Fitz, TB Flashcards
Why should fluoroquinolones NOT be used as first line treatment for TB in endemic areas?
They mask active TB and it promotes resistance of fluoroquinolones.
Signs and symptoms of TB
- Cough for 3 weeks or longer
- Hemoptysis
- Night sweats
- Weight loss
- Weakness
- Fever, chills
- Pain in chest
Name the three things that make TB treatment challenging.
- Primary lesion - caseating granuloma with TB inside macrophages
- Persistent mycobacteria in LYMPH NODES and LUNG
- CAVITATING LESIONS
Three goals of TB treatment
- Eradicate Mycobacterium TB
- Prevent drug resistance
- Prevent relapse
Name the four drugs used in standard therapy of ACTIVE TB and at what stages they’re used.
- Initial stage - Isoniazid, Rifampin, Ethambutol, Pyrazinamide
- Continuation phase - Isoniazid and Rifampin
Length of time in the initial stage of treatment of active TB and the GOAL.
- 8 weeks
- Goal - eradicate the large burden of REPLICATING bacteria
Length of time in the continuation stage of treatment of active TB and the GOAL.
- wk8 to wk26
- Goal - Infiltrate INTRACELLULARLY… non-cavitating lesions
What drug is used for TB patients that cannot take drugs PO?
Streptomycin - NOT a 1st line drug.
Administered parenteral.
Clearance of isoniazid, rifampin, ethambutol, pyrazinamide
Mixed hepatic/renal
Isoniazid spectrum
Narrow spectrum - mycobacteria TB.
BacteriCIDAL in GROWING mycobacteria.
MOA of isoniazid
Disrupts mycolic acid synthesis, making mycobacteria vulnerable to destruction.
What is mycolic acid?
Distinctive component of mycobacteria cell wall.
Describe the location and process of isoniazid activation
- Location: IN the mycobacterium
- Process: INH (prodrug) –> converted to activated metabolite by Catalase Peroxidase (KatG) –> activated metabolite binds to NAD, inhibiting enzymes (InhA and KasA) from forming functional mycolic acid for cell wall.
Describe the 2 mechanisms of resistance to isoniazid.
- Deletion of KatG –> resulting in insufficient metabolite
2. Overexpression/mutation in InhA or KasA (can work in presence of lower NAD levels)
Describe the metabolization process of isoniazid and what the toxic metabolite is.
INH –(NAT+acetylCoA)–> N-Acetyl-INH –> N-Acetyl-Hydrazine (this is toxic) or Isotonic acid
Describe the fast metabolization of INH and what’s excreted
- Fast acetylators (90% of Asians) = 90% of INH excreted as N-Acetyl-INH
Describe slow metabolization of ING and what’s excreted
- Slow acetylators (50% of Whites, Blacks, Hispanics) = 65% of INH excreted as N-Acetyl-INH, so MORE EXPOSURE TO N-Acetylhydralazine (toxic)
A person presents with hepatotoxicity after taking isoniazid. What type of metabolizer is this person and what metabolite is causing the hepatotoxicity?
- Slow acetylator
- N-acetylhadralazine
What are the clinical presentations of the two major adverse reactions to INH?
- Hepatotoxic (slow acetylators) - jaundice, elevated liver enzymes, hepatitis
- Neurologic (slow acetylators) - peripheral neuritis/parasthesias, convusions
Risk factors for N-Acetylhydralazine toxicity.
Age, alcoholism, drug abuse, drugs (liver enzyme inducers), liver disease.
The major molecule and mechanism in isoniazid neuropathy.
Pyridoxal-5-Phosphate is a co-factor for neurotransmitter synthesis (GABA). INH reacts with this and increases its urinary excretion, depleting pyridoxines.
Pyridoxine is aka…
Vitamin B6.
A person presents with peripheral neuropathy, parasthesias, and seizures after taking isoniazid. What type of metabolizer is this person and what metabolite is causing the isoniazid neuropathy?
Slow acetylator
- Vitamin B6/pyridoxine is depleted.
Rifampin spectrum
Broad spectrum - mycobacteria TB + other bacteria BacteriCIDAL extracellular (caseous lesions) and INTRACELLULAR (can get into macrophages in "continuation phase").
Rifampin MOA
Inhibits PROkaryotic RNA polymerase/gene transcription, resulting in zero mRNA.
- Intracellular penetration by rifampin is high. Reaches intracellularly during “continuation” treatment.
Adverse effect of Rifampin
Stains RED - urine, contacts, sweat, etc.
A woman on oral contraceptives should not take what TB drug? Why?
Major rifampin-drug interaction is CYP450 INDUCTION. So any drug (i.e. OCP) metabolized by this will be cleared faster.
Two major Rifampin-drug interactions.
- Induces CYP450
2. Increases clearance of HIV protease inhibitors and non-nucleoside transcriptase inhibitors.
A HIV pt is dx with TB. Do you tx TB or HIV first and what drug should you substitute?
Deal with TB infection first. Substitute RIFABUTIN for Rifampin because Rifampin will increase clearance of HIV protease inhibitors.
Pyrazinamide spectrum
Narrow spectrum - mycobacteria TB at ACIDIC pH’s
Pyrazinamide MOA
Reaches intracellular pathogens and is bacteriCIDAL only at acidic pH - “sterilizing” agent.
Metabolism of pyrazinamide
Hepatic, CYP450
Toxicity of pyrazinamide
- Hepatotoxic
- Renal –> Gout
- **Do not give to pregnant women - possible teratogenicity)
If a patient has severe liver disease or gout, what TB drug should be avoided and how should the drug regimen be changed?
Avoid pyrazinamide.
Same duration of Initiation Phase, but extend Continuation Phase.
Ethambutol spectrum
Narrow - only mycobacteria
Ethambutol MOA
Inhibits arabinosyl transferase which makes (sugar) arabinogalactin in cell wall.
Mechanisms of resistance to rifampin (2).
- Mutation in RNA polymerase
2. Drug permeability (?)
Mechanism of resistance to ethambutol.
Mutation of arabinosyl transferase.
Adverse effects of ethambutol (2).
- Visual - optic neuritis and color disturbance.
2. Renal - gout
Pyrazinamide/Ethambutol Renal reactions and results.
Block tubular secretion of uric acid and cause retention, resulting in hyperuricemia and urate crystals.
What is the drug regiment for latent TB (less mycobacteria)?
Isoniazid and rifapentine 1/week for 12 weeks.
12-dose regimen is not recommended in what types of populations?
Children less than 2yo
Pregnant women
HIV postive
Drug regimen in pregnant women.
Isoniazid, Rifampin, Ethambutol
Four caveats for people with HIV and TB.
TB is #1 killer of HIV patients.
- Initiate TB treatment first, then HIV.
- Avoid weekly INH-rifapentine
- Avoid twice weekly INH-rifampin if CD4 less than 100.
Give rifabutinin..
What drugs is MDR-TB resistant to?
Isoniazid and rifampin.
WHO recommendation of MDR-TB treatment.
20 months of second line drugs (**fluoroquinolones, ethionamide, aminoglycosides, PAS, ethionamide)
What drug is used for MDR-TB that inhibits ATP synthesis in mycobacteria?
Bedaquiline.
Inhibits mycobacterial ATP synthase = bacteriCIDAL.
Regimen if bedaquline is used.
Used in combo with 3 other drugs that the MDR-TB is susceptible to.
