and quinolone antimicrobials. Although the clinical significance of this finding is unknown, concomitant MacroBID and quinolone therapy should be approached with caution.

Pregnancy

Several reproduction studies performed in rabbits and rats with low multiples of human doses and plasma levels revealed no evidence of general reproductive effects, impaired fertility or harm to the fetus. However, in one published study in which pregnant mice were administered 250 mg/kg subcutaneously on three days, growth retardation and a low incidence of malformations were observed. These effects were not observed at 100 mg/kg. In another controlled study in which cultured rat embryos were exposed for 26 hours to concentrations of 48 μg/mL all were malformed. None of those exposed to 60 μg/mL of nitrofurantoin survived.

The relevance of these findings to humans is uncertain. There are, however, no adequate well controlled studies in pregnant women. Though animal reproduction studies are not always predictive of human response, this drug should not be used during pregnancy unless clearly needed.

Labour and Delivery

Nitrofurantoin should not be given to women during labour and delivery, or when the onset of labour is imminent (SEE CONTRAINDICATIONS).

Nursing Mothers

Nitrofurantoin has been detected in trace amounts in breast milk. Caution should be exercised when nitrofurantoin is administered to a nursing woman, especially if the infant is known or suspected to have a glucose-6-phosphate dehydrogenase deficiency (SEE CONTRAINDICATIONS).

Pediatric Use

Nitrofurantoin is contraindicated in infants under one month of age (SEE CONTRAINDICATIONS and DOSAGE AND ADMINISTRATION).

Adverse Reactions

In limited clinical trials, MacroBID 100 mg capsule b.i.d. demonstrated an equivalent side effect profile to Macrodantin 50 mg q.i.d.

In clinical trials of MacroBID the most frequent clinical adverse events that were reported as possibly or probably drug-related were nausea (8%), headache (6%), and flatulence (1.5%).

The following additional clinical adverse events have been reported with the use of nitrofurantoin.

Respiratory

Chronic, subacute or acute pulmonary hypersensitivity reactions may occur with the use of nitrofurantoin (SEE WARNINGS). Chronic pulmonary reactions generally occur in patients who have received continuous treatment for 6 months or longer. Malaise, dyspnea on exertion, cough, and altered pulmonary function are common manifestations which can occur insidiously. Radiologic and histologic findings of diffuse interstitial pneumonitis or fibrosis, or both, are also common manifestations of the chronic pulmonary reaction. Fever is rarely prominent. The severity of chronic pulmonary reactions and the degree of their resolution appear to be related to the duration of therapy after the first clinical signs appear. Pulmonary function may be impaired permanently, even after cessation of nitrofurantoin therapy. The risk is greater when pulmonary reactions are not recognized early.

In subacute pulmonary reactions, fever and eosinophilia occur less often than in the acute form. Upon cessation of therapy, recovery may require several months. If the symptoms are not recognized as being drug-related and nitrofurantoin is not stopped, the symptoms may become more severe.

Acute reactions are commonly manifested by fever, chills, cough, chest pain, dyspnea, pulmonary infiltration with consolidation or pleural effusion on x-ray, and eosinophilia. Acute reactions usually occur within the first week of treatment and are reversible with cessation of therapy. Resolution often is dramatic.

Changes in ECG may occur associated with pulmonary reactions.

Collapse and cyanosis have seldom been reported.

Gastrointestinal

Diarrhea, dyspepsia, abdominal pain, constipation, emesis, sialadenitis, pancreatitis.

Pseudomembranous colititis, including that due to an overgrowth by Colstridium difficile, have been reported rarely with the use of nitrofurantoin.

Hepatic

Hepatic reactions, including hepatitis, cholestatic jaundice, chronic active hepatitis, andhepatic necrosis occur rarely (SEE WARNINGS).

Neurologic

Peripheral neuropathy, including optic neuritis (SEE WARNINGS).

Dizziness, drowsiness, amblyopia, asthenia, vertigo, and nystagmus also have been reported with the use of nitrofurantoin.

Benign intracranial hypertension has seldom been reported.

Confusion, depression, euphoria and psychotic reactions have been reported rarely.

Dermatologic

Alopecia.

Exfoliative dermatitis and erythema multiforme (including Stevens-Johnson Syndrome) have been reported rarely.

Allergic Reactions

Lupus-like syndrome associated with pulmonary reaction to nitrofurantoin has been reported. Also, angioedema; maculopapular, erythematous or eczematous eruptions; pruritis; urticaria; anaphylaxis; arthralgia; myalgia; drug fever; chills; and malaise have been reported.

Hematologic

Glucose-6-phosphate dehydrogenase deficiency anemia (SEE WARNINGS), agranulocytosis, leukopenia, granulocytopenia, hemolytic anemia, thrombocytopenia, megaloblastic anemia, and eosinophilia have occurred. In most cases, these hematologic abnormalities resolved following cessation of therapy. Aplastic anemia has been reported rarely.

Miscellaneous

As with other antimicrobial agents, superinfections with resistant organisms, e.g., Pseudomonas species or Candida species, may occur with the use of nitrofurantoin. Superinfections have been limited to the genitourinary tract.

Increased AST (SGOT), increased ALT (SGPT), decreased hemoglobin and increased serum phosphorus.

Nitrofurantoin may cause a rust yellow to brown discolouration of the urine. The clinical significance is unknown.

Symptoms and Treatment of Overdosage

Occasional incidents of acute overdosage of nitrofurantoin have not resulted in any specific symptomatology other than vomiting. In case vomiting does not occur soon after an excessive dose, induction of emesis is recommended. There is no specific antidote for nitrofurantoin but a high fluid intake should be maintained to promote urinary excretion of the drug. It is dialyzable.

Dosage and Administration

Adults and Children over 12 years

One MacroBID 100 mg capsule twice a day for 7 days (maximum 200 mg/day).

MacroBID should be taken every 12 hours with food or milk to minimize gastric upset.

Therapy for acute urinary tract infections should be continued for 7 days or for at least 3days after sterility of the urine is obtained. Continued infection indicates the need for reevaluation.