ORALLY ADMINISTERED DIMETHYL SULFOXIDE: ITS EFFECTS O N BLOOD CONCENTRATIONS OF SALICYLIC ACID, SULFANILAMIDE, A N D WARFARIN* G. Thomas Passananti, Carol A. Shively, and Elliot S. Vesell Department o$Pharmacology The Milton S . Hershey Medical Center Pennsylvania State University Hershey, Pennsylvania 17033
The effect of DMSO in enhancing the percutaneous penetration of various drugs is well e~tablished,'-~even though the precise mechanisms responsible for this increased permeability remain to be elucidated. The effects of DMSO on the gastrointestinal absorption of commonly used drugs have not been investigated. The present experiments were designed to determine the effects of DMSO on the gastrointestinal absorption of several commonly used drugs. Blood concentrations of salicylic acid,4 s~lfanilamide,~ or warfarin6 were measured in adult male Sprague-Dawley rats after a single oral dose of each drug. For each drug and at each time point, two groups of rats were compared: those treated with the drug alone, and those that received the same oral dose of the drug in combination with a small dose of DMSO. Thus, we studied effects produced by DMSO when administered by the oral route, rather than by the commonly investigated topical route. Recently, the route of drug administration has been shown to be important in determining the pathway of metabolism of certain drug^.^,^ In our experiments, conditions such as the dose, the time of drug administration, and the time of blood sampling each proved critical; changes in each substantially altered the results. Thus, the following results must be considered preliminary, because they were obtained under a limited set of experimental conditions. Future expansion of these experiments to include different drugs, doses, and times of blood sampling may warrant extrapolation to more general conclusions, provided that all the results are consistent. FIGURE1 shows the plasma concentrations of salicylic acid4 2, 4, 6, 8, and 10 hours after a single oral dose of salicylic acid had been administered to two groups of rats: the control group of seven rats (which had fasted overnight) received salicylic acid alone in an aqueous suspension of 100 mg/kg, whereas the second group of seven rats (which had also fasted overnight) received the same oral dose of salicylic acid together with DMSO (Matheson, Coleman and Bell, reagent grade) in a dose of 200 mg/kg (0.02%). Each rat received a total volume of 1 ml solution/100 g body weight; the solution contained either the drug alone or the drug plus DMSO. This volume was maintained for each drug studied. Every point on the curve represents the mean salicylic acid concentration in the plasma of seven rats. No statistically significant difference between the control and the DMSO-treated groups occurred at any of the five time points at which plasma salicylic acid concentrations were measured. Nor were the half-lives of salicylic acid in the plasma (4.1 hours in the control group and 4.6 hours in the DMSO group) significantly different. Thus, *This work was supported in part by grant M H 21327-03 from the National Institute of Mental Health.
Annals New Y o r k Academy of Sciences
400r control o treated
I VI 4:
FIGURE 1. Decay of salicylic acid4 in the plasma of rats 2, 4, 6, 8, and 10 hours after a single oral dose of 100 mg/kg in aqueous suspension, with ( 0 ) and without ( 0 ) DMSO (200 mg/kg). Each point represents the mean value for 7 rats. The plasma half-lives are indicated at the end of each line; they were determined by a computerized least-square analysis.
the control group of seven rats received sulfanilamide alone in aqueous suspension, in a dose of 200 mg/kg, whereas the second group of seven rats received the same salicylic acid 2, 4, 6, 8, and 10 hours after the administration of the drug, or on the plasma half-life of the drug. Different doses of DMSO o r salicylic acid or different timing of the administration of the two drugs o r of blood sampling might yield different results, however. FIGURE 2 shows the blood concentrations of sulfanilamide5 2, 4,6, and 8 hours after a single oral dose of sulfanilamide had been administered to two groups of rats:
FIGURE2. Decay of sulfanilamide in the blood 2, 4, 6, and 8 hours after a single oral dose of 200 mg/kg in aqueous suspension, with ( 0 ) and without ( 0 ) DMSO (200 mg/ n 0 kg). Each point represents m the mean value for 7 rats. The plasma half-lives are indicated at the end of each line; they were determined by a computerized least-square analysis.
P a s s a n a n t i et af.: Orally Administered Drugs
the control group of seven rats received sulfanilamide alone in aqueous suspension, in a dose of 200 mg/kg, whereas the second group of seven rats received the same dose of sulfanilamide together with DM-SO in a dose of 200 mg/kg. (All rats had fasted beforehand.) As in the previous experiment, the total volume administered orally was 1 m1/100 g body weight. Each point on the curve represents the mean sulfanilamide concentration in the blood of seven rats. No statistically significant difference between the control or the DMSO-treated group occurred at any of the four time points at which blood sulfanilamide concentrations were measured. The sulfanilamide half-life in the blood was 3.2 hours in both the control and the DMSOtreated groups. Thus, these experiments suggest that the addition of 200 mg DMSO/kg to an oral dose of 200 mg sulfanilamide/kg had no effect on the blood concentration of sulfanilamide 2,4, 6, and 8 hours after administration of the drug, or on the sulfanilamide half-life in the blood. Different doses of DMSO or sulfanilamide or different timing of administration of the two drugs or of blood sampling might yield different results, however. U p t o this point, each experiment involved rats whose caudal arteries were carefully canulated under ether, so that at least four serial arterial blood specimens came from each animal. The next experiment, however, established that orally administered DMSO has an interesting bimodal effect on warfarin concentrations in the blood. The design of this experiment resembled that of the studies on salicylic acid and sulfanilamide, in that warfarin concentrations were measured in the plasma of each rat four or five times after a single oral dose of warfarin (50 mg/kg) had been administered with or without DMSO. This experiment differed from the preceding ones, however, in that the dose of orally administered DMSO was raised to 500 mg/ kg; as before, the total volume of the solution was 1 m1/100 g body weight. Ten minutes after this oral dose of warfarin had been administered with or without DMSO, a second oral dose of D M S O was given (300 mg/kg, again in a total volume of 0.1 m1/100 g body weight). The purpose of the second dose of DMSO was to provide for the possibility that the first dose had been eliminated from the gastrointestinal tract so rapidly that it would fail to exert its full effect. 3) revealed that DMSO administered in Two out of three experiments (FIGURE this dosage schedule had a bimodal effect on the concentrations of warfarin in plasma. Under these conditions, DMSO reduced the concentration of warfarin in plasma measured 2 hours after administration of the anticoagulant, in two out of 3). At subsequent times, however, the warfarin concenthree experiments (FIGURE trations were consistently higher in all three experiments when warfarin was administered with DMSO. Plasma warfarin half-lives were not significantly changed by orally administered DMSO (FIGURE3), a result similar to that obtained for salicylic acid (FIGURE 1) and sulfanilamide (FIGURE 2). In each case the plasma halflives were calculated by a computerized program of least-square analysis, and the significance of the differences between DMSO-treated and control groups was analyzed by the Student’s 1 test. The mechanisms by which DMSO initially reduced but subsequently augmented the gastrointestinal absorption, and hence the plasma concentrations, of warfarin were investigated. Changes in pH and in gastric emptying time are involved. DMSO administered in an oral dose of 500 mg/kg, followed 10 min later by a dose of 300 mg/kg, significantly raised the p H of the gastric juice both 20 and 30 min after initial administration of the drug (TABLE1). Gastric emptying time, as measured by the phenol red content of the stomach determined at various times after the administration of DMSO and phenol red,Q was unchanged at 30 min but was found to be shortened at 60 min (TABLE2). These results suggest that higher concentrations of warfarin in plasma after the administration of DMSO may arise from direct effects
FIGURE 3. Decay of warfarin6 in plasma after a single oral dose of 50 mg/kg in aqueous suspension, with ( 0 ) and without ( 0 ) DMSO in an initial dose of 500 mg/kg, followed in 10 min by a second dose of 300 mg/kg. Each poifit represents the mean value for 6 rats. Three identically performed experiments are shown. The plasma half-lives are indicated at the end of each line; they were determined by a computerized least-square analysis.
k E w
Passananti et al.: Orally Administered Drugs TABLE1 EFFECTOF ORALLYADMINISTERED DMSO O N STOMACH CONTENTS I N RATS DMSO Dose
p H of Stomach Contents? 20 min after dose 3 0 rnin after dose 4.0 0.4 6.0 f 0.4
3.5 f 0.5
5.6 f 0.4
*An equivalent amount of water was administered to control animals. The differences between the DMSO-treated group and water-treated control group at both 20 and 30 rnin were significant by the Student’s t test ( P < .005). t p H of H 2 0 = 6.0; pH of DMSO + H 2 0 = 5.6. The values given are the means for 6 animals, + SE. TABLE2 EFFECTOF ORALLY ADMINISTERED DMSO O N GASTRICEMPTYING BY THE PHENOL R E D METHOOg TIMEIN RATS, AS DETERMINED Phenol Red Dose
0 800* 0
50 50 50
Phenol Red Retained in Stomach 30 mint 60 mint
5.5 f 1.2
*An initial dose of 500 mg/kg was followed by a second dose of 300 mg/kg 10 min later. Values are the means for 4 animals, f SE. ?The difference between the control group and the DMSO-treated group was not significant by the t test. $ T h e difference between the control group and the DMSO-treated group was significant by the t test ( P < ,010).
of DMSO on the stomach, which raise the gastric pH and thereby accelerate gastric emptying. Since gastrointestinal absorption is generally more rapid in the intestine than in the stomach (due to the greater surface area provided for absorption in the intestine), a rise in pH, which generally accelerates gastric emptying, could increase warfarin absorption and thereby elevate warfarin concentrations in the blood. As FIGURE 3 shows, however, 2 hours after the administration of DMSO, warfarin concentrations in the blood were not elevated. TABLE 2 reveals a possible cause of this delayed effect, since 30 min after the administration of warfarin gastric emptying time is not significantly different in DMSO-treated rats. Only at 60 min does a significant difference in gastric emptying occur. Once that difference in gastric emptying time occurs, several additional hours may be required to permit the enhanced intestinal absorption of warfarin that in turn elevates warfarin concentrations in the blood.
JACOB,S. W., M. BISCHEL & R.J. HERSCHLER. 1964. Dirnethyl sulfoxide: Effects on the permeability of biologic membranes. Current Therap. Res. 6: 193.
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Annals New York Academy of Sciences
STOUGHTON, R. & B. W. FRITSCH.1964. Influence of dimethyl sulfoxide (DMSO) on human percutaneous absorption. Arch. Dermatol. 90: 512. KLIGMAN, A. M. 1965. Topical pharmacology and toxicology of dimethyl sulfoxide. Part 1. J. Amer. Med. Assoc. 193: 796. BRODIE,B. B., S. UDENFRIEND & A. F. COBURN.1944. The determination of salicylic acid in plasma. J. Pharmacol. Exp. Therap. 80: 114. BRALTON,A. C. & E. K. MARSHALL. 1939. A new coupling component for sulfanilamide determination. J. Biol. Chem. 128: 537. VESELL,E. S. & C. A. SHIVELY. 1974. Liquid chromatographic assay of warfarin: Similarity of warfarin half-lives in human subjects. Science. 184: 466. DOLLERY, C. T., D. S. DAVIES& M. E. CONOLLY. 1971. Differences in the metabolism of drugs depending upon their routes of administration. Ann. N.Y. Acad. Sci. 179: 108. WILLIAMS, R. T. 1971. The metabolism of certain drugs and food chemicals in man. Ann. N.Y. Acad. Sci. 179: 141. & G. TORO. 1968. In Bray’s Clinical Laboratory BAUER,J . D., P. G. ACKERMANN Methods, pp. 58-60. The C. V. Mosby Co. St. Louis, Mo.