Pharmacodynamic aspects of two sulphonylurea derivatives glipizide and glibenclamide

Diabetologia, Sep 1973

Summary The results of experiments in dogs with and without two glucose loads and in the isolated pancreas to compare the pharmacodynamics of two low-dosage aryl-sulphonylureas, glipizide and glibenclamide, are described and discussed. — The results agree with those obtained by other authors confirming that glibenclamide shows delayed but prolonged activity on both plasma insulin and glucose levels. Moreover glibenclamide counteracts the hyperglycaemia induced by the second glucose load less efficently. Glipizide acts faster on insulin and glucose levels, which return quickly to normal. When a second glucose load was given it was still more active in reducing plasma glucose levels. The dynamics of insulin secretion following glipizide more closely resembles tolbutamide than glibenclamide.

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Pharmacodynamic aspects of two sulphonylurea derivatives glipizide and glibenclamide

Pharmacodynamic Aspects of Two Sulphonylurea Derivatives Glipizide and Glibenclamide D. Artini 0 R. Abbiati 0 G. OrsinP 0 M.A. Parenti 0 K. Bloch 0 S. Daturi 0 V. Mandelli a 0 0 Carlo Erba geseareh Institute , 1V[ilan , Italy Summary. The results of experiments in dogs with and without two glucose loads and in the isolated pancreas to compare the pharmacodynamics of two low-dosage arylsulphonylureas, glipizide and glibenclamide, are described and discussed. -- The results agree with those obtained by other authors confirming that glibenclamide shows delayed but prolonged activity on both plasma insulin and glucose levels. Moreover glibenclamide counteracts the hyperglycaemia induced by the second glucose load less effieently. Glipizide acts faster on insulin and glucose Glipizide; glibenelamide; in vitro; in vivo; dynamics; of insulin secretion; dynamics of hypoglycaemie activity; effect on repeated glucose loads - During pharmacological trials on a series of pyrazinoyl-amino-ethyl-benzene-sulphonylureas with oral hypoglycaemic activity [ 1, 2, 3, 4 ] the reference substance used was glibenclamide, a low dosage sulphonylurea. Although the new molecules showed a p p r o x i m a t e l y the same degree of hypoglycaemic activity as glibenelamide, the blood insulin and glucose time courses differed, and it did not seem adequate to interpret the differences merely in the light of pharmaeokinetics and bioavailability [ 5, 6 ]. This paper illustrates some p h a r m a e o d y n a m i c aspects of one compound in this series, glipizide or K 4024 (N-{4-[beta-(5-methyl-pyrazine-2-earboxyamido)ethyl] - benzene-sulphonyl} -N'eyelohexyl- urea), compared with glibenelamide. Material and Methods The first experiment was planned to check the plasma glucose and insulin p a t t e r n following oral administration of glipizide or glibenelamide in the dog. Twelve Beagle dogs from our stock were assigned at r a n d o m to the two treatments. The dogs were fasted for 16 h. The products, micronised and suspended in 0.5% Methoeel, were administered b y g a r a g e at the dose of 120 7/kg. Blood samples were t a k e n at time 0 (basal), and 20, 30, 40, 60, 90, 120 and 180 min following administration of the test products. Glucose and insulin assay was carried out on plasma obtained b y centrifuging immediately after taking the sample. The direct o-toluidine method of Frings et al. [ 7 ] was used for glucose assay; insulin 1 Cytopharmaeology Laboratory; 2 Pharmacology Laboratory; 3 Biometry Centre. levels, which return quickly to normal. When a second glucose load was given it was still more active in reducing plasma glucose levels. The dynamics of insulin secretion following glipizide more closely resembles tolbutamide than glibenelamide. was determined b y the radio-immunological double a n t i b o d y method of Hales and Randle [ 8 ], using the insulin immunoassay kit from the Amersham Radiochemical Centre. Statistical analysis was carried out on the results of this trial to show up the following four aspects: 1. comparison of time courses : analysis of variance was carried out using three classification criteria (treatments, dogs,, times). The least significant differenee for p = 0.05 and p -----0.01 was also calculated to compare the means for the two drugs; 2. comparison of m a x i m u m peaks: for each animal the m a x i m u m peak was noted and the means for the two drugs were compared b y analysis of variance; 3. comparison of m a x i m u m peak times: the time required to reach m a x i m u m peak was noted for each animal, and these times were transformed into reciprocals, then compared b y analysis of variance. The harmonic mean of the times was also calculated; 4. comparison of the areas underneath the plasma glucose and insulin time course curves: the area was calculated for each dog, and the means of the areas were compared b y analysis of variance. The second experiment was set up to compare the effects of glipizide and glibenclamide on hyperglyeaemia and hyperinsulinaemia induced b y two glucose loads in the dog. Twelve Beagles were used, acting first as controls; t h e y were then randomly divided in two groups of 6; one was given glipizide and the other glibenclamide. A blood sample was taken, and basal values (time 0) determined. The animals then received either the vehicle alone b y g a r a g e (controls) or else the glipizide or glibenclamide suspension in 0.5% Methoeel at the dose of 120 ,(/kg; immediately after taking the 40 and 420 min samples, the animals were given 4 ml/kg of a 33% glucose solution, b y garage. Plasma glucose and insulin levels were followed every 20 min for 100 min. D. Artini et al. : Pharmaeodynamie Aspects of Glipizide and Glibenelamide firming t h a t glipizide acts faster. Comparison of the areas beneath the plasma glucose concentration curves also shows a significant difference between the two drugs. The results in Fig. 2, regarding plasma insulin levels, confirm t h a t glipizide acts faster t h a n glibenclamide. Analysis of the time to peak shows a highly Glucose and insulin assay methods were as described in the first experiment. In order to evaluate the significance of the differenees between the plasma glucose and insulin means at the different times for the three treatments, Kramer's test [ 9 ] was used, since the three samples involved different numbers. Further statistical analysis was made as described earlier. Another series of experiments was carried out on isolated, perfused rat pancreas using the method described b y Loubatigres [ 10 ]. Outbred SPF CFE male rats from our stock, weighing 350--450 g, were used; access to food and water was ad lib. Anaesthesia was induced b y intraperitoneal injection of ethyl urethane (1 g/kg), and respiration maintained throughout the experiment with a mixture of O~-CO2 (95--5%). The pancreas was separated from all surrounding tissue and perfused at 37~C, using an open circuit system. The basic perfusion medium was K r e b s - g i n g e r solution containing 2~ Grad/V bovine serum albumin (Sigma Ch. Co.) and 0.8 g/1 glucose. The perfusion rate was approximately 2.5 ml/min, pressure 20--30 m m H g . Insulin secretion stabilized in all eases in about 30 rain; from then on the test substance was added to the perfusion medium using an infusion pump, dissolved 2.5 ? in 5 ml of the perfusion solution. Infusion time was 15 min; while flowing through the pancreas the products reached a concentration of 50 ~'/1. When stimulus with the drugs was stopped, perfusion was carried on with the basic solution. Samples for radio-immunological insulin assay [ 8 ] were drawn from the solution as it came out of the pancreas at the times indicated in Fig. 5. The two means at the various times were compared b y a non-parametric statistical method, Wilcoxon's non-paired data test [ 11 ]. Results Plasma Glucose and Insulin in the Dog Following Oral Administration of Glipizide or Glibenclamide significant difference between the two drugs; the harmonic mean was 31 min for glipizide and 72 min for glibenclamide. The main difference between the two drugs, however, is the fact t h a t plasma insulin remains high longer with glibenclamide. With glipizide, following the peak the insulin level decreases rapidly to reach basal values at the 90th min, whereas with glibenelamide the decrease in plasma insulin is much less marked and the plasma levels become normal only after the 180th rain. F r o m the 60th min onwards, there was a highly significant difference between the mean plasma insulin level for the two drugs. Statistical analysis confirms the difference in the plasma insulin levels induced by the two drugs; there is a highly significant interaction times x drugs. I n view of the variations shown by the results, the means of the areas underneath the plasma insulin curves for the two drugs were not significantly different, although the mean for glibenelamide was 50% higher t h a n for glipizide. Effect of Glipizide and Glibenclamide on Plasma Glucose and Insulin ( I R I ) Levels Increase Induced in the Dog by Two Glucose Loads Fig. 3 and Table 1 give the results of this experiment with reference to the plasma glucose levels, and Fig. 4 and Table 2 refer to plasma insulin levels. In animals treated with glipizide the mean plasma glucose level at the 40th rain was already significantly lower than both the controls and the glibenelamide group; this indicates t h a t glipizide acts faster. Throughout the first phase of the experiment (1 st glucose load) the glipizideAndueed plasma glucose pattern remained lower t h a n w i t h the other two treatments; the means were significantly lower up to the 120th min. At the 140th min the means for the two hypoglyeaemie compounds were n o t significantly different, although they differed significantly from the controls. The plasma glucose levels induced by glibenelamide start to differ from the controls only after the 60th min. Seven hours after treatment, the mean plasma glucose level induced by glipizide was not significantly different from the controls, whereas the glibenclamidetreated animals showed a significantly lower mean t h a n both the controls and those treated with glipizide. During the second phase of the experiment, following the second glucose load, plasma glucose levels rose more in the animals treated with glibenelamide and the controls titan irt the group treated with glipizide. The effect of glibenelamide became evident only at the 480th min, and appeared more marked; in fact at the 500th min the glibenelamide-indueed plasma glucose levels were Significantly lower than in the other two groups. Glipizide thus appears to act faster and less drastically, considering t h a t following the stimulus represented by the hyperglyeaemie load, the product lowered plasma glucose to within physiological limits, fairly close to control levels. The figure giving the plasma insulin level time courses (Fig. 4) and the results in Table 2, show t h a t at the 40th min the two groups treated with hypoglyeaemie compounds showed higher plasma insulin levels t h a n controls. However, in actual fact only the 20 40 60 80 100 120 ;40 Time in minutes group receiving glipizide showed a real increase, since by chance the mean basal plasma insulin level in the glibenelamide group was higher t h a n in the other two groups. At 60th min glipizide also induced higher plasma insulin levels, with significantly higher means than * G[ipizide 9 Glibenclomide 9 Controts G 130 glibenclamide. At the 80th min plasma insulin was already decreasing in the group treated with glipizide, but in the glibenclamide and control groups a further rise was noted; after this the decrease in plasma insulin was almost parallel in all groups. D. Artini et al. : Pharmaeodynamic Aspects of Glipizide and Glibenelamide S t a t i s t i c a l analysis of t h e results following t h e first glucose l o a d f u r t h e r confirmed t h e difference b e t w e e n t h e two t r e a t m e n t s . B o t h as r e g a r d s the insulin p e a k s a n d t h e areas b e n e a t h t h e p l a s m a insulin level curves, t h e m e a n s for t h e two h y p o g l y e a e m i c agents are n o t significantly different, b u t t h e y do differ s i g n i f i c a n t l y from the controls. A significant difference was f o u n d b e t w e e n t h e t w o drugs as r e g a r d s t h e t i m e s r e q u i r e d to r e a c h peak. T h e h a r m o n i c m e a n s The t h r e e h a r m o n i c m e a n s for t h e p e a k t i m e s show no significant differences a l t h o u g h t h e glibenclamide m e a n was d e l a y e d 7 m i n as c o m p a r e d to glipizide. I n s u l i n Secretion by the Isolated, Perfused Rat Pancreas Incluced by Glipizide and Glibenelamide t h e two p r o d u c t s , t h e p a n c r e a s r e s p o n d e d r a p i d l y I n t h e second e x p e r i m e n t a l phase, i.e., a f t e r 7 h, to t h e stimulus, a n d a m a r k e d increase was n o t e d in insulin secretion. A t 5 m i n g l i p i z i d e - i n d u c e d secretion was significantly g r e a t e r t h a n t h a t p r o v o k e d b y insulin secretion was g r e a t e r in t h e g r o u p t r e a t e d glibenelamide. w i t h g l i b e n e l a m i d e ; this is e v i d e n t c o m p a r i n g t h e levels from t h e 460th rain onwards, t h e p e a k s a n d t h e areas, which wer6 all h i g h l y significantly g r e a t e r t h a n controls a n d t h e glipizide group. I n s u l i n secretion r e m a i n e d high t h r o u g h o u t t h e s t i m u l u s for b o t h p r o d u c t s ; d u r i n g this p e r i o d no significant differenees were noted. W h e n t h e drugs were w i t h d r a w n from t h e perfusing Glibenelamide (GC) n o . = 6 93.50--3.49 98.17--3.47 118.33--4.98 108.33--3.89 85.17--2.66 77.17--2.69 65.33--2.19 62.00--3.78 120.17--3.47 112.33~-2.40 68.17--2.66 56.33- 2.51 Glibenclamide (GC) n o . = 6 20.00 21.17  2.41 61.67  4.58 84.17 63.33~7.92 36.33:j: 6.34 20.33~: 3.15 16.17 54.33 ~: 3.48 76.83 ::]:5.04 39.17 17.00 solution, a marked difference in behaviour was noted between the glipizide and glibenclamide treated pancreas. After glipizide perfusion insulin secretion returned rapidly to basal values, reaching them at the 35th min. 170 150 130 ~ 1 t 0 E 90 70 50 30 10 * Giipizide 9 Giibendctmide 10 20 30 /,0 50 60 -70 Time in minutes 80 90 Fig. 5. Effect of glipizide and glibenclamide on insulin secretion by the isolated rat pancreas, perfused from time 0 to the 15th rain. Except for times over 45 min, which were obtained with 9 replications, each point represents the mean of l 1 replications After glibenclamide perfusion insulin secretion remained at the levels reached while the product was being perfused until the 30th min, then started to decrease slowly, reaching basal values only after 90 min. F r o m the 20th to the 75th rain the differences between the means for the two treatments were highly significant. D i s c u s s i o n Comparison of glipizide and glibenclamide in the dog with no glucose load has shown t h a t the two hypoglycaemic agents differ markedly. Glipizide acts rapidly, with a prompt hypoglycaemic effect, corresponding to an early insulin secretion peak which returns rapidly to basal levels. With glibenclamide the hypoglycaemic effect becomes evident only after a latent period, and the insulin response is of longer duration. In the present experiment, the products were administered orally as t h e y are used in therapy. Fuccella et al. [ 5 ] demonstrated t h a t in man glipizide is absorbed faster t h a n glibenclamide; this finding might suggest t h a t the difference in the two products' pharmacodynamics was due only to different pharmacokinetics. The differences we observed, however, are similar to those reported by Loubati6res et al. [ 12 ] Loubati6res [ 13 ], Raptis et al. [ 14 ], and by H a u p t et al. [i5] between glibenclamide On the one hand, and tolbutamide, glibornuride and glisoxepide on the other, injecting the products intravenously in man. The results of this experiment therefore suggest that, pharmaeokinetic characteristics apart, glibenclamide shows different pharmacodynamics from other sulphonylurea group drugs, while glipizide resembles them~ The experiment using two glucose loads in the dog, particularly the results referring to the first load, confirm the speed of action of glipizide, which completely inhibits the glucose-induced hyperglycaemia, whereas glibenclamide acts after a lag-time and in fact only partially antagonizes the hyperglycaemia. The delay in glibenclamide's action is also seen in plasma insulin, although surprisingly, the insulin levels after gtibenclamide treatment are not markedly different from those following glipizide, despite the former being only partially able to lower plasma glucose. The plasma insulin pattern after the first glucose load also does not differ between glipizide and glibenelamide, contrary to the findings in the previous experiment on animals t h a t had not received glucose. Similar results were obtained b y Raptis et al. [ 14 ] in experiments comparing glibenelamide and tolbutamide. Immediately before the second glucose load, the plasma glucose in glibenelamide-treated animals was significantly lower than in controls and the glipizide group. This might appear to suggest t h a t glibenclamide shows more persistent action, even if not mediated b y greater and longer-lasting insulin secretion; the results regarding the plasma glucose levels after the second glucose load, however, do not favour this hypothesis, since glibenclamide antagonizes the rise less than glipizide, even though plasma insulin levels were much higher and longer-lasting t h a n in both control and glipizide groups. T h a t the insulin secretion dynamics following glibenclamide differ from those following glipizide, is confirmed b y the results of our experiment on the perfused pancreas. Here the difference was easily seen, and agrees with the findings of Fussg/~nger et al. [ 16 ], Grodsky et al. [ 17 ] and Pfeiffer et a l . [ 18 ] on comparison of glibenclamide with other known sulphonylureas. All these data show t h a t the action of glibenclamide is less intense to start with, but is long-lasting. These findings m a y provide at least a partial explanation of different pharmacodynamies of the two hypoglycaemic agents. R e f e r e n c e s 1. Ambrogi , V. , Bloch , K. , Daturi , S. , Griggi , P. , Logemann , W. , Parenti , M.A. , Rabini , T. , Tommasini , 1 %.: New oral antidiabetic drugs . Part I. ArzneimittelForseh . 21 , 200 -- 204 ( 1971 ) 2. Ambrogi , V. , Bloch , K. , Cozzi , P. , Daturi , S. , Logemann , W. , Parenti , M.A. , Tommasini , R.. New oral antidiabetie drugs. P a r t II. Arzneimittel-Forsch . 21 , 204 -- 208 ( 1971 ) 3. Ambrogi , V. , Bloch , K. , Daturi , S. , Logemann , W. Parenti , M.A. , Tommasini, g . : New oral antidiabetic drugs. P a r t I I I . Arzneimittel-Forsch . 22 , 542 -- 544 ( 1972 ) 4. Ambrogi , V. , Bloch , K. , Daturi , S. , Griggi , P. , Logemann , W. , Mandelli , V. , Parenti , M.A. , g a b i n i , T ., Usardi , M.M. , Tommasini, g . : Pharmacological study on a new oral antidiabetie: N-{4-[fl-(5-methyl- pyrazinc- 2 -carboxamido) - ethyl] -benzenesulphonyl }-N ' - cyelohexyLurea or K 4024 . Arzneimittel-Forsch . 21 , 208 -- 215 ( 1971 ) 5. Fuccella , L.M. , Tamassia , V. , Valzelli , G. : Metabolism and kinetics of the hypoglyeaemie agent glipizide in man. Comparison with glibenelamide . Clin. Pharm. and New Drugs . (In press) 6. Valzelli , G. , Tamassia , V. : Personal communication 7. Frings , C.S. , gatliff, C.1%., Dunn , 1 %.T.: Automated determination of glucose in serum or plasma by direct o-toluidine procedure . Clin. 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Physiological and pharmacological interferenees synergisms and antagonisms . In: Mechanism and regulation of insulin secretion , p. 243 -- 244 . Levine, 1 %., Pfeiffer , E.F. (Eds.). Milano : Casa Editriee "II Ponte" , 1968 14. Raptis , S. , 1 %av, 1 %.M., Schr6der , K.E. , Faulchaber , D.J. , Pfeiffer , E.F. : Comparative study of insulin secretion following repeated administration of glucose, tolbutamide and glibenelamide (HB 419) in diabetic and non-diabetic h u m a n subjects . Horm. Metab. 1%es. 1 suppl. , 65 -- 72 ( 1969 ) 15. t I a u p t , E ., K6berieh, W. , Beyer , J. , Sch6ffling, K. : Pharmaeodynamie aspects of tolbutamide, glibenelamide, glibornuride and glisoxepide. I) Dose response relations and repeated administration in diabetic subjects . II) Repeated administration in combination with glucose . Diabetologia 7 , 449 -- 460 (I 971 ) 16. Fussg/inger, g . D . , Goberna, 1 %., i i n z , M., Jaros , P. , Karsten , C. , Pfeiffer , E . 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D. Artini, R. Abbiati, G. Orsini, M. A. Parenti, K. Bloch, S. Daturi, V. Mandelli. Pharmacodynamic aspects of two sulphonylurea derivatives glipizide and glibenclamide, Diabetologia, 1973, 311-316, DOI: 10.1007/BF01218440