Chapter 42: Chemotherapy of Tuberculosis, Mycobacterium Avium Complex Disease, and Leprosy
A 35-year-old man has developed a tuberculin skin reaction that is 20 mm in size. He is being treated with a triple-drug regimen of isoniazid, rifampin, and pyrazinamide but is concerned because of the number of medications he must take every day. He is a slow acetylator of isoniazid. He asks why other antibiotics like penicillin are not effective in treating tuberculosis. Your answer is that the tuberculosis bacteria
a. have developed a resistance to penicillin.
b. have a rigid cell wall that does not allow penicillin to get inside the cell.
c. destroy the penicillin.
d. multiply too rapidly for the penicillin to be effective.
Answer is b. The name Mycobacterium refers to their waxy appearance due to the composition of their cell walls. More than 60% of their cell wall is lipid, mainly mycolic acids. This extraordinary shield prevents many pharmacological compounds, such as penicillin, from getting into the bacterial cell wall or inside the cell.
On a recent trip to India, a 45-year-old man contracted tuberculosis that was confirmed by culture. Antimicrobial susceptibility was performed and the patient was started on isoniazid, rifampin, and pyrazinamide as definitive therapy for tuberculosis. The patient should be instructed to take his rifampin on an empty stomach because
a. food decreases the peak plasma concentration of rifampin by one-third.
b. rifampin may affect the taste of food.
c. food increases the absorption of rifampin and may cause toxicity.
d. food increases gastric transit.
e. food increases gastric acid secretion which may destroy the rifampin.
Answer is a. After oral administration, the rifamycins are absorbed to variable extents. Food decreases the rifampin CPmax by one-third. A high-fat meal increases the area under the curve (AUC) of rifapentine by 50%.
On a recent trip to India, a 45-year-old man contracted tuberculosis that was confirmed by culture. Antimicrobial susceptibility was performed and the patient was started onisoniazid, rifampin, and pyrazinamide as definitive therapy for tuberculosis.
The plasma concentration of rifampin in the patient is only above the MIC approximately 25% of the dosing interval. This is of little concern because the rifampin
a. t½ in this patient is prolonged.
b. bactericidal activity is ...