- Email: [email protected]
HEPATIC ELIMINATION OF DIAZEPAM: INTERACTIONS WITH ALBUMIN, DESFLURANE AND SEVOFLURANE
British Journal of Anaesthesia 1993; 70: 454-455
HEPATIC ELIMINATION OF DIAZEPAM: INTERACTIONS WITH ALBUMIN, DESFLURANE AND SEVOFLURANE O. DALE, E. J. FRINK, L. THOMMESEN AND A. J. GANDOLFI SUMMARY
Downloaded from http://bja.oxfordjournals.org/ at RMIT University Library on July 11, 2015
We have studied the effect of sevoflurane and desflurane on the hepatic elimination of diazepam, by incubating slices of rat livers in a closed system. Protein free and protein containing (albumin 10 g litre'1) buffers were used to examine the effect of the anaesthetics on enzyme activity and diazepam binding to albumin. Both anaesthetics (in concentrations of 0.5, 1.5 and 3.0mmollitre'1) reduced the elimination of diazepam slightly in the absence of albumin, while the presence of the protein increased elimination to a maximum of 30% at the greatest concentration of the anaesthetics. These data support previous observations that volatile anaesthetics may interact pharmacokinetically with both liver enzyme activity and drug binding to albumin. (Br. J. Anaesth. 1993; 70: 454-455)
excised from male Sprague-Dawley rats killed by decapitation. Slices were prepared according to standard procedures and mounted on the inner wall of a stainless steel mesh cylinder. This cylinder was incubated with the buffer under constant rotation at 37 °C for 2 h in screw-capped incubation vials. The 4 -i
o E
_c •D
2 2
<0
KEY WORDS Anaesthetics, volatile: desflurane, isoflurane diazepam, enzyme activity. Interactions.
Biotransformation,
It has been reported previously that volatile anaesthetics and albumin may interact in vitro with the elimination of diazepam in rat liver by interference with both enzyme activity and drug-protein binding [1], Apparently, enflurane increased the rate of diazepam elimination in the presence of albumin by displacing the drug, while the elimination rate was decreased slightly in the absence of the protein [1]. In contrast, isoflurane had no effect on these processes. Halothane caused the most marked reduction in diazepam elimination in the absence of albumin, probably as a result of inhibition of hepatic drug metabolizing enzymes. In the present study, we have examined the effects of sevoflurane and desflurane on the elimination of diazepam with and without albumin in the rat liver slice model. METHODS AND RESULTS
Sevoflurane and desflurane were obtained from the Maruishi Pharmaceutical Co. (Osaka, Japan) and Anaquest (Madison, WI, U.S.A.), respectively. Human serum albumin (Sigma A-1653) was purchased from Sigma Chemical Co (St Louis, MO, U.S.A.). Diazepam and prazepam were obtained from Roche-Norge A/S, Oslo, Norway. The experimental and analytical procedures have been described elsewhere [1,2]. Briefly, livers were
I
I
I
I
0 2 Sevoflurane concn (mmol litre"1 4 -i
o E T3
1 2 CD
E
a a.
5
b
0 2 Desflurane concn (mmol litre"1)
4
FIG. 1. Effe« of sevoflurane (A) and desflurane (B) on the elimination of diazepam by rat liver slices at 37 °C for 2 h, with no albumin (filled symbols), or with albumin 10 g litre"1 (open symbols). Each point (mean, SD) represents 10 vials from five separate rat livers. *Statistically different from control (P < 0.05). OLA DALE, M.D., PH.D. ; Liv THOMMESEN, B.SC.; University of
Trondheim, Department of Pharmacology and Toxicology, University Clinic, 7005 Trondheim, Norway. EDWARD J. FRINK JR., M.D.; A. JAY GANDOLFI, PH.D.; University of Arizona,
Department of Anesthesiology, Health Sciences Center, Tucson, AZ 85724, U.S.A. Accepted for Publication: October 9, 1992.
HEPATIC ELIMINATION OF DIAZEPAM
COMMENT
We have found that both sevoflurane and desflurane reduced the hepatic elimination of diazepam in rat liver slices in the absence of albumin, probably caused by a slight inhibition of hepatic enzyme activity. The agents were far less potent than halothane in this respect, as they reduced the elimination of diazepam by 15 % in concentrations of approximately 3 mmol litre"1; a similar reduction was produced by halothane 1 mmol litre"1 under the same experimental conditions [1]. As has been reported for enflurane [1], the most significant interaction observed was an increase in elimination of diazepam, in the presence of albumin, with both desflurane and sevoflurane. Hepatic uptake of diazepam is confined to the free fraction. The major binding protein of diazepam in serum is albumin. Its presence in the buffer therefore reduces hepatic uptake of diazepam and consequently also its
elimination, as shown in this and previous studies [1, 5]. If an agent such as enflurane, capable of displacing diazepam from albumin [5] is added to the buffer, increased elimination of diazepam results [1]. It seems likely, therefore, that the increased elimination of diazepam caused by the agents in the presence of albumin, particularly by desflurane, may be explained by an anaesthetic-induced increased free fraction of diazepam. It is worth noting that the real increase in elimination caused by diazepam displacement is not merely 30%, but approximately 45%, because of the 15% reduction in enzyme activity that occurred in the absence of albumin. What is the clinical relevance of our findings? Clinical anaesthesia with sevoflurane results in serum concentrations of about 0.5-0.7 mmol litre"1 [6], which is close to the smallest concentrations used here. When desflurane is used for clinical anaesthesia, the blood concentrations are thought to be in the same range as those for sevoflurane [7]. It seems unlikely, therefore, on the basis of our data, that sevoflurane may undergo any clinically relevant pharmacokinetic interactions with diazepam, but this cannot be ruled out for desflurane.
REFERENCES 1. Dale O, Gandolfi AJ, Brendel K, Schuman S. Rat liver slices and diazepam metabolism: In vitro interactions with volatile anaesthetic drugs and albumin. British Journal of Anaesthesia 1988; 60: 692-696. 2. Dale O, Holten T, Nerkov T. Rat liver slices: Metabolic changes during short-term incubation in glucose-free buffer. Pharmacology and Toxicology 1990; 67: 89-90. 3. Ghantous HN, Fernando J, Gandolfi AJ, Brendel K. Minimal biotransformation and toxicity of desflurane in guinea pig liver slices. Anesthesia and Analgesia 1991; 72: 796-800. 4. Ghantous HN, Fernando J, Gandolfi AJ, Brendel K. Sevoflurane is biotransformed by guinea pig liver slices but causes minimal cytotoxicity. Anesthesia and Analgesia 1992; 75: 436-^40. 5. Dale O, Nilsen OG. Displacement of some basic drugs from human serum proteins by enflurane, halothane and their major metabolites. An in wtro study. British Journal of Anaesthesia 1984; 56: 557-561. 6. Frink EJ, Malan TP, Atlas M, Domingues LM, DiNardo JA, Brown BR jr. Clinical comparison of sevoflurane and isoflurane in healthy subjects. Anesthesia and Analgesia 1992; 74: 241-245. 7. Boban M, Stowe DF, Buljubasic N, Kampine JP, Bosnjak ZJ. Direct comparative effects of isoflurane and desflurane in isolated guinea pig hearts. Antsthesiology 1992; 76: 775-780.
Downloaded from http://bja.oxfordjournals.org/ at RMIT University Library on July 11, 2015
anaesthetics were injected through Teflon-coated screw-caps by microsyringes (Supelco Inc., Bellefonte, Pennsylvania, U.S.A.) to achieve approximate equimolar concentrations of 0.5, 1.5 and 3.0 mmol litre"1 in the buffer analysed as described by Ghantous and colleagues [3,4]. Diazepam elimination was calculated from each vial by subtracting the final concentration from the initial (2.5 umol litre"1) concentration. Results are presented as mean (SD). Groups were compared by ANOVA. P < 0.05 was considered significant (Fischer test) using StatView II (Abacus Inc, Berkeley, California). In the absence of albumin, there was a small, but statistically significant concentration-dependent reduction (15% at 3 mmol litre"1) in hepatic elimination of diazepam with both anaesthetics (fig. 1). The presence of albumin 10 mg ml"1 reduced hepatic elimination of diazepam by about 50% compared with the controls. With the addition of sevoflurane, statistically significant increases in hepatic elimination of diazepam occurred with the larger concentrations (1.5 and 3 mmol litre"1). Desflurane increased the elimination of diazepam at all concentrations. Both anaesthetics increased the elimination by almost 30 % with the greatest concentration.
455
HEPATIC ELIMINATION OF DIAZEPAM: INTERACTIONS WITH ALBUMIN, DESFLURANE AND SEVOFLURANE O. DALE, E. J. FRINK, L. THOMMESEN AND A. J. GANDOLFI SUMMARY
Downloaded from http://bja.oxfordjournals.org/ at RMIT University Library on July 11, 2015
We have studied the effect of sevoflurane and desflurane on the hepatic elimination of diazepam, by incubating slices of rat livers in a closed system. Protein free and protein containing (albumin 10 g litre'1) buffers were used to examine the effect of the anaesthetics on enzyme activity and diazepam binding to albumin. Both anaesthetics (in concentrations of 0.5, 1.5 and 3.0mmollitre'1) reduced the elimination of diazepam slightly in the absence of albumin, while the presence of the protein increased elimination to a maximum of 30% at the greatest concentration of the anaesthetics. These data support previous observations that volatile anaesthetics may interact pharmacokinetically with both liver enzyme activity and drug binding to albumin. (Br. J. Anaesth. 1993; 70: 454-455)
excised from male Sprague-Dawley rats killed by decapitation. Slices were prepared according to standard procedures and mounted on the inner wall of a stainless steel mesh cylinder. This cylinder was incubated with the buffer under constant rotation at 37 °C for 2 h in screw-capped incubation vials. The 4 -i
o E
_c •D
2 2
<0
KEY WORDS Anaesthetics, volatile: desflurane, isoflurane diazepam, enzyme activity. Interactions.
Biotransformation,
It has been reported previously that volatile anaesthetics and albumin may interact in vitro with the elimination of diazepam in rat liver by interference with both enzyme activity and drug-protein binding [1], Apparently, enflurane increased the rate of diazepam elimination in the presence of albumin by displacing the drug, while the elimination rate was decreased slightly in the absence of the protein [1]. In contrast, isoflurane had no effect on these processes. Halothane caused the most marked reduction in diazepam elimination in the absence of albumin, probably as a result of inhibition of hepatic drug metabolizing enzymes. In the present study, we have examined the effects of sevoflurane and desflurane on the elimination of diazepam with and without albumin in the rat liver slice model. METHODS AND RESULTS
Sevoflurane and desflurane were obtained from the Maruishi Pharmaceutical Co. (Osaka, Japan) and Anaquest (Madison, WI, U.S.A.), respectively. Human serum albumin (Sigma A-1653) was purchased from Sigma Chemical Co (St Louis, MO, U.S.A.). Diazepam and prazepam were obtained from Roche-Norge A/S, Oslo, Norway. The experimental and analytical procedures have been described elsewhere [1,2]. Briefly, livers were
I
I
I
I
0 2 Sevoflurane concn (mmol litre"1 4 -i
o E T3
1 2 CD
E
a a.
5
b
0 2 Desflurane concn (mmol litre"1)
4
FIG. 1. Effe« of sevoflurane (A) and desflurane (B) on the elimination of diazepam by rat liver slices at 37 °C for 2 h, with no albumin (filled symbols), or with albumin 10 g litre"1 (open symbols). Each point (mean, SD) represents 10 vials from five separate rat livers. *Statistically different from control (P < 0.05). OLA DALE, M.D., PH.D. ; Liv THOMMESEN, B.SC.; University of
Trondheim, Department of Pharmacology and Toxicology, University Clinic, 7005 Trondheim, Norway. EDWARD J. FRINK JR., M.D.; A. JAY GANDOLFI, PH.D.; University of Arizona,
Department of Anesthesiology, Health Sciences Center, Tucson, AZ 85724, U.S.A. Accepted for Publication: October 9, 1992.
HEPATIC ELIMINATION OF DIAZEPAM
COMMENT
We have found that both sevoflurane and desflurane reduced the hepatic elimination of diazepam in rat liver slices in the absence of albumin, probably caused by a slight inhibition of hepatic enzyme activity. The agents were far less potent than halothane in this respect, as they reduced the elimination of diazepam by 15 % in concentrations of approximately 3 mmol litre"1; a similar reduction was produced by halothane 1 mmol litre"1 under the same experimental conditions [1]. As has been reported for enflurane [1], the most significant interaction observed was an increase in elimination of diazepam, in the presence of albumin, with both desflurane and sevoflurane. Hepatic uptake of diazepam is confined to the free fraction. The major binding protein of diazepam in serum is albumin. Its presence in the buffer therefore reduces hepatic uptake of diazepam and consequently also its
elimination, as shown in this and previous studies [1, 5]. If an agent such as enflurane, capable of displacing diazepam from albumin [5] is added to the buffer, increased elimination of diazepam results [1]. It seems likely, therefore, that the increased elimination of diazepam caused by the agents in the presence of albumin, particularly by desflurane, may be explained by an anaesthetic-induced increased free fraction of diazepam. It is worth noting that the real increase in elimination caused by diazepam displacement is not merely 30%, but approximately 45%, because of the 15% reduction in enzyme activity that occurred in the absence of albumin. What is the clinical relevance of our findings? Clinical anaesthesia with sevoflurane results in serum concentrations of about 0.5-0.7 mmol litre"1 [6], which is close to the smallest concentrations used here. When desflurane is used for clinical anaesthesia, the blood concentrations are thought to be in the same range as those for sevoflurane [7]. It seems unlikely, therefore, on the basis of our data, that sevoflurane may undergo any clinically relevant pharmacokinetic interactions with diazepam, but this cannot be ruled out for desflurane.
REFERENCES 1. Dale O, Gandolfi AJ, Brendel K, Schuman S. Rat liver slices and diazepam metabolism: In vitro interactions with volatile anaesthetic drugs and albumin. British Journal of Anaesthesia 1988; 60: 692-696. 2. Dale O, Holten T, Nerkov T. Rat liver slices: Metabolic changes during short-term incubation in glucose-free buffer. Pharmacology and Toxicology 1990; 67: 89-90. 3. Ghantous HN, Fernando J, Gandolfi AJ, Brendel K. Minimal biotransformation and toxicity of desflurane in guinea pig liver slices. Anesthesia and Analgesia 1991; 72: 796-800. 4. Ghantous HN, Fernando J, Gandolfi AJ, Brendel K. Sevoflurane is biotransformed by guinea pig liver slices but causes minimal cytotoxicity. Anesthesia and Analgesia 1992; 75: 436-^40. 5. Dale O, Nilsen OG. Displacement of some basic drugs from human serum proteins by enflurane, halothane and their major metabolites. An in wtro study. British Journal of Anaesthesia 1984; 56: 557-561. 6. Frink EJ, Malan TP, Atlas M, Domingues LM, DiNardo JA, Brown BR jr. Clinical comparison of sevoflurane and isoflurane in healthy subjects. Anesthesia and Analgesia 1992; 74: 241-245. 7. Boban M, Stowe DF, Buljubasic N, Kampine JP, Bosnjak ZJ. Direct comparative effects of isoflurane and desflurane in isolated guinea pig hearts. Antsthesiology 1992; 76: 775-780.
Downloaded from http://bja.oxfordjournals.org/ at RMIT University Library on July 11, 2015
anaesthetics were injected through Teflon-coated screw-caps by microsyringes (Supelco Inc., Bellefonte, Pennsylvania, U.S.A.) to achieve approximate equimolar concentrations of 0.5, 1.5 and 3.0 mmol litre"1 in the buffer analysed as described by Ghantous and colleagues [3,4]. Diazepam elimination was calculated from each vial by subtracting the final concentration from the initial (2.5 umol litre"1) concentration. Results are presented as mean (SD). Groups were compared by ANOVA. P < 0.05 was considered significant (Fischer test) using StatView II (Abacus Inc, Berkeley, California). In the absence of albumin, there was a small, but statistically significant concentration-dependent reduction (15% at 3 mmol litre"1) in hepatic elimination of diazepam with both anaesthetics (fig. 1). The presence of albumin 10 mg ml"1 reduced hepatic elimination of diazepam by about 50% compared with the controls. With the addition of sevoflurane, statistically significant increases in hepatic elimination of diazepam occurred with the larger concentrations (1.5 and 3 mmol litre"1). Desflurane increased the elimination of diazepam at all concentrations. Both anaesthetics increased the elimination by almost 30 % with the greatest concentration.
455