ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, June 1996, p. 1569–1571 0066-4804/96/$04.0010 Copyright q 1996, American Society for Microbiology
Vol. 40, No. 6
Zidovudine Does Not Affect Transplacental Transfer or Systemic Clearance of Stavudine (29,39-Didehydro-39-Deoxythymidine) in the Pigtailed Macaque (Macaca nemestrina) ALEKSANDRS ODINECS,1 CONNIE NOSBISCH,1
AND
JASHVANT D. UNADKAT1,2*
1
Department of Pharmaceutics and Regional Primate Research Center,2 University of Washington, Seattle, Washington 98195 Received 6 July 1995/Returned for modification 4 September 1995/Accepted 6 April 1996
Stavudine (22 mg/min/kg of body weight) was infused alone (via the femoral vein) or simultaneously with zidovudine (66 mg/min/kg) to three near-term pregnant macaques. No significant differences were found between the mean steady-state plasma stavudine concentrations in the dam (Cssd) and fetus (Cssf), the stavudine concentration in the amniotic fluid (Cssa), and the ratios Cssf/Cssd and Cssa/Cssf when stavudine was infused alone or in combination with zidovudine. The data obtained indicate that zidovudine administration does not affect the transfer of stavudine across the placenta in Macaca nemestrina. intravenous rate of infusion of 22 mg/min/kg of body weight to the dam (15 ml/h via the femoral vein) or simultaneously with zidovudine (66 mg/min/kg) at gestational age 145 6 13 days. Blood samples from the dam (2 ml via the femoral artery) were collected before infusion and at 24, 25.5, 27, 28.5, and 30 h after beginning the administration of the drug. Fetal blood samples (0.3 ml via the jugular vein or carotid artery) were collected before infusion and at 27, 28.5, and 30 h after beginning the infusion. Collection of amniotic fluid samples (2 ml) coincided with blood sampling in the dam. The concentrations of stavudine and zidovudine in the plasma and amniotic fluid samples were determined simultaneously by using a modification of the high-performance liquid chromatographic method developed in our laboratory (17), as described before (15). Plasma clearances for stavudine and zidovudine were calculated as the rate of infusion divided by the mean maternal steady-state concentration in plasma obtained at that infusion rate. Clearance values calculated for stavudine in the presence and in the absence of zidovudine in the same animals (during the same pregnancy), as well as the steady-state concentrations of stavudine in maternal and fetal plasmas and in amniotic fluid, were compared with the paired Student t test. The values of pharmacokinetic parameters obtained in this study are in general agreement with those previously reported for monkeys (2, 8, 19, 20) and humans (5). The fetal/maternal plasma drug concentration ratio (Cssf/Cssd) was determined at steady state, because under non-steady-state conditions this ratio would change constantly as fetal and maternal plasma drug concentrations change in a nonparallel manner. No significant differences (P . 0.05) were found between steady-state concentrations of stavudine in maternal plasma (Cssd), fetal plasma (Cssf), and amniotic fluid (Cssa) after infusion of stavudine alone or in combination with zidovudine (Table 1). Also, the fetal/maternal plasma drug concentration ratio (Cssf/Cssd) and amniotic fluid/fetal plasma drug concentration ratio (Cssa/Cssf) were not significantly different between the two treatment arms. Cssf/Cssd for zidovudine (Table 2) when coadministered with stavudine was not significantly different (P . 0.05, unpaired Student t test) from the corresponding ratio when zidovudine was administered alone (0.83 6 0.07 [9] and 0.76 6 0.06 [unpublished data]) or in combination with didanosine (0.78 6 0.06) in a different group of animals (16).
In Europe and North America, the rate of maternal-fetal transmission of human immunodeficiency virus type 1 (HIV-1) is about 15 to 25% (3). Since results from a clinical trial suggest that treatment of HIV-positive mothers with zidovudine reduces the risk of maternal-fetal HIV transmission (1), there is interest in determining whether zidovudine in combination with other dideoxynucleosides, for example, stavudine, is more efficacious than zidovudine alone in reducing this transmission (12). The toxicity profile of stavudine differs from that of zidovudine in that peripheral neuropathy rather than bone marrow suppression is its principal adverse effect (4, 6, 11). However, potential drug interactions must be taken into account. For example, stavudine and zidovudine could conceivably compete at transport sites. Also, as both these dideoxynucleosides are secreted renally, each could potentially affect the clearance of the other when administered in combination. Because combination therapy with stavudine and zidovudine may become available for use in pregnant women, we have investigated in a representative animal model, Macaca nemestrina, the possibility of a pharmacokinetic interaction between these two drugs, particularly as it may apply to maternal-fetal transfer. We have chosen the macaque as our experimental animal for two reasons. First, its placenta bears anatomical and physiological similarities to the human placenta. Second, the pharmacokinetics of dideoxynucleosides in this species, including the metabolic and renal clearances, are similar to those in humans (10, 17, 18). Moreover, because both HIV-2 (unpublished data from our laboratory) and simian immunodeficiency virus (14) can be transmitted from mother to fetus in M. nemestrina, future studies could be conducted to determine whether the combination of stavudine and zidovudine can reduce maternal-fetal transmission. Stavudine was provided by Bristol-Myers Squibb Co. (Wallingford, Conn.). All other chemicals used were of reagent grade. Three pregnant near-term macaques were chronically catheterized at gestation age 121 6 1 days as described before (13, 15). Animals received stavudine alone for 30 h at an * Corresponding author. Mailing address: Department of Pharmaceutics, Box 357610, University of Washington, Seattle, WA 981957610. Phone: (206) 543-9434. Fax: (206) 543-3204. Electronic mail address:
[email protected]. 1569
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ANTIMICROB. AGENTS CHEMOTHER.
TABLE 1. Steady-state stavudine concentrations after infusion of stavudine (22 mg/min/kg, intravenously) alone or after coinfusion with zidovudine (66 mg/min/kg, intravenously) Drug concn (mg/ml)a in:
Drug regimen and animal no.
Drug concn ratio
Dam
Fetus
Amniotic fluid
Fetus/dam
Amniotic fluid/fetus
Stavudine alone F86363 T84143 T84258 Mean 6 SD
1.51 1.47 1.60 1.53 6 0.07
1.06 1.13 1.28 1.16 6 0.11
1.58 1.62 1.84 1.68 6 0.14
0.70 0.77 0.80 0.76 6 0.05
1.49 1.43 1.44 1.45 6 0.03
Stavudine plus zidovudine F86363 T84143 T84258 Mean 6 SD
1.80 1.56 1.56 1.64 6 0.14*
1.18 1.19 1.20 1.19 6 0.01*
1.76 2.14 1.93 1.94 6 0.19*
0.66 0.76 0.77 0.73 6 0.06*
1.49 1.80 1.61 1.63 6 0.16*
a
Concentrations from dam and fetus were measured in plasma. p, not statistically significant compared with result obtained with stavudine alone (P . 0.05).
Likewise, Cssa/Cssf for zidovudine after coinfusion with stavudine was not significantly different from the corresponding ratio when zidovudine was administered alone (2.72 6 0.86) (unpublished data). Collectively, these data suggest that transplacental transfer of stavudine is unaffected by coadministration of zidovudine and vice versa. The Cssf/Cssd ratio is not only a function of transplacental clearances of the drug across the placenta from the dam to the fetus (CLdf) and from the fetus to the dam (CLfd) but is also a function of CLfo, the irreversible loss of the drug (by metabolism) from the fetus: Cssf/Cssd 5 CLdf/CLfd 1 CLfo. When a drug crosses the placenta by passive diffusion, as do stavudine (15) and zidovudine (9), the magnitude of CLfo with respect to CLdf 1 CLfd will determine the Cssf/Cssd ratio. Thus, Cssf/Cssd ratios for stavudine and zidovudine are lower than unity because of elimination of these drugs by the fetus. Values of these ratios for stavudine and zidovudine also indicate that stavudine, like zidovudine, does not accumulate in the fetus. Similar Cssf/Cssd values for stavudine and zidovudine indicate that exposure of the fetus to both drugs relative to that of the dam is similar. Clearance of stavudine alone (14.4 6 0.6 ml/min/kg) was not significantly different from that after coadministration with zidovudine (13.5 6 1.1 ml/min/kg). Clearance of zidovudine when administered with stavudine (31.1 6 2.2 ml/min/kg) was also not different from that obtained when zidovudine was infused alone to nonpregnant macaques in our laboratory (35.4 6 8.5 ml/min/kg) or to pregnant animals in combination with didanosine (33.0 6 1.7 ml/min/kg) (16, 21). The lack of an interaction between stavudine and zidovudine with respect to the maternal-fetal transfer is in agreement with the finding that transplacental transfer of stavudine and zidovudine is passive (9, 15). Both stavudine and zidovudine
are phosphorylated intracellularly by the same intracellular kinases, and an interaction between these drugs with respect to this metabolic process has been documented (7). However, because the quantity of each drug metabolized by phosphorylation compared with that metabolized by other metabolic processes appears small, an interaction between stavudine and zidovudine with respect to nonphosphorylation metabolism could have been predicted as unlikely, given that stavudine and zidovudine undergo such metabolism via different pathways (2, 9, 19). Both drugs are secreted actively by the kidneys, possibly via the same pathway. Therefore, the possibility of an interaction at a renal clearance level (in both the dam and the fetus), which would manifest itself as changes in systemic clearance, could not have been predicted. Such an interaction would affect the fetal exposure to one or both drugs. Our data, however, indicate that the total clearances of stavudine and zidovudine are not affected by the presence of one another. We conclude that concurrent administration of stavudine and zidovudine does not affect the transfer of either drug across the placenta or the total clearance of either drug in M. nemestrina. Although our data were obtained after intravenous administration, these conclusions should apply to data collected after oral administration for the following reasons. First, drug exposure of the fetus relative to that of the dam is a function of the systemic concentrations achieved in the dam and is, therefore, independent of the bioavailability of the drug. Second, no data which indicate that the bioavailability of either of the two drugs is affected by the presence of the other are available. On the basis of these data, we predict that stavudine and zidovudine will not affect the placental transfer or systemic clearance of each other when administered together to pregnant women, irrespective of the route of administration.
TABLE 2. Steady-state zidovudine concentrations after coinfusion of stavudine (22 mg/min/kg, intravenously) and zidovudine (66 mg/min/kg, intravenously) Drug concn (mg/ml)a in:
Drug concn ratio
Animal no.
F86363 T84143 T84258 Mean 6 SD a
Dam
Fetus
Amniotic fluid
Fetus/dam
Amniotic fluid/fetus
2.08 2.30 2.00
1.50 1.85 1.68
3.70 3.94 4.13
0.72 0.80 0.84
2.47 2.13 2.46
2.13 6 0.16
1.68 6 0.17
3.92 6 0.21
0.79 6 0.06
2.35 6 0.19
Concentrations from dam and fetus were measured in plasma.
VOL. 40, 1996
NOTES
This study was supported by grants RO1 HD27438 and RR00166 from the National Institutes of Health. REFERENCES 1. Connor, E. M., R. S. Sperling, R. Gelber, P. Kiselev, G. Scott, M. J. O’Sullivan, R. VanDyke, M. Bey, W. Shearer, R. L. Jacobson, E. Jimenez, E. O’Neill, B. Bazin, J.-F. Delfraissy, M. Culnane, R. Coombs, M. Elkins, J. Moye, P. Stratton, and J. Balsley. 1994. Reduction of maternal-infant transmission of human immunodeficiency virus type 1 with zidovudine treatment. N. Engl. J. Med. 331:1173–1180. 2. Cretton, E. M., Z. Zhou, L. B. Kidd, H. M. McClure, S. Kaul, M. J. M. Hitchcock, and J.-P. Sommadossi. 1993. In vitro and in vivo disposition and metabolism of 39-deoxy-29,39-didehydrothymidine. Antimicrob. Agents Chemother. 37:1816–1825. 3. Delfraissy, J. F., S. Blanche, C. Rouzioux, and M. J. Mayaux. 1992. Perinatal HIV transmission facts and controversies. Immunodefic. Res. 3:307–327. 4. Du, D.-L., D. A. Volpe, C. K. Grieshaber, and M. J. Murphy, Jr. 1992. In vitro toxicity of 39-azido-39-deoxythymidine, carbovir and 29,39-didehydro29,39-dideoxythymidine to human and murine haematopoietic progenitor cells. Br. J. Haematol. 80:437–445. 5. Dudley, M. N., K. K. Graham, S. Kaul, S. Geletko, L. Dunkle, M. Browne, and K. Mayer. 1992. Pharmacokinetics of stavudine in patients with AIDS or AIDS-related complex. J. Infect. Dis. 166:480–485. 6. Hirsch, M. S., and R. T. D’Aquila. 1993. Therapy for human immunodeficiency virus infection. N. Engl. J. Med. 328:1686–1695. 7. Ho, H.-T., and M. J. M. Hitchcock. 1989. Cellular pharmacology of 29,39dideoxy-29,39-didehydrothymidine, a nucleoside analog active against human immunodeficiency virus. Antimicrob. Agents Chemother. 33:844–849. 8. Kaul, S., and K. A. Dandekar. 1993. Pharmacokinetics of the anti-human immunodeficiency virus nucleoside analog stavudine in cynomolgus monkeys. Antimicrob. Agents Chemother. 37:1160–1162. 9. Lopez-Anaya, A., J. D. Unadkat, L. A. Schumann, and A. L. Smith. 1990. Pharmacokinetics of zidovudine (azidothymidine). I. Transplacental transfer. J. Acquired Immune Defic. Syndr. 3:959–964. 10. Lopez-Anaya, A., J. D. Unadkat, L. A. Schumann, and A. L. Smith. 1991. Pharmacokinetics of zidovudine (azidothymidine). III. Effect of pregnancy. J. Acquired Immune Defic. Syndr. 4:64–68. 11. Mansuri, M. M., M. J. M. Hitchcock, R. A. Buroker, C. L. Bregman, I. Ghazzouli, J. V. Desiderio, J. E. Starrett, R. Z. Sterzycki, and J. C. Martin.
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