Gestational hypertension is becoming more common in pregnancy now, with the condition affecting around 5% of all pregnancies (Mammaro et al, 2009). Gestational hypertension is defined by NICE as a type of high blood pressure that develops in the later stages of pregnancy (after 20 weeks) and goes away within 6 weeks of the baby’s birth. (NICE 2010) This occurs when the systolic blood pressure rises above 140mmHg and the diastolic blood pressure rises above 90mmHg. According to these guidelines, there are three different different groups that a woman with hypertension could be categorised into. These are; Mild Hypertension (Blood Pressure reading of 140/90 to 149/99mmHg), Moderate Hypertension (Blood Pressure reading of 150/100 to 159/109mmHg) or Severe Hypertension (Blood Pressure reading of 160/110mmHg or higher).Mrs Smith has been seen with a blood pressure reading of 165/100mmHg in her 32nd week of pregnancy, meaning that she has developed severe gestational hypertension. This means that she will need to be given oral anti-hypertensive drugs in order to manage her condition. She will need to take this medication because of the risks that are associated with the condition. These include; pre-eclampsia, placental abruption, intrauterine growth restriction, and strokes. In this assignment I will be discussing and comparing two different anti-hypertensive drugs and the pharmacodynamics and pharmacokinetics of both, and how the medication would affect Mrs Smith and her unborn baby, as well as her infant feeding choices.The two anti-hypertensive drugs that will be discussed are Labetalol and Nifedipine, this is because they are widely and commonly used in England when treating hypertension and are deemed as safe to use during pregnancy (James, 2004) The effects of the medication and how they work, also known as the pharmacodynamics, should be explained to Mrs Smith and ensured that she understands what has been discussed with her. Labetalol is a mixed alpha and beta adrenergic antagonist which is used to treat a high blood pressure. This works by acting as an alpha and beta blocker. Beta adrenergic blocking agents work by blocking the release of the hormones adrenaline and noradrenaline, which then slows the heart rate and therefore reduces the rate at which blood is pumped around the body (British Heart Foundation, 2018). This is done by acting on the beta adrenoreceptors which are found throughout the body, for example, Beta1 receptors are found in the heart and they work by raising the heart rate and increasing the heart’s strength of contraction and contractility when stimulated, whereas the Beta2 receptors are found in the bronchioles of the lungs and the arteries of the skeletal muscles. Beta2 receptors work by increasing the diameter of the bronchioles in order to let more air in and out of the lungs when breathing, and dilating the vessels of the skeletal muscle in order to receive the increased blood flow that has been produced by the alpha and beta1 receptors when stimulated (J Upchurch 2017). Beta blockers therefore work by preventing neurotransmitters such as adrenaline and noradrenaline from reaching the beta adrenoreceptors which then prohibits vasoconstriction and decreases the heart rate, therefore decreasing the blood pressure. Beta blockers also prohibit the kidneys from producing a hormone known as angiotension II. When the amount of this hormone in the body is reduced, it allows the blood vessels to relax and widen even more which eases the blood flow and therefore reduces the blood pressure (Saotome et al 1993).Alpha blockers work by blocking the alpha receptors, these alpha receptors are found within the muscles that line the blood vessels and when they are stimulated they trigger the muscle to tighten up, therefore causing a problem for the blood to run smoothly. Alpha blockers therefore work by preventing the stimulation of the alpha receptors by noradrenaline, which means that the muscles will not be triggered to tighten up, and will stay relaxed, meaning that the blood can flow freely through the vessels and will cause the blood pressure to be maintained, or will lower the blood pressure if used when the blood pressure has peaked. As Labetalol is an alpha and beta blocker, both of the alpha and beta adrenoreceptors will be blocked (Ghanem and Movahed 2008).Nifedipine is a dihydropyridine calcium channel blocker which interferes with the inward displacement of calcium ions through the slow channels of the active cell membranes. They influence the cells within the specialised conducting system of the heart, and the vascular smooth muscle. This means that the muscle contractility may be reduced and the electrical impulses within the heart may also be depressed, which then in turn means that the power of the heart will be reduced, which then dilates the blood vessels and lets the blood flow around the body freely and therefore maintains or lowers the blood pressure (BNF 2017).Raised blood pressure is caused when the blood is not able to flow freely and the pressure in the blood vessels build up, which occurs when the muscles of the walls contract and become hard and stiff which makes it difficult for the blood to flow freely through them. Labetalol and Nifedipine therefore work to eliminate the stimulation which causes the muscles to contract and keeps the vessels dilated, and in some instances can dilate them further in order to allow the blood to flow freely and relieve some of the pressure that is being caused, therefore decreasing the blood pressure.Mrs Smith may ask to be given the information of the pharmacokinetics, which is the how the drug interacts with the body in terms of the absorption, distribution, metabolism and excretion. This information would be given to her in order to help her make an informed decision on whether she would want to take the medication or refuse where appropriate.The bioavailability of a drug is the degree to which becomes available to the target tissue after administration (The Medical Dictionary 2018).Both Labetalol and Nifedipine are absorbed in similar ways. When swallowed they are both absorbed by the digestive system through the gastrointestinal tract. They then enter the hepatic portal system, this is where the drug is then transported to the liver, where it reaches the circulatory system. Once they have passed through the liver, it causes a ‘first pass effect’ where the liver then metabolises the medicine so that the concentration of the drug is significantly reduced and passes through to the rest of the circulatory system, which then reduces the bioavailability of the drug. (Cheprasov 2018). The bioavailability of Labetalol is approximately 25%, whereas the bioavailability of Nifedipine is around 55-60%. This means that more of the active drug from Nifedipine enters the circulatory system, meaning that Nifedipine would would more efficiently than Labetalol would. The metabolism of Labetalol occurs by conjugation to glucaronide metabolites found in plasma and are excreted mostly in the urine and are also found in the faeces, which they are transported by bile, around 55-60% of the drug is found in the urine as unchanged labetalol in the first 24 hours. The metabolism of Nifedipine occurs mostly into water soluble inactive metabolites and around 60-80% is excreted in urine in the first 24 hours, with the rest being excreted in faeces as the metabolised form biliary excretion. This shows that more Labetalol is absorbed in the first 24 hours than Nifedipine, which means that more of the active ingredient from Labetalol would be used to reduce the blood pressure compared to Nifedipine in those first 24 hours (Donnelly and Macphee 1991).The half life of a drug can be defined as the period of time required for the concentration or amount of drug in the body to be reduced by one half. This refers to the amount of the drug in plasma. A drug’s plasma half-life will depend on how quickly the drug is eliminated from the plasma (Wharrad 2015). The half life of Labetalol is 8 hours, whereas the half life of Nifedipine is 2 hours. The half life can be affected by diet, other medication and also health problems. As the half life of Labetalol is longer than Nifedipine, it is able to stabilise the blood pressure for a longer period of time, Nifedipine also reduces the blood pressure at a faster rate which could potentially cause the client’s blood pressure to drop too low and cause hypotension (Kirsten et al 1998). A drugs efficiency can also be affected by how much of the drug binds to the proteins in the blood plasma. The more of the drug that binds to proteins, the less efficiently it will be able to enter the cell membranes or diffuse through them. When explaining this to Mrs Smith, it would help to tell her that 50-60% of Labetalol are bound to plasma proteins and around 98% of Nifedipine is bound to the plasma proteins, therefore showing that more Labetalol would be able to enter the cell membranes than Nifedipine would (Fischer et al 2013).As a midwife, it is important to have the correct information about how to safely administer medication and how the client should take the medication. When a drug is prescribed, the midwife needs to ensure that she knows the reason of prescription and also knows of any contraindications of taking the drug, for example, Labetalol is not advised to be taken in the first trimester of pregnancy and should not be given to asthmatics as it can cause bronchospasm as the beta 2 receptors become filled which prevents bronchodilation (Pimenta, 2010). In comparison, Nifedipine is not advised to be take by clients with angina or severe bradycardia as it is a calcium channel blocker, and they reduce the electrical conduction in the heart, which means that the cardiac cycle will be changed which could then affect the heart rhythms. (PubMed 1998). Nifedipine is also not advised in the first 20 weeks of pregnancy (Clark et al 2015).Since Mrs Smith is currently 32 weeks pregnant, she is able to be prescribed either of the medications discussed, however the prescriber of the medication will need to ensure that she has no underlying medical or health problems in order to choose the correct medication to give to her and also ensure that she is not allergic to any of the medications. When administering the medication it is necessary to check that the medication is still in date and that it has not expired, as well as explaining that it needs to be kept in a cool and dry space in order to keep the medication usable (NMC 2015).The dosages of the medication should also be considered and ensured that the dose is appropriate for the client. According to the British National Formulary (BNF 2018) the dose of Labetalol is initially 100mg twice daily, increased if needed at intervals of 14 days. The usual dose is 200mg daily, increased if necessary to a maximum of 800mg daily in 2 doses. The BNF also indicate that the standard dose of Nifedipine is 20-30mg once daily, increased to a maximum of 90mg once daily if necessary.The midwife would also have to discuss the side effects of the antihypertensive medication with the client to ensure that she understands that it is normal if she was to have an experience of any of them. The side effects of Labetalol may include intra-uterine growth restriction, neonatal hypoglycaemia and bradycardia, however, Labetalol is not known to be harmful to the baby in utero (BNF, 2018). Because there is a possibility of hypoglycaemia, the baby may need to have their blood sugars monitored. The side effects of Nifedipine are commonly dizziness, headaches, vomiting and lethargy. Nifedipine can inhibit labour should be avoided in the first 20 weeks of pregnancy. (BNF, 2017). Both Labetalol and Nifedipine can be taken after the baby is born, even when breastfeeding. This should be explained to Mrs Smith as only traceable amount of the medication goes into the breastmilk and will not have any effect on the baby. As previously stated, if the baby is at risk of having hypoglycaemia, the blood sugars of the baby may need to be monitored and the medication may need to be changed (BNF 2018).In conclusion, the purpose of this assignment was to ensure that Mrs Smith is aware that both anti-hypertensive drugs, Labetalol and Nifedipine, are safe to use in pregnancy and also after the baby has been born and if she is wanting to breastfeed her baby. Both drugs works in different ways as Labetalol is an alpha and beta blocker whereas Nifedipine is a calcium channel blocker and this therefore has an effect on the way that the client is treated. As Labetalol reduces the blood pressure at a slower rate over a longer period of time compared to Nifedipine, it is usually trialled first, however this would depend on any underlying medical conditions that the client may already have. After starting the medication the client’s blood pressure would need to be monitored in order to ensure that the drug is working effectively, and does not need to be changed, or if any dosages need to be amended. The client would then be able to give informed consent to take the medication after being given all of the information involved with taking it.
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