Effects of 24 CYP2D6 variants found in Chinese population on the metabolism of clonidine in vitro

Plasma exchange treats severe intrahepatic cholestasis caused by dacomitinib: A case report

RATIONALE

Dacomitinib-induced liver injury is often manifested by mild elevations of transaminases and bilirubin, and severe intrahepatic cholestasis caused by dacomitinib for simultaneous taking orally cytochrome P450 2D6 (CYP2D6) competitive substrates has been rarely reported.

PATIENT CONCERNS

The patient was a 69-year-old woman with non-small cell lung cancer (NSCLC) who was prescribed oral dacomitinib for a month; she was given oral loratadine due to "allergic rhinitis" and metoprolol extended action tablets due to "tachycardia" separately for a few days during the course of dacomitinib treatment. The patient developed liver damage, increased fatigue, yellow urine, and pruritus, with significantly elevated serum levels of bilirubin and glutamyltranspetidase.

DIAGNOSIS

Intrahepatic cholestasis, drug-induced liver injury, and NSCLC.

INTERVENTIONS

After admission, the patient was prescribed adenosylmethionine, acetylcysteine, ursodeoxycholic acid capsule, methylprednisolone and fenofibrate for a month, with progressive elevation of liver biochemical parameters. Through drug enzyme gene assays in the liver tissue after percutaneous liver biopsy, we found both CYP2D6*10/*10 and ATP-binding cassette subfamily B member 1 GG variants (rs1045642) positive. After the poor response to the conventional medication, the patient underwent plasma exchange.

OUTCOMES

The patient was discharged after her liver parameters improved; the parameters remained normal at several follow-up visits, and she renewed the NSCLC regimens without dacomitinib after being evaluated by oncologists.

LESSONS

Dacomitinib can induce severe intrahepatic cholestasis. It is considered that patients with intermediate metabolic CYP2D6 are susceptible to drug-induced liver injury caused by dacomitinib; plasma exchange may be an effective treatment.

Characterisation of seven medications approved for attention-deficit/hyperactivity disorder using in vitro models of hepatic metabolism

The metabolism of most medications approved for the treatment of attention deficit/hyperactivity disorder (ADHD) is not fully understood.In vitro studies using cryopreserved, plated human hepatocytes (cPHHs) and pooled human liver microsomes (HLMs) were performed to more thoroughly characterise the metabolism of several ADHD medications.The use of enzyme-specific chemical inhibitors indicated a role for CYP2D6 in atomoxetine (ATX) metabolism, and roles for CYP3A4/5 in guanfacine (GUA) metabolism.The 4-hydroxy-atomoxetine and N-desmethyl-atomoxetine pathways represented 98.4% and 1.5% of ATX metabolism in cPHHs, respectively. The 3-OH-guanfacine pathway represented at least 2.6% of GUA metabolism in cPHHs, and 71% in HLMs.The major metabolising enzyme for methylphenidate (MPH) and dexmethylphenidate (dMPH) could not be identified using these methods because these compounds were too unstable. Hydrolysis of these medications was spontaneous and did not require the presence of protein to occur.Clonidine (CLD), amphetamine (AMPH), and dextroamphetamine (dAMPH) did not deplete substantially in cPHHs nor HLMs, suggesting that these compounds may not undergo considerable hepatic metabolism. The major circulating metabolites of AMPH and dAMPH (benzoic acid and hippuric acid) were not observed in either system, and therefore could not be characterised. Additionally, inhibition experiments suggested a very minimal role for CYP2D6 in CLD and AMPH metabolism.

The Pharmacogenetic Impact on the Pharmacokinetics of ADHD Medications

ADHD is a common condition in both children and adults. The most prescribed medications for the treatment of ADHD include methylphenidate, mixed amphetamine salts, atomoxetine, guanfacine, and clonidine. While each of these medications have their own distinct pharmacokinetic profile, the extent to which pharmacogenetics effects their pharmacokinetic parameters is best described in atomoxetine, followed by methylphenidate. Atomoxetine is predominantly metabolized by cytochrome p450 2D6 (CYP2D6), while methylphenidate is metabolized by carboxylesterase 1 (CES1). Both CYP2D6 and CES1 have multiple variants resulting in varying levels of enzyme activity; however, to date, the functional consequence of variants and alleles for CYP2D6 is better characterized as compared to CES1. Regarding CYP2D6, individuals who are poor metabolizers prescribed atomoxetine experience up to ten-fold higher exposure as compared to normal metabolizers at comparable dosing. Additionally, individuals prescribed methylphenidate with the rs71647871 variant may experience up to 2.5-fold higher exposure as compared to those without. Having this pharmacogenetic information available may aid clinicians and patients when choosing medications and doses to treat ADHD.

CYP2D6 Gene Polymorphisms and Variable Metabolic Activity in Schizophrenia Patients of Han and Tibetan Populations

BACKGROUND

It has been suggested that the pharmacogenomic response to antipsychotics in schizophrenia patients partially contributed by drug metabolism enzyme polymorphism, including P450 2D6 (CYP2D6). However, CYP2D6 gene polymorphism across populations is largely unknown.

MATERIALS AND METHODS

Here, we investigated the differences of CYP2D6 gene polymorphism between Chinese Han and Tibetan schizophrenia patients. We analyzed five CYP2D6 gene related polymorphic locus in 103 patients with schizophrenia, including 60 Han ethnicity and 43 of Tibetan ethnicity, by nucleic acid MALDI-TOF.

RESULTS

Polymorphisms of rs1065852, rs1135840 and rs16947 were significantly different between Han and Tibetan patients. rs1065852 AA genotype had a low frequency of 9.3% in Tibetan patients in comparison with a frequency of 41.7% in Han patients, whereas rs16947 AA genotype had a low frequency of 3.3% in Han patients in comparison with a frequency of 34.9% in Tibetan patients. Additionally, the two patient groups showed distinct distribution of CYP2D6 haplotypes, with the highest frequency of *10/*10 and *1/*2 in Han and Tibetan patients, respectively. Furthermore, Han and Tibetan patients showed differential CYP2D6 metabolic activity.

DISCUSSION

Taken together, this exploratory study showed the differences of CYP2D6 gene and metabolic polymorphism between Han and Tibetan schizophrenia patients, and therefore may improve our understanding of the pharmacogenomic response to antipsychotics in schizophrenia patients across populations.