Systemic arterial pressures in the fetus are lower than adult values buy discount forzest 20 mg online impotence due to alcohol, whereas fetal pulmonary arterial pressures are higher than those in the adult cheap 20 mg forzest with amex impotence causes cures. Although the maternal systemic arterial pO2 is about 95 torr, the pO2 of the maternal venous side of the placenta is only about 40 torr. Furthermore, the pO2 of fetal blood does not equilibrate totally with the pO2 of maternal blood during passage through the vasculature of the placenta. Due to the higher oxygen binding affinity of fetal hemoglobin, this low pO2 corresponds to an oxygen saturation of about 70%, which is still quite low compared with the normal post- natal systemic oxygen saturation (Figure 1-2. Umbilical venous blood has the highest oxygen saturation in the fetus (70%), having just returned from the placenta (Figure 1-2). This stream of oxygenated blood is then preferentially shunted across the foremen ovale, further increasing the oxygen saturation of the blood entering the left atrium. Blood from the left atrium enters the left ventricle, and from there is delivered mostly to the upper body, brain and (via the coronary arteries) to the myocardium itself. From the right ventricle, blood is pumped via the pulmonary artery across the ductus arteriosus to the descending aorta and primarily supplies the lower body and placenta. A small portion of right ventricular blood (approximately 7%) flows from the pulmonary arteries directly into the lungs. The fetal circulation is essentially a parallel rather than a series one: the right ventricle pumps blood predominantly to the lower body; the left ventricle predominantly to the upper body. Figure 2-3 shows the actual volumes of Fetal Circulation & Congenital Heart Disease - Daniel Bernstein, M. Compare these volumes with the volumes of blood passing through the heart post- natally (Figure 2-4). This degree of right ventricular dominance is less pronounced in the human, mainly because of the much large brain size in the human requiring larger volumes of ascending aortic (and thus left ventricular blood flow). The volumes of blood ml/min/kg that flow through ejected by each ventricle and various chambers and vessels in returning to each atria are similar the late-gestation fetus. About 2/3 of the descending aorta flow goes to the placenta, whereas the rest goes to the fetal lower body. Certainly, heart rate does vary in the fetus, but there is controversy about how important are changes in stroke volume. A lesion which results in even a modest perturbation in the patterns of fetal blood flows, can markedly influence cardiac development. For example, a fetus with a moderate degree of aortic stenosis (valve narrowing) at mid-gestation will have increased resistance to filling of the left ventricle. This will result in less blood flowing across the forman ovale less blood flowing through the left ventricle during fetal development. It has long been hypothesized that normal cardiac chamber development in the fetus is dependent on normal blood flows. We can now prove this hypothesis by following such a fetus serially (from mid-gestation to term) using echocardiography. In many (but not all) cases, the left ventricle will fail to grow proportionately with the rest of the heart, resulting in severe hypoplasia of the left ventricle (hypoplastic left heart syndrome) in the newborn. As we have seen above, fetal pulmonary pressure is high while flow is low, thus fetal pulmonary vascular resistance is high compared to the adult circulation. In the next section we will see how the dramatic changes in pulmonary blood flow occurring in the perinatal period are responsible for many of the changes of the transitional circulation. Three fetal structures are critical for the maintenance of this parallel circulation: the ductus venosus, the foramen ovale, and the ductus arteriosus. The net result of the fetal flow pattern is that the more highly oxygenated and nutrient enriched (umbilical venous) blood tends to be preferentially distributed to the fetal organs which have the greatest metabolic demands: the brain and the heart. Subtle alterations in this pattern of fetal Fetal Circulation & Congenital Heart Disease - Daniel Bernstein, M. Respiratory efforts by the newborn will now cause room air (pO2 approximately 100 torr) to be inhaled while alveolar gases are expelled. Several major changes in the cardiovascular system must therefore occur in order for the transition from the placental to the pulmonary circulation to proceed. Changes also occur in the pulmonary arterial tree such that the lumina enlarge while the walls thin, although this process takes several weeks before it is fully complete. It has been shown that many factors influence pulmonary vascular tone, physical as well as hormonal. For example, expansion of the lungs alone (without altering fetal pO2) decreases pulmonary vascular resistance compared to the unventilated lung. There is then a further decrease in resistance when lung expansion is followed by ventilation of the lungs with oxygen (Fig. Since an increase in fetal alveolar pO2 (which should increase pulmonary venous pO2) can cause pulmonary vasodilation independent of increases in arterial pO2, it has been shown that diffusion of alveolar oxygen into precapillary vessels mediates the vasodilatory response. Of interest, when investigators increased fetal arterial pO2 without expansion of the lungs or Fetal Circulation & Congenital Heart Disease - Daniel Bernstein, M. There are a number of vasoactive agents which have been shown to affect the fetal pulmonary vascular bed. Vasodilators such as acetylcholine, tolazoline, bradykinin, adenosine and histamine all produce vasodilation, although repeated infusion of drugs like acetylcholine results in a diminution of the response (tachyphylaxis). Adrenomedullin, released by the adrenal gland, has also been shown to be a prominent pulmonary vasodilator in some species. The most obvious anatomic change at birth is the separation of the fetus from the placenta, however, major internal changes also occur. The umbilical vessels are sensitive to many vasoactive hormones (see below) and go into spasm, preventing blood loss; these vessels may be cannulated for approximately 7-10 days after birth, and this is often performed for resuscitating sick newborns. The vascular tone of the ductus arteriosus is also sensitive to many of the same vasoactive hormones and small molecules which alter pulmonary vascular tone, although some molecules exert opposite effects upon the pulmonary vasculature and the ductus arteriosus. For example, both bradykinin and oxygen promote ductal constriction, whereas they are pulmonary vasodilators. Prostaglandin E1 is used routinely to maintain ductal patency in infants with certain types of congenital cardiac defects (see Clinical Correlation). Ductus venosus, like the ductus arteriosus, is a vascular structure, and as soon as the placenta is removed from the circuit, it carries no flow; functional closure therefore occurs quite rapidly. Functional closure of the foremen ovale also occurs within the first few days of life, related to changes in the pressure relationships in the right and left atria, as we shall see below. However, probe patency of the foramen may continue for many years, and in up to 15% of adults. The most important physiological change at the time of birth is the abrupt fall in pulmonary vascular resistance which is associated with dilation of the pulmonary vascular bed (Figure 3-1). This is partially due to a rapid vasodilation of pulmonary vessels, however, a second component of this decrease in resistance is related to a remodeling that occurs over the first few weeks and months of life.
This agent is no longer commonly used during pregnancy because of the potential for causing a sinu- soidal heart rate pattern in the fetus (Gray et al forzest 20 mg online erectile dysfunction natural remedies. It may buy forzest 20mg fast delivery erectile dysfunction among young adults, however, cause respiratory depression with chronic maternal use in the third trimester (Regan et al. No birth defects were found among rats given high doses of this drug throughout gestation (Fujinaga et al. In epidemiological investiga- tions, the frequency of congenital anomalies was not increased among the offspring of almost 800 women who used this agent during early pregnancy (Heinonen et al. A few case reports of malformations in the offspring of mothers who utilized propoxyphene during pregnancy have been published (Golden et al. Propoxyphene is not ter- atogenic in rabbit, hamster, rat, or mouse animal models at doses 40-fold greater than the usual human dose (Buttar and Moffatt, 1983; Emmerson et al. Nonsteroidal antiinflammatory agents 159 A neonatal withdrawal syndrome (irritability, hyperactivity, tremors, high-pitched cry) was reported among newborns of mothers who used propoxyphene chronically during late pregnancy (Ente and Mehra, 1978; Klein et al. Propoxyphene is opined to be safe for breastfeeding mothers (American Academy of Pediatrics, 1994). Nalbuphine, as other narcotics, has the potential to result in neona- tal respiratory depression, fetal and neonatal addiction, fetal cardiac function alter- ations, and withdrawal symptoms in the newborn. For example, this agent was associ- ated with a sinusoidal fetal heart rate pattern, similar to that produced by alphaprodine (Feinstein et al. No studies have been published regarding use of this agent during pregnancy during the first trimester. However, according to the manufacturer, this agent was not terato- genic in animal studies. Narcotic antagonists These are agents used primarily for the treatment of central nervous system and car- diorespiratory depression secondary to narcotic agonists. No studies have been published regarding congenital anomalies among the offspring of women who took this drug in the first trimester. In experimental animal studies (hamsters, mice), the frequency of congenital anom- alies was not increased among offspring exposed to naloxone at many times the usual human dose (Geber and Schramm, 1975; Jurand, 1985). It is well known that naloxone may precipitate withdrawal symptoms in newborns whose mothers are addicted to nar- cotics, and who used very high doses of narcotics near the time of delivery. No studies have been published on congenital anomalies after exposure to naltrexone during embryogenesis. Three case series comprising reportedly nonoverlapping patients contained 31 infants whose mothers used naltrexone during the first trimester, and there were no congenital anomalies present (Hulse and O’Neil, 2002; Hulse et al. Notably, these gravidas were given naltrexone as part of a treatment regimen for heroin addiction. According to its manufacturer, this agent was shown to be embryocidal in animal studies. Independent investigators have reported no increased frequency of congenital anomalies among rats or rabbits exposed during embryogenesis. Butalbital is usually combined with aspirin or acetaminophen (with or without caffeine). The most common indication for butalbital-containing analgesic compounds is tension headaches. Barbiturate use in the first trimester was not associated with an increase in the frequency of congenital anomalies in exposed offspring. However, barbiturates have been associated with fetal dependence and newborn withdrawal symptoms when used chronically by the mother in the third trimester. Medical compounds comprised of isometheptene, dichloralphenazine and acetamino- phen (Midrin, Amidrin, Migratine) are used to treat vascular headaches or migraines. This combination is commonly used during pregnancy, but no stud- ies of the risk of congenital anomalies are available for two of the components (isometheptene, dichloralphenazine). Sumatriptan and other triptans Sumatriptan (Imitrex) is a selective 5-hydroxytryptamine receptor agonist. Among 658 infants born to women who used sumatriptan during the first trimester, the frequency of congenital anomalies was no greater than expected (Kallen and Lynger, 2001). According to its manufacturer, it has been shown to cause malformations in rabbits but was not teratogenic in rats. Using the ex vivo isolated perfused cotyledon technique, sumatriptan crossed the placenta by passive transport in the ex vivo isolated perfused cotyledon technique (Schenker et al. Promethazine, in a dose of 25 mg, is also usually given as an adjunct to prevent nausea (Table 8. Analgesia following minor procedures Several oral narcotic agents (hydrocodone, oxycodone) provide satisfactory relief for mod- erate pain associated with minor surgical procedures, such as dental procedures. Narcotic agents should not be used over a protracted period of time (more than 7 days) late in preg- nancy because of the potential for neonatal dependence or withdrawal symptoms. Headache Headaches are common during pregnancy and may increase in frequency during gesta- tion. In all headache syndromes, potential identifiable causes of headaches should be ruled out before a long-term treatment plan is implemented. Headaches are divided into two major categories: (1) tension and (2) vascular (migraine). For mild to moderate headaches, aspirin, acetaminophen, ibuprofen, or naproxen usually provide satisfactory relief. Aspirin should be avoided during pregnancy for hematologic reasons, and especially when headaches occur close to term. If other agents have failed, ibuprofen appears to pose the least risk for increased bleeding and premature ductus closure. Migraine (vascular) headaches are difficult to treat during pregnancy, and they seem to increase in frequency during gestation. The vasoconstrictive agent, ergotamine, is one of the agents used to treat migraine headaches in the nonpregnant patient; however, it is not recommended for use during pregnancy because it has (1) vasoconstrictive and (2) oxy- tocin-like actions. Propranolol at a dose of 40 mg or higher per day (several divided doses) has been effective for the treatment of some migraines in the pregnant patient, and poses a negligible risk to the unborn child. Amitriptyline, a tricyclic antidepressant, has been used to treat migraine headaches in pregnant women. However, this agent should be used as a third line of medical treat- ment for migraine headaches among pregnant women with vascular headaches who have not responded to analgesics or propranolol. The combination of isomethertene, dichloralphenazone, and acetaminophen is also used for treatment of migraine headaches during pregnancy. Importantly, this combination of drugs should be avoided in women with hypertension. The usual dose is two capsules orally at the beginning of an attack and then one capsule every hour; up to five capsules in any one 12-h period (see manufacturer’s prescribing recommendations). Sumatriptan (Imitrex) has been studied sufficiently to state that the risk of congenital anomalies following first trimester exposure is not greater than that in the general pop- ulation (Kallen and Lygner, 2001). As emphasized earlier, narcotic analgesics should not be utilized on a chronic basis for headaches because of the potential for addiction in the mother and withdrawal symp- toms in the fetus. However, narcotic analgesics may be efficacious for the treatment of an acute migraine episode with little to no risk to the fetus. Key references 163 Analgesia following operative procedures The most common indication for acute narcotic analgesic therapy is for postoperative pain relief.
Maximal decreases were noted at 7 to 15 minutes after injection purchase forzest amex impotence leaflets, but rebounded toward control levels by two to four hours after injection (131) buy 20mg forzest free shipping erectile dysfunction recovery. For example, lamotrigine clearance is decreased two- to threefold in patients also taking valproic acid (44). The maximum recommended dose of valproic acid is 60 mg/kg/day (4200 mg/day), which is equivalent to a dose of 0. Ethinylestradiol doubled the fraction of propranolol metabolized to the glucuronide without affecting total body clearance (136). Several case reports have documented an induction of methadone withdrawal symptoms upon introduction of anti- tuberculosis therapy that included rifampin. The area under the pain thresh- old–time curve (cold pressor test) was also significantly reduced by rifampin treatment. In cases where glucuronidation becomes saturated or inhibited, metabolic switching to form reactive metabolites (typically catalyzed by cytochrome P450 enzymes) can occur. This interaction was an important factor in the 1 removal of cerivastatin (Baycol ) from the market. With the availability of cloned, expressed enzymes, detailed kinetic studies of inhibitory interactions may be carried out. Induction potential may be accomplished in human hepatocytes or perhaps by utilization of a reporter gene assay similar to studies conducted with cytochrome P450 enzymes. While outside the scope of this review, interactions involving glucuronide transport may be important as well. Genetic and environmental factors associated with variation of human xenobiotic glucuronidation and sulfation. Neonatal hyperbilirubinemia and mutation of the bilirubin uridine diphosphate-glucuronosyltransferase gene: a common missense mutation among Japanese, Koreans and Chinese. Gilbert syndrome and the development of antiretroviral therapy-associated hyperbilirubinemia. Decreased glucuronidation and increased bioactivation of acetaminophen in Gilbert’s syndrome. Normal pathways for glucuronidation, sulphation and oxidation of paracetamol in Gilbert’s syndrome. Disposition of lorazepam in Gilbert’s syndrome: effects of fasting, feeding, and enterohepatic circulation. Pharmacogenetics of irinotecan: clinical perspectives on the utility of genotyping. Gefitinib enhances the antitumor activity and oral bioavailability of irinotecan in mice. Potential hazard of pharmacokinetic interactions between lopinavir-ritonavir protease inhibitors and irinotecan. A quaternary ammonium glucuronide is the major metabolite of lamotrigine in guinea pigs. Lamotrigine: single-dose pharmacokinetics and initial 1 week experience in refractory epilepsy. Extrahepatic metabolism of propofol in man during the anhepatic phase of orthotopic liver transplantation. Changes in apparent systemic clearance of propofol during transplantation of living related donor liver. Effects of combining propofol and alfentanil on ventilation, analgesia, sedation, and emesis in human volunteers. Disposition of propofol administered as constant rate intravenous infusions in humans. Evidence that tacrolimus augments the bioavailability of mycophenolate mofetil through the inhibition of mycophenolic acid glucuronidation. A comparison of the effect of ciclosporin and sirolimus on the pharmokinetics of mycophenolate in renal transplant patients. Role of Mrp2 in the hepatic disposition of mycophenolic acid and its glucuronide metabolites: effect of cyclosporine. Cyclosporine interacts with mycophenolic acid by inhibiting the multidrug resistance-associated protein 2. Rifampin induces alterations in myco- phenolic acid glucuronidation and elimination: implications for drug exposure in renal allograft recipients. Complementary deoxyribonucleic acid cloning and expression of a human liver uridine diphosphate-glucuronosyltransferase glucuronidating carboxylic acid-containing drugs. A pharmacogenetic study of uridine diphosphate-glucuronosyltransferase 2B7 in patients receiving morphine. Enhanced glucuronide conjugation of drugs in obesity: studies of lorazepam, oxazepam, and acetaminophen. Isoform-specific regulation of uridine diphosphate-glucuronosyltransferase 2B enzymes in the human prostate: differential consequences for androgen and bioactive lipid inactivation. Effect of probenecid on the formation and elimination kinetics of the sulphate and glucuronide conjugates of diflunisal. Negligible excretion of unchanged keto- profen, naproxen, and probenecid in urine. Probenecid-induced changes in the clearance of car- profen enantiomers: a preliminary study. Effect of probenecid on the formation and elimination of acyl glucuronides: studies with zomepirac. The effect of incubation conditions on the enzyme kinetics of udp-glucuronosyltransferases. Human hepatocytes as a key in vitro model to improve preclinical drug development. Sex-difference and the effects of smoking and oral contraceptive steroids on the kinetics of diflunisal. Stimulatory as well as inhibitory effects of ethinyloestradiol on the metabolic clearances of propranolol in young women. Effects of rifampicin and cimetidine on pharmacokinetics and pharmacodynamics of lamotrigine in healthy subjects. Glucuronidation of statins in animals and humans: a novel mechanism of statin lactonization. Determinants of acetaminophen metabolism: effect of inducers and inhibitors of drug metabolism on acetaminophen’s metabolic pathways. Probenecid impairment of acet- aminophen and lorazepam clearance: direct inhibition of ether glucuronide forma- tion. Lorazepam-valproate interaction: studies in normal subjects and isolated perfused rat liver. Disposition of lorazepam in human beings: enterohepatic recirculation and first-passeffect. Pharmacokinetic interaction between zidovudine and valproic acid in patients infected with human immunodeficiency virus. Gender and oral contraceptive steroids as determinants of drug glucuronidation: effects on clofibric acid elimination.
By J. Rendell. Polytechnic University of Puerto Rico. 2019.