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Naproxen and Breastfeeding

Naproxen is frequently used as an anti inflammatory and to add pain relief for instance after surgery. However, there seems to be concern about prescribing it for the breastfeeding mother. I hope this information helps.

pdf of information Naproxen and Breastfeeding factsheet

If it was useful maybe you need to buy the book?

Naproxen is an anti-inflammatory drug used more frequently since concerns were raised about long term cardiovascular risk of diclofenac. It is generally seen as more effective than ibuprofen. Concerns have been raised that its longer half life produces more of a risk to a breastfeeding baby. It is only taken twice a day at 12 hourly intervals.

Naproxen is more than 99% bound to plasma proteins. Davies and Anderson (1997) reported that although naproxen is excreted into breastmilk, the amount of drug transferred comprises only a small fraction of the maternal exposure. Relative infant dose quoted as 3.3% (Hale 2023 online access) lower than 10% regarded as compatible with breastfeeding.

 In Jamali and Stevens’ study (1983) only 0.26% of the mother’s dose was recovered from the infant and adverse effect reports are low.

 The BNF considers that the amount of naproxen distributed into breastmilk is too small to be harmful to a breastfed infant; however, some manufacturers recommend that breastfeeding should be avoided during naproxen therapy, due to licensing considerations rather than potential risk.  

References see Breastfeeding and Medication Text

Quitting Smoking During Pregnancy And Beyond


Before I start talking about quitting smoking, I want to acknowledge that it isnt easy. Nicotine is very addictive, and everyone smokes for their own reasons. Everyone has a habit they would like to break: mine is enjoying too much chocolate. To stop doing anything which you enjoy takes guts and a lot of will power. Maybe your baby is your reason to quit but it also needs to be because YOU want to not just because you have been TOLD to. I hope this information helps you but always happy to help if you want to email me wendy@breastfeeding-and-medication.co.uk

Smoking  in Pregnancy

We know that smoking during pregnancy is associated with risk factors to the baby including low birth weight at delivery, increased risk of miscarriage or stillbirth because carbon monoxide in tobacco smoke reduces the amount of oxygen getting to the placenta and the baby . There are also future risks of respiratory problems including ear, nose and throat. However as at 2020/21 9.5% of women were smoking at the time of delivery which was the lowest on record.

In a 2010 study by the  Office of National Statistics (ONS) 14% of women were smoking before pregnancy but gave up, 12% continued to smoke throughout pregnancy although 9% cut down. The study showed that 1% gave up but went back to smoking during the pregnancy.

A report published by the Royal College of Physicians in 2010 estimated that in the UK, smoking during pregnancy causes up to 5,000 miscarriages, 300 deaths around the time of birth and approximately 2,200 premature births each year.

 (taken from https://ash.org.uk/resources/view/smoking-pregnancy-and-fertility)

Why do mothers smoke during pregnancy?

Why,  might we ask, knowing that smoking during pregnancy is harmful to the baby do so few expectant mothers not quit? The answer is very simple: nicotine is extremely addictive and it is hard to break the habit of smoking. Just as overwight people know that they need to lose weight, try to diet but often return to their original weight or more.

Smoking is often linked to deprivation and women may smoke because they cannot afford to eat. If you live with someone else who smokes, you are six times more likely to smoke throughout pregnancy. Additionally, those who live with a smoker and manage to quit are more likely to relapse once the baby is born. If all your friends smoke, especially if you are younger, it is much harder to quit so peer pressure has much to answer to.

How can you stop smoking?

Over half (53%) of the women in a large 2010 study had been given information on how to stop smoking, and a third had received information on how to cut down smoking (32%) and how their partner could stop smoking (33%) but still had not quit. Maybe you have been given the information and now want to quit but have felt “nagged” into doing so when you aren’t ready?

Midwives, pharmacists, GPs  as well as smoking cessation clinics can provide nicotine replacement products. These are free on the NHS whilst you are pregnant.

In April 2023 Health Minister Neil O’Brien announced that following the success of local schemes, pregnant women will be offered financial incentives to help them stop smoking. This will involve offering vouchers, alongside behavioural support, to all pregnant women who smoke by the end of 2024.

Nicotine replacement therapy

You can use nicotine replacement therapy (NRT) during pregnancy if it will help you stop smoking and you’re unable to stop without it. It’s not recommended that you take stop smoking tablets such as Champix or Zyban during pregnancy.

Text Box: https://www.mums-can.co.uk/

Smoking cessation interventions have been shown to reduce the number of new-borns with low birth weight and preterm births. In one study, compared to ongoing heavy smoking, quitting was associated with a 299g increase in birth weight. The less a premature baby weighs at birth the more interventions it is likely to need and the longer it will stay in NICU (neonatal intensive care unit).

NRT contains only nicotine and none of the hundreds of other damaging chemicals found in cigarette smoke.  Tobacco smoke contains over 7,000 chemical compounds. NRT is a better option than continuing to smoke. It helps you by giving you the nicotine you would have had from a cigarette whilst you break the habit of reaching for a cigarette ( see below for how to break the habit of smoking).

NRT is available as:

  • Patches (The 16-hour NRT patches are preferred to the  24-hour period ones)
  • gum
  • inhalator
  • nasal spray
  • mouth spray
  • oral strips
  • lozenges
  • micro tabs

Sometimes a combination of a sustained release patch together with a rapid delivery method works well. As a pharmacist smoking cessation advisor, I often found that the people I was working with found it easier if they had something to hold in their mouths or their hands, so benefitted from an inhalator even if it didn’t contain a product.

Vaping and pregnancy

The vapour from an e-cigarette does contain some of the potentially harmful chemicals found in cigarette smoke, but at much lower levels. If using an e-cigarette helps you to stop smoking, it is much safer for you and your baby than continuing to smoke.

E-cigarettes may be more effective than nicotine patches for pregnant women trying to quit smoking, research found. One major  study did not raise any new safety concerns with e-cigarettes (vaping) in pregnancy.

Smoking and breastfeeding

  • Nicotine is found in breastmilk of mothers who smoke together with Cotinine, Cadmium, Mercury, Lead and other heavy metals, and  a lower amount of proteins, Vitamin A, C and E and other antioxidants.
  • The flavour of breastmilk collected 30-60 minutes after smoking was identified as tasting more like cigarettes than samples taken at any other time.
  • The levels of cotinine (the chemical into which nicotine is changed in the body) in the urine of breastfed babies whose mothers smoked were ten times higher than those of formula fed babies of smoking mothers.  It appears that this is due to passage through breastmilk and not through exposure to smoke in a room.
  • Babies of mothers who smoke appear to be more likely to suffer from colic.
  • Smoking appears to lower breastmilk production by reducing prolactin levels. More women who smoke believe that they have insufficient milk than non-smokers.
  • Mothers who smoke are likely to breastfeed for a shorter length of time.
  • Many women continue to smoke whilst breastfeeding perceiving that it is the only time that they have for themselves, to overcome tiredness or to reduce their appetite.
  • Passive smoking is related to early onset of wheezing although breastfeeding may reduce the severity of bronchial asthma. Research has shown that babies of mothers who smoke have three times more visits to GP with respiratory and sinus infection and allergy including asthma.
  • Research shows exposure to smoke increases the risk of cot death in babies. If the mother and father smoke the risk is multiplied by seven.
  • There have been reports linking smoking during breastfeeding with risk of obesity and endocrine dysfunction in the baby in later life.

So, there is no doubt that continuing to smoke whilst breastfeeding is harmful to your baby even if you or your partner don’t smoke in the same room as the baby, maybe even outside. Having said that breastfeeding and smoking still has benefits over not breastfeeding at all.

Behavioural Support

Behavioural support involves regular meetings with a trained person, usually a smoking cessation advisor. You are more likely to quit and remain as a non-smoker with behavioural support rather than trying to quit alone. The therapy is normally offered weekly for 4 weeks. It has also been called motivational interviewing – to help you stay motivated to quit.  Normally the level of carbon monoxide (CO)  in exhaled breath will be measured to show that you are quitting and as a positive feedback for you as you see the levels fall.

As an advisor I found on several occasions that I had a positive CO level at the end of the session, despite never having smoked, due to inhalation of second-hand smoke of the clients I was supporting many of whom had “one last cigarette” before the appointment!

How to change the habit of picking up a cigarette

We know that nicotine is highly addictive. However, with NRT there may still be a craving to pick up a cigarette at the times that you have normally smoked. These times may be a routine e.g., after a cup of coffee, after a meal. Think about where you smoke – is it always in the same place e.g., a chair you sit in, outside the kitchen door so in sight or sound of your baby but not with him/her.

 It can help to identify when these times are for you and where you tend to smoke. I recommend keeping a diary for a week during which time you can also think about why you have decided to quit – is it for your baby, for your own health, because of the cost? Is it because you think you OUGHT to or have been told you SHOULD do so. If this has happened how do you feel about that? Shoulds and oughts are often hard to maintain. Plan to stop smoking rather than making  a rapid decision on the spur of the moment, even with the best of intentions.

Decide how you can change each time you smoke – can you distract yourself for 20 minutes? This is the time it usually takes a craving to subside.  Could you wash the floor, sing a song to your baby, make everything ready for the next meal, paint your nails or something else that works for you?  If you smoke to give yourself “5 minutes peace” think about how else you could spend that time positively for you even if it is only to wee by yourself!

On the day you decide to stop, you may choose to tell everyone so that you gain their support, or you may want to keep quiet, so no-one tries to tempt you because they haven’t made their own decision. Some people just want to prove how hard it is and set you up to fail. Only you know whether your friends and family will help you or not.

I would also suggest putting the money that you would have spent on cigarettes in a savings box and at the end of 4 weeks or whatever period you decide, treat yourself to something you would have otherwise not been able to afford. Of course, you might choose that to be a family treat but remember it is also rewarding you for beating the addiction and craving. It isnt easy to give up smoking so be proud of yourself.

IF you have a cigarette one day at a point of weakness, be kind to yourself, accept the slip but carry on your intention to stop – one cigarette doesn’t mean you have failed, it is just one cigarette. Don’t stop giving up!

Have strong tasting sweets around to suck – traditionally these are mints but could be anything you like. Also have lots of healthy snacks so you don’t resort to chocolate or high calorie foods instead.

Nicotine Replacement Therapy (NRT) and Breastfeeding

  • It is safer to use nicotine replacement therapy whilst breastfeeding than to smoke.
  • Babies will be exposed to less nicotine through NRT than through smoking. Smoking produces blood levels of nicotine of 44ng/ml whilst NRT patches produce around 17 ng/ml.
  • NRT avoids exposure to the other chemical compounds in tobacco smoke.
  • Patches applied over a 24-hour period may produce vivid dreams in the mother; it might be advisable to remove the patch overnight so that the baby is exposed to less during night time feeds.
  • NRT products do not cause breastmilk to smell of cigarettes.
  • Nicotine gum produces large variations in nicotine levels whilst patches produce a sustained but lower level. If gum is used it should be chewed immediately after feeds to reduce the baby’s exposure. NRT nasal sprays similarly produce rapid high levels and may best be used after feeds.
  • Exposure of the baby to NRT products is safer than exposure to cigarettes and with appropriate support may help the mother (and ideally her partner) to quit smoking permanently.

Medications to stop smoking and breastfeeding.

These tablets are not generally advised during breastfeeding but everyone has individual needs and they might be what is right for you.

Champix™ ( Varenicline)

• Varenicline is a partial nicotine agonist used to assist smoking cessation.

• One researcher points out that based on animal data on nicotine, varenicline might interfere with normal infant lung development and recommends against its use in nursing mothers.

• Based on its long half-life, poor protein binding and small molecular weight it is anticipated to transfer to human milk.

• Because no information is available on the use of varenicline during breastfeeding, an alternate drug is preferred, especially while nursing a new-born or preterm infant.

• If used monitor the baby for changes in sleep, changes in feeding, vomiting, constipation.

• For more information https://www.ncbi.nlm.nih.gov/books/NBK501688/

Zyban ™ (Bupropion)

• Limited information indicates that maternal bupropion doses of up to 300 mg daily produce low levels in breastmilk and would not be expected to cause any adverse effects in breastfed infants.

• However, there is little reported use in breastfed new-born infants and case reports of a possible seizure in partially breastfed 6-month-olds.

• If bupropion is required by a nursing mother, it is not a reason to discontinue breastfeeding.

• However, another drug may be preferred, especially while nursing a new-born or preterm infant.

• For more information https://www.ncbi.nlm.nih.gov/books/NBK501184/

Vaping and breastfeeding

A Cochrane review has found the strongest evidence yet that e-cigarettes, also known as ‘vapes’, help people to quit smoking better than traditional nicotine replacement therapies, such as patches and chewing gums.

E-cigarettes have become very popular as a safer alternative to cigarette smoking without exposure to tobacco and substances known to cause detrimental effects including lung cancer.

It was reported that an e-cigarette produced peak blood nicotine levels of 1.3 ng/mL in 19.6 minutes, which is comparable to the levels obtained by a nicotine inhaler (2.1 ng/mL in 32 minutes) and much lower than those obtained by a conventional cigarette (13.4 ng/mL in 14.3 minutes). This study further revealed that the reduction in the desire to smoke is similar to that of a nicotine inhaler but that e cigarettes are better tolerated by users.

The amount of nicotine delivered after 10 puffs of a 16 mg e cigarette is little to none. Based on these findings, it can be concluded that the amount of nicotine that transfers into breast milk after an acute inhalation of an e-cigarette is probably minimal, and comparable to that of a nicotine inhaler.  But it is reported that an average e-cigarette user inhales up to 120 puffs/day.


Be proud of yourself – stopping smoking is not easy! Take every day as it comes and celebrate. 


  • Bullen C, McRobbie H, Thornley S, Glover M, Lin R, Laugesen M. Effect of an electronic nicotine delivery device (e cigarette) on desire to smoke and withdrawal, user preferences and nicotine delivery: randomised cross-over trial. Tob Control. 2010 Apr;19(2):98-103.
  • Eissenberg T. Electronic nicotine delivery devices: ineffective nicotine delivery and craving suppression after acute administration. Tob Control. 2010 Feb;19(1):87-88)
  • Etter JF, Bullen C. Electronic cigarette: users’ profile, utilization,satisfaction and perceived efficacy.  Addiction. 2011 Nov;106(11):2017-2028
  • Gov.UK Smokers urged to swap cigarettes for vapes in world first scheme https://www.gov.uk/government/news/smokers-urged-to-swap-cigarettes-for-vapes-in-world-first-scheme
  • NHS Digital Statistics on Women’s Smoking Status at Time of Delivery: England Quarter 4, 2020-21
  • NHS Stop smoking in pregnancy https://www.nhs.uk/pregnancy/keeping-well/stop-smoking
  • NIHR Smoking and Addiction https://evidence.nihr.ac.uk/alert/e-cigarettes-better-than-nicotine-patches-helping-pregnant-women-stop-smoking/
  • Tappin D, Sinclair L, Kee F, McFadden M, Robinson-Smith L, Mitchell A et al. Effect of financial voucher incentives provided with UK stop smoking services on the cessation of smoking in pregnant women (CPIT III): pragmatic, multicentre, single blinded, phase 3, randomised controlled trial BMJ 2022; 379 :e071522 doi:10.1136/bmj-2022-071522
  • Zhao L et al. Parental smoking and the risk of congenital heart defects in offspring: An updated meta-analysis of observational studies. 2020; RCP. Hiding in plain sight: treating tobacco dependency in the NHS. 2018; Pineless BL et al. Systematic review and meta-analysis of miscarriage and maternal exposure to tobacco smoke during pregnancy. 2014; RCP & RCPCH. Passive Smoking and Children. 2010

Migraine and breastfeeding powerpoint

I delivered this presentation for Migraine Ireland and will upload it onto YouTube but sharing the powerpoint slides for training purposes. Happy to answer any questions wendy@breastfeeding-and-medication.co.uk


Available on YouTube https://youtu.be/Lg52tht4XwU

Zuranolone (Zurzuvae™)  and Breastfeeding

Back in August 2023 I posted about a new drug Zuranolone licensed by the FDA in USA to treat perinatal depression. The course lasts just 2 weeks but the manufacturer was recommending that mothers shouldn’t breastfeed on it or for a week after.

However, this afternoon (September 2023)I was listening to a webinar by Dr Tom Hale and Dr Kaytlin Krutsch where they presented data on 15 women who took it but pumped throughout.

“The manufacturer reports minimal transfer into breast milk. The concentration of drug-in-milk quantified in the milk was not disclosed; however, the mean RID was reported as 0.357% at day 5 (dose unknown; 30 to 50 mg per day). The oral bioavailability of zuranolone is unknown, but the reported RID% would likely result in negligible infant exposure.

Zuranolone has a dose-dependent abuse potential; patients report feeling euphoric mood, feeling drunk, and somnolence with zuranolone use. Adverse effects upon discontinuing the drug in the mother may include mild-to-moderate insomnia, palpitations, decreased appetite, paranoia, hyperhidrosis, nausea, and more. For the mother, there is a risk of excessive sedation with the potential inability of the mother to assess the degree of their impairment. This was not noticed in the lactation study. Instead, patients reported mild dizziness and potential memory loss during the treatment.[Poster: An open-label study to evaluate concentrations of zuranolone in the breastmilk of healthy lactating women. Available upon request to the manufacturer. Sage Therapeutics/BioGen Inc. 2021.]

Progesterone is thought to inhibit lactation. Researchers reported the average milk volume trended 8.3% down from a mean of 526 mL on day 1 to 485 mL on day 3 to 5 (when steady-state was reached). Moms were required to exclusively pump for the trial, which may partially explain the drop in volume.”

It is recommended that the baby so exposed through milk is monitored for sedation.

see also LactMed https://www.ncbi.nlm.nih.gov/books/NBK594292/

“Because of the low amounts of zuranolone in milk, it would not be expected to cause any adverse effects in breastfed infants. If zuranolone is required by the mother, it is not a reason to discontinue breastfeeding. Until more data are available, zuranolone should be used with careful infant monitoring for excessive sedation during breastfeeding, especially with higher dosages and in newborn and preterm infants.”

“The manufacturer reports a study in 14 healthy lactating women treated with oral administration of 30 mg of zuranolone daily for 5 days. The daily infant dose was approximately 0.0013 mg/kg, resulting in a mean weight-adjusted relative infant dose of 0.357% compared to the maternal dose. Concentrations of zuranolone in breastmilk were below the level of quantification limit by 4 to 6 days after the last dose.”

To my knowledge this drug is not yet approved in the UK.

  • Mahase  E US approves daily pill for postpartum depression https://www.bmj.com/content/382/bmj.p1822
  • Perinatal depression: a neglected aspect of maternal health https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(23)01786-5.pdf
  • Deligiannidis KM, Meltzer-Brody S, Gunduz-Bruce H, et al. Effect of Zuranolone vs Placebo in Postpartum Depression: A Randomized Clinical Trial. JAMA Psychiatry. 2021;78(9):951–959.
  • Deligiannidis KM, Meltzer-Brody S, Gunduz-Bruce H, Doherty J, Jonas J, Li S, Sankoh AJ, Silber C, Campbell AD, Werneburg B, Kanes SJ, Lasser R. Effect of Zuranolone vs Placebo in Postpartum Depression: A Randomized Clinical Trial. JAMA Psychiatry. 2021 Sep 1;78(9):951-959. doi: 10.1001/jamapsychiatry.2021.1559. Erratum in: JAMA Psychiatry. 2022 Jul 1;79(7):740. Erratum in: JAMA Psychiatry. 2023 Feb 1;80(2):191. PMID: 34190962; PMCID: PMC8246337.
  • An open-label study to evaluate concentrations of zuranolone in the breastmilk of healthy lactating women. Available upon request to the manufacturer. Sage Therapeutics/BioGen Inc. 2021

Phenylephrine and Breastfeeding

I have written extensively about the use of decongestants in the past ( https://breastfeeding-and-medication.co.uk/fact-sheet/coughs-colds-flu-and-covid-when-breastfeeding and https://www.breastfeedingnetwork.org.uk/factsheet/decongestants/)

Pseudoephedrine has been shown to reduce milk supply in some women. The effect of phenylephrine on supply has not been demonstrated but use of oral decongestants is generally not advised for breastfeeding women.

 I have always recommended the use of nasal sprays as decongestants together with the use of steam inhalation as being more effective than oral medication and with no potential  impact on supply.

In September 2023 the FDA reported that oral phenylephrine is not effective at relieving nasal stuffiness. It is important to note that neither FDA nor the Non-prescription Drug Advisory Committee raised concerns about safety issues with use of oral phenylephrine at the recommended dose. (https://www.fda.gov/drugs/drug-safety-and-availability/fda-clarifies-results-recent-advisory-committee-meeting-oral-phenylephrine).

According to one USA website the evidence for efficacy was first questioned in 2007. The manufacturers have cited a survey that many people find its use beneficial as shown by sales volume of cough and cold products.

The vote that formally declared phenylephrine ineffective was in line with a review of pharmacology and clinical data presented by the FDA, which found the oral bioavailability of the drug is less than 1%, compared with 38%, a number often cited in the literature and based on outdated technology. (Medscape https://www.medscape.com/viewarticle/996369).

There appears to be no current UK recommendations although I am sure there is current discussion. Most oral cough and cold remedies currently contain phenylephrine as pseudoephedrine  sales have been restricted.   Between 2007 and 2008, the government introduced restrictions on their use because of concern that medicines containing these active substances could be used in the illicit manufacture of the Class A controlled drug methylamphetamine https://www.gov.uk/drug-safety-update/pseudoephedrine-and-ephedrine-update-on-managing-risk-of-misuse#:~:text=Sales%20restrictions,-Since%20April%202008&text=It%20is%20illegal%20to%20sell,mg%20ephedrine%20without%20a%20prescription

This information has been compiled from a variety of sources and does not imply recommendation other than that nasal decongestants and steam inhalation are effective in reducing symptoms of nasal congestion during breastfeeding without potential impact on supply. Most of us have our own preferred remedies which we find effective and that remains a personal choice

Rimegepant (Vydura™)  and Breastfeeding

Rimegepant (Vydura ™) is indicated for adults who have at least 4 migraine attacks per month but less than 15. It is taken as a wafer which dissolves under the tongue. It works by stopping the release of a protein around the brain that is responsible for the severe pain associated with migraine attacks.

It is recommended as an option for preventing episodic migraine in adults where at least 3 previous preventive treatments have failed (NICE May 2023)

In a study by Baker et al (2022) 12 breastfeeding mothers aged 18-40 years provided plasma and breastmilk samples over a 36 hour period.

It is highly protein bound 96%, with an oral bioavailability 64%, and milk plasma ratio 0.2. On a weight-adjusted basis, infants received an estimated dose that was approximately 0.51% of the maternal dose (Hale).


  • Baker TE, Croop R, Kamen L, Price P, Stock DA, Ivans A, Bhardwaj R, Anderson MS, Madonia J, Stringfellow J, Bertz R, Coric V, Hale TW. Human Milk and Plasma Pharmacokinetics of Single-Dose Rimegepant 75 mg in Healthy Lactating Women. Breastfeed Med. 2022 Mar;17(3):277-282

Fremanezumab (Ajovy™)  and Breastfeeding

Fremanezumab is a humanised monoclonal antibody that binds to the calcitonin gene-related peptide (CGRP) ligand, inhibiting the function of CGRP at its receptor, and thereby preventing migraine attacks (BNF). It is given as a sub cutaneous injection of 225 mg once a month, alternatively 675 mg every 3 months.

Fremanezumab is recommended for patients who have 4 or more migraine days a month and for whom at least 3 preventive drug treatments have failed and the drug is supplied by the company under a commercial agreement agreed with NICE. It is unclear if fremanezumab works better than botulinum toxin type A (NICE)

It has a molecular weight of 148,000 and assumed low oral bioavailability. However, there are no studies in breastfeeding mothers and babies although any passing into milk  is presumed to be destroyed in the infant gut (LactMed)


GP Presentation

Sharing a presentation which was given to GPs in the south west. Hopefully it is useful for professionals wanting to know more about prescribing for breastfeeding mothers

Timing of breastfeeds if taking medication

I keep getting emails/ Facebook messages that mothers have been advised to pump and dump their breastmilk for a period of time after taking medication in order to minimise / prevent exposure of the baby to the drug. This has often been undertaken when the drug is compatible with breastfeeding and resulted in the unnecessary exposure of the baby to formula milk.

For most drugs taken for more than 3 days the amount in milk is constant across 24 hours. So timing feeds with respect to breastfeeding or dumping of the breastmilk is pointless. The half life of a drug is very important but just one of the factors in determining the compatibility with normal breastfeeding. If you want to know more please consider buying “Breastfeeding and Medication”

pdf of information Timing of medication and breastfeeds

Timing of drugs with respect to medication does not help to minimise levels to which babies are exposed in chronic conditions. Although the time to maximum level is often quoted, drugs reach a steady state 3-5 days after therapy begins and the levels then remain constant across the 24-hour period. Just as it takes approximately 5 half- lives for a drug to leave the body totally, it takes 5 half-lives to reach steady state. Before this time the levels increase gradually with every dose until they reach this point. Trying to time feeds disrupts normal breastfeeding and may result in engorgement with no benefit in milk levels to which the baby will be exposed. See Fig  1 below

Fig 1 accumulation of drug until it reaches steady state after 5 half lives (here taken to be 24 hours)

The half-life of a drug defines how long it takes to reach steady state and also how long it takes for it to be totally cleared from the mother’s body and milk. Five half-lives are taken as the closest measure in both cases.

Fig 2 Percentage of drug left where half-life is 24 hours

If the half-life of the drug is more than 24 hours the level may begin to accumulate in the baby’s body and be more likely to produce adverse effects e.g. diazepam half-life 43 hours.   Drugs with short half lives are preferred during breastfeeding. In  general long acting / slow release formulations are better avoided if possible.

Fig 2 Percentage of drug left where half-life is 24 hours

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