AUVELITY is a combination of dextromethorphan and bupropion. Bupropion inhibits the metabolism of dextromethorphan via CYP2D6. Dextromethorphan when co-administered with bupropion displays nonlinear pharmacokinetics at steady state, with greater than dose-proportional changes in AUC and Cmax for varying doses of dextromethorphan [60 to 120 mg (0.67-1.33 times the maximum recommended dose of AUVELITY)] and less than dose-proportional changes for varying doses of bupropion [150 to 300 mg (0.71-1.43 times the maximum recommended dose of AUVELITY)].
Steady state plasma concentrations of dextromethorphan and bupropion when given as AUVELITY are achieved within 8 days. The accumulation ratios for dextromethorphan at steady state when given as AUVELITY are 20 and 32, respectively based on Cmax and AUC0‑12, compared to 1.3 and 1.4, respectively, for dextromethorphan given without bupropion. The accumulation ratios for bupropion at steady state are 1.1 and 1.5, respectively based on Cmax and AUC0-12.
Absorption
The median Tmax of dextromethorphan and bupropion when given as AUVELITY was 3 hours and 2 hours, respectively.
The Cmax of the hydroxybupropion metabolite occurred approximately 3 hours post-dose and was approximately 14 times the peak level of bupropion and its AUC0-12 was about 19 times that of bupropion. The Cmax of the erythrohydroxybupropion and threohydroxybupropion metabolites occurred approximately 4 hours post-dose and were approximately equal to and 5 times that of bupropion, respectively. The AUC0-12 values were 1.2 and 7 times that of bupropion, respectively.
Effect of Food
AUVELITY can be taken with or without food. Dextromethorphan Cmax and AUC0-12 were unchanged and decreased by 14%, respectively, and bupropion Cmax and AUC0-12 were increased by 3% and 6%, respectively, when AUVELITY was administered with food.
Distribution
The plasma protein binding of dextromethorphan is approximately 60-70% and bupropion is 84%. The extent of protein binding of the hydroxybupropion metabolite is similar to that for bupropion; whereas, the extent of protein binding of the threohydroxybupropion metabolite is about half that seen with bupropion.
Elimination
Following 8 days of administration of AUVELITY in extensive metabolizers, the mean elimination half-life of dextromethorphan was increased approximately 3-fold to 22 hours, as compared to dextromethorphan given without bupropion.
The mean elimination half-life of dextromethorphan and bupropion was 22 hours and 15 hours, respectively. The apparent elimination half-life of hydroxybupropion, erythrohydroxybupropion and threohydroxybupropion metabolites were approximately 35, 44 and 33 hours, respectively.
Metabolism
Dextromethorphan is primarily metabolized by CYP2D6 to dextrorphan. Bupropion is extensively metabolized with three active metabolites: hydroxybupropion, which is formed via hydroxylation of the tert-butyl group of bupropion, and the amino-alcohol isomers, threohydroxybupropion and erythrohydroxybupropion, which are formed via reduction of the carbonyl group. In vitro findings suggest that CYP2B6 is the principal isoenzyme involved in the formation of hydroxybupropion, while cytochrome P450 enzymes are not involved in the formation of threohydroxybupropion. Oxidation of the bupropion side chain results in the formation of a glycine conjugate of meta-chlorobenzoic acid, which is then excreted as the major urinary metabolite. The potency and toxicity of the metabolites relative to bupropion have not been fully characterized. However, it has been demonstrated in an antidepressant screening test in mice that hydroxybupropion is one-half as potent as bupropion, while threohydroxybupropion and erythrohydroxybupropion are 5‑fold less potent than bupropion.
Excretion
In CYP2D6 extensive metabolizers, approximately 37-52% of the orally administered dose of dextromethorphan is recovered in the urine. Less than 2% of the administered dose is excreted as unchanged parent drug in the urine. In CYP2D6 poor metabolizers, approximately 45-83% of the administered dose is recovered in the urine. Approximately 26% of the administered dose is excreted as unchanged parent drug in the urine.
Following oral administration of 200 mg of 14C-bupropion in humans, 87% and 10% of the radioactive dose were recovered in the urine and feces, respectively. Only 0.5% of the oral dose was excreted as unchanged bupropion.
Specific Populations
Geriatric Patients
An open-label, multiple-dose study was conducted to evaluate the pharmacokinetics of AUVELITY at the maximum recommended dose at steady-state in 18 healthy geriatric (aged 65 to 85 years) and 10 healthy adult (aged 18 to 45 years) subjects. Following oral administration of AUVELITY, steady state was reached by Day 8 for dextromethorphan, bupropion, and all assessed metabolites, and their exposures, as measured by AUC and Cmax, were generally comparable between the geriatric and young adult age groups on Day 1, and on Day 8.
The geometric mean ratios and 90% confidence intervals (CIs) of pharmacokinetic parameters (Cmax and AUC) of dextromethorphan and bupropion following administration of AUVELITY in healthy geriatric (age 65 to 85) and healthy adult (aged 18 to 45) subjects are summarized in Figure 1.
Pediatric Patients
The pharmacokinetics of AUVELITY in pediatric patients have not been studied.
Male and Female/ Racial or Ethnic Groups
No significant pharmacokinetic differences based on sex and race have been observed for AUVELITY.
Patients with Renal Impairment, Patients with Hepatic Impairment, and CYP2D6 Poor Metabolizers
The effects of renal impairment, hepatic impairment, and CYP2D6 poor metabolizer status on the exposure to AUVELITY are summarized in Figure 1 [see Dosage and Administration (2.4, 2.6)].
Figure 1: Effects of Age, Renal Impairment, Hepatic Impairment, and CYP2D6 Poor Metabolizer Status on AUVELITY PK
Results are based on plasma concentrations of AUVELITY after 8 days of twice daily dosing. Reference = healthy adults 18-45 years of age for the geriatric study, matched healthy subjects for renal and hepatic impairment studies, and extensive or ultra-extensive CYP2D6 metabolizers. AUC = area under the plasma concentration-time curve from zero to 12 hours; BUP = bupropion; CI = confidence interval; Cmax = maximum plasma concentration; DM = dextromethorphan; GMRs = geometric mean ratios; PK = pharmacokinetics.
Drug Interaction Studies
In Vitro Assessment of Drug Interactions
The potential for dextromethorphan and bupropion to inhibit or induce cytochrome P450 in vitro were evaluated in human liver microsomes.
Bupropion and its metabolites (hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion) are inhibitors of CYP2D6. At therapeutically relevant concentrations dextromethorphan does not inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4. Dextromethorphan does not cause induction of CYP1A2, CYP3A4, or CYP2B6.
Dextromethorphan is a substrate of the human P-gp transporter. Dextromethorphan does not inhibit transporters at therapeutically relevant concentrations.
In Vivo Assessment of Drug Interactions
The effects of other drugs on the exposure to AUVELITY are summarized in Figure 2 [see Dosage and Administration (2.5)].
Figure 2: Effects of Co-administered Compounds on AUVELITY PK
Results are based on steady state plasma concentrations of twice daily dosing of AUVELITY. Data are GMRs and 90% CIs. AUC = area under the plasma concentration-time curve from zero to 12 hours; BUP = bupropion; CI = confidence interval; Cmax = maximum plasma concentration; DM = dextromethorphan; GMRs = geometric mean ratios; PK = pharmacokinetics.
Digoxin
Literature data showed that digoxin exposure was decreased when a single oral dose of 0.5-mg digoxin was administered 24 hours after a single oral dose of extended-release 150 mg bupropion in healthy volunteers.