Secondary objectives To study the influence of these polymorphisms on clindamycin clearance, before combination therapy with rifampin (clindamycin monotherapy) To study the influence of these polymorphisms on CYP450 activity before combination therapy with rifampin (clindamycin monotherapy) To study the influence of these polymorphisms on the increase of CYP450 activity after clindamycin/rifampin combination therapy To study the difference between the expected and observed clindamycin serum concentrations after dosage adjustment, in patients with clindamycin dosage adjustment after combination therapy with rifampin