[Urinary bladder tuberculosis and Bacillus Calmette-Guérin instillation: reduced efficacy of bisoprolol in hypertension].

History And Admission Findings: A 71-year-old patient with a superficial carcinoma of the urinary bladder and high risk of recurrence was treated with intravesical instillation of Bacillus Calmette-Guérin (BCG) after transurethral resection. As a complication of the catheterization during BCG-instillation therapy the patient suffered from tuberculosis. The patient received a tuberculosis triple-therapy including rifampicin 600 mg once daily, isoniazid 300 mg once daily and ethambutol 400 mg thrice daily. The existing arterial hypertension had successfully been controlled by 3.75 mg bisoprolol medication once daily for the last 15 years. An increase of blood pressure and cardiac arrhythmia were seen after combining the β1-receptor blocker treatment with the triple-therapy.

Investigations And Diagnosis: The blood pressure was 160/90 mm Hg. The heart rate reflected a value of 98 beats per minute. In the resting ECG monotopic ventricular extrasystoles could be diagnosed.

Treatment And Course: The dosage of bisoprolol was changed to 3.75 mg in the morning and additional 1.875 mg in the evening. Due to this increase of dosage the blood pressure could be controlled sufficiently.

Conclusion: Rifampicin is one of the best known potent enzyme inducing drugs. It strongly induces the expression of cytochrome P450 3A4 in the liver. The enzyme induction enhance the hepatic bisoprolol metabolism, hence the metabolic clearance of the drug increased. The maximal plasma level of bisoprolol decrease and in our use the arterial hypertension could not be treated sufficiently. It is well known that half the dose of bisoprolol undergoes oxidative metabolism in the liver and the rest eliminated unchanged in the kidney. A dosage adjustment of bisoprolol is necessary if the clinical status of the patient requires treatment with the antituberculosis drug rifampicin.