Effect of rifampicin on the pharmacokinetics of pioglitazone

Br J Clin Pharmacol. 2006 Jan;61(1):70-8. doi: 10.1111/j.1365-2125.2005.02515.x.


Aims: The effect of enzyme induction on the pharmacokinetics of pioglitazone, a thiazolidinedione antidiabetic drug that is metabolized primarily by CYP2C8, is not known. Rifampicin is a potent inducer of several CYP enzymes and our objective was to study its effects on the pharmacokinetics of pioglitazone in humans.

Methods: In a randomized, two-phase crossover study, ten healthy subjects ingested either 600 mg rifampicin or placebo once daily for 6 days. On the last day, they received a single oral dose of 30 mg pioglitazone. The plasma concentrations and cumulative excretion of pioglitazone and its active metabolites M-IV and M-III into urine were measured up to 48 h.

Results: Rifampicin decreased the mean total area under the plasma concentration-time curve (AUC(0-infinity)) of pioglitazone by 54% (range 20-66%; P = 0.0007; 95% confidence interval -78 to -30%) and shortened its dominant elimination half-life (t(1/2)) from 4.9 to 2.3 h (P = 0.0002). No significant effect on peak concentration (C(max)) or time to peak (t(max)) was observed. Rifampicin increased the apparent formation rate of M-IV and shortened its t(max) (P < 0.01). It also decreased the AUC(0-infinity) of M-IV (by 34%; P = 0.0055) and M-III (by 39%; P = 0.0026), shortened their t1/2 (M-IV by 50%; P = 0.0008, and M-III by 55%; P = 0.0016) and increased the AUC(0-infinity) ratios of M-IV and M-III to pioglitazone by 44% (P = 0.0011) and 32% (P = 0.0027), respectively. Rifampicin increased the M-IV/pioglitazone and M-III/pioglitazone ratios in urine by 98% (P = 0.0015) and 95% (P = 0.0024). A previously unrecognized metabolite M-XI, tentatively identified as a dihydroxy metabolite, was detected in urine during both phases, and rifampicin increased the ratio of M-XI to pioglitazone by 240% (P = 0.0020).

Conclusions: Rifampicin caused a substantial decrease in the plasma concentration of pioglitazone, probably by induction of CYP2C8. Concomitant use of rifampicin with pioglitazone may decrease the efficacy of the latter drug.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Area Under Curve
  • Cross-Over Studies
  • Drug Interactions
  • Enzyme Induction
  • Enzyme Inhibitors / administration & dosage*
  • Female
  • Humans
  • Hypoglycemic Agents / administration & dosage
  • Hypoglycemic Agents / blood
  • Hypoglycemic Agents / pharmacokinetics*
  • Male
  • Pioglitazone
  • Rifampin / administration & dosage*
  • Thiazolidinediones / administration & dosage
  • Thiazolidinediones / blood
  • Thiazolidinediones / pharmacokinetics*


  • Enzyme Inhibitors
  • Hypoglycemic Agents
  • M-II compound
  • M-IV compound
  • Thiazolidinediones
  • Rifampin
  • Pioglitazone