THROMBOSIS RESEARCH 61; 477-487,199l 0049-3848/91 $3.00 + .OO Printed in the USA. Copyright (c) 1991 Pergamon Press pk. All rights reserved.
PHARMACOKINETICS OF A LOW MOLECULAR WEIGHT HEPARIN, LOGIPARIN, AFTER INTRAVENOUS AND SUBCUTANEOUS ADMINISTRATION TO HEALTHY VOLUNTEERS.
P.C. Pedersen*, P.B. Bstergaard*, U. Hedner*, D. Berggvist**, T. Mltzsch**. Novo Nordisk A/S*, Copenhagen, Denmark, and Department of Surgery**, General Hospital, Malmoe, Sweden. (Received 22.3.1990; accepted in revised form 12.12.1990
by Editor U. Abildgaard)
ABSTRACT In six healthy volunteers we have estimated the pharmacokinetic parameters of the anti factor Xa (AXa) and anti factor IIa (AIIa) activities of a LMW heparin, Logiparin. For the AXa the following parameters were estimated in a l-compartment model (mean and 95% confidence limits in brackets): elimination half life 82 minutes (60-127 min), absorption half life (s.c.inj.) 200 minutes (137-368 min), bioavailability 90% (24-156 %), and apparent volume of distribution 3.9 1 (3.1-5.2 1). The plasma activity was linearly correlated to the dose given and to the body weight of the volunteer. For the AIIa the parameters estimated in a l-compartment model were: elimination half life 71 minutes (52-115 min), absorption half life 257 minutes (133-3442 min), bioavailability 67% (44-90 %), and apparent volume of distribution 10.1 1 (7.2-16.7 1). The plasma activity was dependent on dose and body weight but it also seemed to be influenced by individual factors. This study shows that the absorption rate is the rate limiting factor and the explanation for the long lasting effect of this LMW heparin after subcutaneous injection. The slow absorption rate and the high bioavailability are probably the major advantages of LMW heparins compared to conventional heparin.
Key words: Heparin, Low molecular weight heparin, Pharmacokinetics, Enzymatic depolymerization, Heparinase. 477
478
PHARMACOKINETICS
OF A LMW HEPARIN
Vol 61, Nos. St6
INTRODUCTION Low molecular weight heparin (IMW heparin) like conventional heparin is a polydisperse anticoagulant drug consisting of unbranched polysaccharide molecules of different chain lengths and slightly different chemical composition (1). The application of classic pharmacokinetic theories to describe in vivo effects of heterogeneous compounds like heparins is disputable and combined with several pitfalls. It is, however, the only possible way to estimate to which degree and at what rate such substances are absorbed after a subcutaneous injection. The methodology of determining the level of heparin in blood samples is limited by the available assays which generally allow only the biological effects to be measured and not directly the substance itself. We have previously described the effects of a low molecular weight heparin (LHN-1, Logiparin) after subcutaneous injection of 2500, 5000, or 10.000 anti factor Xa units or intravenous injection of 5000 anti factor Xa units to healthy volunteers as compared to conventional heparin (2). The aim of this study was to estimate the rates of absorption and elimination and the bioavailability of Logiparin based on the previously published data. Furthermore, we have investigated whether the conclusion drawn from calculations based on peak activity data in our previous paper can be confirmed by statistical calculations based on areas under the curves (AUC's). MATERIALS AND METHODS The LMW-heparin, the experimental procedure, and the laboratory methods have been described in detail previously (2). LMW-heDarin LMW-heparin (LHN-1, Logiparin, Novo Nordisk A/S, Copenhagen, Denmark) prepared by enzymatic depolymerization of porcine mucosal heparin with heparinase from Flavobacterium Heparinum (lot No. 84001, MW 4900 Daltons, 82 AXa IU/mg, 38 AIIa IU/mg, 1. Int. IMW-heparin standard, NIBSC, London). Three injection solutions containing 5,000, 10,000, and 20,000 AXa IU/ml were used. COnVeIItiOnal
heDarin
Commercial grade porcine mucosal sodium heparin lot 5864, 196 AXa units/mg, MW: z 15,000 Daltons. An injection solution containing 10,000 units/ml was prepared. Exoerimental Drocedure Six fully informed healthy volunteers (2 female, 4 male: 27-39 years of age; mean body weight 80 kg, range 52-93) participated in the study. The study was approved by the Medical Ethics COm-
Vol61, Nos. 5/6
PHARMACOKINETICS
OF A LMW HEPARIN
479
mittee, University of Lund, Sweden, and was performed according to the Declaration of Helsinki. The preparations were administered subcutaneously in single dose injections (0.50 ml) in the thigh or intravenously with an interval of at least one week in a double-blind randomized order. The S.C. doses of LMW heparin were 2500, 5000, and 10,000 AXa u (29, 58, and 116 mg, respectively) while 5000 AXa u (58 mg) was given i.v. Sodium heparin was given S.C. in a dose of 5000 AXa u (26 mg). Blood samples for the analysis of AXa and AIIa activities were collected before and later at 15 and 30 minutes and 1, 2, 4, 6, 8, and 24 hours after S.C. injection. In case of intravenous injection, samples were drawn before and at 2, 5, 10, 15, and 30 minutes and after 1, 2, 4, 6, 8, and 24 hours. Citrated plasma was prepared as described by Nilsson (3). The samples were frozen and stored at -24°C until analyzed. Laboratory methods Anti-factor Xa activity (AXa activity) in plasma was assayed in duplicate by the method originally described by Teien et al. (4) but modified as previously described (2). The reference curves used for the calculations of the AXa activity in plasma were linear up to 0.8 IU/ml. Activity results above 0.8 IU/ml have been excluded from the mathematical calculations. Preinjection values differed in many cases from zero presumably due to differences between the pooled plasma used for the reference curves and the plasma of the individual volunteers. For the calculations reported here the base line activity of the individual volunteers was calculated as the mean of the preinjection activity and the activity at 24 hours. Anti-factor IIa activity (AIIa activity) in plasma was determined as previously described (2). In these assays all plasma samples were within the range of the standard dilutions. MATHEMATICAL METHODS Volume of distribution, elimination rate
bioavailabilitv.
absorntion
and
The calculations were based on two-compartment models for the plasma activities following i.v. and S.C. injection. -at -at (i.v.) C, = C, + Ae + Be , t>o A B -k,t A -at B -Bt (S.C.) C, = C, + Fk,((+ -)e --e --e ) a-k, A-k, a-k, B-k, Where C, is the plasma activity at the time t. F is the fraction of the administered dose absorbed following S.C. administration (the bioavailability). Ka, a og /3 are rate constants for absorption, distribution and elimination. A and B are constants.
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The absorption half life is ln2/k, and the elimination half life is ln2/8. The volume of distribution in the central compartment is V = dose/A+B). In a preliminary investigation the i.v. and S.C. data were fitted to the two models separately. Comparisons between the independent estimates of the rate constants thus obtained indicated that k, < 8. This means that the rate of disappearance following S.C. administration is determined by the absorption rate constant kp, while A reflects the rate of disappearance following 1.~. administration. As the S.C. data alone were insufficient for fitting to the two compartment model, these analyses had to be based on one-compartment models, proximately obtained by omitting the a-term from the above % pressions. In the analyses of i.v. data using one-compartment models plasma activities corresponding to t c 30 min. were ignored. Assuming that A, B, a and l3were common parameters in the i.v. and S.C. models estimates of the volume of distribution (V), the bioavailibility (F), the absorption rate constant (k,) and the elimination rate constant (D) were obtained by fitting the i.v. and S.C. data simultaneously to the compound model for the plasma activities following i.v. and S.C. administration. In the analyses of the AXa activities the models were reduced to one-compartment models as most of the values from samples taken before 60 minutes after i.v. injection were above the standard curve range. The AIIa activities were analyzed using both one-compartment and two-compartment models. In the two-compartment model the estimates of the volume of distribution were, as mentioned above, V = dose/(A+B). In the one-compartment model the estimates of the volume of distribution were calculated as V = dose/B. The estimations were carried out by the least square method using a modified Gauss-Newton algorithm (PCNONLIN by Carl Metzler and Daniel L. Weiner, Statistical COnSUltantS Inc., Lexington, Kentucky). The mean values were calculated as follows: = ln2/5;,. Half lives:
o-
~..-_r
hw.-7-_-T-
50
80
70
60
90
+-7 100
50
kg body might
Fig. 2 Graphs of areas under curves (AUCs) data versus body weight. The straight linear regression lines. 0 10.000 AXau Logiparin cl A . 5.000 AXau Logiparin
60
I
I
70
60
-v-7-
90
kg body
100 weight
of AXa (A) and AIIa (B) lines are the calculated 2.500 AXau Logiparin 5.000 AXau Sodium heparin
Vol61, Nos. 516
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485
activity for PK 10169 after i.v. and S.C. injections, neither did Harenberg et al. (7) for CY 216 at a high dose. At a lower dose Harenberg observed a somewhat longer half life after S.C. than after i.v. injection. Numerically, the half lives after S.C. administration are very similar for the different LMWheparins (PK 10169: 275 min.: Fragmin: 228 min.: CY 216: 201214 min.: Logiparin: 200 min.). We have previously calculated the half lives after intravenous injection by simple regression analysis to be 111 minutes for the AXa activity and 76 minutes for the AIIa activity (2). These estimates are not significantly different from those obtained here using better mathematical procedures. The bioavailability of the molecules with the AXa activity is very high (go%), whereas the bioavailability of the AIIa active molecules is less (67%), but still much higher than the bioavailability normally reported for conventional heparin (e.g. Dawes et al. (6) 15-29%). Similar high bioavailabilities have also been found for other U4W-heparins (PK 10169: 91% (6); CY 216: 98-99% (7); Fragmin: 87% (5)). It has been shown that longer chain lengths are needed for AIIa activity than for AXa activity (8). The difference in bioavailability between AXa and AIIa activity may thus indicate that the bioavailability is dependent on molecular weight, which has also been shown by Emanuele and Fareed in primates (9). The apparent volume of distribution estimated for the AXa active subgroup of molecules is about 4.0 1, which corresponds to the expected plasma volume (5% (v/w) of mean body weight 80 kg = 4.0 1 (10)). The estimate of the apparent volume of distribution of the AIIa active fraction, however, is considerably larger than the plasma volume (see Tables 2). This is probably due to protein binding, especially binding to platelet factor 4. It has been shown that the AIIa activity of heparin is more easily neutralized by Platelet factor 4 than the AXa activity (11). As seen from Figures 2 and 3 the plasma activities of LMW heparin after subcutaneous injection depend on body weight as well as on the dose given. This is what should be expected for a compound with high bioavailability. The correlation between body weight and plasma activities indicates that this IJiWheparin should be given in adjusted doses according to body weight as has been proposed for conventional heparin (12,13) and for another LMW heparin (14). Sodium heparin gives statistically significantly lower plasma concentrations than the same dose of LMW heparin, which is essentially a reflection of the differences in bioavailability. For the AXa data the only systematic variation between the area under the curve and volunteer was the body weight, whereas other factors also seem to influence the AIIa results. One factor could be the concentration of heparin neutralizing substances (PF 4) in plasma from individual volunteers.
486
PHARMACOKINETICS
OF A LMW HEPARIN
Vol61, Nos. 516
In summary we have estimated pharmacokinetic parameters of the AXa or AIIa activities of Logiparin. We have shown that the bioavailability of the AXa activity is high and that the absorption rate is the rate limiting factor. The plasma concentration of AXa activity is dependent on dose and body weight. The apparent volume of distribution equals the plasma volume. The results for the AIIa data are less clear, probably due to protein interaction. ACKNOWLEDGEMENTS This stydy was supported by Council (no. 00759).
the
Swedish Medical
Research
REFERENCES 1.
Comper W.D. Heparin (and related polysaccharides). Polymer Monographs; vol. 7. Gordon and Breach Science Publishers, Inc. New York, 1981.
2.
Matzsch T., Berggvist D., Hedner U., Bstergaard P. Effects of an enzymatically depolymerized heparin as compared with conventional heparin in healthy volunteers. Thromb. Haemostas. 57:97-101, 1987.
3.
Nilsson I.M. Haemorrhagic and thrombotic diseases. Wiley Sons Ltd. London 1974.
4.
Teien A.N., Lie M., Abildgaard U. Assay of heparins in plasma using a chromogenic substrate for activated Factor X. Thrombosis Res. 8:549-553, 1976.
5.
Bratt G., Tornebohm E., Widlund L., Lockner D. Low molecular weight heparin (Kabi 2165, Fragmin): Pharmacokinetics after intravenous and subcutaneous administration in human volunteers. Thrombosis Res. 42:613-620, 1986.
6.
Dawes J., Bara L., Billaud E., Samama M. Relationship between biological activity and concentration of a low molecular weight heparin (PK 10169) and unfractionated heparin after intravenous and subcutaneous administration. Haemostasis 16:116-122, 1986.
7.
Harenberg J., WiirznerB., Zimmermann F., Schettler G. Bioavailability and antagonization of the low molecular weight heparin CY 216 in man. Thrombosis Res. 44:549-554, 1986.
8.
Holmer E., Curachi K., Soderstrom G. The molecular-weight dependence of the rate-enhancing effect of heparin on the inhibition of thrombin, factor Xa, factor IXa, factor XIIa, and kallikrein by antithrombin. Biochem. J. 193: 395-400, 1981.
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OF A LMW HEPARIN
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9.
Emanuele R.M., Fareed J. The effect of molecular weight on the bioavailability of heparin. Thrombosis Res. 48:591596, 1987.
10.
Ganong W.F. Review of Medical Physiology. 9th edition, Lange Medical Publications, Los Altos, California, USA.
11.
Lane D.A., Denton J., Flynn A.M., Thunberg L., Lindahl U. Anticoagulant activities of heparin oligosaccharides and their neutralization by platelet factor 4. Biochem. J. m:725-732, 1984.
12.
Beermann B., Lahnborg G. Pharmacokinetics of heparin in healthy and obese subjects and combination with dehydroergotamine. Thromb. Haemostas. 45:24-26, 1981.
13.
Cipolle R.J., Seifert R.D., Nielan B.A., Zaske D.E., Hans E. Heparin kinetics: Variable related to disposition and dosage. Clin. Pharmacol. Ther. 29:387-393, 1981.
14.
LY B., Arnesen K.E., Holm H-A., Handeland G.E., Abildgaard U. Subcutaneous LMW or unfractionated heparin in deep vein thrombosis: A randomized double-blind study with dose adjustment according to heparin concentrations in plasma. Thromb. Haemost. 54:91 (Abstr.), 1985.
PHARMACOKINETICS OF A LOW MOLECULAR WEIGHT HEPARIN, LOGIPARIN, AFTER INTRAVENOUS AND SUBCUTANEOUS ADMINISTRATION TO HEALTHY VOLUNTEERS.
P.C. Pedersen*, P.B. Bstergaard*, U. Hedner*, D. Berggvist**, T. Mltzsch**. Novo Nordisk A/S*, Copenhagen, Denmark, and Department of Surgery**, General Hospital, Malmoe, Sweden. (Received 22.3.1990; accepted in revised form 12.12.1990
by Editor U. Abildgaard)
ABSTRACT In six healthy volunteers we have estimated the pharmacokinetic parameters of the anti factor Xa (AXa) and anti factor IIa (AIIa) activities of a LMW heparin, Logiparin. For the AXa the following parameters were estimated in a l-compartment model (mean and 95% confidence limits in brackets): elimination half life 82 minutes (60-127 min), absorption half life (s.c.inj.) 200 minutes (137-368 min), bioavailability 90% (24-156 %), and apparent volume of distribution 3.9 1 (3.1-5.2 1). The plasma activity was linearly correlated to the dose given and to the body weight of the volunteer. For the AIIa the parameters estimated in a l-compartment model were: elimination half life 71 minutes (52-115 min), absorption half life 257 minutes (133-3442 min), bioavailability 67% (44-90 %), and apparent volume of distribution 10.1 1 (7.2-16.7 1). The plasma activity was dependent on dose and body weight but it also seemed to be influenced by individual factors. This study shows that the absorption rate is the rate limiting factor and the explanation for the long lasting effect of this LMW heparin after subcutaneous injection. The slow absorption rate and the high bioavailability are probably the major advantages of LMW heparins compared to conventional heparin.
Key words: Heparin, Low molecular weight heparin, Pharmacokinetics, Enzymatic depolymerization, Heparinase. 477
478
PHARMACOKINETICS
OF A LMW HEPARIN
Vol 61, Nos. St6
INTRODUCTION Low molecular weight heparin (IMW heparin) like conventional heparin is a polydisperse anticoagulant drug consisting of unbranched polysaccharide molecules of different chain lengths and slightly different chemical composition (1). The application of classic pharmacokinetic theories to describe in vivo effects of heterogeneous compounds like heparins is disputable and combined with several pitfalls. It is, however, the only possible way to estimate to which degree and at what rate such substances are absorbed after a subcutaneous injection. The methodology of determining the level of heparin in blood samples is limited by the available assays which generally allow only the biological effects to be measured and not directly the substance itself. We have previously described the effects of a low molecular weight heparin (LHN-1, Logiparin) after subcutaneous injection of 2500, 5000, or 10.000 anti factor Xa units or intravenous injection of 5000 anti factor Xa units to healthy volunteers as compared to conventional heparin (2). The aim of this study was to estimate the rates of absorption and elimination and the bioavailability of Logiparin based on the previously published data. Furthermore, we have investigated whether the conclusion drawn from calculations based on peak activity data in our previous paper can be confirmed by statistical calculations based on areas under the curves (AUC's). MATERIALS AND METHODS The LMW-heparin, the experimental procedure, and the laboratory methods have been described in detail previously (2). LMW-heDarin LMW-heparin (LHN-1, Logiparin, Novo Nordisk A/S, Copenhagen, Denmark) prepared by enzymatic depolymerization of porcine mucosal heparin with heparinase from Flavobacterium Heparinum (lot No. 84001, MW 4900 Daltons, 82 AXa IU/mg, 38 AIIa IU/mg, 1. Int. IMW-heparin standard, NIBSC, London). Three injection solutions containing 5,000, 10,000, and 20,000 AXa IU/ml were used. COnVeIItiOnal
heDarin
Commercial grade porcine mucosal sodium heparin lot 5864, 196 AXa units/mg, MW: z 15,000 Daltons. An injection solution containing 10,000 units/ml was prepared. Exoerimental Drocedure Six fully informed healthy volunteers (2 female, 4 male: 27-39 years of age; mean body weight 80 kg, range 52-93) participated in the study. The study was approved by the Medical Ethics COm-
Vol61, Nos. 5/6
PHARMACOKINETICS
OF A LMW HEPARIN
479
mittee, University of Lund, Sweden, and was performed according to the Declaration of Helsinki. The preparations were administered subcutaneously in single dose injections (0.50 ml) in the thigh or intravenously with an interval of at least one week in a double-blind randomized order. The S.C. doses of LMW heparin were 2500, 5000, and 10,000 AXa u (29, 58, and 116 mg, respectively) while 5000 AXa u (58 mg) was given i.v. Sodium heparin was given S.C. in a dose of 5000 AXa u (26 mg). Blood samples for the analysis of AXa and AIIa activities were collected before and later at 15 and 30 minutes and 1, 2, 4, 6, 8, and 24 hours after S.C. injection. In case of intravenous injection, samples were drawn before and at 2, 5, 10, 15, and 30 minutes and after 1, 2, 4, 6, 8, and 24 hours. Citrated plasma was prepared as described by Nilsson (3). The samples were frozen and stored at -24°C until analyzed. Laboratory methods Anti-factor Xa activity (AXa activity) in plasma was assayed in duplicate by the method originally described by Teien et al. (4) but modified as previously described (2). The reference curves used for the calculations of the AXa activity in plasma were linear up to 0.8 IU/ml. Activity results above 0.8 IU/ml have been excluded from the mathematical calculations. Preinjection values differed in many cases from zero presumably due to differences between the pooled plasma used for the reference curves and the plasma of the individual volunteers. For the calculations reported here the base line activity of the individual volunteers was calculated as the mean of the preinjection activity and the activity at 24 hours. Anti-factor IIa activity (AIIa activity) in plasma was determined as previously described (2). In these assays all plasma samples were within the range of the standard dilutions. MATHEMATICAL METHODS Volume of distribution, elimination rate
bioavailabilitv.
absorntion
and
The calculations were based on two-compartment models for the plasma activities following i.v. and S.C. injection. -at -at (i.v.) C, = C, + Ae + Be , t>o A B -k,t A -at B -Bt (S.C.) C, = C, + Fk,((+ -)e --e --e ) a-k, A-k, a-k, B-k, Where C, is the plasma activity at the time t. F is the fraction of the administered dose absorbed following S.C. administration (the bioavailability). Ka, a og /3 are rate constants for absorption, distribution and elimination. A and B are constants.
460
PHARMACOKINETICS
OF A LMW HEPARIN
Vol61, Nos. 516
The absorption half life is ln2/k, and the elimination half life is ln2/8. The volume of distribution in the central compartment is V = dose/A+B). In a preliminary investigation the i.v. and S.C. data were fitted to the two models separately. Comparisons between the independent estimates of the rate constants thus obtained indicated that k, < 8. This means that the rate of disappearance following S.C. administration is determined by the absorption rate constant kp, while A reflects the rate of disappearance following 1.~. administration. As the S.C. data alone were insufficient for fitting to the two compartment model, these analyses had to be based on one-compartment models, proximately obtained by omitting the a-term from the above % pressions. In the analyses of i.v. data using one-compartment models plasma activities corresponding to t c 30 min. were ignored. Assuming that A, B, a and l3were common parameters in the i.v. and S.C. models estimates of the volume of distribution (V), the bioavailibility (F), the absorption rate constant (k,) and the elimination rate constant (D) were obtained by fitting the i.v. and S.C. data simultaneously to the compound model for the plasma activities following i.v. and S.C. administration. In the analyses of the AXa activities the models were reduced to one-compartment models as most of the values from samples taken before 60 minutes after i.v. injection were above the standard curve range. The AIIa activities were analyzed using both one-compartment and two-compartment models. In the two-compartment model the estimates of the volume of distribution were, as mentioned above, V = dose/(A+B). In the one-compartment model the estimates of the volume of distribution were calculated as V = dose/B. The estimations were carried out by the least square method using a modified Gauss-Newton algorithm (PCNONLIN by Carl Metzler and Daniel L. Weiner, Statistical COnSUltantS Inc., Lexington, Kentucky). The mean values were calculated as follows: = ln2/5;,. Half lives:
o-
~..-_r
hw.-7-_-T-
50
80
70
60
90
+-7 100
50
kg body might
Fig. 2 Graphs of areas under curves (AUCs) data versus body weight. The straight linear regression lines. 0 10.000 AXau Logiparin cl A . 5.000 AXau Logiparin
60
I
I
70
60
-v-7-
90
kg body
100 weight
of AXa (A) and AIIa (B) lines are the calculated 2.500 AXau Logiparin 5.000 AXau Sodium heparin
Vol61, Nos. 516
PHARMACOKINETICS
OF A LMW HEPARIN
485
activity for PK 10169 after i.v. and S.C. injections, neither did Harenberg et al. (7) for CY 216 at a high dose. At a lower dose Harenberg observed a somewhat longer half life after S.C. than after i.v. injection. Numerically, the half lives after S.C. administration are very similar for the different LMWheparins (PK 10169: 275 min.: Fragmin: 228 min.: CY 216: 201214 min.: Logiparin: 200 min.). We have previously calculated the half lives after intravenous injection by simple regression analysis to be 111 minutes for the AXa activity and 76 minutes for the AIIa activity (2). These estimates are not significantly different from those obtained here using better mathematical procedures. The bioavailability of the molecules with the AXa activity is very high (go%), whereas the bioavailability of the AIIa active molecules is less (67%), but still much higher than the bioavailability normally reported for conventional heparin (e.g. Dawes et al. (6) 15-29%). Similar high bioavailabilities have also been found for other U4W-heparins (PK 10169: 91% (6); CY 216: 98-99% (7); Fragmin: 87% (5)). It has been shown that longer chain lengths are needed for AIIa activity than for AXa activity (8). The difference in bioavailability between AXa and AIIa activity may thus indicate that the bioavailability is dependent on molecular weight, which has also been shown by Emanuele and Fareed in primates (9). The apparent volume of distribution estimated for the AXa active subgroup of molecules is about 4.0 1, which corresponds to the expected plasma volume (5% (v/w) of mean body weight 80 kg = 4.0 1 (10)). The estimate of the apparent volume of distribution of the AIIa active fraction, however, is considerably larger than the plasma volume (see Tables 2). This is probably due to protein binding, especially binding to platelet factor 4. It has been shown that the AIIa activity of heparin is more easily neutralized by Platelet factor 4 than the AXa activity (11). As seen from Figures 2 and 3 the plasma activities of LMW heparin after subcutaneous injection depend on body weight as well as on the dose given. This is what should be expected for a compound with high bioavailability. The correlation between body weight and plasma activities indicates that this IJiWheparin should be given in adjusted doses according to body weight as has been proposed for conventional heparin (12,13) and for another LMW heparin (14). Sodium heparin gives statistically significantly lower plasma concentrations than the same dose of LMW heparin, which is essentially a reflection of the differences in bioavailability. For the AXa data the only systematic variation between the area under the curve and volunteer was the body weight, whereas other factors also seem to influence the AIIa results. One factor could be the concentration of heparin neutralizing substances (PF 4) in plasma from individual volunteers.
486
PHARMACOKINETICS
OF A LMW HEPARIN
Vol61, Nos. 516
In summary we have estimated pharmacokinetic parameters of the AXa or AIIa activities of Logiparin. We have shown that the bioavailability of the AXa activity is high and that the absorption rate is the rate limiting factor. The plasma concentration of AXa activity is dependent on dose and body weight. The apparent volume of distribution equals the plasma volume. The results for the AIIa data are less clear, probably due to protein interaction. ACKNOWLEDGEMENTS This stydy was supported by Council (no. 00759).
the
Swedish Medical
Research
REFERENCES 1.
Comper W.D. Heparin (and related polysaccharides). Polymer Monographs; vol. 7. Gordon and Breach Science Publishers, Inc. New York, 1981.
2.
Matzsch T., Berggvist D., Hedner U., Bstergaard P. Effects of an enzymatically depolymerized heparin as compared with conventional heparin in healthy volunteers. Thromb. Haemostas. 57:97-101, 1987.
3.
Nilsson I.M. Haemorrhagic and thrombotic diseases. Wiley Sons Ltd. London 1974.
4.
Teien A.N., Lie M., Abildgaard U. Assay of heparins in plasma using a chromogenic substrate for activated Factor X. Thrombosis Res. 8:549-553, 1976.
5.
Bratt G., Tornebohm E., Widlund L., Lockner D. Low molecular weight heparin (Kabi 2165, Fragmin): Pharmacokinetics after intravenous and subcutaneous administration in human volunteers. Thrombosis Res. 42:613-620, 1986.
6.
Dawes J., Bara L., Billaud E., Samama M. Relationship between biological activity and concentration of a low molecular weight heparin (PK 10169) and unfractionated heparin after intravenous and subcutaneous administration. Haemostasis 16:116-122, 1986.
7.
Harenberg J., WiirznerB., Zimmermann F., Schettler G. Bioavailability and antagonization of the low molecular weight heparin CY 216 in man. Thrombosis Res. 44:549-554, 1986.
8.
Holmer E., Curachi K., Soderstrom G. The molecular-weight dependence of the rate-enhancing effect of heparin on the inhibition of thrombin, factor Xa, factor IXa, factor XIIa, and kallikrein by antithrombin. Biochem. J. 193: 395-400, 1981.
Vol61, Nos. 516
PHARMACOKINETICS
OF A LMW HEPARIN
487
9.
Emanuele R.M., Fareed J. The effect of molecular weight on the bioavailability of heparin. Thrombosis Res. 48:591596, 1987.
10.
Ganong W.F. Review of Medical Physiology. 9th edition, Lange Medical Publications, Los Altos, California, USA.
11.
Lane D.A., Denton J., Flynn A.M., Thunberg L., Lindahl U. Anticoagulant activities of heparin oligosaccharides and their neutralization by platelet factor 4. Biochem. J. m:725-732, 1984.
12.
Beermann B., Lahnborg G. Pharmacokinetics of heparin in healthy and obese subjects and combination with dehydroergotamine. Thromb. Haemostas. 45:24-26, 1981.
13.
Cipolle R.J., Seifert R.D., Nielan B.A., Zaske D.E., Hans E. Heparin kinetics: Variable related to disposition and dosage. Clin. Pharmacol. Ther. 29:387-393, 1981.
14.
LY B., Arnesen K.E., Holm H-A., Handeland G.E., Abildgaard U. Subcutaneous LMW or unfractionated heparin in deep vein thrombosis: A randomized double-blind study with dose adjustment according to heparin concentrations in plasma. Thromb. Haemost. 54:91 (Abstr.), 1985.
