Women who want to become pregnant have been warned not to take the popular pain drugs Celebrex and Vioxx because of emerging evidence that they can cause temporary infertility.
Rob Norman, an Adelaide IVF specialist, said the drugs could prevent ovulation or delay it until the egg was no longer viable, greatly reducing the chance of conceiving. Because the woman’s menstrual cycle would not be affected, she would have no way of guessing what was amiss.
The drugs, known as COX-2 inhibitors, might also prevent implantation of embryos or trigger early miscarriage, said Professor Norman, head of reproductive medicine at the University of Adelaide.
“Normal women of childbearing age attempting to have a baby should avoid taking these drugs or reduce their dose while seeking pregnancy,” he wrote in the journal Fertility and Sterility, published by the American Society for Reproductive Medicine.
Professor Norman said the COX-2 drugs blocked the action of prostaglandins hormone-like substances that cause inflammation and pain. But prostaglandins were also essential in rupturing mature follicles in the ovary – to allow an egg to be released into the fallopian tube and without them normal ovulation might never or rarely occur.
He cited a Swedish study that found the egg-releasing follicles in ovaries of women taking Vioxx grew on average 50 per cent larger than those in women taking a placebo – suggesting they were overripe and less likely to result in healthy pregnancy.
The study found that ovulation returned to normal after the women stopped taking Vioxx.
Hormone levels would be unaffected, giving doctors unaware of the COX-2 connection no clue why a woman could not become pregnant. “Our standard way of assessing ovulation [with blood hormone tests] isn’t relevant to these women.”
Professor Norman said non-steroidal anti-inflammatory drugs and even aspirin might potentially dampen fertility in the same way.
COX-2 inhibitors, which have surged in popularity in recent years, are intended for severe conditions such as arthritis, but some doctors prescribe them after injury or for more trivial pain.