Disposition of a new rate-controlled formulation of prazosin in the treatment of hypertension during pregnancy: transplacental passage of prazosin

• Published in: European journal of drug metabolism and pharmacokinetics Vol. 20; no. 3; p. 233
• Main Authors: Bourget, P, Fernandez, H, Edouard, D, Lesne-Hulin, A, Ribou, F, Baton-Saint-Mleux, C, Lelaidier, C
• Format: Journal Article
• Language: English
• Published: France 01.07.1995
• Subjects: Adrenergic alpha-Antagonists - blood; Adrenergic alpha-Antagonists - pharmacokinetics; Adrenergic alpha-Antagonists - therapeutic use; Adult; Antihypertensive Agents - blood; Antihypertensive Agents - pharmacokinetics; Antihypertensive Agents - therapeutic use; Delayed-Action Preparations; Female; Humans; Hypertension - drug therapy; Hypertension - metabolism; Maternal-Fetal Exchange; Prazosin - blood; Prazosin - pharmacokinetics; Prazosin - therapeutic use; Pregnancy; Pregnancy Complications, Cardiovascular - drug therapy; Pregnancy Complications, Cardiovascular - metabolism
• ISSN: 0378-7966; 2107-0180
• DOI: 10.1007/BF03189675

Prazosin (PRZ) in conventional tablet form (P-CT) has the disadvantages of a relatively short terminal half-life, a slight solubility in water and the well-recognized adverse effect of symptomatic orthostatic hypotension. The pharmacokinetic study of a new rate-controlled formulation of prazosin (Prazosin-Gastrointestinal System: P-GS) was performed in 9 pregnant women during the third trimester of pregnancy. Patients had persistent elevation of blood pressure. The subjects gave their informed consent for oral administration of 1 daily dose of 5 mg P-GS at 8 a.m. A first analysis period on day 1 enabled definition of the initial pharmacokinetic behavior of the drug, while the aim of a second was to evaluate its fate at plateau. The clinical course of both mother and fetus was subsequently monitored. This was an open, non-randomized study, each patient serving as her own control. For 3 patients, we aimed to determine the possible transplacental passage of PRZ at delivery. PRZ levels were measured by HPLC and data were analysed by noncompartmental linear pharmacokinetic methods. The data show: (i) P-GS was well tolerated by all patients and there were no significant changes in fetal heart rate during the study. (ii) A significant decrease in diastolic blood pressure was observed after the 36th hour following the first dose of P-GS while a reduction in systolic blood pressure was observed on day 4. (iii) An approximated relative bioavailability (f'P-GS) of 36.5% was calculated. P-GS appears to have a lower bioavailability than P-CT in women of similar gestational age. (iv) Both Cmax and AUC0-->infinity are significantly increased at plateau. Further, terminal half-life is increased with regard to the value determined with P-CT. No accumulation of PRZ was noted at steady-state. (v) P-GS is an example of an oral zero-order absorption product that offers one approach to control and improve the outcome of hypertensive therapy during pregnancy. This treatment could represent an alternative to methyldopa as a first treatment of pregnancy-associated hypertension. (vi) There is a slight transplacental passage of the drug (of the order of 10-20%).