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Rifamycin Delayed-Release Tablets

TABLE OF CONTENTS

1. DESCRIPTION 8. USE IN SPECIFIC POPULATIONS
2. INDICATIONS AND USAGE 9. OVERDOSAGE
3. DOSAGE AND ADMINISTRATION 10. MECHANISM OF ACTION
4. CONTRAINDICATIONS 11. PHARMACODYNAMICS
5. WARNINGS AND PRECAUTIONS 12. PHARMACOKINETICS
6. ADVERSE REACTIONS 13. HOW SUPPLIED/STORAGE AND HANDLING
7. DRUG INTERACTIONS

 

1. DESCRIPTION

Rifamycin, delayed-release tablet, for oral administration, contains 194 mg of rifamycin equivalent to 200 mg of rifamycin sodium.

Rifamycin sodium is a rifamycin antibacterial. It is designated chemically as: Sodium (2S,12Z,14E,16S,17S,18R,19R,20R,21S,22R,23S,24E)-21-(acetyloxy)-6,9,17,19-tetrahydroxy-23-methoxy-2,4,12,16,18,20,22-heptamethyl-1,11-dioxo-1,2-dihydro-2,7-(epoxypentadeca[1,11,13]trienimino)naphtho[2,1-b]furan-5-olate. Its structural formula is:

Empirical formula: C37H46NNaO12 - Molecular weight: 720 g/mol

Rifamycin sodium is a fine or slightly granular powder, soluble in water, and freely soluble in anhydrous ethanol.

Rifamycin, delayed-release tablets are enteric coated with a pH-resistant polymer film which breaks down above pH 7. The tablet core contains rifamycin. The tablets are yellow brown and ellipsoidal.

Each tablet contains the following inactive ingredients: ammonio methacrylate copolymer (Type B), ascorbic acid, glyceryl distearate, lecithin, magnesium stearate, mannitol, methacrylic acid and methyl methacrylate copolymer (1:2), polyethylene glycol 6000, colloidal silicon dioxide, talc, titanium dioxide, triethylcitrate, yellow ferric oxide.

2. INDICATIONS AND USAGE

2.1 Travelers’ Diarrhea

Rifamycin is indicated for the treatment of travelers’ diarrhea (TD) caused by non-invasive strains of Escherichia coli in adults.

Limitations of Use

Rifamycin is not indicated in patients with diarrhea complicated by fever or bloody stool or due to pathogens other than noninvasive strains of Escherichia coli [see Warnings and Precautions (5), Clinical Studies].

2.2 Usage

To reduce the development of drug-resistant bacteria and maintain the effectiveness of rifamycin and other antibacterial drugs, rifamycin should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

3. DOSAGE AND ADMINISTRATION

3.1 Basic Dosing Information

The recommended dose of rifamycin is 388 mg (two tablets) orally twice daily (in the morning and evening) for three days. Take each dose with a glass of liquid (6-8 ounces). Do NOT take rifamycin concomitantly with alcohol. Rifamycin can be taken with or without food.

3.2 Important Administration Instructions

Rifamycin must be taken orally. Swallow the tablets whole. Do NOT crush, break or chew the delayed-release tablets.

4. CONTRAINDICATIONS

Rifamycin is contraindicated in patients with a known hypersensitivity to rifamycin, any of the other rifamycin class antimicrobial agents (e.g. rifaximin), or any of the components in rifamycin.

5. WARNINGS AND PRECAUTIONS

5.1 Risk of Persistent or Worsening of Diarrhea Complicated by Fever and/or Bloody Stool

Rifamycin was not shown to be effective in patients with diarrhea complicated by fever and/or bloody stool. Patients with these conditions treated with rifamycin had prolonged time to last unformed stool (TLUS). The effectiveness of rifamycin in travelers’ diarrhea caused by pathogens other than E. coli has not been demonstrated. Rifamycin is not recommended for use in patients with diarrhea accompanied by fever or bloody stools or due to pathogens other than noninvasive strains of E. coli [see Indications and Usage (2), Clinical Studies].

Discontinue rifamycin if diarrhea gets worse or persists more than 48 hours and consider alternative antibacterial therapy.

5.2 Clostridium difficile-Associated Diarrhea

Clostridium difficile-associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon which may lead to overgrowth of C. difficile.

C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile may cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibacterial drug use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.

If CDAD is suspected or confirmed, antibacterial drug use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, specific antibiotic treatment of C. difficile, and/or surgical evaluation should be instituted as clinically indicated.

5.3 Development of Drug-Resistant Bacteria

Prescribing rifamycin in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

6. ADVERSE REACTIONS

6.1 Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The safety of oral rifamycin 388 mg twice daily was assessed in 619 adults with travelers’ diarrhea in two controlled clinical trials (Trial 1 and Trial 2) with 96% of patients receiving three or four days of treatment. These patients had a mean age of 36.2 years (range 18 to 87 years) with 7% ≥ 65 years old; 49% were male, 84% were White, and 4% were Hispanic.

Discontinuation of rifamycin due to adverse reactions occurred in 1% of patients. The most frequent adverse reactions leading to discontinuation of rifamycin were abdominal pain (0.5%) and pyrexia (0.3%).

In Trial 1 (placebo-controlled), the adverse reaction that occurred in at least 2% of rifamycin-treated patients (n = 199) and with an incidence higher than in the placebo group was constipation (3.5% rifamycin, 1.5% placebo).

In Trial 2 (active comparator), the adverse reaction that occurred in at least 2% of rifamycin-treated patients (n = 420) and with an incidence higher than in the ciprofloxacin group was headache (3.3% rifamycin, 1.9% ciprofloxacin).

Adverse reactions reported in <2% of patients receiving rifamycin 388 mg twice daily with a higher incidence than the comparator group was dyspepsia.

7. DRUG INTERACTIONS

No clinical Drug-Drug Interactions (DDIs) have been studied. Based on the minimal systemic rifamycin concentrations observed after the recommended dose of rifamycin, clinically relevant DDIs are not expected [see Clinical Pharmacology].

8. USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Risk Summary

There are no available data on rifamycin use in pregnant women to inform any drug associated risks for major birth defects, miscarriage, or adverse maternal or fetal outcomes. Systemic absorption of rifamycin in humans is negligible following oral administration of the recommended dose of rifamycin [see Clinical Pharmacology]. Due to the negligible systemic exposure, it is not expected that maternal use of rifamycin will result in fetal exposure to the drug.

In animal reproduction studies, no malformations were observed in pregnant rats or rabbits at exposures 25,000 and 500 times (based on AUC), respectively, the human exposure achieved with the recommended clinical dose of rifamycin. Treatment of pregnant rats with rifamycin at more than 1,000 times the maximum plasma concentration (Cmax) and 25,000 times the systemic exposure (based on AUC) during the period of organogenesis resulted in maternal toxicity, decreased fetal weight, and variations in diaphragm formation. Similarly, treatment of pregnant rabbits with rifamycin at more than 10 times the maximum human plasma concentration (Cmax), resulted in maternal toxicity, decreased fetal weight, and slightly delayed fetal ossifications [See Data].

All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. Advise pregnant women of the potential risk to a fetus.

Animal Data

Embryofetal toxicity studies in rats and rabbits did not show malformations up to the maximum tested doses of 855 and 85.5 mg/kg, (25,000 and 500 times greater plasma exposure based on AUC), respectively, of rifamycin given orally during the period of organogenesis (gestational days 6-17/18). In rats, the high dose of 855 mg/kg/day caused reduction in maternal food consumption, reduced fetal weight and a higher number of fetuses with thin tendinous diaphragm. In rabbits, the high dose of 85.5 mg/kg/day caused a reduction in food consumption and bodyweight gain in pregnant dams, as well as reduced fetal weights and slight delay in ossification, including slightly higher incidences of fetuses with skull suture bone variations, enlarged skull fontanelle and incompletely ossified digit 5 medial phalanx of both forelimbs. No adverse fetal effects were observed in rats and rabbits administered lower doses of oral rifamycin.

8.2 Lactation

Risk Summary

There is no information regarding the presence of rifamycin in human milk, the effects on the breastfed infant, or the effects on milk production. Systemic absorption of rifamycin in humans is negligible following oral administration of the recommended dose of rifamycin; therefore, exposure to a breastfed infant through breastmilk is expected to be negligible [see Clinical Pharmacology]. There are no animal lactation data following oral rifamycin administration. Following single intravenous injection of rifamycin to lactating ewes, rifamycin has been shown to pass into milk.

The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for rifamycin and any potential adverse effects on the breast-fed infant from rifamycin or from the underlying maternal condition.

8.4 Pediatric Use

The safety and effectiveness of rifamycin has not been established in pediatric patients less than 18 years of age with travelers’ diarrhea.

8.5 Geriatric Use

Clinical studies with rifamycin for travelers’ diarrhea did not include sufficient numbers of patients aged 65 and older to determine whether they respond differently than younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients.

8.6 Renal Impairment

The pharmacokinetics of rifamycin in patients with impaired renal function has not been studied. Given the minimal systemic exposure of rifamycin (taken as rifamycin) and minor role of renal excretion in elimination of rifamycin, renal impairment is not expected to have a clinically meaningful effect on rifamycin systemic exposure necessitating a dose adjustment.

8.7 Hepatic Impairment

The pharmacokinetics of rifamycin in patients with impaired hepatic function has not been studied. Given the minimal systemic exposure of rifamycin (taken as rifamycin) hepatic impairment is not expected to have a clinically meaningful effect on rifamycin systemic exposure necessitating a dose adjustment.

9. OVERDOSAGE

No specific information is available on the treatment of overdose with rifamycin. In the case of overdose, discontinue rifamycin, treat symptomatically, and institute supportive measures as required.

10. MECHANISM OF ACTION

Rifamycin is an antibacterial drug.

Mechanism of Action

Rifamycin belongs to the ansamycin class of antibacterial drugs and acts by inhibiting the beta-subunit of the bacterial DNA-dependent RNA polymerase, blocking one of the steps in DNA transcription. This results in inhibition of bacterial synthesis and consequently growth of bacteria.

Resistance

Resistance to rifamycin is associated with mutations in the RNA polymerase beta subunit. Among E. coli strains, the spontaneous mutation frequency rate of rifamycin ranged from 10-6 to 10-10 at 4x – 16x MIC; the mutation frequency was independent of rifamycin concentration. Increases in the minimum inhibitory concentrations were observed both in vitro and while on treatment following exposure to rifamycin. Cross-resistance between rifamycin and other ansamycins have been observed.

Antibacterial Activity

Rifamycin has been shown to be active against most isolates of the following pathogen both in vitro and in clinical studies of travelers’ diarrhea:

Escherichia coli (enterotoxigenic and enteroaggregative isolates).

11. PHARMACODYNAMICS

Rifamycin exposure-response relationships and time course of pharmacodynamic response are unknown.

12. PHARMACOKINETICS

Plasma Concentrations

In healthy adults receiving the recommended dose of 388 mg rifamycin (taken as rifamycin) twice daily for 3 days, the maximum observed rifamycin concentration in plasma was 8.72 ng/mL (6 hours after the last dose). A majority (67%) of rifamycin concentrations in plasma were below the limit of quantification (< 2 ng/mL) at this time point.

Absorption

Rifamycin (taken as rifamycin) has limited systemic exposure after oral administration of the recommended dosage. Based on total urinary excretion data, bioavailability was < 0.1% under fasting conditions.

Food Effect

A food-effect study involving administration of rifamycin to healthy volunteers under a fasted state and with a meal (approximately 1,000 kcal including 500 kcal from fat) indicated that food decreased systemic exposure of rifamycin. The decrease in systemic exposure of rifamycin is not expected to be clinically relevant [see Dosage and Administration (3.2)].

Distribution

Plasma protein binding was approximately 80% in vitro. Binding was primarily to albumin and was inversely proportional to concentration.

Elimination

The apparent half-life of orally administered rifamycin (taken as rifamycin) in plasma is unknown.

Metabolism

Cytochrome P450 (CYP) based metabolism of rifamycin was not observed in vitro.

Excretion

After a single oral dose of 400 mg rifamycin (388 mg rifamycin base) in fasting healthy adults, fecal excretion of rifamycin was on average 86% of the nominal dose.

Specific Populations

The pharmacokinetics of rifamycin (taken as rifamycin) in patients with impaired renal or hepatic function have not been studied.

Drug Interaction Studies

Clinical drug-drug interaction studies of rifamycin (taken as rifamycin) have not been conducted.

In Vitro Transporter Studies where Drug Interaction Potential Was Not Further Evaluated Clinically

Rifamycin is a substrate of P-glycoprotein (P-gp) and anticipated to be an inhibitor of P-gp and breast cancer resistant protein (BCRP) in the gut.

Rifamycin is an inhibitor of renal transporters organic anion transporter (OAT) 3, multidrug and toxin extrusion (MATE) 1, and MATE2-K transporters in vitro, however, based on systemic concentrations of rifamycin observed after administration of the recommended dose, clinically relevant inhibition of these transporters in vivo is unlikely.

In Vitro Cytochrome P450 (CYP) Studies where Drug Interaction Potential Was Not Further Evaluated Clinically

Rifamycin is an inhibitor of CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4/5 in vitro, however, based on systemic concentrations of rifamycin observed after administration of the recommended dose clinically relevant inhibition of these enzymes in vivo is unlikely.

Rifamycin is an inducer of CYP3A4 and CYP2B6 but not CYP1A2 in vitro, however, based on systemic concentrations of rifamycin observed after administration of the recommended dose, clinically relevant induction of these enzymes in vivo is unlikely.

Rifamycin is not a substrate of CYPs 1A2, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4/5.

13. HOW SUPPLIED/STORAGE AND HANDLING

How Supplied:

AEMCOLO delayed-release tablets contain194 mg of rifamycin (equivalent to 200 mg of rifamycin sodium), and are yellow brown, ellipsoidal and film coated. These are packaged in blister cards of 12 tablets contained in a cardboard carton. They are supplied as follows:

NDC (71068-001-10) : child resistant box of 12 tablets.

NDC (71068-001-11) : box of 36 tablets.

Storage and Handling:

Store at 20° to 25°C (68° to 77°F); excursions permitted to 15°C to 30°C (59°F to 86°F) [see USP Controlled Room Temperature].

Rx only

Rev 11/18