The pharmacokinetics and metabolism of DuP 532, a non-peptide angiotensin II receptor antagonist, in rats and dogs

Comparative study of the cardiovascular effects of losartan in normal and in water- and salt-depleted sheep

The cardiovascular effects of losartan, a non-peptidic angiotensin II (ANG II) receptor antagonist, were studied in sheep. Eight normotensive, conscious sheep were tested twice: first under normal conditions and second when subjected to water and electrolytic depletion (furosemide 5 mg/kg twice a day for 3 days). Intravenous injection of 30 mg/kg losartan lowered the mean arterial blood pressure (MABP) in both control and water- and electrolyte-depleted sheep alike. The maximal decrease in MABP was significantly greater in diuretic-treated sheep than in controls (20.0 +/- 2.7 vs 9.3 +/- 1.1 mmHg) and occurred earlier (8.0 +/- 3.3 min vs 12.1 +/- 2.9 min). The decrease in blood pressure was associated with tachycardia in both controls and diuretic-treated sheep (+5.5 +/- 1.8 vs +11.3 +/- 3.9 beats/min). The vasopressor response to 0.1 microg/kg ANG II administered 30 min after losartan was completely antagonized. Two hours after losartan administration, MABP was on the increase in all animals and ANG II receptor blockade was partially obliterated in control sheep. The more marked cardiovascular effects recorded in diuretic-treated sheep as compared to control animals were associated with an increased activation of the renin-angiotensin system (plasma renin concentration: 6.51 +/- 1.33 vs 1.42 +/- 0.37 ng angiotensin I/ml/hr).

The pharmacokinetics and metabolism of CP-191,166, an angiotensin II receptor antagonist, in rats and dogs

CP-191,166 is an orally active, non-peptide angiotensin II (AII) receptor antagonist developed for the treatment of hypertension and congestive heart failure (CHF). In this study, the intravenous (iv) and oral (po) single dose pharmacokinetics (PK), oral multiple dose PK and P450-mediated metabolism of CP-191,166 were determined in rats and dogs. CP-191,166 was administered in both single and multiple (22-29 day) doses to Sprague-Dawley rats (3 mg/kg iv and 5, 10, 25 and 200 mg/kg po) and to beagle dogs (5 mg/kg iv and 5, 15 and 50 mg/kg po). Blood samples were collected between 0 and 48 h and plasma CP-191,166 concentrations were determined using high performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The in vitro metabolism of CP-191,166 was also evaluated with rat and dog liver microsomes. The results of these studies suggest that in both species, there may be saturable clearance occurring with higher doses, T(max) was at or near the earliest sample time point for all doses, suggesting that the drug was rapidly absorbed, and CP-191,166 was eliminated with t(1/2) values of 8-9 h. No rat or dog microsomal metabolism was observed, suggesting that metabolites detected in vivo in dogs were non-P450-mediated.

DuP 532, an angiotensin II receptor antagonist: first administration and comparison with losartan

We investigated the tolerability and angiotensin II antagonist activity of oral DuP 532 in healthy male subjects. DuP 532 (1 to 200 mg) was well tolerated, with no effect on blood pressure or heart rate. Compared with losartan (100 mg), DuP 532 (200 mg) was a weak antagonist of pressor responses to intravenous angiotensin II. Maximum inhibition of diastolic pressor response was 86% (95% confidence interval [CI], 84%, 88%) approximately 4.6 hours after losartan and 48% (95% CI, 38%, 56%) 8.7 hours after DuP 532. Twenty-four hours after dosing, inhibition by losartan and DuP 532 was similar (40% to 45%). DUP 532 is extensively bound in human plasma, with an in vitro free fraction of 0.06. Although DuP 532 and EXP3174 (losartan's active metabolite) have similar AT1-receptor potency, and plasma concentrations of DuP 532 were much greater than losartan/EXP3174, the level of antagonism was much less for DuP 532. These results indicate that multiple factors determine the in vivo potency of angiotensin II antagonists, including affinity for and distribution to the receptor as modulated by plasma binding.

Effects of structural modifications on the intestinal permeability of angiotensin II receptor antagonists and the correlation of in vitro, in situ, and in vivo absorption

PURPOSE

The effects of structural modifications on the membrane permeability of angiotensin II (Ang II) receptor antagonists and the usefulness of in vitro and in situ intestinal absorption models in predicting in vivo absorption or bioavailability were investigated.

METHODS

Intestinal permeability was determined in vitro using Caco-2 cell monolayers and in situ using a perfused rat intestine method. Several physicochemical parameters were either measured or computed, and correlated with intestinal permeation.

RESULTS

Permeation coefficients (Pa) across Caco-2 cell monolayers correlated well with both in situ absorption rate constants (ka) and in vivo bioavailability or % absorption. For these Ang II antagonists, Pa values larger than 3 x 10(-6) cm sec-1 and in situ ka values of 2 x 10(-4) min-1 cm-1 or above were associated with good in vivo absorption. Structural modifications at the R5 position, where a COOH group was substituted with either a CHO or CH2OH group, enhanced the permeability of the Ang II receptor antagonists up to 100-fold. There were good correlations between permeability and log P(octanol/buffer), log PHPLC, charge, solvation/desolvation energy and assigned hydrogen bonding potential.

CONCLUSIONS

The correlations obtained in this study indicate that both the Caco-2 cell model and the in situ perfused rat intestine could be used to predict intestinal absorption in vivo. Structural modifications of the Ang II antagonists had a significant impact on the intestinal permeability. Charge, solvation energy, and hydrogen bonding are predominant determinants of intestinal permeability and oral bioavailability of these compounds.