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Injection (Depo-Provera)

 

How they Work; Pros and Cons

 

Composition

Depo-medroxyprogesterone acetate

Mechanism of Action

The sustained level of medroxyprogesterone acetate suppresses ovulation in the majority of women. It also renders cervical mucus impenetrable to sperm and induces a thin endometrium (atrophy), which is unsuitable for implantation.

Dosage

150 mg of Depo-Provera is given intramuscularly every 12 weeks. Depo-Provera should be administered during the first five days of a normal menstrual cycle, in order to avoid inadvertent administration during pregnancy. It may also be given immediately post partum or following pregnancy termination. Contraceptive effectiveness is achieved within 24 hours.

Advantages
  1. No day-to-day user participation required beyond attending for repeat injections every three months. 
  2. May be used in women with contraindications to the combined oral contraceptive pill (such as thromboembolic disease and myocardial disease) 
  3. May be used in women over 35 who smoke, during breastfeeding, and when the combined pill is discontinued before major surgery 
  4. No estrogen-related side effects 
  5. Scanty menses or amenorrhea with reduction in the occurrence of anemia and dysmenorrhea. 
  6. Reduced risk of endometrial cancer and ovarian cancer. 
  7. Reduced risk of pelvic inflammatory disease and ectopic pregnancy. 
  8. A reduction in symptoms associated with endometriosis, premenstrual syndrome and chronic pelvic pain. 
  9. Reduced frequency of seizures in those with epilepsy. 
Disadvantages/Side Effects
  1. Intermenstrual bleeding /menstrual cycle disturbance 
  2. Potential weight gain. 
  3. Headaches 
  4. Alterations in mood 
  5. Decreased bone density-In general, current DMPA users have decreased bone mineral density compared with non-users; this decrease  is usually within one standard deviation of normal values. Limited evidence shows decreased bone mineral  density over time among adolescent DMPA users. No studies have examined whether DMPA use among adolescents  affects peak bone mass levels. Older DMPA users have decreased bone mineral density compared with  non-users. However, evidence found that women gained bone mass following discontinuation of DMPA prior to menopause. Further, among postmenopausal women, there was no difference in bone mineral density between former DMPA  users and never users. The majority of the bone loss is recovered when the DMPA is discontinued, and there  has been no increase in the rate of clinical fractures. BMD testing is not recommended routinely. Patients  with other significant risk factors for osteoporosis may be considered for BMD testing. Patients should be  counselled about “bone health”, including calcium and vitamin D intake, weight bearing exercise,  decreasing alcohol and caffeine intake, and quitting smoking. 
Efficacy

Depo-Provera is a highly effective form of contraception, with a Pearl Index of 0.3 (failure rate for 100 women using the method for one year).

Contraindications/Poor candidates
Absolute
  1. Known or suspected pregnancy 
  2. Current diagnosis of breast cancer
Relative
  1. Unexplained vaginal bleeding (before investigation) 
  2. History of ischemic heart disease or stroke 
  3. Severe cirrhosis, active viral hepatitis, and liver tumors
 
Follow-up

Every 12-13 weeks for their next injection.

Delayed Injection

If it has been less than 14 weeks since the last injection, the next injection can be given immediately.

If it has been more than 14 weeks since the last injection, confirm that she is not pregnant (do a pregnancy test) and the next DMPA injection may be given if the pregnancy test is negative. Back-up contraception should be used for the next two weeks. If she has been sexually active in the week prior to her appointment, give the DMPA if the pregnancy test is negative. The pregnancy test should be repeated two weeks later to rule out preganancy. There are no teratogenic effects if the injection is given inadvertently during pregnancy. There is no need to wait for a woman’s next menstrual cycle to give the repeat injection.