Chemical formula: C₂₈H₂₇NO₄S Molecular mass: 473.583 g/mol PubChem compound: 5035
As a selective oestrogen receptor modulator (SERM), raloxifene has selective agonist or antagonist activities on tissues responsive to oestrogen. It acts as an agonist on bone and partially on cholesterol metabolism (decrease in total and LDL-cholesterol), but not in the hypothalamus or in the uterine or breast tissues.
Raloxifene’s biological actions, like those of oestrogen, are mediated through high affinity binding to oestrogen receptors and regulation of gene expression. This binding results in differential expression of multiple oestrogen-regulated genes in different tissues. Data suggests that the oestrogen receptor can regulate gene expression by at least two distinct pathways which are ligand-, tissue-, and/or gene-specific.
Raloxifene is absorbed rapidly after oral administration. Approximately 60% of an oral dose is absorbed. Presystemic glucuronidation is extensive. Absolute bioavailability of raloxifene is 2%. The time to reach average maximum plasma concentration and bioavailability are functions of systemic interconversion and enterohepatic cycling of raloxifene and its glucuronide metabolites.
Raloxifene is distributed extensively in the body. The volume of distribution is not dose dependent. Raloxifene is strongly bound to plasma proteins (98-99%).
Raloxifene undergoes extensive first pass metabolism to the glucuronide conjugates: raloxifene-4'-glucuronide, raloxifene-6-glucuronide, and raloxifene-6, 4'-diglucuronide. No other metabolites have been detected. Raloxifene comprises less than 1% of the combined concentrations of raloxifene and the glucuronide metabolites. Raloxifene levels are maintained by enterohepatic recycling, giving a plasma half-life of 27.7 hours.
Results from single oral doses of raloxifene predict multiple dose pharmacokinetics. Increasing doses of raloxifene result in slightly less than proportional increase in the area under the plasma time concentration curve (AUC).
The majority of a dose of raloxifene and glucuronide metabolites are excreted within 5 days and are found primarily in the faeces, with less than 6% excreted in urine.
Less than 6% of the total dose is eliminated in urine. In a population pharmacokinetic study, a 47% decrease in lean body mass adjusted creatinine clearance resulted in a 17% decrease in raloxifene clearance and a 15% decrease in the clearance of raloxifene conjugates.
The pharmacokinetics of a single dose of raloxifene in patients with cirrhosis and mild hepatic impairment (Child-Pugh class A) have been compared to that in healthy individuals. Plasma raloxifene concentrations were approximately 2.5-fold higher than in controls and correlated with bilirubin concentrations.
In a 2-year carcinogenicity study in rats, an increase in ovarian tumors of granulosa/theca cell origin was observed in high-dose females (279 mg/kg/day). Systemic exposure (AUC) of raloxifene in this group was approximately 400 times that in postmenopausal women administered a 60 mg dose. In a 21-month carcinogenicity study in mice, there was an increased incidence of testicular interstitial cell tumours and prostatic adenomas and adenocarcinomas in males given 41 or 210 mg/kg, and prostatic leiomyoblastoma in males given 210 mg/kg. In female mice, an increased incidence of ovarian tumours in animals given 9 to 242 mg/kg (0.3 to 32 times the AUC in humans) included benign and malignant tumours of granulosa/theca cell origin and benign tumours of epithelial cell origin. The female rodents in these studies were treated during their reproductive lives, when their ovaries were functional and highly responsive to hormonal stimulation. In contrast to the highly responsive ovaries in this rodent model, the human ovary after menopause is relatively unresponsive to reproductive hormonal stimulation.
Raloxifene was not genotoxic in any of the extensive battery of test systems applied. The reproductive and developmental effects observed in animals are consistent with the known pharmacological profile of raloxifene. At doses of 0.1 to 10 mg/kg/day in female rats, raloxifene disrupted estrous cycles of female rats during treatment, but did not delay fertile matings after treatment termination and only marginally reduced litter size, increased gestation length, and altered the timing of events in neonatal development. When given during the preimplantation period, raloxifene delayed and disrupted embryo implantation resulting in prolonged gestation and reduced litter size but development of offspring to weaning was not affected. Teratology studies were conducted in rabbits and rats. In rabbits, abortion and a low rate of ventricular septal defects (≥0.1 mg/kg) and hydrocephaly (≥10 mg/kg) were seen. In rats retardation of foetal development, wavy ribs and kidney cavitation occurred (≥1 mg/kg).
Raloxifene is a potent antioestrogen in the rat uterus and prevented growth of oestrogen-dependent mammary tumours in rats and mice.
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