RIFAMPIN — rifampin capsule, coated
State of Florida DOH Central Pharmacy
To reduce the development of drug-resistant bacteria and maintain the effectiveness of rifampin capsules 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.
Rifampin capsules, USP contain 150 mg or 300 mg rifampin per capsule. The 150 mg and 300 mg capsules also contain, as inactive ingredients: colloidal silicon dioxide, corn starch, FD&C Blue No. 1, FD&C Red No. 40, gelatin, lactose monohydrate, magnesium stearate, sodium lauryl sulfate, talc, and titanium dioxide.
The printing ink contains ammonium hydroxide, isopropyl alcohol, n-butyl alcohol, pharmaceutical glaze, propylene glycol, simethicone, and titanium dioxide
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-2,4,12,16,20,22-heptamethyl-8-[N-(4-methyl-1-piper-azinyl)formimidoyl]-2,7-(epoxypentadeca[1,11,13]trienimino)naphtho[2,1-b]furan-1,11(2H)-dione 21-acetate. Its structural formula is:
Rifampin is readily absorbed from the gastrointestinal tract. Peak serum concentrations in healthy adults and pediatric populations vary widely from individual to individual. Following a single 600 mg oral dose of rifampin in healthy adults, the peak serum concentration averages 7 mcg/mL but may vary from 4 to 32 mcg/mL. Absorption of rifampin is reduced by about 30% when the drug is ingested with food.
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.
In healthy adults, the mean biological half-life of rifampin in serum averages 3.35 ± 0.66 hours after a 600 mg oral dose, with increases up to 5.08 ± 2.45 hours reported after a 900 mg dose. With repeated administration, the half-life decreases and reaches average values of approximately 2 to 3 hours. The half-life does not differ in patients with renal failure at doses not exceeding 600 mg daily, and consequently, no dosage adjustment is required. Following a single 900 mg oral dose of rifampin in patients with varying degrees of renal insufficiency, the mean half-life increased from 3.6 hours in healthy adults to 5.0, 7.3, and 11.0 hours in patients with glomerular filtration rates of 30 to 50 mL/min, less than 30 mL/min, and in anuric patients, respectively. Refer to the WARNINGS section for information regarding patients with hepatic insufficiency.
Rifampin is rapidly eliminated in the bile, and an enterohepatic circulation ensues. During this process, rifampin undergoes progressive deacetylation so that nearly all the drug in the bile is in this form in about 6 hours. This metabolite is microbiologically active. Intestinal reabsorption is reduced by deacetylation, and elimination is facilitated. Up to 30% of a dose is excreted in the urine, with about half of this being unchanged drug.
In one study, pediatric patients 6 to 58 months old were given rifampin suspended in simple syrup or as dry powder mixed with applesauce at a dose of 10 mg/kg body weight. Peak serum concentrations of 10.7 ± 3.7 and 11.5 ± 5.1 mcg/mL were obtained 1 hour after preprandial ingestion of the drug suspension and the applesauce mixture, respectively. After the administration of either preparation, the t1/2 of rifampin averaged 2.9 hours. It should be noted that in other studies in pediatric populations, at doses of 10 mg/kg body weight, mean peak serum concentrations of 3.5 mcg/mL to 15 mcg/mL have been reported.
Rifampin inhibits DNA-dependent RNA polymerase activity in susceptible cells. Specifically, it interacts with bacterial RNA polymerase but does not inhibit the mammalian enzyme. Rifampin at therapeutic levels has demonstrated bactericidal activity against both intracellular and extracellular Mycobacterium tuberculosis organisms.
Organisms resistant to rifampin are likely to be resistant to other rifamycins.
Rifampin has bactericidal activity against slow and intermittently growing M. tuberculosis organisms. It also has significant activity against Neisseria meningitidis isolates (see INDICATIONS AND USAGE).
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.
Rifampin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.
- Aerobic Gram-Negative Microorganisms:
- Neisseria meningitidis
- “Other” Microorganisms:
- Mycobacterium tuberculosis
The following in vitro data are available, but their clinical significance is unknown.
Rifampin exhibits in vitro activity against most strains of the following microorganisms; however, the safety and effectiveness of rifampin in treating clinical infections due to these microorganisms have not been established in adequate and well controlled 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
β-lactamase production should have no effect on rifampin activity.
Prior to initiation of therapy, appropriate specimens should be collected for identification of the infecting organism and in vitro susceptibility tests.
In vitro testing for Mycobacterium tuberculosis isolates:
Two standardized in vitro susceptibility methods are available for testing rifampin against M tuberculosis organisms. The agar proportion method (CDC or NCCLS(1) M24-P) utilizes Middlebrook 7H10 medium impregnated with rifampin at a final concentration of 1.0 mcg/mL to determine drug resistance. After three weeks of incubation MIC99 values are calculated by comparing the quantity of organisms growing in the medium containing drug to the control cultures. Mycobacterial growth in the presence of drug, of at least 1% of the growth in the control culture, indicates resistance.
The radiometric broth method employs the BACTEC 460 machine to compare the growth index from untreated control cultures to cultures grown in the presence of 2.0 mcg/mL of rifampin. Strict adherence to the manufacturer’s instructions for sample processing and data interpretation is required for this assay.
Susceptibility test results obtained by the two different methods can only be compared if the appropriate rifampin concentration is used for each test method as indicated above. Both procedures require the use of M tuberculosis H37Rv ATCC 27294 as a control organism.
The clinical relevance of in vitro susceptibility test results for mycobacterial species other than M tuberculosis using either the radiometric or the proportion method has not been determined.
In vitro testing for Neisseria meningitidis isolates:
Dilution Techniques: Quantitative methods that are used to determine minimum inhibitory concentrations provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure uses a standardized dilution method2,4 (broth, agar, or microdilution) or equivalent with rifampin powder. The MIC values obtained should be interpreted according to the following criteria for Neisseria meningitidis:
A report of “susceptible” indicates that the pathogen is likely to be inhibited by usually achievable concentrations of the antimicrobial compound in the blood. A report of “intermediate” indicates that the result should be considered equivocal, and if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where the maximum acceptable dose of drug can be used. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of “resistant” indicates that usually achievable concentrations of the antimicrobial compound in the blood are unlikely to be inhibitory and that other therapy should be selected.
Measurement of MIC or minimum bactericidal concentrations (MBC) and achieved antimicrobial compound concentrations may be appropriate to guide therapy in some infections. (See CLINICAL PHARMACOLOGY section for further information on drug concentrations achieved in infected body sites and other pharmacokinetic properties of this antimicrobial drug product.)
Standardized susceptibility test procedures require the use of laboratory control microorganisms. The use of these microorganisms does not imply clinical efficacy (see INDICATIONS AND USAGE); they are used to control the technical aspects of the laboratory procedures. Standard rifampin powder should give the following MIC values:
|Staphylococcus aureus||ATCC 29213||0.008 — 0.06|
|Euterococcus faecalis||ATCC 29212||1 — 4|
|Escherichia coli||ATCC 25922||8 — 32|
|Pseudomouas aeruginosa||ATCC 27853||32 — 64|
|Haemophilus influenzae||ATCC 49247||0.25 — 1|
Diffusion Techniques: Quantitative methods that require measurement of zone diameters provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure3,4 that has been recommended for use with disks to test the susceptibility of microorganisms to rifampin uses the 5 mcg rifampin disk. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for rifampin.
Reports from the laboratory providing results of the standard single-disk susceptibility test with a 5 mcg rifampin disk should be interpreted according to the following criteria for Neisseria meningitidis.
Interpretation should be as stated above for results using dilution techniques.
As with standard dilution techniques, diffusion methods require the use of laboratory control microorganisms. The use of these microorganisms does not imply clinical efficacy (see INDICATIONS AND USAGE); they are used to control the technical aspects of the laboratory procedures. The 5 mcg rifampin disk should provide the following zone diameters in these quality control strains:
|Microorganism||Zone Diameter (mm)|
|S. aureus||ATCC 25923||26 — 34|
|E. coli||ATCC 25922||8 — 10|
|H. influenzae||ATCC 49247||22 — 30|
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