Abstract | PURPOSE: The goal of this study was to develop physiologically based pharmacokinetic (PBPK) models for 2',3'-dideoxyinosine (ddI) in rats when the drug was administered alone (ddI model) and with pentamidine (ddI + pentamidine model), and to use these models to evaluate the effect of our previously reported pentamidine-ddI interaction on tissue ddI exposure in humans. METHODS: The PBPK models consisted of pharmacologically relevant tissues (blood, brain, gut, spleen, pancreas, liver, kidney, lymph nodes, muscle) and used the assumptions of perfusion-rate limited tissue distribution and linear tissue binding of ddI. The required physiologic model parameters were obtained from the literature, whereas the pharmacokinetic parameters and the tissue-to-plasma partition coefficients were calculated using plasma and tissue data. RESULTS: The ddI model in rats yielded model-predicted concentration-time profiles that were in close agreement with the experimentally determined profiles after an intravenous ddI dose (5% deviation in plasma and 20% deviation in tissues). The ddI + pentamidine model incorporated the pentamidine-induced increases of ddI partition in pancreas and muscle. The two PBPK models were scaled-up to humans using human physiologic and pharmacokinetic parameters. A comparison of the model-predicted plasma concentration-time profiles with the observed profiles in AIDS patients who often received ddI with pentamidine showed that the ddI model underestimated the terminal half-life (t1/2, beta) by 39% whereas the ddI + pentamidine model yielded identical t1/2, beta and area-under-the-curve as the observed values (< 1% deviation). Simulations of ddI concentration-time profiles in human tissues using the two models showed that pancreas and lymph nodes received about 2- to 30-fold higher ddI concentration than spleen and brain, and that coadministration of pentamidine increased the AUC of ddI in the pancreas by 20%. CONCLUSIONS: Data of the present study indicate that the plasma ddI concentration-time profile in patients were better described by the ddI + pentamidine model than by the ddI model, suggesting that the pentamidine-induced changes in tissue distribution of ddI observed in rats may also occur in humans.
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Authors | H J Kang, M G Wientjes, J L Au |
Journal | Pharmaceutical research
(Pharm Res)
Vol. 14
Issue 3
Pg. 337-44
(Mar 1997)
ISSN: 0724-8741 [Print] United States |
PMID | 9098877
(Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
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Topics |
- Animals
- Brain
(metabolism)
- Didanosine
(pharmacokinetics)
- Female
- Humans
- Intestinal Mucosa
(metabolism)
- Kidney
(metabolism)
- Liver
(metabolism)
- Lymph Nodes
(metabolism)
- Models, Biological
- Muscles
(metabolism)
- Pancreas
(metabolism)
- Pentamidine
(pharmacology)
- Rats
- Rats, Inbred F344
- Spleen
(metabolism)
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