WO2000043003A1

WO2000043003A1 - The therapeutic use of r-warfarin as anticoagulant

Info

Publication number: WO2000043003A1
Application number: PCT/GB2000/000154
Authority: WO
Inventors: Hazel Judith Bardsley; Ann Katherine Daly
Original assignee: Darwin Discovery Limited
Priority date: 1999-01-21
Filing date: 2000-01-21
Publication date: 2000-07-27
Also published as: AU3064800A

Abstract

R-warfarin is useful as an anticoagulant in a patient with increased sensitivity to racemic warfarin or S-warfarin, and for treating and preventing complications, such as bleeding, associated with the use of racemic warfarin.

Description

THE THERAPEUTIC USE OF R-WARFARIN AS ANTICOAGULANT Field of the Invention

This invention relates to the therapeutic use of R-warfarin. Background of the Invention Warfarin is very well known as an anticoagulant. For oral administration, it is often the agent of choice. A problem associated with the use of warfarin is the need for hospitalisation and retitration of patients.

There is widespread variation in the response of individuals to a given dose of warfarin. The prediction of accurate maintenance dose is therefore difficult. Typically, daily doses of 0.5 to 60 mg are used. There are also patients who are sensitive to warfarin or who cannot be stabilised on warfarin.

Warfarin is a chiral molecule. The respective enantiomers are known, but are not commercially available. S-Warfarin is the more potent enantiomer.

R- and S-warfarin have different pharmacokinetic and anticoagulant properties. Their different metabolisms mean that their drug interaction characteristics are different.

O'Reilly, N. Engl. J. Med. (1976) 295:354-7, suggests that drug interactions can be reduced or avoided if racemic warfarin is replaced by R-warfarin, for anticoagulant therapy.

Wingard et al, Clin. Pharmacol. Ther. (1978) 212-6, describes the pharmacokinetics of warfarin enantiomers. It is concluded that the maintenance dose of racemic warfarin required by an individual patient may be a useful predictor of the maintenance dose of S(-)-warfarin which will produce a comparable degree of anticoagulation. No such predictability is evident with respect to R(+)-warfarin. It is suggested that this effectively undermines the potential of the R-warfarin as being the more promising enantiomer, in terms of avoiding drug interactions.

Steward etal, Pharmacogenetics (1997) 7: 361-7, discloses a genetic association between sensitivity to warfarin and expression of CYP2C9*3. Furuya et al, Pharmacogenetics (1995) 5:389-92, describes the genetic polymorphism of CYP2C9 and its effect on warfarin maintenance dose requirement in patients undergoing anticoagulation therapy. US-A-5891633 discloses the identification of mutations in alleles of the drug metabolism gene, CYP2C9 and CYP2A6, and a test for the mutations. US-A-5686631 discloses an asymmetric synthesis of R- and S-warfarin. US-A- 5856525 discloses crystalline R-warfarin.

Finn et al, Ann. Intern. Med. (1996) 124:970-9, reports on the risk and severity of bleeding complications in elderly patients treated with warfarin. Summary of the Invention

The present invention is based at least in part on the discovery of an association of polymorphisms in the cytochrome P450 CYP2C9 with warfarin dose requirements. CYP2C9 genotyping has identified a sub-group of patients who have difficulty at induction of warfarin therapy, and are potentially at a higher risk of bleeding complications. The present invention is based also on the realisation that patients expressing certain allelic variants ofCYP2C9 (e.g. CYP2C9* l/*2;* l/*3;*2/*3;*2/*2) are particularly susceptible to problems that are apparently associated with the administration of S- warfarin. An alternative expression, of the discovery on which the invention is based, is that R-warfarin can be given to patients without the risk of incurring such problems. Accordingly, R-warfarin is inherently a safer anticoagulant. For example, patients requiring an unusually high dose of warfarin for effective anticoagulant therapy can use R-warfarin more safely.

According to one aspect of the present invention, such patients, and also those who are sensitive to, or cannot be stabilised on, racemic warfarin, are given R-warfarin as an anticoagulant. Especially for such individuals, a low dosage of the active component (or at least a lower dosage than would be expected given its lower potency) can be used effectively.

According to a second aspect of this invention, S-warfarin can be used to detect the presence of the allelic variants of CYP2C9 in a sample taken from a human. Description of the Invention

Patients suitable for therapy according to the present invention can be readily identified. Firstly, many people who cannot be stabilised on racemic warfarin are already known, and may have been offered alternative treatment. Others can be readily identified by the same means. Secondly, individuals exhibiting the indicated CYP2C9 variants can be identified by a simple diagnostic test; see the discussion of genotyping below. Alternatively, S-warfarin can be used for this purpose. Individuals for whom the invention is particularly suitable include those taking non- steroidal anti-inflammatory drugs or antibiotics, as drug interactions with warfarin may be avoided. Further, the invention may be particularly suitable for the treatment of individuals suffering from cardiovascular disease, and also the old, e.g. 50, 60, 70 or older, and/or obese. These are merely examples of patient populations that may benefit from the administration of R-warfarin. It may be noted that patients requiring warfarin therapy will typically be taking other medicaments.

More particularly, R-warfarin is suitably administered to patents also undergoing treatment with another drug that is metabolised by CYP2C9, such as metronidazole, fluconazole, NSAIDs, phenytoin or tolbutamide, that inhibit CYP2C9 metabolism, such as sulfaphenazole or sulfinpyrazone, or that induces CYP2C9, such as xenobiotics or alcohol, infampicin or barbiturates. R-warfarin may be given to patients sensitive to racemate, such as the elderly and those with Werner's syndrome or any other ageing disorder. Other suitable patients for treatment include those with renal and kidney diseases, impotence, osteoporosis or bone disease, vitamin deficiency, acne, dementia, Parkinsons disease, allergic disorders, infections, wounds, burns, epilepsy, gastrointestinal disorders, urological disorders, insomnia, pain, migraine, obesity, poor nutritional status, low weight, cardiovascular disease, addictive disorders, autoimmune disease, central nervous system disorder, neurological disease, endocrine disease, gynaecological disorders, pregnancy, cancer, skin disease, respiratory disease, orthopaedic conditions including hip fracture, or disorders of ears, nose and throat, patients who are immunocompromised, on contraception, being anaesthetised, post surgical or needing anticoagulation therapy, antiemetic therapy or treatment for vertigo who are on concurrent medication. Further, based on the ASA classification system used by anaesthetists and surgeons to classify patients' general state of health, the present invention is particularly suitable for those people on warfarin who are likely to be in categories II, III, or IN, i.e. of relatively poor health.

The active agent may be made up into a suitable composition, and administered by means known to those skilled in the art. Suitable compositions and routes of administration include those that have already been used for racemic warfarin. Suitable effective doses will depend on the usual factors, such as the severity of the condition being treated, the condition of the patient and other factors, but can readily be determined by the skilled man. By way of example, the daily dose of R-warfarin may be at least 0.1, 0.5, 1, 2, 5 mg or more, up to 10, 20, 50, 100 or 1000 mg.

The R-warfarin that is used in this invention is substantially free of S-warfarin. For example, it may be present in an enantiomeric excess of at least 90%, preferably at least 95%. The term "warfarin" is used herein to define the compound itself or any salt, prodrug or other derivative which releases the active component on administration. The evidence on which this invention is based will now be described. Patients were identified, whose warfarin dose requirement was 1.5 mg per day or less, had a stable warfarin dose requirement for at least 3 consecutive clinic visits with a target International Normalized Ratio (INR) of 2.0 to 3.0 and no apparent cause for low dose requirement such as drug interactions or liver disease. 36 patients (17 male, 19 female) aged 55-88 yr. (median 73 yr.) agreed to take part in the study, and formed the "low dose group". 52 subjects (26 male, 26 female) aged 33-94 yr. (median 70.5 yr.) with a wide range of daily warfarin dose requirement, formed a "clinic control group". A "community control group" consisted of 100 individuals (58 male, 42 female) aged 38-91 yr. (median 69 yr.) recruited from the same area.

Blood (10 ml) was collected from each subject; DNA was extracted as described by Daly et al, Methods Enzymol. (1996) 272:199-210, and subjected to PCR analysis. Genotyping for the CYP2C9*2 and CYP2C9*3 alleles was carried out as described by

Wang et al, Pharmacogenetics (1995) 5:37-42, using Avail digestion to detect the

CYP2C9*2 allele and Nsil digestion for CYP2C9*3.

All records from in-patient admissions and visits to the anticoagulation clinic for the patients in the low dose group and the clinic control group were reviewed. To determine the presence of difficulties during the induction of anticoagulation the details of dosage regime used, peak INR during the first week and the medical consequences (delayed discharges, outpatient visits, referrals) resulting from poor control of anticoagulation during the induction were noted.

Bleeding complications related to raised INR above the therapeutic range (>4) were classified as minor (requiring no additional testing, referral or outpatient visits), serious (requiring medical evaluation, blood transfusion of 2 units or fewer) or life- threatening (requiring surgical or angiographic intervention, transfusion of 3 or more units of blood, leading to irreversible sequelae), see Finn et al, supra. Bleeding episodes that occurred within the first four weeks of anticoagulation were classified as early, the rest as late.

Comparisons of genotype frequency and frequency of complications of anticoagulation between the groups were made using Fisher's exact test. Odds or rate ratios with 95% confidence intervals were calculated where appropriate. Age and duration of follow-up in the low dose group and random clinic group were compared using the

Mann- Whitney U test.

CYP2C9 genotype distributions in low dose warfarin group compared with the clinic controls and the community controls are summarized in Table 1. In the low dose warfarin group, 29 out of the 36 patients (81%) had one or more of the variant alleles present compared with 40 out of 100 (40%) in the control group. The odds ratio for individuals with a low warfarin dose requirement having one or more CYP2C9 variant alleles compared with the normal population was 6.21 (95% CI 2.48-15.6). When possession of either one or two variant alleles was considered separately, the odds ratio for a low dose warfarin patient possessing one variant allele only compared with the general population was 2.68 [95% CI 1.22-5.86] and two variant alleles 7.8 [95% CI 1.90- 32.1].

Genotype and allele frequencies were determined in the clinic controls to determine whether particular CYP2C9 genotypes might be associated with an increased risk of requiring anticoagulant treatment. There was no significant difference in CYP2C9 genotype frequencies between the clinic controls and the community control group. Age and sex were not confounders between the low dose group and clinic controls because the groups were not significantly different with respect to these factors. A further control group of 37 random anticoagulant clinic patients from another clinic in the same region studied had the same CYP2C9 genotype frequencies as the community control group (data not shown). Allele frequencies of 0.785 for CYP2C9*!, 0.110 for CYP2C9*2 and 0.105 for CYP2C9*3 in the controls are comparable to those of 0.79, 0.125 and 0.085 for CYP2C9*1, *2 and *3 alleles respectively, reported by Stubbins et al, Pharmacogenetics (1996) 6:429-30, from a study of a British Caucasian population.

All the patients in the study group were started on warfarin as in-patients. Each patient received an initial dose of 10 mg of warfarin with further dose requirements determined by a modified Fennerty formula (Drug Ther. Bull. (1992) 30:77-80) with regular estimations of INR. Peak INR during the first week of warfarin treatment in the low-dose group ranged from 2-10 (median 4.4). 20 out of 36 patients (2 patients with *1/*1 genotype and 18 with one or more of the mutant alleles) had a peak INR above the therapeutic range (>4) during induction of warfarin therapy when compared with 9/52 patients in the clinic control group (odds ratio: 5.97 [2.26-15.82]). Out of 20 patients in the low dose group with supra-therapeutic INR during induction, 9 had their in-patient stay prolonged for 1-9 days (median 2 days) while optimal anticoagulation was achieved. In 7 additional patients, raised INR resulted in frequent visits to anticoagulant clinic and/or additional investigations. No patient in the clinic control group had their hospital stay prolonged because of poor control of anticoagulation.

Duration of warfarin treatment was 0.2-17 yr. (median 2 yr.) for patients in the low dose group and 0.1-30 yr. (median 3.1 yr.) for patients in the clinic control group. In the low dose group, during 132.8 patient years of warfarin treatment, 7 minor, 5 serious and 6 life-threatening bleeding episodes occurred in 11 patients, including 1 patient where bleeding contributed to death. This compares with 6 minor, 5 serious and 2 life threatening bleeding episodes in 11 patients during 311.1 patient years of warfarin therapy in the clinic control group. In the low dose group, 6 minor and 1 major bleeding episodes occurred in 5 patients with in the first 4 weeks of induction of warfarin therapy. Each of these patient had one or more variant CYP2C9 alleles. The incidence of minor bleeding episodes was higher in the low dose group (7/132.8 patient years) when compared with that in random clinic controls (6/311.1 patient years), though this did not reach statistical significance (Rate Ratio: 2.73 [95% CI 0.92-8.1]; p=0.07). Significantly higher numbers of major (serious and life-threatening) bleeding episodes occurred in the low dose group (11/132.8 patient years) when compared with the random clinic controls (7/311.1 patient years) (Rate Ratio: 3.68 [95% CI 1.43-9.50]; p=0.007). Comparison between the low dose group and the random clinic controls is shown in Table 2.

This study demonstrates a strong relationship between CYP2C9 genotype and warfarin sensitivity. An individual requiring a low warfarin dose is 6 times more likely to be positive for one or more of the variant alleles associated with impaired S-warfarin metabolism (CYP2C9*2 and CYP2C9*3) compared with the general population. CYP2C9 genotyping appears to have the potential to identify a sub-group of individuals who are poor metabolisers of warfarin, hence requiring very low dose. The findings also indicate that significant proportion of these subjects have significant difficulties at the time of induction of warfarin therapy and have an increased risk of bleeding complications when compared with clinic controls. With the exception of homozygosity for CYP2C9 *3, all the other combinations of variant alleles occurred more frequently in the low-dose group compared with the controls. One out of 100 controls was homozygous for CYP2C9*3 while none in the low- dose group had this genotype. It is predicted from the control genotype frequencies that 8 subjects attending the anticoagulation clinic would be expected to be CYP2C9*3 homozygotes, making the absence of CYP2C9*3 homozygotes in the low warfarin dose group unexpected. However, since in vitro studies have demonstrated extremely slow hydroxylation of S-warfarin when CYP2C9*3 is expressed, it is possible that individuals homozygous for this allele have such a low warfarin dose requirement that stabilization is not successful and treatment with warfarin is abandoned. Interestingly, Steward et al, supra, reported diminished clearance of S-warfarin with exacerbated response to normal doses of warfarin in a patient who was homozygous for CYP2C9*3.

Impaired metabolism of a low therapeutic index drug such as warfarin has significant clinical consequences. Difficulty in establishing optimal anticoagulation were experienced in 20 out of 36 (56%) patients in the low dose group with their peak LNR raising above the target range following a fixed dose regime. Eighteen of these patients carried one or more variant CYP2C9 alleles. Difficult induction resulted in delayed discharges, multiple visits to the clinics as well as additional investigations in an attempt to seek an explanation for warfarin sensitivity. A smaller warfarin dose requirement may be associated with greater variability of IN (Finn et al, supra) and this, coupled with a low therapeutic index inherent to warfarin, may lead to bleeding complications. These are likely to occur later during the course of warfarin therapy, presumably when the monitoring regime is relaxed. Consistent with this, the incidence of major bleeding complications in the low dose group was 4 times higher than that in the clinic controls. Table 1 CYP2C9 genotype distribution in low dose warfarin patients and controls

The OR for the subjects on low warfarin dose having 1 or more CYP2C9 variant alleles compared with the community controls: 6.21 [2.48-15.6].

OR for a low dose warfarin patient possessing one variant allele: 2.68 [1.22-5.86]. OR for a low dose warfarin patient possessing two variant alleles: 7.8 [1.90-32.1].

Table 2 Comparison of low dose group with random clinic controls

Claims

1. Use of R-warfarin for the manufacture of a medicament for use as an anticoagulant in a patient with increased sensitivity to racemic warfarin or S-warfarin.

2. Use of R-warfarin for the manufacture of a medicament for use as an anticoagulant in a patient exhibiting inability to be stabilised on racemic warfarin.

3. Use ofR-warfarin for the manufacture of a medicament for use as an anticoagulant in a patient requiring a dose of more than 10 mg per day as an effective anticoagulant.

4. Use of R-warfarin for the manufacture of a medicament for use as an anticoagulant in a patient who exhibits bleeding using warfarin as an effective anticoagulant.

5. Use ofR- warfarin for the manufacture of a medicament for use as an anticoagulant in a patient of ASA status π, IE or IN.

6. Use of R-warfarin for the manufacture of a medicament for use as an anticoagulant for the prevention of complications associated with the administration of racemic warfarin.

7. Use according to any preceding claim, wherein the dose of R-warfarin is 0.1 to 1000 mg per day.

8. Use of S-warfarin as a diagnostic agent, to detect the presence of the allelic variants of CYP2C9 in a sample taken from a human.