Efficacy

• Quoted as >99% effective
• Described as: if taken correctly, then during the course of 1 year, <1% of women using the injection will become pregnant

Mechanism

Prevent ovulation – and may stop periods

• Other methods of progesterone only contraception will often make periods lighter, and may prevent them in some women. However, progestogen injection will be more likely to prevent ovulation and regular menstrual bleeding in a higher proportion of women.
• This is the main benefit of this treatment over other options
• Some women may get heavier or irregular periods

Thickens cervical mucus
Alters lining of the uterus, making it difficult for implantation to take place

Cautions and contraindications

Should not be first line in women <18 or >45 due to risk of reduction in bone density

• In women <18 can alter the formation of new bone, as bones are still developing
• In women over 45 can increase the rate of bone density reduction
• The reduction in bone density is greatest in the first 2-3 years of use, then stabilises.

Should be avoided when other RF’s for osteoporosis are present

• Low oestrogen due to amenorrhoea for >6 months – e.g. due to extreme dieting, exercise or eating disorder
• Smoker
• Heavy drinker
• Long-term steroid use
• FH of osteoporosis (1^st degree relatives)

Side effects

• Bleeding may be heavier for the first 3-4 months, but will usually settle down, and most women ultimately do not have periods
• Mood swings
• Reduction in bone density / increased risk of osteoporosis in later life
• Weight gain – typically 2-3Kg per year

Benefits over oral POP

More likely to inhibit ovulation, thus:

• Less likelyhood of periods
• Recued risk of ovarian cysts and ectopic pregnancy
• Also, no interaction with non-enzyme inducing antibacterials

Drug interactions

Enzyme-inducing drugs

• E.g. St John’s Wort
• TB, epilepsy and HIV medications
• If the patient also takes any of these, it is recommended to use additional contraception (e.g. condoms) for the duration of the treatment and for 4 weeks after

Prescribing and administration

Given IM, usually into the gluteal muscles. Depo-provera may be given in the leg or arm

• Noristat is a more viscous solution and may be more painful during administration

If there is any chance of pregnancy, the patient must have a pregnancy test before commencing treatment.

• Administration during pregnancy can masculinise the fetus

Treatment should be commenced within 5 days of the start of the cycle

• If started at any other day in the cycle, another method of contraception (e.g. condoms) should be used for the first 7 days.

After pregnancy

• o   Usually started 6 weeks after pregnancy. This reduces the risk of heavy / irregular periods.
  • Can be given after 21 days on request
  • If given at 6 weeks, then an alternative form of contraception (e.g. condoms) should be used between 21 days and 6 weeks
  • Pregnancy cannot occur in the first 21 days after the birth of a previous child

After miscarriage / abortion

• Treatment can be started immediately, and will be immediately effective

General advice

• Breast-feeding is not affected
• Missing an injection
• You can be up to two weeks late for the next appointment, and still be fully ptorected:
  • i.e. 10 weeks for Noristerat
  • 14 weeks for Depo-Provera
• Duration of treatment – Providing there are no contra-indications, or RF’s for osteoporosis, treatment can be continued until menopause
• topping treatment
  • Fertility can take several months to return after treatment is stopped.
  • Important to warn patients they can get pregnant after cessation of treatment but before their first normal period.

References

• Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
• Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
• Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

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