Chapter 17 Drugs used in obstetrics, gynaecology and urinary tract disorders
INTRODUCTION
Sexual health services have been developed to meet the greatly increased demands placed on them. Many specialities are involved in providing sexual health services, and there needs to be an effective working relationship between genitourinary medicine and family planning services. Changes in lifestyle leading to an increase in the number of sexual partners of both men and women have led to a massive increase in sexually transmitted infections. Early diagnosis, tracing of sexual partners and effective antimicrobial therapy must be made available to all who need this care. The spread of HIV and other blood-borne viral diseases is an increasing cause for concern. In the developed world, retroviral drugs are normally available, but issues relating to the lack of availability of these drugs in some parts of the world where the need is great remain largely unresolved.
ANATOMY AND PHYSIOLOGY
The female reproductive system consists of two ovaries, two fallopian/uterine tubes, the uterus, the vagina and external genitalia (Fig. 17.1). The ovary contains ovarian follicles, each of which contains an ovum. Under the influence of the gonadotrophic hormones, follicle-stimulating hormone and luteinising hormone from the pituitary, the ovarian hormones oestrogen and progesterone, respectively, are produced. If the ovum is fertilised, it embeds itself in the uterine wall, where it grows and develops into an embryo; if not, the corpus luteum degenerates, menstruation follows and the cycle begins again. Oestrogen is secreted in the first phase of the cycle and prepares the reproductive system for possible pregnancy; progesterone is produced if the ovum is not fertilised and is produced in the second (secretory) phase of the cycle. Hormonal control of the female reproductive system is complex and depends on a hormonal inter-relationship that is illustrated in Figure 17.2.
Fig. 17.1 The female reproductive system.
(From Page CP, Hoffman BF, Curtis M et al. 2006 Integrated pharmacology. Mosby, Edinburgh. With permission of Mosby.)
DRUGS USED IN OBSTETRICS
The main drugs used in obstetrics are the oxytocics and the prostaglandins. These drugs are used to induce abortion, induce or augment labour and minimise blood loss. A summary of the main products is given in Table 17.1 and Boxes 17.1 and 17.2. All these drugs act by inducing uterine contractions. Such contractions are accompanied by pain, depending on the strength of the contractions induced. Whenever these drugs are used, the importance of monitoring fetal health cannot be overemphasised.
| Product | Main indications |
|---|---|
| Carboprost | Used for the treatment of postpartum haemorrhage when the patient is unresponsive to ergometrine and oxytocin. It is given by deep IM injection 250 micrograms, repeated if necessary at intervals of 1½ h. Total dose should not exceed 2 mg (8 × 250 micrograms). The side-effects include gastrointestinal effects, bronchospasm, respiratory disturbances and pain at injection site. |
| Dinoprostone | Available as vaginal tablets, pessaries and gel for the induction of labour. Care must be taken to use the correct product, as the gel and vaginal tablet are not bioequivalent. Doses: pessary 5 mg over 12 h; vaginal gel 1 mg followed by 1–2 mg after 6 h. The injection is seldom used. The side-effects are similar to those of other prostaglandins. |
| Gemeprost | Induction of abortion. By vaginal pessary – the dose will depend on the procedure being undertaken and the stage of pregnancy. A dose of 1–3 mg softens and dilates the cervix, which facilitates surgical procedures. In second-trimester abortion, 1 mg every 3 h for five administrations. A second course 24 h after the start of the first treatment may be given. In second-trimester uterine death, 1 mg is given every 3 h up to a maximum of 5 mg. Side-effects include vaginal bleeding; uterine pain; central nervous system, respiratory and flu-like symptoms; and cardiovascular disturbances. Mifepristone, an antiprogestogenic steroid, sensitises the myometrium to prostaglandin-induced contractions, and it softens and dilates the cervix. It is given in a dose of 200–600 mg orally prior to the gemeprost. |
aThese are potent drugs with significant side-effects. Please consult specialist literature for further information on the use of these important drugs.
Box 17.1 Actions and uses of oxytocin
Clinical outline of applications
Box 17.2 Actions and uses of ergometrine maleate
Outline of clinical applications
Drugs are also used to postpone premature labour and are used to reduce harm to the child. The delay can be used to administer therapy or take measures designed to improve perinatal health. The drugs used are outlined in Table 17.2.
Table 17.2 Drugs used in the management of premature labour
| Drug | Mode of action | Dose and notes |
|---|---|---|
| Antobisan | Oxytocin receptor antagonist | IV 6.75 mg over 1 min. Then used to delay labour in uncomplicated premature labour between 24 and 33 weeks of gestation. This drug may be preferred to the β2 agonists, because cardiovascular problems are fewer. |
| Nifedipine (unlicensed indication; see p. 211) | Calcium-channel blocker | 20 mg initially, then 10–20 mg three or four times daily according to response. May have fewer side-effects than β2 agonists. |
| Ritodrine hydrochloride | β2 agonist (see p. 144) | Given by IV infusion, initially 50 micrograms/min every 10 min (see specialist literature). The side-effects of this drug, especially on the cardiovascular system, are potentially serious. It is essential to avoid fluid overload. |
| Salbutamol | β2 agonist | Similar indications to the above (uncomplicated premature labour). Also similar side-effects. See specialist literature. |
| Terbutaline | β2 agonist |
HORMONAL CONTRACEPTION
ORAL CONTRACEPTIVES
Oral contraception has proved to be a very acceptable and convenient method of contraception for many women. Despite some problems and contraindications, well-managed hormonal contraception is relatively safe and highly effective. Two basic types of routine oral contraceptive products are available: a combined pill containing both an oestrogen and a progestogen, and a progestogen-only pill (Table 17.3). Hormonal emergency oral contraception may be required for women who have had unprotected intercourse or experienced failure of a contraceptive barrier device (Table 17.4). The key points relating to the prescribing and contraindications of oral contraceptives are summarised in the tables.
Table 17.3 Hormonal contraception
