Tucatinib AUC0-INF and Cmax increases proportionally over a dosage range from 50 mg to 300 mg (0.17 to 1 times the approved recommended dosage). Tucatinib exhibited 1.7-fold accumulation for AUC and 1.5-fold accumulation for Cmax following administration of TUKYSA 300 mg twice daily for 14 days. Time to steady state was approximately 4 days.
Absorption
The median time to peak plasma concentration of tucatinib was approximately 2 hours (range 1 to 4 hours).
Effects of Food
Following administration of a single oral dose of TUKYSA in 11 subjects after a high-fat meal (approximately 58% fat, 26% carbohydrate, and 16% protein), the mean AUC0-INF increased by 1.5-fold, the Tmax shifted from 1.5 hours to 4 hours, and Cmax was unaltered. The effect of food on the pharmacokinetics of tucatinib was not clinically meaningful.
Distribution
The geometric mean (CV%) apparent volume of distribution of tucatinib was approximately 1670 L (66%). The plasma protein binding was 97.1% at clinically relevant concentrations.
Elimination
The geometric mean (CV%) half-life of tucatinib was approximately 8.5 (21%) hours and apparent clearance was 148 L/h (55%).
Metabolism
Tucatinib is metabolized primarily by CYP2C8 and to a lesser extent via CYP3A.
Excretion
Following a single oral dose of 300 mg radiolabeled tucatinib, approximately 86% of the total radiolabeled dose was recovered in feces (16% of the administered dose as unchanged tucatinib) and 4.1% in urine with an overall total recovery of 90% within 13 days post-dose. In plasma, approximately 76% of the plasma radioactivity was unchanged, 19% was attributed to identified metabolites, and approximately 5% was unassigned.
Specific Populations
Age (< 65 (n =211); ≥ 65 (n = 27)), albumin (25 to 52 g/L), creatinine clearance (creatinine clearance [CLcr] 60 to 89 mL/min (n = 89); CLcr 30 to 59 mL/min (n = 5)), body weight (41 to 138 kg), and race (White (n=168), Black (n=53), or Asian (n=10)) did not have a clinically meaningful effect on tucatinib exposure.
Renal Impairment
No clinically significant differences in the pharmacokinetics of tucatinib were observed in patients with mild to moderate renal impairment (creatinine clearance: 30 to 89 mL/min by Cockcroft-Gault). The effect of severe renal impairment (creatinine clearance: < 30 mL/min) on the pharmacokinetics of tucatinib is unknown.
Hepatic Impairment
Mild (Child-Pugh A) and moderate (Child-Pugh B) hepatic impairment had no clinically relevant effect on tucatinib exposure. Tucatinib AUC0-INF was increased by 1.6 fold in subjects with severe (Child-Pugh C) hepatic impairment compared to subjects with normal hepatic function.
Drug Interaction Studies
Clinical Studies
Table 7: Effect of Other Drugs on TUKYSA Concomitant Drug (Dose) | TUKYSA Dose | Ratio (90% CI) of Tucatinib Exposure With and Without Concomitant Drug |
| Cmax | AUC |
Strong CYP3A Inhibitor Itraconazole (200 mg BID) |
300 mg single dose | 1.3 (1.2, 1.4) | 1.3 (1.3, 1.4) |
Strong CYP3A/Moderate 2C8 Inducer Rifampin (600 mg once daily) | 0.6 (0.5, 0.8) | 0.5 (0.4, 0.6) |
Strong CYP2C8 Inhibitor Gemfibrozil (600 mg BID) | | 1.6 (1.5, 1.8) | 3.0 (2.7, 3.5) |
Table 8: Effect of TUKYSA on Other Drugs- Tucatinib reduced the renal clearance of metformin without any effect on glomerular filtration rate (GFR) as measured by iohexol clearance and serum cystatin C.
|
Concomitant Drug (Dose) | TUKYSA Dose | Ratio (90% CI) of Exposure Measures of Concomitant Drug with/without Tucatinib |
| Cmax | AUC |
CYP2C8 Substrate Repaglinide (0.5 mg single dose) |
300 mg twice daily | 1.7 (1.4, 2.1) | 1.7 (1.5, 1.9) |
CYP3A Substrate Midazolam (2 mg single dose) | 3.0 (2.6, 3.4) | 5.7 (5.0, 6.5) |
P-gp Substrate Digoxin (0.5 mg single dose) | | 2.4 (1.9, 2.9) | 1.5 (1.3, 1.7) |
MATE1/2-K substratea Metformin (850 mg single dose) | | 1.1 (1.0, 1.2)
| 1.4 (1.2, 1.5) |
No clinically significant difference in the pharmacokinetics of tucatinib were observed when used concomitantly with omeprazole (proton pump inhibitor) or tolbutamide (sensitive CYP2C9 substrate).
In Vitro Studies
Cytochrome P450 (CYP) Enzymes: Tucatinib is a reversible inhibitor of CYP2C8 and CYP3A and a time-dependent inhibitor of CYP3A, but is not an inhibitor of CYP1A2, CYP2B6, CYP2C9, CYP2C19, or CYP2D6.
Uridine diphosphate (UDP)-glucuronosyl transferase (UGT) Enzymes: Tucatinib is not an inhibitor of UGT1A1.
Transporter Systems: Tucatinib is a substrate of P-gp and BCRP, but is not a substrate of OAT1, OAT3, OCT1, OCT2, OATP1B1, OATP1B3, MATE1, MATE2-K, or BSEP.
Tucatinib inhibits MATE1/MATE2-K-mediated transport of metformin and OCT2/MATE1-mediated transport of creatinine. The observed serum creatinine increase in clinical studies with tucatinib is due to inhibition of tubular secretion of creatinine via OCT2 and MATE1.