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Mifepristone (RU 486)
How it works and what it does
Assoc Professor Anne Tonkin, Clinical Pharmacologist,
University of Adelaide and Royal Adelaide Hospital
Former member, Australian Drug Evaluation Committee
and Pharmaceutical Benefits Advisory Committee
How it works (1)
In exactly the same way as dozens of
other drugs
 Prevents the action of a body
“messenger” (in this case, a hormone)
 Similar approach for drugs used for heart
disease, high blood pressure, etc etc
 NOT a toxin or poison; causes no direct
harm

How it works (2)
Control of many body functions uses
“lock and key” approach
 Hormones (“keys”) act only in parts of
the body where the right shaped
receptors (“locks”) are present

Key fits
this lock
and
opens it
Hormone
This key
does not
fit this
lock
How it works (3)

Many drugs are “false keys” – fit the lock
but will not turn it
true key can’t reach lock
 “receptor antagonists / blockers”

“False
key” fits
but lock
does not
open
Drug
“True key”
cannot
reach lock
Hormone
How it works (3)

Many drugs are “false keys” – fit the lock
but will not turn it
true key can’t reach lock
 “receptor antagonists / blockers”

Drug (“false
key”) fits but
receptor is not
activated
Drug
Hormone
can’t reach
receptor
No hormone effect
Hormone
How it works (4)

Mifepristone blocks progesterone
receptors
prevents normal effects of progesterone on
uterus (needed to maintain early pregnancy)
 effect is similar to insufficient production of
progesterone (causing natural miscarriage)
 also reduces stimulatory effect of
progesterone on endometriosis, tumour
growth, etc

What it does (1)

Prevents progesterone from having its usual
effects in early pregnancy




pregnancy can no longer be maintained and is
miscarried (very similar to natural miscarriage)
side effects are very similar to complications of
natural miscarriage
about 95% can avoid anaesthesia/operation
side effects of the drug itself are minimal (absence
of progesterone effect causes few if any symptoms)

fatigue, loss of appetite, nausea in a few
What it does (2)

Other uses demonstrated in clinical trials:







Contraception
Endometriosis
Breast cancer
Meningiomas (benign brain tumours)
Uterine tumours (benign and malignant)
Alzheimer’s disease
Stigmatization as an “abortion drug” has
inhibited research on some of these uses

May have been a different debate if treatment of
fibroids had been developed first?
Drug regulation: Benefits vs risks

Drug regulatory system is specifically
designed to assess benefit:risk balance
 Other drugs involved in the process of medical
termination



have other well-established uses such as gastric
ulcer prevention (misoprostol) or arthritis
(methotrexate)
these are regulated in the usual TGA system
Mifepristone has several potential uses in
addition to termination of pregnancy, all of
which should be assessed by the TGA system
Benefits vs risks

Methods of non-surgical abortion



most effective is combination of mifepristone and a
prostaglandin drug
less effective alternative is methotrexate and a
prostaglandin (both available in Australia)
Mifepristone combination method is used
widely around the world


UK since 1991, Sweden since 1992, USA
studies on women’s preferences consistently favour
medical over surgical abortion
Main messages

Mifepristone is a drug like any other



Blocks progesterone receptors
Has a variety of established and potential uses
apart from non-surgical abortion
Other drugs used for non-surgical abortion are
regulated in the usual TGA system and
available in Australia
 There is no scientific or medical reason for
continuing the special arrangements for
mifepristone