Mechanism of Action

Repaglinide lowers blood glucose levels by stimulating the release of insulin from the pancreas. This action is dependent upon functioning beta (ß) cells in the pancreatic islets. Insulin release is glucose-dependent and diminishes at low glucose concentrations.

Repaglinide closes ATP-dependent potassium channels in the ß-cell membrane by binding at characterizable sites. This potassium channel blockade depolarizes the ß-cell, which leads to an opening of calcium channels. The resulting increased calcium influx induces insulin secretion. The ion channel mechanism is highly tissue selective with low affinity for heart and skeletal muscle.

Pharmacokinetics

Absorption: After oral administration, repaglinide is rapidly and completely absorbed from the gastrointestinal tract. After single and multiple oral doses in healthy subjects or in patients, peak plasma drug levels (Cmax) occur within 1 hour (Tmax). Repaglinide is rapidly eliminated from the blood stream with a half-life of approximately 1 hour. The mean absolute bioavailability is 56%. When repaglinide was given with food, the mean Tmax was not changed, but the mean Cmax and AUC (area under the time/plasma concentration curve) were decreased 20% and 12.4%, respectively.

Distribution: After intravenous (IV) dosing in healthy subjects, the volume of distribution at steady state (Vss) was 31 L, and the total body clearance (CL) was 38L/h. Protein binding and binding to human serum albumin was greater than 98%.

Metabolism: Repaglinide is completely metabolized by oxidative biotransformation and direct conjugation with glucuronic acid after either an IV or oral dose. The major metabolites are an oxidized dicarboxylic acid (M2), the aromatic amine (M1), and the acyl glucuronide (M7). The cytochrome P-450 enzyme system, specifically 2C8 and 3A4, have been shown to be involved in the N-dealkylation of repaglinide to M2 and the further oxidation to M1. Metabolites do not contribute to the glucose-lowering effect of repaglinide.

Repaglinide appears to be a substrate for active hepatic uptake transporter (organic anion transporting protein OATP1B1).

Excretion: Within 96 hours after dosing with 14C-repaglinide as a single, oral dose, approximately 90% of the radiolabel was recovered in the feces and approximately 8% in the urine. Only 0.1% of the dose is cleared in the urine as parent compound. The major metabolite (M2) accounted for 60% of the administered dose. Less than 2% of parent drug was recovered in feces.

Pharmacokinetic Parameters: The pharmacokinetic parameters of repaglinide obtained from a single-dose, crossover study in healthy subjects and from a multiple-dose, parallel, dose-proportionality (0.5, 1, 2 and 4 mg) study in patients with type 2 diabetes are summarized in the following table:

These data indicate that repaglinide did not accumulate in serum. Clearance of oral repaglinide did not change over the 0.5 - 4 mg dose range, indicating a linear relationship between dose and plasma drug levels.

Variability of Exposure: Repaglinide AUC after multiple doses of 0.25 to 4 mg with each meal varies over a wide range. The intra-individual and inter-individual coefficients of variation were 36% and 69%, respectively. AUC over the therapeutic dose range included 69 to 1005 ng/mL*hr, but AUC exposure up to 5417 ng/mL*hr was reached in dose escalation studies without apparent adverse consequences.

Special Populations

Geriatric: Healthy volunteers were treated with a regimen of 2 mg taken before each of3 meals. There were no significant differences in repaglinide pharmacokinetics between the group of patients <65 years of age and a comparably sized group of patients ≥65 years of age (See PRECAUTIONS, Geriatric Use).

Pediatric: No studies have been performed in pediatric patients.

Gender: A comparison of pharmacokinetics in males and females showed the AUC over the 0.5 mg to 4 mg dose range to be 15% to 70% higher in females with type 2 diabetes. This difference was not reflected in the frequency of hypoglycemic episodes (male: 16%; female: 17%) or other adverse events. With respect to gender, no change in general dosage recommendation is indicated since dosage for each patient should be individualized to achieve optimal clinical response.

Race: No pharmacokinetic studies to assess the effects of race have been performed, but in a U.S. 1-year study in patients with type 2 diabetes, the blood glucose-lowering effect was comparable between Caucasians (n=297) and African-Americans (n=33). In a U.S. dose-response study, there was no apparent difference in exposure (AUC) between Caucasians (n=74) and Hispanics (n=33).

Drug-Drug Interactions

Drug interaction studies performed in healthy volunteers show that PRANDIN had no clinically relevant effect on the pharmacokinetic properties of digoxin, theophylline, or warfarin. Co-administration of cimetidine with PRANDIN did not significantly alter the absorption and disposition of repaglinide.

Additionally, the following drugs were studied in healthy volunteers with co-administration of PRANDIN. Listed below are the results:

CYP2C8 and CYP3A4 Inhibitors/Inducer

Gemfibrozil and Itraconazole: Co-administration of gemfibrozil (600 mg) anda single dose of 0.25 mg PRANDIN (after 3 days of twice-daily 600 mg gemfibrozil) resulted in an 8.1-fold higher repaglinide AUC andprolonged repaglinide half-lifefrom 1.3 to 3.7 hr. Co-administration with itraconazoleand a single dose of 0.25 mg PRANDIN (on the third day of a regimen of 200 mg initial dose, twice-daily 100 mgitraconazole) resulted in a 1.4-fold higher repaglinide AUC. Co-administration of both gemfibrozil and itraconazole with PRANDIN resulted in a 19-fold higher repaglinide AUC and prolonged repaglinide half-lifeto 6.1 hr. Plasma repaglinide concentration at 7 h increased 28.6-fold with gemfibrozil co-administration and 70.4-fold with the gemfibrozil-itraconazole combination (see CONTRAINDICATIONS,PRECAUTIONS, Drug-Drug Interactions).

Fenofibrate: Co-administration of 200 mg fenofibrate with a single dose of 0.25 mg repaglinide (after 5 days of once daily fenofibrate 200 mg) resulted in unchanged AUC and Cmax values for both drugs.

Ketoconazole: Co-administration of 200 mg ketoconazole and a single dose of 2 mg PRANDIN (after 4 days of once daily ketoconazole 200 mg) resulted in a 15% and 16% increase in repaglinide AUC and Cmax, respectively. The increases were from 20.2 ng/mL to 23.5 ng/mL for Cmax and from 38.9 ng/mL*hr to 44.9 ng/mL*hr for AUC.

Trimethoprim: Co-administration of 160 mg trimethoprim and a single dose of 0.25 mg PRANDIN (after 2 days of twice daily and one dose on the third day of trimethoprim 160 mg) resulted in a 61% and 41% increase in repaglinide AUC and Cmax, respectively. The increase in AUC was from 5.9 ng/mL*hr to 9.6 ng/mL*hr and the increase in Cmax was from 4.7 ng/mL to 6.6 ng/mL.

Cyclosporine: Co-administration of 100 mg cyclosporine with a single dose of 0.25 mg repaglinide (after two 100 mg doses of cyclosporine twelve hours apart) increased the repaglinide (0.25 mg) Cmax 1.8-fold and the AUC 2.5-fold in an interaction study with healthy volunteers (see PRECAUTIONS, Drug-Drug Interactions).

Rifampin: Co-administration of 600 mg rifampin and a single dose of 4 mg PRANDIN (after 6 days of once daily rifampin 600 mg) resulted in a 32% and 26% decrease in repaglinide AUC and Cmax, respectively. The decreases were from 40.4 ng/mL to 29.7 ng/mL for Cmax and from 56.8 ng/mL*hr to 38.7 ng/mL*hr for AUC.

In another study, co-administration of 600 mg rifampin and a single dose of 4 mg PRANDIN (after 6 days of once daily rifampin 600 mg) resulted in a 48% and 17% decrease in repaglinide median AUC and median Cmax respectively. The median decreases were from 54 ng/mL*hr to 28 ng/mL*hr for AUC and from 35 ng/mL to 29 ng/mL for Cmax. PRANDIN administered by itself (after 7 days of once daily rifampin 600 mg) resulted in an 80% and 79% decrease in repaglinide median AUC and Cmax respectively. The decreases were from 54 ng/mL*hr to 11 ng/mL*hr for AUC and from 35 ng/mL to 7.5 ng/mL for Cmax.

Levonorgestrel & Ethinyl Estradiol: Co-administration of a combination tablet of 0.15 mg levonorgestrel and 0.03 mg ethinyl estradiol administered once daily for 21 days with 2 mg PRANDIN administered three times daily (days 1-4) and a single dose on Day 5 resulted in 20% increases in repaglinide, levonorgestrel, and ethinyl estradiol Cmax. The increase in repaglinide Cmax was from 40.5 ng/mL to 47.4 ng/mL. Ethinyl estradiol AUC parameters were increased by 20%, while repaglinide and levonorgestrel AUC values remained unchanged.

Simvastatin: Co-administration of 20 mg simvastatin and a single dose of 2 mg PRANDIN (after 4 days of once daily simvastatin 20 mg and three times daily PRANDIN 2 mg) resulted in a 26% increase in repaglinide Cmax from 23.6 ng/mL to 29.7 ng/mL. AUC was unchanged.

Nifedipine: Co-administration of 10 mg nifedipine with a single dose of 2 mg PRANDIN (after 4 days of three times daily nifedipine 10 mg and three times daily PRANDIN 2 mg) resulted in unchanged AUC and Cmax values for both drugs.

Clarithromycin: Co-administration of 250 mg clarithromycin and a single dose of 0.25 mg PRANDIN (after 4 days of twice daily clarithromycin 250 mg) resulted in a 40% and 67% increase in repaglinide AUC and Cmax, respectively. The increase in AUC was from 5.3 ng/mL*hr to 7.5 ng/mL*hr and the increase in Cmax was from 4.4 ng/mL to 7.3 ng/mL.

Renal Insufficiency: Single-dose and steady-state pharmacokinetics of repaglinide were compared between patients with type 2 diabetes and normal renal function (CrCl > 80 mL/min), mild to moderate renal function impairment (CrCl = 40 – 80 mL/min), and severe renal function impairment (CrCl = 20 – 40 mL/min). Both AUC and Cmax of repaglinide were similar in patients with normal and mild to moderately impaired renal function (mean values 56.7 ng/mL*hr vs 57.2 ng/mL*hr and 37.5 ng/mL vs 37.7 ng/mL, respectively.) Patients with severely reduced renal function had elevated mean AUC and Cmax values (98.0 ng/mL*hr and 50.7 ng/mL, respectively), but this study showed only a weak correlation between repaglinide levels and creatinine clearance. Initial dose adjustment does not appear to be necessary for patients with mild to moderate renal dysfunction. However, patients with type 2 diabetes who have severe renal function impairment should initiate PRANDIN therapy with the 0.5 mg dose – subsequently, patients should be carefully titrated. Studies were not conducted in patients with creatinine clearances below 20 mL/min or patients with renal failure requiring hemodialysis.

Hepatic Insufficiency: A single-dose, open-label study was conducted in 12 healthy subjects and 12 patients with chronic liver disease (CLD) classified by Child-Pugh scale and caffeine clearance. Patients with moderate to severe impairment of liver function had higher and more prolonged serum concentrations of both total and unbound repaglinide than healthy subjects (AUChealthy: 91.6 ng/mL*hr; AUCCLD patients: 368.9 ng/mL*hr; Cmax, healthy: 46.7 ng/mL; Cmax, CLD patients: 105.4 ng/mL). AUC was statistically correlated with caffeine clearance. No difference in glucose profiles was observed across patient groups. Patients with impaired liver function may be exposed to higher concentrations of repaglinide and its associated metabolites than would patients with normal liver function receiving usual doses. Therefore, PRANDIN should be used cautiously in patients with impaired liver function. Longer intervals between dose adjustments should be utilized to allow full assessment of response.

Clinical Trials

Monotherapy Trials

A four-week, double-blind, placebo-controlled dose-response trial was conducted in 138 patients with type 2 diabetes using doses ranging from 0.25 to 4 mg taken with each of three meals. PRANDIN therapy resulted in dose-proportional glucose lowering over the full dose range. Plasma insulin levels increased after meals and reverted toward baseline before the next meal. Most of the fasting blood glucose-lowering effect was demonstrated within 1-2 weeks.

In a double-blind, placebo-controlled, 3-month dose titration study, PRANDIN or placebo doses for each patient were increased weekly from 0.25 mg through 0.5, 1, and 2 mg, to a maximum of 4 mg, until a fasting plasma glucose (FPG) level <160 mg/dL was achieved or the maximum dose reached. The dose that achieved the targeted control or the maximum dose was continued to end of study. FPG and 2-hour post-prandial glucose (PPG) increased in patients receiving placebo and decreased in patients treated with repaglinide. Differences between the repaglinide- and placebo-treated groups were -61 mg/dL (FPG) and -104 mg/dL (PPG). The between-group change in HbA1c, which reflects long-term glycemic control, was 1.7% units.

PRANDIN vs. Placebo Treatment: Mean FPG, PPG, and HbA1c Changes from baseline after 3 months of treatment:

* p < 0.05 for between group difference
	FPG (mg/dL)		PPG (mg/dL)		HbA1c (%)
	PL	R	PL	R	PL	R
Baseline	215.3	220.2	245.2	261.7	8.1	8.5
Change from Baseline (at last visit)	30.3	-31.0*	56.5	-47.6*	1.1	-0.6*
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