6.7 Important drug interactions

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Many TB patients have concomitant illnesses. At the start of TB treatment, all patients should be asked about medicines they are currently taking. The most important interactions with anti-TB drugs are due to rifampicin. Rifampicin induces pathways that metabolize other drugs, thereby decreasing the concentration and effect of the other drugs. To maintain a therapeutic effect, dosages of the other drug may need to be increased. When rifampicin is discontinued, its metabolism-inducing effect resolves within about two weeks, and dosages of the other drug will then need to be decreased again.

Rifampicin substantially decreases the concentrations of certain drugs. The most important ones are as under:

  • Antimicrobials
    • Antibacterial – Clarithromycin, Doxycycline, Chloramphenicol, Linezolid.
    • Antifungals – Fluconazole, Itracanazole, Ketoconazole
    • Antiretrovirals
  • Hormones – Oestrogen, Progestogen, Levothyroxine
  • Corticosteroids
  • Tamoxifen
  • Methadone
  • Anticoagulants – Warfarin, Apixaban, Rivaroxaban
  • Immuno suppressives – Cyclosporin, Mycophenolate, Tacrolimus
  • Anticonvulsants – Carbamazepine, Phenytoin
  • Cardiovascular agents - Digoxin, Calcium channel blockers (Verapamil, Nifedipine, Diltiazem), Beta blockers (Propranolol, Metoporol)
  • Theophylline
  • Hypoglycaemics – Sulfonylureas
  • Lipid lowering drugs – Atorvastatin, Simvastatin
  • Antipsychotics – Haloperidol
  • Anxiolytics – Benzodiazepines
  • Cytotoxics – Gefitinib, Imantinib