Introduction
Pioglitazone is an antihyperglycemic used as an adjunct to diet, exercise, and other antidiabetic medications to manage type 2 diabetes mellitus. It is administered as a racemic mixture, though there is no pharmacologic difference between the enantiomers and they appear to interconvert in vivo with little consequence. The thiazolidinedione class of medications, which also includes rosiglitazone and troglitazone, exerts its pharmacological effect primarily by promoting insulin sensitivity and the improved uptake of blood glucose via agonism at the peroxisome proliferator-activated receptor-gamma (PPARγ). PPARs are ligand-activated transcription factors that are involved in the expression of more than 100 genes and affect numerous metabolic processes, most notably lipid and glucose homeostasis.
Thiazolidinediones, including pioglitazone, have fallen out of favor in recent years due to the presence of multiple adverse effects and warnings regarding their use (e.g. congestive heart failure, bladder cancer) and the availability of safer and more effective alternatives for patients with type 2 diabetes mellitus.
Uses
Pioglitazone is a thiazolidinedione used adjunctively with diet and exercise to normalize glycemic levels in adults with type 2 diabetes mellitus.
Pioglitazone is indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus. It is also available in combination with metformin, glimepiride, or alogliptin for the same indication.
Associated Conditions
Pharmacodynamics
Pioglitazone enhances cellular responsiveness to insulin, increases insulin-dependent glucose disposal, and improves impaired glucose homeostasis. In patients with type 2 diabetes mellitus, these effects result in lower plasma glucose concentrations, lower plasma insulin concentrations, and lower HbA1c values.
Significant fluid retention leading to the development/exacerbation of congestive heart failure has been reported with pioglitazone - avoid its use in patients in heart failure or at risk of developing heart failure. There is some evidence that pioglitazone may be associated with an increased risk of developing bladder cancer. Pioglitazone should not be used in patients with active bladder cancer and should be used with caution in patients with a history of bladder cancer.
Mechanism of Action
Pioglitazone is a selective agonist at peroxisome proliferator-activated receptor-gamma (PPARγ) in target tissues for insulin action such as adipose tissue, skeletal muscle, and liver. Activation of PPARγ increases the transcription of insulin-responsive genes involved in the control of glucose and lipid production, transport, and utilization. Through this mechanism, pioglitazone both enhances tissue sensitivity to insulin and reduces the hepatic production of glucose (i.e. gluconeogenesis) - insulin resistance associated with type 2 diabetes mellitus is therefore improved without an increase in insulin secretion by pancreatic beta cells.
Absorption
Following oral administration of pioglitazone, peak serum concentrations are observed within 2 hours (Tmax) - food slightly delays the time to peak serum concentration, increasing Tmax to approximately 3-4 hours, but does not alter the extent of absorption. Steady-state concentrations of both parent drug and its primary active metabolites are achieved after 7 days of once-daily administration of pioglitazone. Cmax and AUC increase proportionately to administered doses.
Volume of Distribution
The average apparent volume of distribution of pioglitazone is 0.63 ± 0.41 L/kg.
Protein Binding
Pioglitazone is >99% protein-bound in human plasma - binding is primarily to albumin, although pioglitazone has been shown to bind other serum proteins with a lower affinity. The M-III and M-IV metabolites of pioglitazone are >98% protein-bound (also primarily to albumin).
Route of Elimination
Approximately 15-30% of orally administered pioglitazone is recovered in the urine. The bulk of its elimination, then, is presumed to be through the excretion of unchanged drug in the bile or as metabolites in the feces.
Half Life
The mean serum half-life of pioglitazone and its metabolites (M-III and M-IV) range from 3-7 hours and 16-24 hours, respectively.
Clearance
The apparent clearance of orally administered pioglitazone is 5-7 L/h.
Toxicity
The oral TDLo observed in mice is 24 mg/kg for 4 days and for rats is 3 mg/kg for 6 days.
One instance of overdose was reported during clinical trials with pioglitazone in which a patient took an oral dose of 120mg daily for four days, followed by 180mg daily for seven days - this patient did not report any adverse clinical symptoms during this time. In the event of overdosage, employ symptomatic and supportive measures according to the patient's clinical status.
Food Interactions
- Take with or without food. Food delays drug absorption, but not to a clinically significant extent.
Dosage
Maximum recommended daily dose of Pioglitazone should not exceed 45 mg since doses higher than 45 mg have not been studied in placebo controlled clinical studies. Besides, no placebo controlled clinical studies of more than 30 mg once daily have been conducted in combination therapy.
