The pharmacokinetic parameters of fidaxomicin and its main metabolite OP-1118 following a single dose of 200 mg in healthy adult males (N=14) are summarized in Table 4.
Table 1: Mean (± Standard Deviation) Pharmacokinetic Parameters of Fidaxomicin 200 mg in Healthy Adult MalesParameter | Fidaxomicin | OP-1118 |
| N | Value | N | Value |
Cmax (ng/mL) | 14 | 5.20 ± 2.81 | 14 | 12.0 ± 6.06 |
Tmax (h)
| 14 | 2.00 (1.00-5.00) | 14 | 1.02 (1.00-5.00) |
AUC0-t (ng-h/mL) | 14 | 48.3 ± 18.4 | 14 | 103 ± 39.4 |
AUC0-∞ (ng-h/mL) | 9 | 62.9 ± 19.5 | 10 | 118 ± 43.3 |
t1/2 (h) | 9 | 11.7 ± 4.80 | 10 | 11.2 ± 3.01 |
Absorption
Fidaxomicin has minimal systemic absorption following oral administration, with plasma concentrations of fidaxomicin and OP-1118 in the ng/mL range at the therapeutic dose. In fidaxomicin-treated patients from controlled trials, plasma concentrations of fidaxomicin and OP-1118 obtained within the Tmax window (1-5 hours) were approximately 2- to 6-fold higher than Cmax values in healthy adults. Following administration of fidaxomicin tablets 200 mg twice daily for 10 days, OP-1118 plasma concentrations within the Tmax window were approximately 50%-80% higher than on Day 1, while concentrations of fidaxomicin were similar on Days 1 and 10.
In a food-effect study involving administration of fidaxomicin to healthy adults (N=28) with a high-fat meal versus under fasting conditions, Cmax of fidaxomicin and OP-1118 decreased by 21.5% and 33.4%, respectively, while AUC0-t remained unchanged. This decrease in Cmax is not considered clinically significant, and thus, fidaxomicin may be administered with or without food.
Distribution
Fidaxomicin is mainly confined to the gastrointestinal tract following oral administration. In selected patients (N=8) treated with fidaxomicin 200 mg twice daily for 10 days from controlled trials, fecal concentrations of fidaxomicin and OP-1118 obtained within 24 hours of the last dose ranged from 639-2710 µg /g and 213-1210 µg /g, respectively. In contrast, plasma concentrations of fidaxomicin and OP-1118 within the Tmax window (1-5 hours) ranged 2-179 ng/mL and 10-829 ng/mL, respectively.
Elimination
Metabolism
Fidaxomicin is primarily transformed by hydrolysis at the isobutyryl ester to form its main and microbiologically active metabolite, OP-1118. Metabolism of fidaxomicin and formation of OP-1118 are not dependent on cytochrome P450 (CYP) enzymes.
At the therapeutic dose, OP-1118 was the predominant circulating compound in healthy adults, followed by fidaxomicin.
Excretion
Fidaxomicin is mainly excreted in feces. In one trial of healthy adults (N=11), more than 92% of the dose was recovered in the stool as fidaxomicin and OP-1118 following single doses of 200 mg and 300 mg. In another trial of healthy adults (N=6), 0.59% of the dose was recovered in urine as OP-1118 only following a single dose of 200 mg.
Specific Populations
Geriatric Patients
In controlled trials of patients treated with fidaxomicin 200 mg twice daily for 10 days, mean and median values of fidaxomicin and OP-1118 plasma concentrations within the Tmax window (1-5 hours) were approximately 2- to 4-fold higher in elderly patients (≥65 years of age) versus non-elderly patients (<65 years of age). Despite greater exposures in elderly patients, fidaxomicin and OP-1118 plasma concentrations remained in the ng/mL range [see Use in Specific Populations (8.5)].
Pediatric Patients
Pediatric use information is approved for Cubist Pharmaceuticals LLC’s DIFICID® (fidaxomicin) tablets. However, due to Cubist Pharmaceuticals LLC’s marketing exclusivity rights, this drug product is not labeled with that information.
Male and Female Patients
Plasma concentrations of fidaxomicin and OP-1118 within the Tmax window (1-5 hours) did not vary by gender in patients treated with fidaxomicin tablets 200 mg twice daily for 10 days from controlled trials. No dose adjustment is recommended based on gender.
Patients with Renal Impairment
In controlled trials of patients treated with fidaxomicin 200 mg twice daily for 10 days, plasma concentrations of fidaxomicin and OP-1118 within the Tmax window (1-5 hours) did not vary by severity of renal impairment (based on creatinine clearance) between mild (51-79 mL/min), moderate (31-50 mL/min), and severe (≤ 30 mL/min) categories. No dose adjustment is recommended based on renal function.
Patients with Hepatic Impairment
- The impact of hepatic impairment on the pharmacokinetics of fidaxomicin has not been evaluated. Because fidaxomicin and OP-1118 do not appear to undergo significant hepatic metabolism, elimination of fidaxomicin and OP-1118 is not expected to be significantly affected by hepatic impairment.
Drug Interaction Studies
In vivo studies were conducted to evaluate intestinal drug-drug interactions of fidaxomicin as a P-gp substrate, P-gp inhibitor, and inhibitor of major CYP enzymes expressed in the gastrointestinal tract (CYP3A4, CYP2C9, and CYP2C19).
Table 5 summarizes the impact of a co-administered drug (P-gp inhibitor) on the pharmacokinetics of fidaxomicin
[see Drug Interactions (7.1)].
Table 2: Pharmacokinetic Parameters of Fidaxomicin and OP-1118 in the Presence of a Co-Administered DrugParameter | Cyclosporine 200 mg + Fidaxomicin 200 mg (N=14) | Fidaxomicin 200 mg Alone (N=14) | Mean Ratio of Parameters With/Without Co-Administered Drug (90% CI ) No Effect = 1.00 |
| N | Mean | N | Mean |
Fidaxomicin | | | | | |
Cmax (ng/mL) | 14 | 19.4 | 14 | 4.67 | 4.15 (3.23-5.32) |
AUC0-∞ (ng-h/mL)
| 8 | 114 | 9 | 59.5 | 1.92 (1.39-2.64) |
OP-1118 | | | | | |
Cmax (ng/mL) | 14 | 100 | 14 | 10.6 | 9.51 (6.93-13.05) |
AUC0-∞ (ng-h/mL)
| 12 | 438 | 10 | 106 | 4.11 (3.06-5.53) |
Fidaxomicin had no significant impact on the pharmacokinetics of the following co-administered drugs: digoxin (P-gp substrate), midazolam (CYP3A4 substrate), warfarin (CYP2C9 substrate), and omeprazole (CYP2C19 substrate). No dose adjustment is warranted when fidaxomicin is co-administered with substrates of P-gp or CYP enzymes.