Obstetrics, gynaecology and urinary

This chapter discusses drugs used in the fields of obstetrics, gynaecology and urology, including contraceptives, mifepristone, oxybutynin, oxytocin and phosphodiesterase type 5 inhibitors. For each drug, it explores the mechanism of action, indications, cautions and contra-indications, side-effects, metabolism and half-life, drug monitoring, drug interactions and important points. Mifepristone can reduce the efficacy of corticosteroid therapy (including inhaled steroids) for 3 - 4 days. A single oral dose of mifepristone is given with a dose of misoprostol for medical termination of pregnancy. Side-effects of this drug include gastrointestinal (GI) cramps, uterine contractions, vaginal bleeding and urticarial rash. Oxybutynin exerts its effects by blocking M 2 and M 3 receptors of the bladder and detrusor muscle. In patients with detrusor instability or hyperreflexia this serves to increase bladder capacity. Oxybutynin antagonises the effects of metoclopramide on the GI tract. Antimuscarinic side-effects will increase when oxybutynin taken with tricyclic antidepressants (TCAs) and sedating antihistamines.