GASTROENTEROLOGY
1991;101:943-947
Omeprazole Treatment Does Not Affect the Metabolism of Caffeine TOMMY ANDERSSON, ROBERT BERGSTRAND, CHRISTER CEDERBERG, SVEN ERIKSSON, and INGER S&BERG PER-OLOF LAGERSTROM, Research Laboratories,
AB Hlssle, Mtilndal, Sweden
This study was performed to investigate the possible influence of repeated omeprazole dosing on the metabolism of caffeine, which has been shown to reflect the activity of one specific enzyme within the hepatic cytochrome P450 family, P45OIA2. Ten healthy, nonsmoking young men participated in this placebo-controlled double-blind trial. Each subject was given omeprazole, 20 mg, every morning for 1 week and placebo every morning for 1 week in random order and separated by a 2-3-week washout period. On the sixth and seventh days of each period urine was collected twice daily, and urinary metabolites of caffeine were determined by high-performance liquid chromatography. The urinary metabolite ratio of three paraxanthine ir-demethylation products relative to a paraxanthine-hydroxylation product corresponds to caffeine clearance and, therefore, to P45OIA2 activity. This calculated ratio was 4.8 (95% confidence interval, 3.9-5.6) in the placebo and 4.6 (95% confidence interval, 3.6-5.5) in the omeprazole period. These results show that the metabolism of caffeine was unaltered following omeprazole treatment, indicating that omeprazole treatment has no influence on cytochrome P45OIA2 activity in the clinical situation.
0
meprazole is a substituted benzimidazole that effectively suppresses gastric acid secretion by inhibiting the gastric proton pump, hydrogen-potassium adenosine triphosphatase (H’,K’-ATPase) (1,2). This enzyme is the final step in acid formation, and omeprazole is therefore an effective inhibitor of gastric acid secretion. The improved control of gastric acid secretion achieved by omeprazole in comparison with HZ-receptor antagonists has been shown to result in an improved clinical efficacy in both peptic ulcer disease and reflux oesophagitis (3-5). Most lipophilic drugs and other xenobiotics are metabolized by the hepatic cytochrome P450 enzyme superfamily to produce hydrophilic metabolites,
which are then more readily excreted by the kidney. Early literature data on the cytochrome P45O enzymes referred almost exclusively to rodents. However, lately extensive work has been conducted on human tissue, and considerable information regarding different enzymes of the human cytochrome P450 has been gathered, which in some cases has also been verified in vivo in a clinical situation. At least eight families of enzymes have been identified in the human cytochrome P450 superfamily (6). Three of these (I, II, and III) have been considered to be involved mainly in the hepatic metabolism of drugs (6,7). Each family contains several closely related enzymes (6). The cytochrome 4501A subfamily consists of the enzymes IA1 and IA2; only IA2 is present in normal livers in detectable amounts (8). The enzyme IA2 is responsible for the metabolism of only a few drugs such as IA2 paracetamol, theophylline, and caffeine (8-11). activity can be specifically inhibited by furafylline (ll), and the best documented inducers of these enzymes are polycyclic hydrocarbons (7). Enzymes of family II metabolize many drugs, including diazepam (12) and metoprolol (13). These enzymes can also be inhibited by different drugs (14) as well as being induced, mainly by phenobarbital (7). Family III is responsible for the metabolism of drugs such as quinidine, midazolam, and steroids (7). The P450111 enzymes have been suggested to be competitively inhibited by drugs metabolized by the same enzyme. These enzymes can also be induced, particularly by glucocorticoids (7). In a study by Diaz et al. (15,16), omeprazole was suggested to be an inducer of the cytochrome P450IA Abbreviations used in this paper: AFMU, 5-acetylamino-6formylamino-3-methyluracil; NAT, N-acetyl transferase; CI, confidence interval; 17U, 1,7-dimethyluric acid; HPLC, high-performance liquid chromatography; lU, l-methyluric acid: 1X, l-methylxanthine; X0, xanthine oxidase. o 1991 by the American Gastroenterological Association 0016-5065/91/$3.00
944 ANDERSSON ET AL.
both in vitro and in vivo. The in vitro study was conducted in primary cultures of human hepatocytes taken from patients with hepatic cancers. The in vivo results were obtained by measuring P450IA activity in liver biopsy specimens from five patients with tumors in the digestive tract taken five days before and during surgery. In the meantime, the patients received omeprazole, 20 mg, every morning for 4 days. A serious shortcoming of this study is its lack of any control group. A more reliable way of investigating whether omeprazole treatment influences the activity of a specific enzyme in the clinical situation is to perform interaction studies in humans with drugs known to be substrates for the enzyme of concern. Therefore, several interaction studies have been performed with omeprazole vs. other drugs (17-27). For the minority of these drugs, a somewhat decreased metabolism resulted from concomitant omeprazole treatment. However, for no drug did omeprazole treatment result in an enhanced metabolism indicative of enzyme induction. Particularly relevant, in view of possible induction of the IA subfamily, are the results obtained in an interaction study with theophylline, because the metabolism of this drug has been suggested to be mediated mainly via the cytochrome P450IA2 (9). Treatment with omeprazole, 40 mg, every morning for 1 week did not alter the clearance of theophylline (21), indicating that omeprazole treatment has no effect on P450IA2 activity in the clinical situation. To further evaluate whether omeprazole treatment might alter the activity of P450IA2 in humans, we performed a study with caffeine, which has been also shown to be metabolized via this enzyme (10,ll). Materials and Methods Subjects Ten healthy nonsmoking men of median age 26 years (range, 20-28 years) and median weight 82 kg (range, 66-86 kg) participated in the study, which was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Sahlgrenska Hospital, Gothenburg University, Sweden. The subjects were informed verbally and in writing about the purpose of the study and the possible risks associated with it. Written consent was obtained from all subjects before they participated in the study.
Methods This was a randomized cross-over placebo-controlled double-blind study, and each subject was given 1 weeks treatment with omeprazole, 20 mg, every morning and 1 week’s treatment with placebo, separated by a washout period of 2-3 weeks. On the sixth and seventh days of each treatment period, urine samples for determination of four different caffeine metabolite levels were col-
GASTROENTEROLOGYVol. 101.No. 4
lected at 1 PM and 4 PM (each collection interval was 3 hours). The subjects received breakfast with two cups of coffee at 10 AM and lunch with one cup of coffee at 1 PM on these days, and the meals were standardized. Furthermore, blood samples for determination of omeprazole levels in plasma were taken on day 7 in each period before and at 0.5, 1, 1.5, 2, 3, 4, 5, 6, and 8 hours after omeprazole or placebo administration (-8 AM). Subjects were not allowed to consume alcohol or medications, including over-thecounter drugs, during either treatment period. The subjects were asked to avoid excessive alcohol intake during the washout period. They were also told to eat a normal diet and to avoid broccoli, white cabbage, and charcoal-grilled beef, as well as hard physical training during the entire study, because these factors have been previously shown to alter the activity of P450IA2 (28,29). Omeprazole (20 mg) was administered as enteric-coated granules dispensed in hard gelatin capsules. Granules without omeprazole but otherwise similar were dispensed in identical capsules and used as placebo. Each capsule was taken with a glass of water at 8 AM during the treatment periods. Caffeine was administered as two cups of coffee at 10 AM and one cup of coffee at 1 PM on the experimental days. Urine was collected, and lo-mL aliquots were acidified to pH 3.5 and stored at -20°C until analysis. The samples were analyzed for l-methylxanthine (lx), l-methyluric acid (lU), 5-acetylamino-6-formylamino-3-methyluracil (AFMU), and 1,7-dimethyluric acid (17U). The analyses were performed at the Department of Bioanalytical Chemistry, AB Hassle, using high-performance liquid chromatography (HPLC) with ultraviolet (W) detection (30,311. P450IA2 activity was determined as the ratio of the sum of three paraxanthine 7-demethylation products (1X + 1U + AFMU) relative to a paraxanthine 8-hydroxylation product (li'u), which previously has been shown to correlate with caffeine clearance (32). The activities of N-acetyl transferase (NAT) and xanthine oxidase (X0) were also estimated. The ratio of AFMU to 1X has been shown to be representative of NAT activity (311, and the ratio of 1U to 1X reflects X0 activity (33). Blood samples (5 mL) were collected via an indwelling cannula and were centrifuged and stored at -20°C until analysis. The plasma samples were analyzed for omeprazole at the Department of Bioanalytical Chemistry, AB Hassle, using HPLC with UV detection (34).
Calculations The area under the plasma concentration-vs.-time curve for omeprazole from time zero to the last determinable concentration was calculated using the linear trapezoidal rule. For each treatment period (omeprazole or placebo), the enzyme activity was defined as the mean caffeine metabolite ratio obtained from the four urine samples taken on the last 2 days of each study period. Differences between placebo and omeprazole treatment in regard to the ratios representing activity of P450IA2 and X0 are given as mean differences with 95% confidence intervals (CIs). N-Acetyl transferase activity is given as median values for the 3 subjects
October
1991
NO EFFECT
who were shown to be rapid acetylators, and median values are given for the other 7 subjects, who were shown to be slow acetylators [according to the criteria of Vistisen et al. (28)l. The possible period and carry-over effects have been tested according to the methods described by Pocock (35). Results
All subjects completed the study, and no adverse events were reported. Analyses of the data showed no significant period or carry-over effect. The individual areas under the curves for omeprazole are tabulated in Table 1, and are consistent with those previously reported (18). Individual and mean values with 95% CIs are given for the urinary metabolite ratios representing P450IA2 activity (Table 1). Table 2 shows mean values with 95% CIs for the ratios representing X0 activity together with median values for NAT activity in rapid and slow acetylators. The values for P450IA2 activity showed rather small interindividual variations with very similar means for the two treatments; mean values were 4.8 in the placebo period and 4.6 in the omeprazole period. The mean values representing X0 activity were 1.42 following placebo treatment and 1.48 following omeprazole treatment. Three of the 10 subjects had ratios of NAT activity of >0.5, which characterized them as rapid acetylators. The other 7 subjects had Table 1. Urinary Caffeine Metabolite Ratios Representing Cytochrome P450L42 Enzyme Activity Together With IndividualAreas Under the Curves for Omeprazole P450IAZ Subject 1
activity”
Placebo
Omeprazole
3.88
(/Lmol h/L1
4.60 6.20
0.58 2.18 1.26
4.37
3.65
4.78
4.63
4.10
1.05
6
6.52
4.41
2.33
7
4.55
4.06
1.97
8
5.64
7.19
1.08
1991;101:943-947
Omeprazole Treatment Does Not Affect the Metabolism of Caffeine TOMMY ANDERSSON, ROBERT BERGSTRAND, CHRISTER CEDERBERG, SVEN ERIKSSON, and INGER S&BERG PER-OLOF LAGERSTROM, Research Laboratories,
AB Hlssle, Mtilndal, Sweden
This study was performed to investigate the possible influence of repeated omeprazole dosing on the metabolism of caffeine, which has been shown to reflect the activity of one specific enzyme within the hepatic cytochrome P450 family, P45OIA2. Ten healthy, nonsmoking young men participated in this placebo-controlled double-blind trial. Each subject was given omeprazole, 20 mg, every morning for 1 week and placebo every morning for 1 week in random order and separated by a 2-3-week washout period. On the sixth and seventh days of each period urine was collected twice daily, and urinary metabolites of caffeine were determined by high-performance liquid chromatography. The urinary metabolite ratio of three paraxanthine ir-demethylation products relative to a paraxanthine-hydroxylation product corresponds to caffeine clearance and, therefore, to P45OIA2 activity. This calculated ratio was 4.8 (95% confidence interval, 3.9-5.6) in the placebo and 4.6 (95% confidence interval, 3.6-5.5) in the omeprazole period. These results show that the metabolism of caffeine was unaltered following omeprazole treatment, indicating that omeprazole treatment has no influence on cytochrome P45OIA2 activity in the clinical situation.
0
meprazole is a substituted benzimidazole that effectively suppresses gastric acid secretion by inhibiting the gastric proton pump, hydrogen-potassium adenosine triphosphatase (H’,K’-ATPase) (1,2). This enzyme is the final step in acid formation, and omeprazole is therefore an effective inhibitor of gastric acid secretion. The improved control of gastric acid secretion achieved by omeprazole in comparison with HZ-receptor antagonists has been shown to result in an improved clinical efficacy in both peptic ulcer disease and reflux oesophagitis (3-5). Most lipophilic drugs and other xenobiotics are metabolized by the hepatic cytochrome P450 enzyme superfamily to produce hydrophilic metabolites,
which are then more readily excreted by the kidney. Early literature data on the cytochrome P45O enzymes referred almost exclusively to rodents. However, lately extensive work has been conducted on human tissue, and considerable information regarding different enzymes of the human cytochrome P450 has been gathered, which in some cases has also been verified in vivo in a clinical situation. At least eight families of enzymes have been identified in the human cytochrome P450 superfamily (6). Three of these (I, II, and III) have been considered to be involved mainly in the hepatic metabolism of drugs (6,7). Each family contains several closely related enzymes (6). The cytochrome 4501A subfamily consists of the enzymes IA1 and IA2; only IA2 is present in normal livers in detectable amounts (8). The enzyme IA2 is responsible for the metabolism of only a few drugs such as IA2 paracetamol, theophylline, and caffeine (8-11). activity can be specifically inhibited by furafylline (ll), and the best documented inducers of these enzymes are polycyclic hydrocarbons (7). Enzymes of family II metabolize many drugs, including diazepam (12) and metoprolol (13). These enzymes can also be inhibited by different drugs (14) as well as being induced, mainly by phenobarbital (7). Family III is responsible for the metabolism of drugs such as quinidine, midazolam, and steroids (7). The P450111 enzymes have been suggested to be competitively inhibited by drugs metabolized by the same enzyme. These enzymes can also be induced, particularly by glucocorticoids (7). In a study by Diaz et al. (15,16), omeprazole was suggested to be an inducer of the cytochrome P450IA Abbreviations used in this paper: AFMU, 5-acetylamino-6formylamino-3-methyluracil; NAT, N-acetyl transferase; CI, confidence interval; 17U, 1,7-dimethyluric acid; HPLC, high-performance liquid chromatography; lU, l-methyluric acid: 1X, l-methylxanthine; X0, xanthine oxidase. o 1991 by the American Gastroenterological Association 0016-5065/91/$3.00
944 ANDERSSON ET AL.
both in vitro and in vivo. The in vitro study was conducted in primary cultures of human hepatocytes taken from patients with hepatic cancers. The in vivo results were obtained by measuring P450IA activity in liver biopsy specimens from five patients with tumors in the digestive tract taken five days before and during surgery. In the meantime, the patients received omeprazole, 20 mg, every morning for 4 days. A serious shortcoming of this study is its lack of any control group. A more reliable way of investigating whether omeprazole treatment influences the activity of a specific enzyme in the clinical situation is to perform interaction studies in humans with drugs known to be substrates for the enzyme of concern. Therefore, several interaction studies have been performed with omeprazole vs. other drugs (17-27). For the minority of these drugs, a somewhat decreased metabolism resulted from concomitant omeprazole treatment. However, for no drug did omeprazole treatment result in an enhanced metabolism indicative of enzyme induction. Particularly relevant, in view of possible induction of the IA subfamily, are the results obtained in an interaction study with theophylline, because the metabolism of this drug has been suggested to be mediated mainly via the cytochrome P450IA2 (9). Treatment with omeprazole, 40 mg, every morning for 1 week did not alter the clearance of theophylline (21), indicating that omeprazole treatment has no effect on P450IA2 activity in the clinical situation. To further evaluate whether omeprazole treatment might alter the activity of P450IA2 in humans, we performed a study with caffeine, which has been also shown to be metabolized via this enzyme (10,ll). Materials and Methods Subjects Ten healthy nonsmoking men of median age 26 years (range, 20-28 years) and median weight 82 kg (range, 66-86 kg) participated in the study, which was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Sahlgrenska Hospital, Gothenburg University, Sweden. The subjects were informed verbally and in writing about the purpose of the study and the possible risks associated with it. Written consent was obtained from all subjects before they participated in the study.
Methods This was a randomized cross-over placebo-controlled double-blind study, and each subject was given 1 weeks treatment with omeprazole, 20 mg, every morning and 1 week’s treatment with placebo, separated by a washout period of 2-3 weeks. On the sixth and seventh days of each treatment period, urine samples for determination of four different caffeine metabolite levels were col-
GASTROENTEROLOGYVol. 101.No. 4
lected at 1 PM and 4 PM (each collection interval was 3 hours). The subjects received breakfast with two cups of coffee at 10 AM and lunch with one cup of coffee at 1 PM on these days, and the meals were standardized. Furthermore, blood samples for determination of omeprazole levels in plasma were taken on day 7 in each period before and at 0.5, 1, 1.5, 2, 3, 4, 5, 6, and 8 hours after omeprazole or placebo administration (-8 AM). Subjects were not allowed to consume alcohol or medications, including over-thecounter drugs, during either treatment period. The subjects were asked to avoid excessive alcohol intake during the washout period. They were also told to eat a normal diet and to avoid broccoli, white cabbage, and charcoal-grilled beef, as well as hard physical training during the entire study, because these factors have been previously shown to alter the activity of P450IA2 (28,29). Omeprazole (20 mg) was administered as enteric-coated granules dispensed in hard gelatin capsules. Granules without omeprazole but otherwise similar were dispensed in identical capsules and used as placebo. Each capsule was taken with a glass of water at 8 AM during the treatment periods. Caffeine was administered as two cups of coffee at 10 AM and one cup of coffee at 1 PM on the experimental days. Urine was collected, and lo-mL aliquots were acidified to pH 3.5 and stored at -20°C until analysis. The samples were analyzed for l-methylxanthine (lx), l-methyluric acid (lU), 5-acetylamino-6-formylamino-3-methyluracil (AFMU), and 1,7-dimethyluric acid (17U). The analyses were performed at the Department of Bioanalytical Chemistry, AB Hassle, using high-performance liquid chromatography (HPLC) with ultraviolet (W) detection (30,311. P450IA2 activity was determined as the ratio of the sum of three paraxanthine 7-demethylation products (1X + 1U + AFMU) relative to a paraxanthine 8-hydroxylation product (li'u), which previously has been shown to correlate with caffeine clearance (32). The activities of N-acetyl transferase (NAT) and xanthine oxidase (X0) were also estimated. The ratio of AFMU to 1X has been shown to be representative of NAT activity (311, and the ratio of 1U to 1X reflects X0 activity (33). Blood samples (5 mL) were collected via an indwelling cannula and were centrifuged and stored at -20°C until analysis. The plasma samples were analyzed for omeprazole at the Department of Bioanalytical Chemistry, AB Hassle, using HPLC with UV detection (34).
Calculations The area under the plasma concentration-vs.-time curve for omeprazole from time zero to the last determinable concentration was calculated using the linear trapezoidal rule. For each treatment period (omeprazole or placebo), the enzyme activity was defined as the mean caffeine metabolite ratio obtained from the four urine samples taken on the last 2 days of each study period. Differences between placebo and omeprazole treatment in regard to the ratios representing activity of P450IA2 and X0 are given as mean differences with 95% confidence intervals (CIs). N-Acetyl transferase activity is given as median values for the 3 subjects
October
1991
NO EFFECT
who were shown to be rapid acetylators, and median values are given for the other 7 subjects, who were shown to be slow acetylators [according to the criteria of Vistisen et al. (28)l. The possible period and carry-over effects have been tested according to the methods described by Pocock (35). Results
All subjects completed the study, and no adverse events were reported. Analyses of the data showed no significant period or carry-over effect. The individual areas under the curves for omeprazole are tabulated in Table 1, and are consistent with those previously reported (18). Individual and mean values with 95% CIs are given for the urinary metabolite ratios representing P450IA2 activity (Table 1). Table 2 shows mean values with 95% CIs for the ratios representing X0 activity together with median values for NAT activity in rapid and slow acetylators. The values for P450IA2 activity showed rather small interindividual variations with very similar means for the two treatments; mean values were 4.8 in the placebo period and 4.6 in the omeprazole period. The mean values representing X0 activity were 1.42 following placebo treatment and 1.48 following omeprazole treatment. Three of the 10 subjects had ratios of NAT activity of >0.5, which characterized them as rapid acetylators. The other 7 subjects had Table 1. Urinary Caffeine Metabolite Ratios Representing Cytochrome P450L42 Enzyme Activity Together With IndividualAreas Under the Curves for Omeprazole P450IAZ Subject 1
activity”
Placebo
Omeprazole
3.88
(/Lmol h/L1
4.60 6.20
0.58 2.18 1.26
4.37
3.65
4.78
4.63
4.10
1.05
6
6.52
4.41
2.33
7
4.55
4.06
1.97
8
5.64
7.19
1.08
