Rate-Limiting Steps in Oral Absorption of a Leucotriene D4 Antagonist in the Beagle Dog TUGRUL T.
KARARLIX AND JAMES STOlZENBACH
Received January 28, 1991, from G. 0. Searle Research and Development, 4907 Searle Parkway, Skokie, lL 60077. November 25, 1991. Abstract 0 Oral administration of a leucotriene D, antagonist drug (1) in the Beagle dog at doses of 2, 20, 100, 300,and 800 rng/kg resulted in dose-dependent bbavailabilii values (4-50700).To understand the dose dependence of the absorption of 1 in the dog, initial rates of absorption of 1, which were estimatedfrom Loo-Riielman analysisof the concentration in blood data, were analyzed in terms of dissolution and absorption rates. From the Loo-Riielman pbts, the initial rates of absorption of 1 were estimated as8.2, 41.9,41.1, 76.1, and 72.8 pg-mL-' * h-', respectively, for the doses given earlier. These data, w h i i indicate leveling of the initial absorption rates at high doses,were consistent with an absorption model in w h i i the dissolution rate Is the rateamtrolling step in the intestinal absorption of 1 at doses 4 0 0 M g . The powder dissolution rate of 1 in 17 mM bile salt solution was estimated as 14 and 700 pg .mL-' * h-' for amounts of 1 equivalent to the amounts given to dogs at 2- and 100-mg/kg doses,respectively. After considerationof the volume of distribution and the volume of intestinal fluid in the dog, the value of the initial dissolution rate was much lower than the initial absorption rates at the 2-mg/kg dose.Oral administration of 1 at 2 mgikg in a 39/0Porysotbate 80 solution enhanced both the rate and the extent of absorption of the compound. These results confirm the validity of the anrdusbn that the intestinal absorptbn of 1 is limited by dissolution rate at low doses.
Accepted for publication
In this study, the oral bioavailability of 1 from various formulations was determined in the dog. The initial rates of absorption of 1, which were obtained from Loo-Riegelman plots of absorption data after administration of 2-800-mgkg oral capsule formulations, were examined in terms of dissolution and absorption rates to determine the rate-limiting steps in the intestinal absorption of 1.In addition, the powder dissolution rate of 1, which was measured in a medium containing bile salt, was correlated with the initial rates of absorption.
Experimental Section
M a t e r i a l d o m p o u n d 1 was synthesized at G. D. Searle & Company (Skokie, ILL Sodium taurocholate (NaTC) was obtained from Aldrich Chemical Company (Milwaukee, WI).Polysorbate 80 was obtained from J. T. Baker Company (Phillipsburg, NJ). All solvents used were HPLC grade. Powder Dissolution-Powder dissolution rate measurements were made with a beaker method in a Hanson dissolution station by adding either 100 or 200 mg of 1 into 300 mL of pH 7.0, 0.01 M phosphate buffer containing 17 mM NaTC. The solutions were maintained at 37 "C in a water-jacketed vessel and stirred at 100 rpm. At appropriate time intervals, a 5-mL sample was withdrawn from During drug development, new drugs are administered to the vessel and replaced by the same volume of the dissolution animals to define absorption parameters before they are medium. The solutions were centrifuged to remove the undissolved introduced to humans. For orally administered drugs, dissodrug. The concentrations of 1 were measured with a Cary 2200 lution and membrane diffusion rates are two of the major spectrophotometer set at 280 nm (the extinction coefficient of 1 at 280 nm is 0.042 ml/mg/cm). determinants controlling the rate and the extent of drug Animal Studie-Three female beagle dogs weighing 8-12 kg were absorption in the intestine. Examples of compounds exhibitused. The animals were fasted for 18-24 h prior to dose administraing dissolution-rate-limited absorption include theophylline,' tion. For each formulation and dose, the same three dogs were used. tetracycline,* sulfonamides,3digoxin,q and griseofulvin.6 SevAt least 1 week was allowed to elapse between two consecutive eral investigators1.6J have incorporated dissolution rates, studies. For the intravenous (iv) delivery studies, the solution transit times, and membrane absorption rates in models to formulation of 1 was injected into the cephalic vein. For all studies, predict the rate of absorption from oral formulations. For new blood was withdrawn from the jugular or cephalic vein at predeterdrugs, assessment of the effect of these factors on oral mined time points. Formulations-Three formulations of 1 were used: solution, in absorption may lead to the optimum formulation required for which 1 was solubilized in water at a concentration of 1 mg/mL by the desired pharmacologic activity. 7-[3-(4-Acetyl-3-hydroxy-2-propylphenoxy)propoxyl-3,4- a4justing the pH to 10.0 with dilute NaOH (this formulation wm used for both oral and iv studies); gelatin capsules; and polysorbate 80 dihydr0-8-propyl-2H-l-benzopyran-2-propionic acid (1; see solution [same as earlier solution except for the addition of 3% structure), a leukotriene D, (LTD,) antagonist, is intended for polysorbate 80 (w/w)]. the treatment of asthma. The orally administered compound Analysis of Plasma S a m p l e g P l a s m a samples ( 1 mL) were was found to be active in the guinea pig LTD,-induced thawed and acidified with formic acid, and the internal standard was bronchoconstriction model (unpublished results). Because 1 added prior to extraction on a C,, Bond-Elut column. The organic was intended as an oral product, its absorption characteristics eluate from this column was analyzed by high-pressure liquid chromatography. The mobile phase was methanol :distilled after oral administration were of interest. water:acetic acid (82: 16:2, vlvlv), and the flow rate was 2 mumin. An octadecylsilane analytical column (Dupont Golden Series ODS) was used. Compound 1 was detected by an ultraviolet detector at 280 nm, peak height ratios were used for quantitation, and the sensitivity of the assay was 10 ng/mL. Data Analyeig-The concentrations of 1 in dog plasma samples after iv administration were fit to a two-compartmental body model by a nonlinear least-squares method to obtain the values of the pharmacokinetic parameters shown in eq 1. 1
OO22-3549/92/0900-0875$02.50/0 Q 1992, American Pharmaceutical Assxiation
(1) Journal of Pharmaceutical Sciences / 875 Vol. 87, No. 9, September 7992
The previous equation in the MichaelieMenten form is as follows:
k12
> Drug i n T i s s u e
Drug i n p l a s m a
I
k10
KARARLIX AND JAMES STOlZENBACH
Received January 28, 1991, from G. 0. Searle Research and Development, 4907 Searle Parkway, Skokie, lL 60077. November 25, 1991. Abstract 0 Oral administration of a leucotriene D, antagonist drug (1) in the Beagle dog at doses of 2, 20, 100, 300,and 800 rng/kg resulted in dose-dependent bbavailabilii values (4-50700).To understand the dose dependence of the absorption of 1 in the dog, initial rates of absorption of 1, which were estimatedfrom Loo-Riielman analysisof the concentration in blood data, were analyzed in terms of dissolution and absorption rates. From the Loo-Riielman pbts, the initial rates of absorption of 1 were estimated as8.2, 41.9,41.1, 76.1, and 72.8 pg-mL-' * h-', respectively, for the doses given earlier. These data, w h i i indicate leveling of the initial absorption rates at high doses,were consistent with an absorption model in w h i i the dissolution rate Is the rateamtrolling step in the intestinal absorption of 1 at doses 4 0 0 M g . The powder dissolution rate of 1 in 17 mM bile salt solution was estimated as 14 and 700 pg .mL-' * h-' for amounts of 1 equivalent to the amounts given to dogs at 2- and 100-mg/kg doses,respectively. After considerationof the volume of distribution and the volume of intestinal fluid in the dog, the value of the initial dissolution rate was much lower than the initial absorption rates at the 2-mg/kg dose.Oral administration of 1 at 2 mgikg in a 39/0Porysotbate 80 solution enhanced both the rate and the extent of absorption of the compound. These results confirm the validity of the anrdusbn that the intestinal absorptbn of 1 is limited by dissolution rate at low doses.
Accepted for publication
In this study, the oral bioavailability of 1 from various formulations was determined in the dog. The initial rates of absorption of 1, which were obtained from Loo-Riegelman plots of absorption data after administration of 2-800-mgkg oral capsule formulations, were examined in terms of dissolution and absorption rates to determine the rate-limiting steps in the intestinal absorption of 1.In addition, the powder dissolution rate of 1, which was measured in a medium containing bile salt, was correlated with the initial rates of absorption.
Experimental Section
M a t e r i a l d o m p o u n d 1 was synthesized at G. D. Searle & Company (Skokie, ILL Sodium taurocholate (NaTC) was obtained from Aldrich Chemical Company (Milwaukee, WI).Polysorbate 80 was obtained from J. T. Baker Company (Phillipsburg, NJ). All solvents used were HPLC grade. Powder Dissolution-Powder dissolution rate measurements were made with a beaker method in a Hanson dissolution station by adding either 100 or 200 mg of 1 into 300 mL of pH 7.0, 0.01 M phosphate buffer containing 17 mM NaTC. The solutions were maintained at 37 "C in a water-jacketed vessel and stirred at 100 rpm. At appropriate time intervals, a 5-mL sample was withdrawn from During drug development, new drugs are administered to the vessel and replaced by the same volume of the dissolution animals to define absorption parameters before they are medium. The solutions were centrifuged to remove the undissolved introduced to humans. For orally administered drugs, dissodrug. The concentrations of 1 were measured with a Cary 2200 lution and membrane diffusion rates are two of the major spectrophotometer set at 280 nm (the extinction coefficient of 1 at 280 nm is 0.042 ml/mg/cm). determinants controlling the rate and the extent of drug Animal Studie-Three female beagle dogs weighing 8-12 kg were absorption in the intestine. Examples of compounds exhibitused. The animals were fasted for 18-24 h prior to dose administraing dissolution-rate-limited absorption include theophylline,' tion. For each formulation and dose, the same three dogs were used. tetracycline,* sulfonamides,3digoxin,q and griseofulvin.6 SevAt least 1 week was allowed to elapse between two consecutive eral investigators1.6J have incorporated dissolution rates, studies. For the intravenous (iv) delivery studies, the solution transit times, and membrane absorption rates in models to formulation of 1 was injected into the cephalic vein. For all studies, predict the rate of absorption from oral formulations. For new blood was withdrawn from the jugular or cephalic vein at predeterdrugs, assessment of the effect of these factors on oral mined time points. Formulations-Three formulations of 1 were used: solution, in absorption may lead to the optimum formulation required for which 1 was solubilized in water at a concentration of 1 mg/mL by the desired pharmacologic activity. 7-[3-(4-Acetyl-3-hydroxy-2-propylphenoxy)propoxyl-3,4- a4justing the pH to 10.0 with dilute NaOH (this formulation wm used for both oral and iv studies); gelatin capsules; and polysorbate 80 dihydr0-8-propyl-2H-l-benzopyran-2-propionic acid (1; see solution [same as earlier solution except for the addition of 3% structure), a leukotriene D, (LTD,) antagonist, is intended for polysorbate 80 (w/w)]. the treatment of asthma. The orally administered compound Analysis of Plasma S a m p l e g P l a s m a samples ( 1 mL) were was found to be active in the guinea pig LTD,-induced thawed and acidified with formic acid, and the internal standard was bronchoconstriction model (unpublished results). Because 1 added prior to extraction on a C,, Bond-Elut column. The organic was intended as an oral product, its absorption characteristics eluate from this column was analyzed by high-pressure liquid chromatography. The mobile phase was methanol :distilled after oral administration were of interest. water:acetic acid (82: 16:2, vlvlv), and the flow rate was 2 mumin. An octadecylsilane analytical column (Dupont Golden Series ODS) was used. Compound 1 was detected by an ultraviolet detector at 280 nm, peak height ratios were used for quantitation, and the sensitivity of the assay was 10 ng/mL. Data Analyeig-The concentrations of 1 in dog plasma samples after iv administration were fit to a two-compartmental body model by a nonlinear least-squares method to obtain the values of the pharmacokinetic parameters shown in eq 1. 1
OO22-3549/92/0900-0875$02.50/0 Q 1992, American Pharmaceutical Assxiation
(1) Journal of Pharmaceutical Sciences / 875 Vol. 87, No. 9, September 7992
The previous equation in the MichaelieMenten form is as follows:
k12
> Drug i n T i s s u e
Drug i n p l a s m a
I
k10
