Oral contraceptives dosage

Serax, Tranxene, Valium, Xanax, and others) tranquilizer effects including psychomotor impairment during drug-free week in oral contraceptive dosage... 

A study in 12 healthy women taking a combined oral contraceptive (ethi-nylestradiol/norethisterone 35 micrograms/1 mg) found that atorvastatin 40 mg daily increased the AUC of norethisterone and ethinylestradiol by about 28% and 19%, respectively, and increased their maximum plasma levels by 24% and 30%, respectively. These increases are only moderate and unlikely to be clinically important, but the manufacturers say that they should be considered when selecting an appropriate oral contraceptive dosage for women given atorvastatin. ... 

The oral contraceptives have changed a great deal since their introduction in the 1960s. Today the levels of hormones provide lower dosages of hormones compared with the older formulations, while retaining the same degree of effectiveness (>99% when used as prescribed). 

Coadministration with other hormonal contraceptive preparations or hormone replacement therapy Although the effect of other hormonal contraceptive preparations or replacement therapy on the pharmacokinetics of lamotrigine has not been evaluated, the effect may be similar to oral contraceptives. Therefore, similar adjustments to the dosage of lamotrigine may be needed. 

Sustained-release formulations can produce stable serum concentrations with once or twice daily dosage. Therapeutic effects occur at blood levels > 5 mg/1, and side effects increase considerably at levels > 15 mg/1. Smoking, alcohol, anticonvulsants, and rifampicin induce the drug-metabolizing enzyme system in liver and reduce the half-life of theophylline. On the other hand, heart and liver failure, sustained fever, old age and drugs such as cimeti-dine, ciprofloxacin, and oral contraceptives reduce theophylline clearance and thereby increase serum concentrations. 

A low dosage of progestin ( mini-pill ) is used, in the form of medroxyprogesterone acetate, which is active at a very low dose. The mini-pill does not inhibit ovulation, but rather interferes with the endometrium and the cervical mucus. The use of this pill prevents most of the side effects of oral contraception, specifically nausea, water retention, and in some cases thrombophlebitis. However, a lower success rate and other frequent side effects have reduced the widespread acceptance of this preparation. Nevertheless, the mini-pill has a role to play in certain specific situations. For example, in an uncommon form of epilepsy called catamenial epilepsy, female patients will experience seizures at particular times during their menstrual cycle, reflecting the fact that seizure focus is stimulated by estrogens but inhibited by progestins. In such women, the mini-pill may afford not only birth control but also improved seizure control. 

Several case reports have suggested that the elimination of ciclosporin can be impaired by oral contraceptives, resulting in increased plasma ciclosporin concentrations. Ciclosporin undergoes hydroxylation and /V-dcmethyla-tion, in which cytochrome P450 is involved, so competitive enzyme inhibition probably explains the interaction. Dosages of ciclosporin should be reviewed carefully (340). 

The clearances of both theophylline and caffeine are reduced in oral contraceptive users and half-lives are increased, probably because of inhibition of hepatic metabolism by cytochrome P450 (348). Caution in dosage is advisable. 

---