Antipyrine elimination in saliva after low-dose combined or progestogen-only oral contraceptive steroids

The effect of oral contraceptives on the pharmacokinetics of melatonin in healthy subjects with CYP1A2 g.-163C>A polymorphism

The effect of oral contraceptives (OCs) on melatonin metabolism was studied in 29 subjects genotyped for CYP1A2 SNP g.-163C>A polymorphism. Plasma melatonin and 6-OH-melatonin concentrations were measured after a 6-mg dose of melatonin using a validated liquid chromatography/mass spectrometry method. The mean melatonin AUC and C(max) values were 4- to 5-fold higher in OC users than in non-OC users (P < .0001), whereas the weight-adjusted clearance was significantly lower in OC users (P < .0001). No significant difference in melatonin pharmacokinetics between the genotypes and no additional effect by the genotype on the OC-induced increase in melatonin exposure were evident. Melatonin exposure had no significant effect on the subjects' state of alertness. In conclusion, a significant inhibitory effect of OCs on the CYP1A2-catalyzed melatonin metabolism was seen; thereby, OC use can alter CYP1A2-phenotyping results.

Lack of gender differences and large intrasubject variability in cytochrome P450 activity measured by phenotyping with dextromethorphan

Gender-based differences in cytochrome P450 (CYP) activity may occur due to endogenous hormonal fluctuations with the menstrual cycle, which are altered by oral contraceptives. This study assessed the average activity and within-subject variability in CYP3A4 and CYP2D6 in men, women taking Triphasil, and regularly menstruating women not receiving oral contraceptives. Thirty-three healthy volunteers participated in this 28-day pilot study (12 women receiving Triphasil) (OCs), 11 regularly menstruating women not on exogenous progesterone or estrogen (no OCs), and 10 men. CYP3A4 and CYP2D6 activities were phenotyped with dextromethorphan (DM) on study days 7, 14, 21, and 28 using urinary ratios of DM:3-methoxymorphinan (3MM) and DM:dextrorphan (DX), respectively. Serial blood concentrations of estrogen and progesterone and menstrual diaries were used to determine menstrual phase in both groups of women. Average urinary DM:3MM and DM:DX in the 28 extensive metabolizers of CYP2D6 did not differ between the three study populations (p = 0.86 and 0.93, respectively). Post hoc power analysis indicated that more than 1000 subjects would be needed for 80% power (alpha = 0.05) to detect a +/- 15% difference from the population mean in the urinary ratios of dextromethorphan and its metabolites 3MM and DX. Variability in CYP3A4 and CYP2D6 activity, characterized by intrasubject standard deviation, also did not differ. The varying doses of levonorgesterol and ethinyl estradiol in Triphasil, fluctuations in estrogen and progesterone, and menstrual phase did not influence CYP3A4 or CYP2D6 activity. It was concluded that CYP3A4 and CYP2D6 activity and intrasubject variability were not different in the three study populations, and thus a clinically important difference between men, women on Triphasil, and women not receiving oral contraceptives is unlikely. High inter- and intrasubject variability in DM:3MM and DM:DX were clearly demonstrated and limit the use of dextromethorphan to phenotype endogenous CYP3A4 and CYP2D6 activity.

Oral contraceptive effects on methylprednisolone pharmacokinetics and pharmacodynamics

OBJECTIVE

Oral contraceptive (OC) steroids alter the disposition of numerous drugs, including corticosteroids. We investigated the pharmacokinetics and pharmacodynamics of methylprednisolone.

METHODS

Twelve women (six women used OC steroids and six women did not) received intravenous methylprednisolone (0.6 mg/kg ideal body weight). Methylprednisolone disposition was assessed from plasma concentrations. Pharmacodynamic parameters measured were plasma cortisol, whole blood histamine (reflecting basophils), and blood helper T lymphocytes.

RESULTS

Methylprednisolone clearance was significantly decreased in the women who used OC steroids (0.298 versus 0.447 L/hr/kg), resulting in a longer elimination half-life (2.20 versus 1.72 hours). With use of indirect response models, significant differences were observed with the cortisol and basophil responses. A larger value for the concentration that inhibits the zero-order production rate by 50% (0.37 versus 0.11 ng/ml) was observed in the women who used OC steroids for suppression of cortisol secretion, indicating less sensitivity to the suppressive effects of methylprednisolone. Greater net suppression of basophils was observed in the users of OC steroids (area under the response curve, 694 versus 401 ng x hr/ml). No differences were observed for helper T-cell responses.

CONCLUSION

OC steroids appear to inhibit methylprednisolone metabolism. However, mixed changes in several responses occur, indicating that women can probably receive similar doses of methylprednisolone irrespective of OC steroid use.

Pharmacokinetic and pharmacologic variation between different estrogen products

Due to the complex nature of endogenous and exogenous hormone concentration, formation, and metabolism and assay complexity, the pharmacokinetics of estrogen are difficult to study. Oral estrogens have minimal systemic bioavailability (2% to 10%) due to gut and liver (first-pass) metabolism. High concentrations of estrone are achieved with oral administration, whereas higher concentrations of estradiol are generally achieved after percutaneous absorption. Although vaginal products (such as gel, rings, etc.) are administered locally, they achieve high serum concentrations. Estradiol and estrone concentrations and estradiol-to-estrone ratios vary with different estrogen therapies. Approximately 95% to 98% of estradiol is bound loosely to albumin or tightly to sex hormone binding globulin, the major binding protein. The terminal half lives for the different estrogen compounds (after oral or intravenous administration) vary from 1-12 hours. Some conversion rates have been calculated between estrogen and its metabolites. Smoking decreases achievable estrogen concentrations, and has a greater effect on oral products. Oral contraceptives have been found to decrease antipyrine clearance. In the one study evaluating conjugated estrogens, antipyrine clearance was not altered. Oral contraceptives have a variable effect on the elimination of medications. Acetaminophen clearance is increased, whereas clearance of some benzodiazepines, caffeine,and prednisolone is decreased. Phenytoin increases the metabolism of conjugated estrogens. The various estrogen products may produce different clinical effects based on composition. The metabolites (minor components) of conjugated estrogens have been found to have significant effects on lipid concentrations, uterine weight, liver generated compounds, and bone resorption. Because transdermal products bypass the first-pass effect, delayed or decreased effects on lipid profiles and liver generated compounds have been observed.

Lack of effect of oral contraceptive use on the pharmacokinetics of quinine

The pharmacokinetics of quinine after a single 600 mg oral dose of quinine sulphate were studied in seven female subjects who used oral contraceptives and in seven age-matched female controls who did not. There were no significant differences (P greater than 0.05) in the maximum plasma concentration (Cmax) and the time of peak concentration (tmax) between the subjects who used oral contraceptives (Cmax = 5.3 +/- 1.0 (s.d.) mg l-1; tmax = 1.4 +/- 0.7 h) and the control subjects (Cmax = 5.6 +/- 0.9 mg l-1; tmax = 2.1 +/- 0.9 h). The mean elimination half-life of quinine in the oral contraceptives user group (12.5 +/- 1.9 h) was similar (P greater than 0.05) to that in the control group (11.8 +/- 2.7 h). The oral clearance of quinine in the oral contraceptive user group was 0.133 +/- 0.055 l h-1 kg-1 (range 0.073-0.233) and was not significantly different (P greater than 0.05) from that observed in the control group (0.125 +/- 0.025 l h-1 kg-1, range 0.075-0.148).

Oral contraceptives stimulate the excretion of clofibric acid glucuronide in women and female rats

1. Glucuronidation of clofibric acid, the pharmacologically active form of the hypolipidemic drug clofibrate was investigated in a human population, either in vitro with liver homogenates from biopsies, or after ingestion of the drug and determination of the urinary metabolite. No difference in the glucuronidation rate according to age of the patients was observed. Bilirubin but not clofibric acid glucuronidation was significantly higher in women (106% increase), when expressed per gram of tissue. 2. The excretion of clofibryl glucuronide in women who took oral contraceptives was significantly enhanced by 25%. 3. In female rats, treatment with the contraceptive agent norethindrone also stimulated by 48% the formation of clofibrylglucuronide in liver microsomes.

Influence of sex and oral contraceptive steroids on paracetamol metabolism

Paracetamol metabolism was investigated in eight healthy males, eight healthy females and eight healthy females receiving oral contraceptive steroids (OCS). Paracetamol clearance was 22% greater in males compared to the control female group. This difference was entirely due to increased activity of the glucuronidation pathway in males, there being no sex-related differences in the sulphation or oxidative metabolism of paracetamol. Paracetamol clearance in females using OCS was 49% greater than in the control females. Glucuronidation and oxidative metabolism were both induced in OCS users (by 78% and 36% respectively) but sulphation was not altered. Although sex-related differences in paracetamol metabolism are unlikely to be of clinical importance, induction of paracetamol metabolism by OCS may have clinical and toxicological consequences.

Differential effects of oral contraceptive steroids on the metabolism of benzodiazepines

The effects of oral contraceptive steroids (OCS) on the disposition and elimination of lorazepam, oxazepam, and chlordiazepoxide were examined. Lorazepam and oxazepam are metabolized via glucuronidation while chlordiazepoxide is metabolized by oxidation in the liver. The disposition and elimination of lorazepam, oxazepam, and chlordiazepoxide was studied in females not taking OCS and females taking OCS (norethindrone acetate, 1 mg; ethinyl estradiol, 50 micrograms) for 6 months or more. The t1/2 (beta) for lorazepam was significantly reduced in women taking OCS (6.0 +/- 3.1 vs. 14.0 +/- 6.2 hr) (p less than 0.005) as compared to controls, and the t1/2 (beta) for oxazepam was reduced in women taking OCS (7.71 +/- 3.23 vs. 12.09 +/- 5.08 hr) as compared to controls, but did not reach statistical significance. The plasma clearance of both lorazepam and oxazepam was significantly increased in women taking OCS [(288.9 +/- 165.9 vs. 77.5 +/- 3.29 ml per min) (p less than 0.01) and (251.2 +/- 106.9 vs. 97.86 +/- 69.4 ml per min) (p less than 0.01), respectively] as compared to controls. The volumes of distribution of lorazepam and oxazepam were significantly increased in women taking OCS (p less than 0.05) while plasma binding of these drugs was similar in both groups. In contrast, the t1/2 (beta) of chlordiazepoxide was significantly prolonged (20.58 +/- 8.08 vs. 11.63 +/- 5.91 hr) (p less than 0.05), and the plasma clearance was significantly reduced (13.41 +/- 4.69 vs. 33.22 +/- 12.37 ml per min) (p less than 0.05) in the OCS group as compared to controls. The volumes of distribution of chlordiazepoxide were similar in both groups, and the plasma binding of chlordiazepoxide tended to be lower in the OCS group but did not reach statistical significance. We conclude that OCS exert a differential effect on the elimination of benzodiazepines, whereby oxidation of chlordiazepoxide is impaired while the glucuronidation of lorazepam and oxazepam is enhanced by OCS.