Major
Rifampicin × Theophylline
Antituberculous antibiotic×Methylxanthine
Mechanism
Rifampicin strongly induces CYP1A2 – the main theophylline metabolic route. Theophylline plasma levels fall by 30–50%; bronchodilator effect weakens.
Symptoms
Recurrence of asthma or COPD symptoms: dyspnoea, wheezing, need for additional short-acting β2-agonist doses.
Management
During anti-TB therapy, increase theophylline 1.5- to 2-fold with level monitoring at 1 week. Alternative bronchodilators: long-acting inhaled β2-agonists (formoterol, salmeterol) with anticholinergics.