Rifampin

RIFAMPIN- rifampin injection, powder, lyophilized, for solution
Hikma Pharmaceuticals USA Inc.

Rx only

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Rifampin for Injection, USP and other antibacterial drugs, rifampin should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria.

DESCRIPTION

Rifampin for Injection, USP contains rifampin 600 mg, sodium formaldehyde sulfoxylate 10 mg, and sodium hydroxide to adjust pH.

Rifampin is a semisynthetic antibiotic derivative of rifamycin SV. Rifampin is a red-brown crystalline powder very slightly soluble in water at neutral pH, freely soluble in chloroform, soluble in ethyl acetate and in methanol. Its molecular weight is 822.95 and its chemical formula is C43 H58 N4 O12 . The chemical name for rifampin is either:

3-[[(4-Methyl-1-piperazinyl)imino]methyl]rifamycin

or

5,6,9,17,19,21-hexahydroxy-23-methoxy-2,4,12,16,18, 20,22– heptamethyl-8-[N-(4-methyl-1-piperazinyl)formimidoyl]-2,7-(epoxypentadeca [1,11,13]trienimino)naphtho[2,1-b ]furan-1,11(2H)-dione 21-acetate.

Its structural formula is:

Chemical structure
(click image for full-size original)

CLINICAL PHARMACOLOGY

Intravenous Administration

After intravenous administration of a 300 or 600 mg dose of rifampin infused over 30 minutes to healthy male volunteers (n=12), mean peak plasma concentrations were 9.0 ± 3.0 and 17.5 ± 5.0 mcg/mL, respectively. Total body clearances after the 300 and 600 mg IV doses were 0.19 ± 0.06 and 0.14 ± 0.03 L/hr/kg, respectively. Volumes of distribution at steady state were 0.66 ± 0.14 and 0.64 ± 0.11 L/kg for the 300 and 600 mg IV doses, respectively. After intravenous administration of 300 or 600 mg doses, rifampin plasma concentrations in these volunteers remained detectable for 8 and 12 hours, respectively (see Table).

Plasma Concentrations (mean ± standard deviation, mcg/mL)
Rifampin Dosage IV 30 min 1 hr 2 hr 4 hr 8 hr 12 hr
300 mg 8.9 ± 2.9 4.9 ± 1.3 4.0 ± 1.3 2.5 ± 1.0 1.1 ± 0.6 <0.4
600 mg 17.4 ± 5.1 11.7 ± 2.8 9.4 ± 2.3 6.4 ± 1.7 3.5 ± 1.4 1.2 ± 0.6

Plasma concentrations after the 600 mg dose, which were disproportionately higher (up to 30% greater than expected) than those found after the 300 mg dose, indicated that the elimination of larger doses was not as rapid.

After repeated once-a-day infusions (3-hr duration) of 600 mg in patients (n=5) for 7 days, concentrations of IV rifampin decreased from 5.81 ± 3.38 mcg/mL 8 hours after the infusion on day 1 to 2.6 ± 1.88 mcg/mL 8 hours after the infusion on day 7.

Rifampin is widely distributed throughout the body. It is present in effective concentrations in many organs and body fluids, including cerebrospinal fluid. Rifampin is about 80% protein bound. Most of the unbound fraction is not ionized and therefore diffuses freely into tissues.

Rifampin is rapidly eliminated in the bile and undergoes progressive enterohepatic circulation and deacetylation to the primary metabolite, 25-desacetyl-rifampin. This metabolite is microbiologically active. Less than 30% of the dose is excreted in the urine as rifampin or metabolites. Serum concentrations do not differ in patients with renal failure at a studied dose of 300 mg, and consequently, no dosage adjustment is required.

Pediatrics

Intravenous Administration. In pediatric patients 0.25 to 12.8 years old (n=12), the mean peak serum concentration of rifampin at the end of a 30-minute infusion of approximately 300 mg/m2 was 25.9 ± 1.3 mcg/mL; individual peak concentrations 1 to 4 days after initiation of therapy ranged from 11.7 to 41.5 mcg/mL; individual peak concentrations 5 to 14 days after initiation of therapy were 13.6 to 37.4 mcg/mL. The individual serum half-life of rifampin changed from 1.04 to 3.81 hours early in therapy to 1.17 to 3.19 hours 5 to 14 days after therapy was initiated.

Microbiology

Mechanism of Action

Rifampin inhibits DNA-dependent RNA polymerase activity in susceptible Mycobacterium tuberculosis organisms. Specifically, it interacts with bacterial RNA polymerase but does not inhibit the mammalian enzyme.

Resistance

Organisms resistant to rifampin are likely to be resistant to other rifamycins.

In the treatment of both tuberculosis and the meningococcal carrier state (see INDICATIONS AND USAGE), the small number of resistant cells present within large populations of susceptible cells can rapidly become predominant. In addition, resistance to rifampin has been determined to occur as single-step mutations of the DNA-dependent RNA polymerase. Since resistance can emerge rapidly, appropriate susceptibility tests should be performed in the event of persistent positive cultures.

Activity in vitro and in vivo

Rifampin has bactericidal activity in vitro against slow and intermittently growing M. tuberculosis organisms.

Rifampin has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections (see INDICATIONS AND USAGE):

Aerobic Gram-Negative Microorganisms:

Neisseria meningitidis

“Other” Microorganisms:

Mycobacterium tuberculosis

The following in vitro data are available, but their clinical significance is unknown.

At least 90% of the following bacteria exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for rifampin against isolates of similar genus or organism group. However, the efficacy of rifampin in treating clinical infections caused by these bacteria has not been established in adequate and well-controlled clinical trials

Aerobic Gram-Positive Microorganisms: Staphylococcus aureus (including Methicillin-Resistant S. aureus /MRSA) Staphylococcus epidermidis

Aerobic Gram-Negative Microorganisms:

Haemophilus influenzae

“Other” Microorganisms:

Mycobacterium leprae

ß-lactamase production should have no effect on rifampin activity.

Susceptibility Testing

For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC .

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