What it's for (Indications)
- Isoniazid and rifampicin combination therapy is primarily indicated for the treatment of active pulmonary and extrapulmonary tuberculosis (TB) caused by susceptible strains of Mycobacterium tuberculosis.
- It is a cornerstone of multi-drug regimens recommended by national and international guidelines for both the initial intensive phase and continuation phase of TB treatment.
- This fixed-dose combination aims to improve patient adherence and reduce the development of drug resistance by providing two potent anti-tuberculosis agents in a single formulation.
- It may also be used in certain situations for the treatment of latent tuberculosis infection (LTBI) as part of specific regimens, particularly when monotherapy is not appropriate or higher efficacy is desired, always in accordance with current clinical practice guidelines.
- The judicious use of this combination is crucial in the management of mycobacterial infections to ensure optimal outcomes and minimize resistance.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | Dosage of isoniazid and rifampicin combination therapy must be individualized based on the patient's weight, clinical condition, and the specific tuberculosis treatment regimen prescribed. For adults, common fixed-dose combination formulations are often available (e.g., 150 mg isoniazid + 300 mg rifampicin, or 75 mg isoniazid + 150 mg rifampicin) and are typically administered once daily. The precise dose and duration of therapy depend on whether it is for the intensive phase (often 2 months) or the continuation phase (often 4 months or longer) of active TB treatment, or for latent TB infection. Dosing should adhere strictly to current guidelines from authoritative bodies such as the World Health Organization (WHO) or national public health agencies (e.g., CDC). Administration should preferably be on an empty stomach (at least 1 hour before or 2 hours after meals) to optimize absorption. Renal and hepatic adjustments may be necessary in patients with impaired organ function, requiring careful monitoring and potential dose modification to avoid toxicity. |
Safety & Warnings
Common Side Effects
- Common side effects associated with isoniazid and rifampicin combination include gastrointestinal disturbances such as nausea, vomiting, abdominal pain, and anorexia.
- Hepatotoxicity is a significant concern, manifesting as elevated liver enzymes (transaminases), hepatitis, and jaundice; this can range from asymptomatic elevations to severe and sometimes fatal liver injury.
- Rifampicin is known to cause orange-red discoloration of body fluids including urine, sweat, tears, saliva, and contact lenses, which is harmless but can be alarming.
- Isoniazid can cause peripheral neuropathy, especially in malnourished patients, those with diabetes, alcoholics, or slow acetylators; this risk can be mitigated by concomitant pyridoxine (vitamin B6) supplementation.
- Other possible side effects include hypersensitivity reactions (rash, fever, flu-like syndrome), thrombocytopenia, leukopenia, hemolytic anemia, optic neuritis (isoniazid), drug-induced lupus erythematosus, and psychiatric disturbances.
- Patients should be closely monitored for adverse reactions throughout treatment, and any new or worsening symptoms should be promptly evaluated by a healthcare professional.
Serious Warnings
- Black Box Warning: SEVERE AND SOMETIMES FATAL HEPATOTOXICITY: Both isoniazid and rifampicin, particularly isoniazid, are associated with a significant risk of severe and sometimes fatal hepatitis. This risk is dose-related for rifampicin and can be idiosyncratic for isoniazid, with the incidence of fatal hepatitis with isoniazid increasing with age (especially in individuals over 35 years old) and with daily alcohol consumption. Patients with pre-existing liver disease, chronic alcohol abuse, or those who are rapid acetylators may also be at higher risk. Liver function should be carefully monitored with baseline and periodic testing of serum transaminases (ALT, AST), bilirubin, and alkaline phosphatase throughout the treatment course. Patients must be thoroughly counselled to immediately report any symptoms suggestive of liver injury, including but not limited to unexplained fatigue, anorexia, nausea, persistent vomiting, dark urine, yellow skin or eyes (jaundice), light-colored stools, fever, or rash. Treatment should be immediately discontinued if clinical evidence or significant laboratory abnormalities (e.g., transaminase elevations greater than 3-5 times the upper limit of normal with associated symptoms, or elevations exceeding 5 times the upper limit of normal without symptoms) of hepatic damage occur, as continued administration can lead to irreversible and potentially fatal liver failure. Re-challenging with the drug is generally not recommended following a significant hepatotoxic reaction.
- Isoniazid and rifampicin combination therapy carries several critical warnings.
- The most prominent is the risk of severe and sometimes fatal hepatotoxicity, particularly with isoniazid; liver function should be monitored closely with baseline and periodic testing, especially in high-risk patients (e.
- g.
- , those over 35 years old, with alcohol abuse, or pre-existing liver disease).
- Peripheral neuropathy is a known adverse effect of isoniazid, and concomitant administration of pyridoxine (vitamin B6) is strongly recommended, especially in patients at higher risk (e.
- g.
- , diabetics, alcoholics, malnourished individuals, pregnant women).
- Rifampicin is a potent inducer of hepatic cytochrome P450 enzymes (CYP3A4, CYP2C9, CYP2C19, CYP2D6), leading to numerous significant drug interactions that can reduce the efficacy of co-administered medications (e.
- g.
- , oral contraceptives, antiretrovirals, anticoagulants, corticosteroids, antidiabetic agents, immunosuppressants).
- Optic neuritis has been reported with isoniazid, necessitating ophthalmic evaluation if visual disturbances occur.
- Hypersensitivity reactions, including rash, fever, and flu-like syndrome, can occur and may require drug discontinuation.
- Patients should be advised about the harmless orange-red discoloration of body fluids caused by rifampicin.
- Regular blood counts should be monitored periodically.
How it Works (Mechanism of Action)
The therapeutic efficacy of isoniazid and rifampicin combination stems from their distinct and synergistic bactericidal mechanisms against Mycobacterium tuberculosis. Isoniazid (INH) is a pro-drug that is activated by the mycobacterial catalase-peroxidase enzyme (KatG) to form active metabolites. These metabolites inhibit the synthesis of mycolic acid, a crucial component of the mycobacterial cell wall, thereby disrupting its integrity and leading to bacterial death. Isoniazid is particularly effective against rapidly dividing bacilli. Rifampicin (RMP) acts by binding to the beta-subunit of bacterial DNA-dependent RNA polymerase. This binding prevents the initiation of RNA synthesis, thereby inhibiting bacterial transcription and protein synthesis, ultimately leading to bactericidal effects. Rifampicin is active against both rapidly multiplying and metabolically less active mycobacteria. The combination of these two agents provides a powerful dual-pronged attack, enhancing bactericidal activity, achieving higher cure rates, and significantly reducing the likelihood of resistance development compared to monotherapy.
Commercial Brands (Alternatives)
No other brands found for this formula.