Mefenamic Acid Risk Summary

Risk Factor: CM*
Class: CENTRAL NERVOUS SYSTEM DRUGS / Nonsteroidal Anti-inflammatory Drugs

Fetal Risk Summary

Mefenamic acid, a nonsteroidal anti-inflammatory drug (NSAID), is used for the short-term treatment of pain and for primary dysmenorrhea. It is in the same NSAID subclass (fenamates) as meclofenamate.

Although mefenamic acid causes toxic effects in pregnant animals similar to those produced by other agents in this class (decreased fertility, delayed parturition, increase in the number of resorptions, and decreased pup survival), no congenital malformations were observed in studies involving rats, rabbits, and dogs at doses up to 10 times those used in humans (1). In one study of pregnant rats, inhibition of parturition by mefenamic acid appeared to be dose-related (2).

Consistent with its low molecular weight (about 241), mefenamic acid crosses the human placenta to the fetus. Fetal concentrations of the drug, 40180 minutes after a 500-mg dose administered to 13 women at 1522 weeks' gestation, were 32%54% of the maternal plasma concentrations (3).

A combined 2001 population-based observational cohort study and a case-control study estimated the risk of adverse pregnancy outcome from the use of NSAIDs (4). The use of NSAIDs during pregnancy was not associated with congenital malformations, preterm delivery, or low birth weight, but a positive association was discovered with spontaneous abortions (SABs) (see Ibuprofen for details).

Mefenamic acid, 500 mg 3 times a day, was used as a tocolytic in a double-blind, randomized human study (5). Compared with controls, preterm delivery occurred less in the mefenamic acid group (15% vs 40%, p<0.005), and birth weights were higher. No adverse effects were observed in the newborns exposed in utero to mefenamic acid.

An infant, delivered by urgent cesarean section at 34 weeks' gestation, had marked cyanosis after in utero exposure to mefenamic acid used to prevent premature delivery (6). Echocardiography of the infant demonstrated a small (1- to 2-mm) patent ductus arteriosus. The authors concluded that the maternal drug therapy was responsible for the premature closure of the ductus.

Constriction of the ductus arteriosus in utero is a pharmacologic consequence arising from the use of prostaglandin synthesis inhibitors during pregnancy, as is inhibition of labor, prolongation of pregnancy, and suppression of fetal renal function (see also Indomethacin) (7). Persistent pulmonary hypertension of the newborn may occur if these agents are used in the 3rd trimester close to delivery (7). Women attempting to conceive should not use any prostaglandin synthesis inhibitor, including mefenamic acid, because of the findings in a variety of animal models that indicate these agents block blastocyst implantation (8,9). Moreover, as noted above, NSAIDs have been associated with SABs.

[*Risk Factor D if used in 3rd trimester or near delivery.]

Breast Feeding Summary

Small amounts of mefenamic acid are excreted into breast milk and absorbed by the nursing infant (10). Ten nursing mothers in the immediate postpartum period were given a 500-mg oral loading dose followed by 250 mg 3 times daily for 3 days. Blood and milk samples were obtained 2 hours after the first daily dose on postpartum days 24. Blood and urine samples were obtained from the infants 1 hour after nursing on postpartum day 4. The averages of the mean daily concentrations of mefenamic acid in maternal plasma and milk were 0.94 and 0.17 g/mL, respectively, corresponding to a milk:plasma ratio of 0.18. In three of the mothers, breast milk concentrations of mefenamic acid plus metabolites ranged from 0.62 to 1.99 g/mL. The mean infant blood concentration of mefenamic acid was 0.08 g/mL, whereas the mean urine concentration of mefenamic acid plus metabolites was 9.8 g/mL.

One reviewer concluded that, because of the potential toxicity of mefenamic acid, other agents (diclofenac, fenoprofen, flurbiprofen, ibuprofen, ketoprofen, ketorolac, and tolmetin) were safer alternatives if a NSAID was required during nursing (11). However, the American Academy of Pediatrics classifies mefenamic acid as usually compatible with breast feeding (12).

References

1. Product information. Ponstel. Parke-Davis, 1995.
2. Powell JG Jr, Cochrane RL. The effects of a number of non-steroidal anti-inflammatory compounds on parturition in the rat. Prostaglandins 1982;23:46988.
3. MacKenzie IZ, Graf AK, Mitchell MD. Prostaglandins in the fetal circulation following maternal ingestion of a prostaglandin synthetase inhibitor during mid-pregnancy. Int J Gynaecol Obstet 1985;23:4558.
4. Nielsen GL, Sorensen HT, Larsen H, Pedersen L. Risk of adverse birth outcome and miscarriage in pregnant users of non-steroidal anti-inflammatory drugs: population based observational study and case-control study. Br Med J 2001;322:26670.
5. Mital P, Garg S, Khuteta RP, Khuteta S, Mital P. Mefenamic acid in prevention of premature labor. J R Soc Health 1992;112:2146.
6. Menahem S. Administration of prostaglandin inhibitors to the mother; the potential risk to the fetus and neonate with duct-dependent circulation. Reprod Fertil Dev 1991;3:48994.
7. Levin DL. Effects of inhibition of prostaglandin synthesis on fetal development, oxygenation, and the fetal circulation. Semin Perinatol 1980;4:3544.
8. Matt DW, Borzelleca JF. Toxic effects on the female reproductive system during pregnancy, parturition, and lactation. In Witorsch RJ, ed. Reproductive Toxicology. 2nd ed. New York, NY: Raven Press, 1995:17593.
9. Dawood MY. Nonsteroidal anti-inflammatory drugs and reproduction. Am J Obstet Gynecol 1993;169:125565.
10. Buchanan RA, Eaton CJ, Koeff ST, Kinkel AW. The breast milk excretion of mefenamic acid. Curr Ther Res Clin Exp 1968;10:5926.
11. Anderson PO. Medication use while breast feeding a neonate. Neonatal Pharmacol Q 1993;2:314.
12. Committee on Drugs, American Academy of Pediatrics. The transfer of drugs and other chemicals into human milk. Pediatrics 1994;93:13750.

Questions and Answers

is it safe for a pregnant like me to take a medicine like antibiotics and mefenamic acid?

i went to the dentist for third molar extraction and i've found out that im 5 days pregnant at that time.i have experienced spotting and abdominal pain but gone after a few days.i had my ultrasound and the embryo are in good activity.the cervix is closed but subchorionic hemorrhage as described.it measures 1.5 X 1.7 X 0.8 cm.

unfortunately when u get pregnant u aren't really allowed to take many medicines but the only way to know about any specific medicines is to go to a doctor and ask them or look it up online. i doubt very many people on this site would know specifically which medicines u can and can't take.

Is mefenamic acid-pain reliever harmful for a 7 month pregnant ?

she is having a toothache and she is taking a mefenamic-pain reliever is it harmful for her that she is 7 month pregnant?

I would stay away from any anti-inflammatory pain killers (like mefenamic acid) while pregnant and stick to acetaminophen/tylenol.

The reason being that they affect prostaglandins to block pain and those same prostaglandins have an effect in childbirth. I seem to remember it is more or a problem closer to term but why risk it?

Tylenol is definately the safer choice

Can my baby be normal? I had undergone two chest x-rays and taken mefenamic acid and amoxicillin.?

My last period was on the 14th of October and tested positive last Nov. 19. My x-rays were on Nov. 7 & 8. I had taken the mefenamic acid for recent frequent headache and didn't know i was pregnant. Now i'm scared that the baby will come out abnormal.

Have you talked to your GP. I would say that I don't think it will have caused any damage but you need a medical opinion !!

Congratulations and good luck !!!

Am I still pregnant after my D & C as indicated by a thin faint pink line on the pregnancy test?

I decided to have a D & C last Oct 21 due to twice bleeding of my 7th week pregnancy as of Oct 20, and due to the number of medicines (unprescribed) which i have taken prior to D& C. Three days after my D&C, i tested my urine with a pregnancy test, there was a faint line on the lower line (test band) while the upper line was darker. Every after 2 days I did test my urine again, same results appeared. Until my 5th test, there was still a faint pink line on the lower line. I haven't consulted the doctor that performed the D&C since then, but days after the procedure I experienced bleding and was even given antibacterial capsules, methergens and mefenamic acids. Please give me your opinions whether this faint line is normal after the D&C or I am still pregnant?I haven't had any sexual activity after the D&C.

It takes a few weeks for your hcg levels to be gone out of your system after a d/c, that's why you are getting a faint positive line. You would not be still pregnant after a d/c! Sorry for your loss.

nausea, bleeding..pregnant?

on May 5th i had sex and a 5 days later i suddenly had nausea and vomited all afternoon and next day. I continued to have severe nausea for weeks after. On 20th May i had my period (which lasted 5 days and seemed normal) i continued to have nausea started having headaches and after my period nausea continued on a daily basis. went to GP who had no idea what was wrong and prescribed some tablets (which i didnt take). advised to take a pregnancy test anyway but it came up negative. i took a blood test also and the results were normal.
on the 11th June, i woke up with pain and was bleeding. It was not heavy but it was bright red with no clots. It started to get heavier and the pain continued, also nausea. I was very worried so i went to a walk in centerl. did another urine test, which came up negative on pregnancy and normal - no infections, nothing.
He pres MEFENAMIC acid tablets (500mg) to stop the bleeding and pain. (had a smear test last summer and no abnormalities)
pls ,any thoughts

could be something like endometriosis or poly cystic ovarian synDrome keep pestering your dr until he refers you for tests

Severe abdominal pain ( between navel and breast bone ) during periods. Any remedy ?

I suffer from this particular ailment where during my periods I get this awful pain, that causes me to literally double up. At times it so severe that I collapse and get cold sweats and my pulse rate drops lips become white. I also suffer from Irritible Bowel Syndrome kind of symptons during this phase only - loose motions followed by constipation.I have been prescribed Meftal Spas (Mefenamic Acid & Dicyclomine HCI tablets ), along with Domperidone tabs and Omeprazole, but they just reduce the severity of the pain which remains unbearable most of the times.Incidentally this pain first started in 1996 when I was pregnant with my second child after that I get this pain only during my periods. I am 43. Any remedy anyone ?

Since the prescription meds are not helping, would you consider seeing a naturopath? There are so many homeopathic remedies and procedures that conventional medicine knows nothing about. I wish you well.

period 3 weeks late, in absolute agony..?

I AM NOT PREGNANT.
just wanted to clear that up before we start..

okay so i'm only fourteen but i started my period about 2 years ago and up until october this year i was completely regular. in october i skipped a period but then in november i was back to normal. i havent had a period this month though and after reading through a million websites i'm worrying. this is now the 51st day and i usually get my period around the 28th or 29th day.

there have been no changes to my lifestyle; i'm eating the same, sleeping in the same, and i'm under no more stress (in fact i'm probably under less).

and being a virgin, i'm certain i'm not pregnant.

also, last month i took mefenamic acid in order to lighten my period (they're usually about 9 days, this shortened it to 5) but that shouldn't have affected this months, should it?


i've also been in absolute agony for the last week and a half. last monday morning i was in so much pain i could hardly move. it's worst just below my ribs, and right down into my stomach on both sides (not to much in the middle), all the way up my back, and my neck, but pretty much every part of my body aches.

i'm planning on seeing my doctor sometime between christmas and new year, but does anyone have ANY IDEA what could be wrong with me?

thanks :]

it's normal.
young girls have to get used to it.
it will even out.
good luck :)

PCOS and Endometriosis?

I know some people here have PCOS or Endometriosis but does anyone have both of these conditions?

Im 19 and have both and would like to hear from women who have both on how they cope with it and what treatment they are receiving? Also if you know the fertility rate for women with both these conditions?

Is anyone else on as much medication as myself? I have yet to see a specialist but in the mean time my doctor has put me on the following medications to help with the symptoms:
~Dianette
~Mefenamic Acid
~Spasmonal Forte
~Lansoprazole

Does everyone get the symptoms of feeling completely exhausted; being sick or feeling sick; not wanting to eat; being in extreme pain; depression; being overweight; wanting to cry a lot?

I know that 30-40% of women with endometriosis may have difficulties in becoming pregnant and im not sure what the figure is for women with PCOS but am I right to assume that if you have both it will be extremely difficult to have children in the future?

I have endo, and have been told i will only conceive through assisted conception.

If you are the person who is suffering from the symptons you have listed then stop taking the mefanamic acid. If you have endo it doesn't work and makes you feel sick all the time. get your doctor to prescribe some decent pain killers like dihydrocodeine and anti inflammatorys like naproxen. very effectice for pain relief.

Continue reading here: Phenytoin Risk Summary

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