What it's for (Indications)
- Rifampicin and isoniazid fixed-dose combination (e.
- g.
- , Rifinah) is indicated for the treatment of all forms of tuberculosis (TB) caused by susceptible strains of *Mycobacterium tuberculosis*.
- This includes both pulmonary and extrapulmonary manifestations of the disease.
- It is typically employed as part of a multi-drug regimen, primarily during the initial intensive phase of treatment, usually for the first two months.
- The fixed-dose combination aims to enhance patient adherence to the prescribed regimen, which is critical for successful treatment outcomes and for minimizing the development of drug resistance.
- Its broad spectrum bactericidal activity against rapidly multiplying *Mycobacterium tuberculosis* ensures efficacy in interrupting the disease progression and reducing infectivity.
- The use of this combination must always be guided by susceptibility testing results, clinical judgment, and adherence to national and international tuberculosis treatment guidelines.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | Dosage of rifampicin and isoniazid fixed-dose combinations is highly individualized and primarily based on the patient's body weight, typically administered once daily. For adults, common regimens involve rifampicin at approximately 10 mg/kg/day (maximum 600 mg) and isoniazid at 5 mg/kg/day (maximum 300 mg). The fixed-dose combination tablets are formulated to deliver these components in specific ratios, simplifying administration and improving compliance. It is crucial that the medication be taken on an empty stomach (at least one hour before or two hours after meals) to optimize absorption. This combination is generally used in the intensive phase, usually for the first 56 doses (8 weeks), followed by a continuation phase using different drug combinations or dosages as per established treatment protocols. Pediatric dosing requires meticulous calculation based on body weight. Dosage adjustments may be necessary in patients with severe renal impairment or significant hepatic dysfunction, although extreme caution is warranted given the hepatotoxic potential of both drugs. Strict adherence to the prescribed regimen is paramount for treatment efficacy and preventing the emergence of drug resistance. |
Safety & Warnings
Common Side Effects
- The use of rifampicin and isoniazid can lead to a range of side effects, some common and others potentially severe.
- **Common side effects** often include gastrointestinal disturbances such as nausea, vomiting, abdominal pain, and anorexia.
- Rifampicin commonly causes an innocuous orange-red discoloration of urine, sweat, saliva, tears, and other body fluids, which patients should be counselled about.
- Other frequent complaints include mild skin rashes, fever, headache, dizziness, and transient, asymptomatic elevations in liver transaminases.
- **Serious side effects** include severe hepatotoxicity, ranging from mild elevations in liver enzymes to severe hepatitis, jaundice, and fulminant hepatic failure, which can be fatal.
- Peripheral neuropathy, often preventable or reversible with pyridoxine (Vitamin B6) supplementation, is a notable concern with isoniazid.
- Hypersensitivity reactions (e.
- g.
- , fever, chills, arthralgia, acute renal failure, thrombocytopenia, hemolytic anemia, severe cutaneous adverse reactions like DRESS syndrome, SJS, TEN) can occur.
- Other serious, though less frequent, adverse events include optic neuritis, psychiatric disturbances, drug-induced lupus erythematosus, and a flu-like syndrome, particularly with intermittent, high-dose rifampicin regimens.
- Careful monitoring for these adverse effects, especially liver function and neurological symptoms, is essential throughout the entire course of treatment.
Serious Warnings
- Black Box Warning: ### **WARNING: SEVERE AND FATAL HEPATOTOXICITY** **BOTH RIFAMPICIN AND ISONIAZID ARE ASSOCIATED WITH SEVERE, AND IN SOME INSTANCES FATAL, HEPATOTOXICITY.** The risk of developing drug-induced hepatitis is significantly increased with advancing age (especially patients over 35 years), daily alcohol consumption, pre-existing liver disease, malnutrition, and in the postpartum period. Patients must be closely monitored for signs and symptoms of liver damage throughout the entire course of treatment. These symptoms include, but are not limited to, persistent fatigue, malaise, anorexia, nausea, vomiting, dark urine, yellowing of the skin or eyes (jaundice), or tenderness in the upper right quadrant of the abdomen. Liver function tests (serum transaminases [AST/ALT], bilirubin, and alkaline phosphatase) should be performed at baseline prior to initiating therapy and monitored regularly, particularly during the first 2-3 months of treatment and in individuals with identified risk factors. **Treatment with this combination MUST BE DISCONTINUED IMMEDIATELY if clinical signs or symptoms of hepatitis occur or if liver enzyme elevations are clinically significant (e.g., AST/ALT >3-5 times the upper limit of normal with symptoms, or >5 times ULN without symptoms).** Delaying discontinuation can lead to irreversible liver damage, acute liver failure, or death. While pyridoxine (Vitamin B6) co-administration is recommended to prevent isoniazid-induced peripheral neuropathy, it DOES NOT prevent or mitigate hepatotoxicity. Patients must be explicitly educated on the critical importance of promptly reporting any symptoms of liver injury to their healthcare provider to ensure timely intervention and prevent severe outcomes.
- Several critical warnings and precautions are associated with the use of rifampicin and isoniazid.
- **Hepatotoxicity**: Both rifampicin and isoniazid are significant hepatotoxins.
- The risk of developing drug-induced hepatitis, which can be severe and fatal, is increased in older patients (especially those over 35), individuals with a history of liver disease, chronic alcohol users, postpartum women, and those receiving other hepatotoxic medications.
- Baseline liver function tests (LFTs) should be obtained prior to initiation of therapy and monitored regularly, particularly during the first 2-3 months of treatment and in patients with identified risk factors.
- Patients must be thoroughly educated to recognize and immediately report symptoms indicative of liver injury, such as persistent fatigue, weakness, loss of appetite, nausea, vomiting, dark urine, yellowing of the skin or eyes (jaundice), or pain in the upper right abdomen.
- Treatment should be discontinued if clinical signs of hepatitis emerge or if LFT elevations are clinically significant.
- **Drug Interactions**: Rifampicin is a potent inducer of hepatic cytochrome P450 enzymes (CYP3A4, CYP2C9, CYP2C19, CYP1A2), leading to accelerated metabolism and reduced plasma concentrations and efficacy of numerous co-administered drugs.
- This includes, but is not limited to, oral contraceptives, warfarin, corticosteroids, antiepileptics (e.
- g.
- , phenytoin, carbamazepine), oral hypoglycemics (sulfonylureas), antiretrovirals (e.
- g.
- , PIs, NNRTIs), digoxin, and methadone.
- Isoniazid can also inhibit some CYP enzymes (e.
- g.
- , CYP2C9, CYP2C19, CYP3A4), potentially increasing levels of drugs like phenytoin and carbamazepine.
- A comprehensive review of all concomitant medications is essential to manage potential interactions.
- Alternative contraceptive methods are advised for women.
- **Peripheral Neuropathy**: Isoniazid can cause peripheral neuropathy due to pyridoxine (Vitamin B6) deficiency, particularly in malnourished individuals, alcoholics, diabetics, HIV-infected patients, pregnant women, and those with chronic renal failure.
- Routine pyridoxine supplementation (e.
- g.
- , 10-50 mg daily) is recommended for all patients on isoniazid, especially those at high risk.
- **Hypersensitivity Reactions**: Severe cutaneous adverse reactions (SCARs), including Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) syndrome, Stevens-Johnson Syndrome (SJS), and toxic epidermal necrolysis (TEN) have been reported.
- If such reactions occur, the drug should be immediately discontinued.
- **Optic Neuritis**: Isoniazid can induce optic neuritis.
- Patients should be advised to report any visual changes promptly.
- Close monitoring is warranted in patients with pre-existing ocular conditions.
- **Renal Impairment**: While both drugs are primarily metabolized in the liver, metabolites can accumulate in severe renal impairment, necessitating dose adjustments and careful monitoring.
- **Diabetic Patients**: Rifampicin may impair glucose tolerance, requiring careful monitoring of blood glucose levels in diabetic patients.
How it Works (Mechanism of Action)
The therapeutic efficacy of the rifampicin and isoniazid combination stems from their distinct yet synergistic bactericidal mechanisms against *Mycobacterium tuberculosis*.
**Rifampicin** exerts its action by specifically inhibiting bacterial DNA-dependent RNA polymerase. This enzyme is crucial for the transcription of bacterial DNA into RNA, which is a fundamental step in protein synthesis. By binding to the beta-subunit of this polymerase, rifampicin effectively blocks the initiation of RNA synthesis, thereby preventing the proliferation of susceptible bacterial cells. Its ability to penetrate well into host cells and tissues allows it to act on both extracellular and intracellular bacilli, including those residing within macrophages. This unique mechanism contributes significantly to its potent bactericidal activity and makes it a cornerstone of combination regimens for tuberculosis.
**Isoniazid (isonicotinic acid hydrazide)** is a prodrug that requires activation by the mycobacterial catalase-peroxidase enzyme, KatG. Once activated, the resulting metabolites covalently bind to and inhibit key enzymes involved in the synthesis of mycolic acids. Mycolic acids are essential, unique components of the mycobacterial cell wall, contributing to its structural integrity and impermeability. By disrupting mycolic acid synthesis, isoniazid impairs cell wall formation, leading to cell death. Isoniazid is highly specific for mycobacteria and is particularly bactericidal against rapidly growing *M. tuberculosis* bacilli, especially those found extracellularly. The distinct targets of these two drugs minimize the development of resistance when used in combination and provide comprehensive coverage against diverse populations of bacilli.
Commercial Brands (Alternatives)
No other brands found for this formula.