Kinetic analysis of effects of mouth washing on removal of drug residues following inhalation of fluticasone propionate dry powder.

Fluticasone propionate dry powder inhaler (FP-DPI) is widely used for the treatment of asthma. However, local adverse effects such as oropharyngeal candidiasis are often seen and mouth washing after inhaling is recommended. In our previous study, we reported a nonlinear relationship between the amount of drug residue and number of times mouth washing was employed. Thus, we developed a compartment model, in which the inhaled drugs were distributed in both easy and difficult to remove areas. Using this model, we analyzed drug removal efficiency in each area with different mouth washing procedures. Three methods of mouth washing were studied; gargling and rinsing in combination, rinsing alone, and gargling alone, following administration of FP-DPI by sprinkling or inhaling. The amounts of drugs recovered from areas considered to be easy to remove (X(1)) and difficult to remove (X(2)) were determined using a nonlinear least-squares program, while the removal efficiency of each of the 3 methods was also calculated. The ratios of X(1) after sprinkling and inhalation were 63.9% and 21.8%, respectively, while those of X(2) were 6.0% and 12.4%, respectively. The numbers of mouth washings required to remove half doses from easy and difficult to remove areas were 0.2 and 1.4 times, respectively, with a combination of gargling and rinsing following inhalation of FP-DPI, while those were 0.3 and 3.6 times, respectively, with rinsing alone, and 0.4 and 5.8 times, respectively, with gargling only, thus demonstrating significant differences among the mouth washing methods for efficiency in the difficult to remove area. The present results show that the employed methods of mouth washing had a significant influence on the removal of drug residues following inhalation of FP-DPI, with gargling and rinsing in combination considered to be the most effective.

Effects of mouth washing procedures on removal of budesonide inhaled by using Turbuhaler.

Mouth washing after inhalation of corticosteroids is effective for prevention of local adverse effects. We determined the amounts of drug residues remaining on the oropharyngeal mucosa following inhalation of budesonide (BUD) via a Turbuhaler (BUD-TH) (100 microg). Further, we studied the effects of mouth washing on the removal of drug residues by quantification of BUD in expectorated wash solution using an HPLC method. The amount of BUD recovered after gargling and rinsing for 5 s each was 19.4+/-9.4 microg, as compared to 23.8+/-13.6 microg after rinsing alone for 10 s and 18.3+/-8.9 microg after gargling alone for 10 s, though the differences were not significant. Our results indicated that about 20% of the dose was remaining on the oropharyngeal mucosa after inhalation. In a comparison of washing times, the amounts of BUD recovered were 26.3+/-3.2 microg after gargling and rinsing for 3 s each, and 19.4+/-9.3 microg after those for 5 s each. As for the effect of lag time before beginning mouth washing, the ratio of BUD recovered following mouth washing with a lag time of 1 min was 73.2%, while it was reduced to 27.8% after 10 min, as compared to immediate mouth washing following administration. Our results suggest that the amount of BUD removed by mouth washing is associated with the lag time between inhalation and mouth washing, however, not with the duration of mouth washing. We concluded that immediate mouth washing after inhalation is most useful for the removal of drugs following BUD-TH administration.

Analysis of pharmacological effects of drugs used for treatment of urinary disturbance based on anticholinergic and smooth muscle-relaxing effects.

Propiverine hydrochloride, oxybutynin hydrochloride and terodiline hydrochloride have both anticholinergic and antispasmodic effects, and are used for the management of urinary frequency and incontinence. The average standard therapeutic doses of these drugs differ greatly. We retrospectively analyzed their pharmacological effects with consideration given to muscarinic acetylcholine receptor binding affinities, anticholinergic activities, and inhibitory effects on KCl-induced contraction. Muscarinic acetylcholine receptor occupancies and the inhibitory ratios of the drugs for both acetylcholine-induced and KCl-induced contraction in a steady state after oral administration of standard doses were calculated based on pharmacokinetics and the receptor occupancy theory. The average muscarinic acetylcholine receptor occupancy and inhibitory ratio of acetylcholine-induced contraction were estimated to be 12.6+/-1.06% and 3.27+/-0.74%, respectively, with no significant differences found between the drugs for those parameters. A significant linear relationship was found between muscarinic acetylcholine receptor occupancy and the maximum ratio of increase in bladder urinary capacity. On the other hand, the inhibitory ratios of KCl-induced contraction varied from 0.01 to 0.48%. The present results suggest that muscarinic acetylcholine receptor occupancy is a principal determinant of the therapeutic effect of a drug used for treatment of urinary disturbance.

Relationship between amount of drug delivered to lungs and amount released from Diskhaler by inhalation with tapping.

It is well known that drug residue remains in a fluticasone propionate Diskhaler (FP-DH) following a single inhalation. Thus, the inspiratory ability of the patient has an influence on the effects of the drug. In a previous study, we reported that the amount of drug remaining in an FP-DH was decreased by tapping the device after the first inhalation. In the present study, we investigated the relationship between the amount of drug delivered to the lungs and amount of drug released from the FP-DH by inhalation along with tapping using an in vitro model. We measured the amounts delivered to the throat, stage 1, and stage 2 of a twin impinger device by HPLC-UV, following inhalation and tapping of 100 microg of FP-DH at various inspiratory flow rates, which ranged from 11.5 to 73.6 l/min for 2 s. A positive linear correlation between the amount of drug released from the FP-DH and that deposited in stage 2 was observed. Amounts deposited in stage 2 following tapping were estimated to be 6.0 microg at an inspiratory flow rate of 20 l/min and 10.6 microg at 60 l/min, while those without tapping were 2.0 microg and 10.2 microg, respectively. Notably, at an inspiratory flow rate of 20 l/min, the amount of drug deposited in stage 2 by tapping was increased about 3-fold in comparison to that without tapping. Our results indicate that the amount of drug deposited in stage 2, i.e., the lung in our model, is increased by tapping of the device, which would be particularly helpful for patients with a lower level of inspiratory ability.

[Analysis of antiemetic effect of various dosage regimens of azasetron hydrochloride based on 5-HT3 receptor occupancy of serotonin].

Antineoplastic drugs have been shown to exert direct effects on the gut and induce the release of serotonin from the enterochromaffin cells of small intestinal mucosa. It is thought that released serotonin stimulates vagal afferent fibers through 5-HT3 receptors located in the vagal afferent terminals in the gastrointestinal tract and initiates sensory signals to the area postrema and the emetic center, thereby initiating nausea and vomiting. A 5-HT3 antagonist competitively inhibits serotonin at its specific binding sites, 5-HT3 receptors, and thereby elicits an antiemetic effect. Therefore 5-HT3 receptor occupancy of serotonin may be an appropriate indicator of the antiemetic activity of 5-HT3 antagonists. We analyzed 5-HT3 receptor occupancy of serotonin by integrating pharmacokinetic and receptor-binding kinetic parameters based on the receptor occupancy theory to compare the strength of the antiemetic effects of three dosage regimens of azasetron hydrochloride. The inhibitory effects on the binding of serotonin to 5-HT3 receptor of regimen 2 (an intravenous bolus injection of 5 mg of azasetron hydrochloride before and 8 h after chemotherapy) and regimen 3 (an intravenous bolus injection of 2.5 mg followed by 7.5 mg continuous intravenous infusion for 24 h) were longer-lasting than those of regimen 1 (an intravenous bolus injection of 10 mg before the start of chemotherapy). Furthermore, a positive relationship was found between the time of inhibitory effects on the binding of serotonin to 5-HT3 receptor and antiemetic effects of azasetron hydrochloride. From these results, dosage regimens 2 and 3 were considered to be more effective in the long term than regimen 1 in prophylaxis of nausea and vomiting induced by cisplatin.

Analysis of relationship between peak inspiratory flow rate and amount of drug delivered to lungs following inhalation of fluticasone propionate with a Diskhaler.

A Diskhaler is a dry powder type of inhaler that utilizes a breath controlled drug delivery system. The inspiratory flow rate of the patient would have a significant influence on the effects of drugs administered by a Diskhaler. Thus, we investigated the relationship between inspiratory flow rate and amount of drug delivered into the lungs when using a fluticasone propionate dry powder inhaler with a Diskhaler (FP-DH). To investigate the amount of drug inhaled, we used an inhalation simulator, which consisted of a flow recorder placed in a plastic air-tight box that covered the FP-DH equipped with a twin impinger and a vacuum pump. Drugs located in a plastic box, as well as the device, throat, and stage 1 and stage 2, were assayed by HPLC-UV, following in vitro inhalation at the various flow rates ranged from 18.7 to 77.3 l/min for 2 s. The relationship between peak inspiratory flow rate and amount of drug released from the device was analyzed. A positive linear correlation between the dose released from the device and amount of drug deposited in stage 2 was observed (r=0.899, p<0.001). The doses deposited in stage 2 were estimated to be 2.9 microg at a flow rate of 20 l/min, 6.6 microg at 30 l/min, 8.4 microg at 40 l/min, 10.1 microg at 60 l/min, and 11.3 microg at 90 l/min. It was suggested that the amount of drug in the lungs decreased along with a decrease in peak inspiratory flow rate when it was lower than 60 l/min. Our results were found to be very useful to estimate lung deposition by using peak inspiratory flow rate for administration planning, especially in patients with a flow rate of less than 60 l/min.

[Analysis of the factors associated with drugs remaining in the Diskhaler following inhalation of fluticasone propionate].

Because it is well known that drug remains in the fluticasone propionate Diskhaler (FP-DH) following a single inhalation, the following patient information is recommended. "Please inhale more than once or twice if any drug remains in the device after inhalation". It is believed the inspiratory flow rate of the individual patient has an influence on the amount of drug that remains in the device. If the dosing performance of FP-DH is dependent on inspiratory effort, establishment of a method of inhalation that makes it independent of inspiratory flow rate is important in clinical practice. In the present study, we investigated the influence of various methods of inhalation of drug remaining in the FP-DH. No significant differences were observed regarding the drug remaining in the device among the inhalation times examined (range, 0.5-2.5 s) or the number of inhalations (range, 1-3 times). On the other hand, the amount of drug remaining in the device did decrease by tapping the device before the second inhalation. The results suggest that the amount of drug remaining in the device can be decreased by tapping the device after the first inhalation if the patient's inspiratory flow rate is low.

Influence of mouth washing procedures on the removal of drug residues following inhalation of corticosteroids.

Mouth washing after inhalation of corticosteroids is effective for prevention of local adverse effects such as hoarseness and oropharyngeal candidiasis. To establish an optimal procedure for such mouth washing, we investigated the removal rates of drug residues remaining on the oropharyngeal mucosa using various mouth washing methods following inhalation. A beclomethasone dipropionate metered dose inhaler (BDP-MDI) (100 microg) and a fluticasone propionate dry powder inhaler (FP-DPI) (100 microg) were used. The effects of different mouth washing methods were evaluated by quantification of drugs in the expectorated rinse solution using an HPLC method. The amounts of BDP recovered in the rinse after gargling and rinsing for 5 s each were 47.1+/-13.6 microg, while they were 42.9+/-9.4 microg after rinsing alone for 10 s and 38.7+/-9.2 microg after gargling alone for 10 s. Under the same conditions, FP amounts were 32.9+/-7.3 microg, 28.9+/-2.4 microg, and 27.1+/-7.9 microg, respectively. In a comparison of washing time, the amounts of BDP recovered were 49.8+/-9.7 microg after gargling and rinsing for 2 s each, 53.5+/-10.2 microg after those for 3 s each, and 47.1+/-13.6 microg after those for 5 s each, while the amounts of FP under the same conditions were 36.4+/-2.4 microg, 33.3+/-6.4 microg, and 32.9+/-7.4 microg, respectively. As for the effect of time lag before mouth washing, the amount of BDP recovered decreased by 65.7% with a lag time of 1 min and by 5.6% after 10 min, while that of FP decreased by 51.1% with a lag time of 1 min and by 7.7% after 10 min. Our results suggest that the amount of drugs removed by mouth washing is significantly associated with the time lag between inhalation and mouth washing. We concluded that immediate gargling and rinsing after inhalation is most useful for the removal of drugs following inhalation of corticosteroids.

Influence of glutathione S-transferase A1 polymorphism on the pharmacokinetics of busulfan.

BACKGROUND: High-dose oral busulfan is used for myeloablative chemotherapy before hematopoietic stem-cell transplantation. Fatal adverse effects or relapse may occur with excess or insufficient busulfan exposure. Glutathione S-transferase (GST) A1, whose genetic polymorphism in its promoter region has been reported, is responsible for busulfan metabolism. We investigated the polymorphism of GSTA1 on busulfan pharmacokinetics. METHODS: Blood samples (6 or 7 points) were taken from patients receiving high-dose oral busulfan (approximately 1 mg/kg every 6 h) on Doses 1 and 5. Pharmacokinetic parameters were calculated from plasma busulfan concentration. RESULTS: Twelve patients were enrolled in this study. Nine patients were genotyped as wildtype (GSTA1*A/*A), and 3 as heterozygous variants (GSTA1*A/*B). At Dose 5, the heterozygous group had significantly lower elimination constant (0.176+/-0.038 vs. 0.315+/-0.021 h-1; P=0.008) and clearance corrected by bioavailability (0.118+/-0.013 vs. 0.196+/-0.011 l/h/kg; P=0.004), and significantly higher mean plasma busulfan concentration (1344+/-158 vs. 854+/-44 ng/ml; P=0.001) than the wildtype. CONCLUSIONS: This is the first report on the significant influence of GSTA1 polymorphism on busulfan elimination. This may account for the large inter-individual variance in busulfan pharmacokinetics, and with more information confirming our study, busulfan high-dose therapy may be optimized by GSTA1 genotyping in advance.

Effects of the CYP3A5 genetic polymorphism on the pharmacokinetics of diltiazem.

BACKGROUND: The cytochrome P450 (CYP) 3A subfamily plays an important role in the metabolism of various endogenous and exogenous compounds. Among CYP3A subfamily members, CYP3A5 is polymorphically expressed and the CYP3A5*3 and CYP3A5*6 alleles are known not to express functional CYP3A5. Thus, these mutant alleles are thought to be responsible for interindividual variability of CYP3A activity. METHODS: Subjects possessing CYP3A5*1/*1, *1/*3 or *3/*3 received oral administration of diltiazem hydrochloride (60 mg), and plasma and urinary concentrations of diltiazem and its metabolite N-desmethyldiltiazem were measured. Before drug intake, cortisol metabolic clearance in each subject was measured to estimate in vivo CYP3A4 activity. RESULTS: The mean values of total oral diltiazem clearance of subjects with *1/*1, *1/*3 and *3/*3 were 183.4 +/- 39.4, 197.9 +/- 49.6 and 293.6 +/- 141.1 (l/h), respectively, and were not significantly different among the 3 genotype groups. The cortisol metabolic clearance was not significantly different among the three genotype groups, indicating that the CYP3A4 activity is not significantly different. CONCLUSION: The results suggest that CYP3A5*3 has only a minor effect on the pharmacokinetics and metabolism of diltiazem. Although our results did not indicate significance of CYP3A5, the effects of CYP3A5*3 on the metabolism of other CYP3A substrates remain to be investigated.

Investigation of mouth washing by patients after inhaling corticosteroids.

We report an effective method for mouth washing after inhalation of corticosteroids for the prevention of local adverse effects such as hoarseness and oropharyngeal candidiasis. This method involves gargling and rinsing immediately after inhalation, repeated at least twice. We performed a questionnaire survey on mouth washing after inhalation of corticosteroids of 19 inpatients who used inhaled corticosteroids at the University of Tokyo Hospital. The questions concerned: 1) awareness of local adverse effects of inhaled corticosteroids; 2) gargling and rinsing habits; 3) repeating mouth washing at least twice; and 4) mouth washing immediately after inhalation. The percentage of patients correctly performing the individual maneuvers were: 1) 63.2%; 2) 36.8%; 3) 36.8%; and 4) 63.2%. The percentage of patients performing our recommended method of mouth washing (all four elements) was 11%. These results suggest that patients receiving inhaled corticosteroids poorly comprehend mouth washing procedures after inhalation of corticosteroids. It is important that pharmacists advise patients on the correct method of mouth washing.

High-throughput detection of multiple genetic polymorphisms influencing drug metabolism with mismatch primers in allele-specific polymerase chain reaction.

Because of genetic polymorphisms of drug-metabolizing enzyme genes, the activities of the enzymes in humans vary widely and alter the metabolism of commonly used clinical agents. Severe adverse effects or resistance to therapy may result. We have developed a rapid and high-throughput genotyping method for detecting polymorphisms of the drug-metabolizing enzyme genes CYP2C9*3, CYP2C19*2, *3, CYP2D6*2, *4, *10, *14, *21, NAT2*5, *6, *7, and TPMT*3 using allele-specific polymerase chain reaction (PCR) with mismatch primers (ASPCR-MP) and CYP2D6*5, *36, and CYP2D6xN using stepdown PCR with detection by SYBR Green I. We analyzed genomic DNA from 139 Japanese volunteers. Identical genotyping results were obtained by using ASPCR-MP, stepdown PCR, and conventional PCR. We found that the methods clearly differentiate three specific profiles with no overlap in the signals. Moreover, both ASPCR-MP and stepdown PCR for genotyping took less than 3-4h. To our knowledge, this is the first report of successful simultaneous detection of multiple genetic polymorphisms with point mutations using ASPCR-MP or multiple genetic polymorphisms with large structural alterations using stepdown PCR. In conclusion, ASPCR-MP and stepdown PCR appear to be suitable for large clinical and epidemiological studies as methods that enable highly sensitive genotyping and yield a high-throughput.

Pharmacokinetic/pharmacodynamic analysis of neutrophil proliferation induced by rhG-CSF in patients receiving antineoplastic drugs.

In the present study, we analyzed the effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on neutrophil counts in cancer patients undergoing chemotherapy using a previously developed pharmacokinetic/pharmacodynamic model.(7)) The time profiles of neutrophil counts in blood after repeated administration of rhG-CSF to lung cancer patients undergoing chemotherapy could be analyzed by this model by considering the inhibition of neutrophil production by antineoplastic drugs. Although deviation was observed between the predicted and observed neutrophil counts in ovarian cancer patients, it may be possible to use this model for determining a rational dosage regimen of rhG-CSF for patients undergoing chemotherapy.

A long PCR assay to distinguish CYP2D6*5 and a novel CYP2D6 mutant allele associated with an 11-kb EcoRI haplotype.

BACKGROUND: We found a genomic DNA (N=1) associated with an unidentified 11-kb EcoRI haplotype of CYP2D6 and with amplification of the CYP2D6*5 specific polymerase chain reaction (PCR) product without the 11.5-kb XbaI haplotype in a Japanese woman. We developed a long PCR assay to distinguish CYP2D6*5 and the novel mutant allele, and we evaluated the PCR method on 162 different genomic DNA samples. METHODS: Long PCR assays were performed to amplify a fragment specific for the novel mutant allele and to exclude coamplification of CYP2D6*5. RESULTS: A 1692-bp PCR product was amplified from the DNA sample with the novel mutant allele, while the PCR product was not amplified from any of the 162 DNA samples. CONCLUSIONS: The long PCR assay enabled the detection of the novel mutant allele associated with an 11-kb EcoRI haplotype. Further population studies are required to confirm the frequency of the novel mutant allele in various populations, as it may be contained in samples reported as CYP2D6*5.

Genetic analysis of glutathione S-transferase A1 and T1 polymorphisms in a Japanese population.

Novel allelic variants have been found in the glutathione S-transferase (GST) A1 and T1 genes. The former GSTA1*B allele is associated with low expression and the latter GSTT1*B allele lacks GSTT1 activity. The information on frequencies of both variants is poorly documented in the Japanese population. In this study we determined the frequencies of allelic variants of GSTA1 and GSTT1 in a Japanese population using PCR-restriction fragment length polymorphism and allele-specific PCR. The frequencies of GSTA1*B, GSTT1*0 and GSTT1*B alleles in the subjects were 16.0%, 71.1% and 0%, respectively. This is the first report on the frequencies of allelic variants of GSTA1 and GST-1 in a Japanese population.

Metabolic activity of dextromethorphan O-demethylation in healthy Japanese volunteers carrying duplicated CYP2D6 genes: duplicated allele of CYP2D6*10 does not increase CYP2D6 metabolic activity.

BACKGROUND: This study was designed to assess the metabolic activities of dextromethorphan O-demethylation in healthy Japanese subjects carrying duplicated CYP2D6 alleles, CYP2D6*1 x 2, CYP2D6*2 x 2 or CYP2D6*10 x 2. METHODS: Forty-one unrelated healthy Japanese subjects containing carriers who had previously been genotyped as CYP2D6*1 x 2/*2, CYP2D6*1/*2 x 2, and CYP2D6*10/*10 x 2 were phenotyped with dextromethorphan. RESULTS: The metabolic ratios of dextromethorphan/dextrorphan in subjects with CYP2D6*1 x 2/*2 or CYP2D6*1/*2 x 2 were lower than those in subjects with CYP2D6*1/*2, while the metabolic ratios in subjects with CYP2D6*10/*10 x 2, as well as homozygotes for CYP2D6*10, were significantly (P<0.01) higher than those in homozygotes for CYP2D6*1. CONCLUSIONS: The results suggested that carriers with three functional CYP2D6 genes, CYP2D6*1 x 2/*2 or CYP2D6*1/*2 x 2, are ultrarapid metabolizer phenotypes in Japanese. The results also suggested that there is no gene-dose effect with the dextromethorphan O-demethylation activities between carriers with two and three CYP2D6*10 mutated genes per genome. Therefore, CYP2D6*10 x 2 may play an important role for the treatment of Japanese patients as well as CYP2D6*10 which is mainly responsible for the intermediate metabolizers in Japanese.

Development and evaluation of pharmaceutical services in the ICU/CCU by medical staffs.

Questionnaires were sent out to the staffs (13 physicians, 52 nurses and 5 medical engineers) of the ICU/CCU at the University of Tokyo Hospital, to evaluate pharmaceutical services by analyzing problems in the services offered. Four components of pharmaceutical services were evaluated: inventory control of drugs, check of drug usage and doses, mixing of injections, and offering drug information. Almost all responses from medical staffs evaluated pharmaceutical services overall as "good". The high response rate (96%) from the nursing staff was attributed to the fact that they were familiar with the pharmacist's role with drug inventory, and mixing injections, when nursing was not available for these tasks. Although 50% of physicians rated the pharmaceutical services of providing drug information as "good", this value was lower than responses on other items of the questionnaires, which suggests some dissatisfaction. The occurrences of drug information obtained by passive offering (121 subjects) was 4 times as common as drug information obtained by active offering (30 subjects). From this finding, and comments on the questionnaires from physicians, it suggests that physicians require more drug information for dosage regimens, and prefer the drug information to be provided more actively. Further, an important comment from physicians and nurses was that the services of pharmacists are not available on all shifts/all days of the week to provide consultation for drug information and mixing of injections. Although having a pharmacist available daily around the clock is desirable and ideal to the medical team, the number of pharmacists under the present system cannot support this. As a solution, we think that it is crucial that pharmacists educate medical staff when they are present to in order to optimize therapy and patient care over time.

Receptor occupancy theory-based analysis of antiemetic effects and standard doses of 5-HT3 receptor antagonists in cancer patients.

PURPOSE: The aim of this study was to determine the usefulness of receptor occupancy theory-based analysis using pharmacokinetic and pharmacodynamic parameters for predicting the average receptor occupancy (PhiB) in humans of each of five 5-HT3 antagonists administered at standard doses. METHODS: The relationship between the PhiB value and the complete vomiting inhibition rate after a single intravenous administration of cisplatin (not less than 50 mg/m2) was analyzed. RESULTS: The predicted PhiB values after intravenous administration and oral administration of 5-HT3 antagonists were more than 65% and 50%, respectively, suggesting that relatively high receptor occupancy is required to elicit sufficient antiemetic effects of 5-HT3 antagonists. Moreover, significant ( P<0.05) linear relationships were found between PhiB values and complete vomiting inhibition rates of 5-HT3 antagonists in preventive cisplatin therapy, with correlation coefficients higher than 0.9, suggesting that the 5-HT3 receptor occupancy is an appropriate index of clinical efficacy of 5-HT3 antagonists, with higher receptor occupancy indicating more extensive antiemetic action. CONCLUSION: The receptor occupancy theory-based analysis of the antiemetic effect of a 5-HT3 receptor antagonist used in this study should be very useful for not only estimating a rational dosage regimen but also determining the standard dose of a new drug using experimental data obtained in a preclinical study.

Frequency distribution of thiopurine S-methyltransferase activity in red blood cells of a healthy Japanese population.

Thiopurine S-methyltransferase (TPMT), which exhibits a genetic polymorphism, plays an important role in the metabolism of thiopurine drugs such as mercaptopurine, thioguanine, and azathioprine. To determine the frequency distribution of TPMT activity in 157 Japanese subjects with different TPMT genotypes, ie, TPMT*1/*1 and TPMT*1/*3, the authors measured levels of 6-methylmercaptopurine formed from 6-mercaptopurine in red blood cells lysates by HPLC. The TPMT activities in our Japanese subjects ranged from 11.0 to 42.6 pmol/h/mgHb. Although the mean value of TPMT activities in 6 subjects with TPMT*1/*3C (20.3 +/- 8.1 pmol/h/mgHb) was 25% lower than that in 151 subjects with TPMT*1/*1 (27.0 +/- 5.1 pmol/h/mgHb), there was overlap. The ranges of TPMT activity in subjects with TPMT*1/*1 and those with TPMT*1/*3C were similar. The median values in TPMT*1/*3C and TPMT*1/*1 individuals were 20.1 (11.0-31.2) and 26.8 pmol/h/mgHb (15.7-42.7), respectively (Mann-Whitney U-test: median difference 6.7 pmol/h/mgHb, 95% CI 0-25.5, P < 0.05). This observation may have relevance for the use of 6-mercaptopurine and azathioprine as therapeutic agents in Japanese patients.