Tuberculosis (TB) is an airborne infection caused by a tiny pathogen called Mycobacterium Tuberculosis. In most cases, the TB infection targets the lung parenchyma but the mycobacterium can sometimes travel to the meninges, kidneys, bones and lymph nodes. The goal of Tuberculosis Pharmacology is to kill off the infecting pathogen, stop the transmission of the disease and support the respiratory system.
In these notes we’ll be going over the different medications used in the medical management of TB, but before we get into that, make sure that you’ve understood The Pathophysiology of TB.
Introduction to Tuberculosis Pharmacology
The medical treatment of TB can be divided into two phases, there is the Initial Phase which lasts for about 8 weeks from the day of diagnosis and the Continuation Phase lasting between 4 to 7 months.
Once diagnosed, TB patients enter the Initial Phase of the treatment where the infection is treated aggressively using a multiple-medication regimen of antibiotics to kill of the infecting pathogen (mycobacterium tuberculosis). In addition some physicians prescribed a Vitamin B6 supplement to counteract the numbing and tingling of extremities caused by some of these antibiotics.
The multiple-medication regimen of antibiotics to treat TB includes 4 antibiotics. The most commonly used antibiotics are:
Isoniazid
Rifampin
Pyrazinamide
Ethambutol
All four antibiotics are taken orally once a day for eight weeks, but this doesn’t mean that they need to stay in isolation for the full eight weeks. By the 2nd or 3rd week of receiving full consistent medical therapy most patient will be non-infectious and can reintegrate into the community. However they will need to continue taking the four antibiotics daily until they finish the full 8 weeks of the initial phase treatment.
After that, the patient will move on into the continuation phase where they will be prescribed two antibiotics for the next 4 to 7 months. At this stage, most physicians will prescribed a combination of:
Isoniazid and Rifampin, or
Isoniazid and Rifapentine
Most patients will stay on the continuation phase for 4 months, but if their sputum culture tests positive after 2 months of treatment then their continuation phase is extended to 7 months.
Below you can see an overview of the antibiotics used in the multidrug regimen against TB. All of which are considered to be Antitubercular Agents.
*This table is for educational purposes only, it does not contain the full list of side effects and interactions*
Drug | Side Effects | Interactions |
Isoniazid | Peripheral Neuropathy Abnormal Liver Function Tests Nausea Vomiting | Alcohol Phenytoin-synergistic Anatabuse |
Rifampin | Hepatotoxicity Thrombocytopenia Epigastric Distress | Saquinavir Hepatotoxic drugs |
Rifabutin | Diarrhoea Upset stomach Skin rash | Protease Inhibitors |
Rifapentine | Abnormal Liver Function Tests Headache Joint Pain | Protease Inhibitors Reverse Transcriptase Inhibitors |
Pyazinamide | Heaptoxicity Hyperuricemia Skin Rash | Interferes with urine tests causing a pink-brown colour |
Ethambutol | Joint Pain Itching Headache | Antacids containing Aluminium Hydroxide |
Tuberculosis Pharmacology in Multi-Drug Resistant TB (MDR TB)
Like many other infections, some patients become resistant to the selected antibiotics used in the treatment of TB. In most cases, this occurs in individuals that are immunocompromised, hospitalized or homeless and those that do not adhere to the prescribed treatment. Having MDR TB, makes it very challenging to treat the infection, however obtaining a sputum culture can help the medical team to select the right treatment that targets the patient’s sensitivity.
Tuberculosis Pharmacology as a Prophylaxis
As you must be well aware by now, treating TB is no easy task and prevention is key. So in cases where patients are at risk of developing or contracting TB, Isoniazid is prescribed prophylactically. Typically this would be done for household members of patients with active TB.
Moreover, prophylactic treatment is also given to individuals that have a 10mm induration and reaction to the Tuberculin skin test and have one of these conditions or criteria:
Currently on IV drugs
Have a chronic illness
High risk and underserved populations
Hospitalised patients
If a patient has HIV, a 5mm induration and reaction to the TB skin test is enough to qualify for prophylactic treatment.
Tuberculosis Pharmacology Supportive Medication
Alongside the Antitubercular agents that fight off the pathogen directly, the medical team might prescribe additional medication to support the patient’s physiological status. These might include:
Paracetamol: To treat fever
Mucolytics/Expectorants: To aid the patient in coughing up sputum
Oxygen therapy: If patient has low oxygen saturation