By C. Gunock. Ohio University.
Other adverse reactions include bruising order 20 mg omeprazole otc, hematoma formation buy generic omeprazole 20 mg, necrosis of skin or other tissue generic 10mg omeprazole otc, and thrombocytopenia omeprazole 10 mg overnight delivery. Drug interactions • Because heparin acts synergistically with all oral anticoagu- lants, the risk of bleeding increases when the patient takes both drugs together. Another reason to quit • Drugs that antagonize or inactivate heparin include antihista- mines, cephalosporins, digoxin, neomycin, nicotine, nitroglycerin, penicillins, phenothiazines, quinidine, and tetracycline. It binds extensively to plasma albumin and is metabo- absorbed quickly, it lized in the liver and excreted in urine. Although warfarin is ab- can take a couple of sorbed quickly, its effects don’t occur for about 48 hours, with the days for their full full effect taking 3 to 4 days. Because warfarin is highly plasma-protein-bound and is metab- olized by the liver, administration of warfarin with other medica- tions may alter the amount of warfarin in the body. This may in- crease the risk of bleeding or clotting, depending upon the med- ications administered. However, clotting factors already in the blood- stream continue to coagulate blood until they become depleted, so anticoagulation doesn’t begin immediately. Patients with this disorder begin taking the medication while still receiving heparin. However, outpatients at high risk for thromboembolism may begin oral anticoagulants without first re- ceiving heparin. To decrease the risk of arterial clotting, oral anticoagulants warfarin levels are sometimes combined with an antiplatelet drug, such as as- pirin, clopidogrel, or dipyridamole. Patients taking warfarin need close monitoring of Drug interactions prothrombin time and In- ternational Normalized Many patients who take oral anticoagulants also receive other Ratios to make sure they drugs, placing them at risk for serious drug interactions. Examples include acetaminophen, allopurinol, amiodarone, If laboratory results fall cephalosporins, cimetidine, ciprofloxacin, clofibrate, danazol, dia- outside the accepted zoxide, disulfiram, erythromycin, fluoroquinolones, glucagon, he- range, warfarin dosage parin, ibuprofen, isoniazid, ketoprofen, methylthiouracil, metron- should be adjusted. Examples include barbiturates, carba- Adverse mazepine, corticosteroids, corticotropin, mercaptopurine, naf- cillin, hormonal contraceptives containing estrogen, rifampin, reactions spironolactone, sucralfate, and trazodone. The primary adverse re- Other interactions include the following: action to oral anticoagu- • A diet high in vitamin K reduces the effectiveness of warfarin. Acute alcohol intoxication increases the ing can occur, however, risk of bleeding. Necrosis or Aspirin, clopidogrel, dipyridamole, sulfinpyrazone, and ticlopi- gangrene of the skin and dine are examples of oral antiplatelet drugs. Quick fix The effects of oral anti- Pharmacokinetics coagulants can be re- When taken orally, antiplatelet drugs are absorbed very quickly versed with phytona- and reach peak concentration in 1 to 2 hours. Sulfinpyra- zone may require several days of administration before its anti- platelet effects occur. The effects of these drugs occur within 15 to 20 minutes of administration and last about 6 to 8 hours. Elderly patients and patients with renal failure may have de- creased clearance of antiplatelet drugs, which would prolong the antiplatelet effect. It lengthens platelet survival and prolongs the patency of arteriovenous shunts used for hemodialysis. Salve for surgery Dipyridamole is used with a coumarin compound to prevent thrombus formation after cardiac valve replacement. Adverse reactions to antiplatelet drugs Hypersensitivity reactions, particularly anaphylaxis, can occur. Tales of toxicity • Aspirin increases the risk of toxicity of methotrexate and val- proic acid. You just don’t know Because guidelines haven’t been established for administrating ticlopidine with heparin, oral anticoagulants, aspirin, or fibrinolyt- ic drugs, these drugs should be discontinued before ticlopidine therapy begins. Pharmacokinetics Direct thrombin inhibitors are typically administered by continu- ous I. They may also be given as an intra-coronary bo- lus during cardiac catheterization. In that case, the drug begins acting in 2 minutes, with a peak response of 15 minutes and a du- ration of 2 hours. In patients with heparin-induced thrombocytopenia, platelet count recovery becomes apparent within 3 days. Bivalirudin and lepirudin are metabolized by the liver and kidneys and excreted in urine Pharmacodynamics Direct thrombin inhibitors interfere with blood clotting by directly blocking all thrombin activity. These drugs offer several advan- tages over heparin: direct thrombin inhibitors act against soluble as well as clot-bound thrombin (thrombin in clots that have al- ready formed); their anticoagulant effects are more predictable than those of heparin; and their actions aren’t inhibited by the platelet release reaction. Also, the dosage of bivalirudin and lepirudin may need Adverse to be reduced in patients with impaired renal function.
The distribution coeffcient order omeprazole 40 mg line, D discount omeprazole 20 mg visa, is the ratio of the sum of the con- centrations of all forms of the compound between n-octanol and water generic 10mg omeprazole mastercard. Thus discount omeprazole 10mg mastercard, while log P only considers the unionized form of the compounds, log D takes into account both ionized and unionized forms of the compound. It is noteworthy that, as with log P values , pKa values  can also be mathematically predicted. Once the drug enters the bloodstream, it encounters a differ- ent pH environment of about 7. To account for acidic and basic compounds, the difference between the fractions of the neutral form at pH 6. Compounds with positive Δlog D values are acidic, whereas compounds with negative values are basic. Acidic compounds tend to have better bioavailability characteristics, because in the acidic pH 6. In other words, acidic compounds have a lower risk than basic compounds of entering the liver and being degraded. As another beneft for slightly acidic drugs, highly ionized drugs, either acidic or basic, may also cause patient discomfort due to direct irritation of the gastrointesti- nal lining. Taken together what we have discussed, slightly acidic drugs are favored for improved gastrointestinal absorption, less frst-pass metabolism, and less mucosal irritation. In general, hydrophobic compounds are often favored for pharmacological activity over hydrophilic compounds due to desolvation entropy . Simply put, a hydropho- bic compound is more entropically favored to release water molecules before binding to the often hydrophobic active site of the target biological substance. Hydrophobic compounds need to spend less energy to part with water because they have fewer interactions with water. Interestingly, compounds with high hydrogen bond poten- tials can interact with water and would thus exhibit unfavored desolvation entropy. Hence, lipophilicity is pre- ferred in both pharmacodynamics and pharmacokinetics. One of the goals of rational drug design is to optimize lipid solubility for membrane permeation while retaining a signifcant pharmacological activity. However, simply increasing the lipid solubility of a drug may have undesired effects such as decreasing water solubility and bioavail- ability, increasing plasma protein binding with a high affnity, and increasing uptake by the liver and spleen macrophages. Such inad- vertent binding delays and prevents the drug from reaching its target site of action. Hence, the less bound a drug is, the more effciently it can traverse cell membranes. Acidic and neutral drugs will primarily bind to albumin, which is basic, or to lipopro- tein when albumin becomes saturated. Only the unbound drug exhibits pharmacologic effects, is metabolized and is excreted. Generally speaking, protein binding should be minimized to reduce unpre- dictable pharmacokinetic factors. The activity of a thrombin inhibitor is lower if it has high plasma protein bind- ing . Dabigatran is a univalent direct thrombin inhibitor that was derived from a peptide drug. In the design of dabigatran, a carboxylate function was purposely imple- mented to increase hydrophilicity, which would decrease plasma protein binding and increase inhibitory activity (Figure 8. The carboxylate function was attached such that it would not greatly affect the interactions between the drug and the target enzyme, thrombin. Indeed, for certain cases, a fne tuning of a drug design could potentially reduce plasma protein binding. This high protein binding decrease drug effcacy, and a larger quantity of the drug would need to be given to compensate. This increase in pill burden subsequently introduces risks of adverse drug reactions, compliance, and cost issues. Hence, despite its lower plasma protein binding profle, hepatic metabolism of indinavir greatly reduces its biological half-life to an impractical 2 h. The fne balance between plasma protein binding and hepatic metabolism has yet to be resolved. However, one should recall that a hydrophilic drug also tends to have higher clearance than a lipophilic drug, which has higher membrane permeability (Section 8. Of course, the choice of salt form for ionized compounds would affect the extent of solubilization. It should be noted that the water solubility factor has already been taken into account by the distribution coeffcient, because water solubility correlates well with log D6. Moreover, one should not forget that from a very simplistic viewpoint, the word “hydrophilic” suggests that the compound would “love to be in water. A way of improving water solubility in a peptide drug is to introduce a water solubilization moiety.
Menadione can be prepared by oxidizing 2-methylnaphthalene with chromic acid or hydrogen peroxide (Weber & Rüttimann purchase 20 mg omeprazole mastercard, 1996) generic omeprazole 40 mg overnight delivery. A process based on biotechno- logical techniques has been reported in Japan (Van Arnum order 10mg omeprazole visa, 1998) cheap omeprazole 40mg. Menadione sodium bisulfite can be prepared by reacting menadione with sodium bisulfite. The compound readily regenerates menadione on treatment with mild alkali and behaves as a typical ketone–sodium bisulfite addition compound (Gennaro, 1985; Van Arnum, 1998). Menadiol sodium phosphate can be prepared by reducing menadione to the diol, followed by double esterification with hydriodic acid, metathesis of the resulting 1,4- diiodo compound with silver phosphate and neutralization of the bis(dihydrogen phosphate) ester with sodium hydroxide (Gennaro, 1995). The modification is catalysed by a micro- somal enzyme called γ-glutamyl or vitamin K-dependent carboxylase, which is present in most tissues. The best-known vitamin K-dependent proteins are those synthesized in the liver, which play a role in the maintenance of normal haemostasis. Vitamin K-dependent proteins, of uncertain function, are also known to occur in a variety of other tissues such as bone, kidney, pancreas, placenta, spleen and lungs. They include the bone protein osteocalcin (also called bone Gla protein) and matrix Gla protein; there is growing evidence that these proteins may be important for bone health and other regulatory functions in calcium metabolism. Naturally occurring phylloquinone and menaquinones all γ-carboxylate the vitamin K-dependent coagulation proteins. Synthetic forms of menadione (and related water-soluble salts) that lack a side-chain at the 3-position have biological activity in vivo only after side-chain alkylation, which results in the specific synthesis of menaquinone-4 (Suttie, 1991; see also section 4). Neonates are born with very limited vitamin K stores, but most infants do not show relevant hypoprothrombinaemia at birth (von Kries et al. Biochemical signs of vitamin K deficiency are common during the first week of life, however, unless sufficient amounts of vitamin K are ingested. The natural diet of newborns is human milk, which contains vitamin K at concentrations of 0. This condi- tion was originally called ‘classical haemorrhagic disease of the newborn’; the present nomenclature is ‘classical vitamin K deficiency bleeding’ (Sutor et al. During the first three months of life, exclusively breast-fed infants remain at risk for vitamin K deficiency bleeding. In many of these infants, the bleeding episode, which is often intracranial haemorrhage, is the first perceived symptom of an under- lying cholestatic disease. In 10–30% of the cases, however, no underlying disease can be found (von Kries et al. After the first three months of life, vitamin K deficiency is almost completely confined to patients with cholestatic diseases (congenital or acquired obstruction of the bile duct), malabsorption syndromes or cystic fibrosis (Houwen et al. The predominant patterns were to give either selective intramuscular prophylaxis only to infants presumed to be at special risk for bleeding (mainly premature and low-birth-weight Table 1. In the early 1950s, water-soluble menadiol sodium phosphate was widely used, until haemolysis due to high doses of this preparation in neonates was identified (Meyer & Angus, 1956). In most countries, phylloquinone has been used since that time, although in some third-world countries water-soluble menadione sodium bisulfite still seems to be used (Sharma et al. Because it is technically difficult to dissolve phylloquinone, only a limited number of preparations became available. The Roche preparation (Konakion®) in which Cremo- phor (polyethoxylated castor oil) is used as an emulsifying vehicle has been widely available in Europe and North America. In Japan, an oral preparation of menaquinone-4 is used instead of phylloquinone (Hanawa, 1992). Almost all cases of vitamin K deficiency bleeding can be prevented by intramuscular administration of 1 mg of vitamin K at birth (von Kries & Hanawa, 1993). Clinical obser- vations and laboratory investigations have also clearly shown that a single oral dose of vitamin K protects against classical vitamin K deficiency bleeding (Clark & James, 1995) but is less effective for prevention of this condition later in life (Tönz & Schubiger, 1988; Ekelund, 1991). Without vitamin K prophylaxis, the incidence of late vitamin K deficiency bleeding in Europe was estimated to be 40–100 per million livebirths, whereas in Asia the condition appears to be considerably more common (Hanawa, 1992; Choo et al. Since intramuscular vitamin K prophylaxis has proven effective against late defi- ciency bleeding, 1 mg of vitamin K at birth was recommended in most western countries (von Kries, 1991). After reports of a potential association between vitamin K prophylaxis and the risk for childhood cancer (Golding et al. In most cases, however, vitamin K deficiency is detectable only by measuring the plasma concentrations of vitamin K or with sensitive biochemical markers of vitamin K deficiency (Cornelissen et al. Additional risk factors, such as therapy with antibiotics that interfere with vitamin K metabolism, may cause bleeding in patients with cystic fibrosis (Nowak et al. Some patients with this disease are given vitamin K supplements, although there are no uniform recom- mendations (Durie, 1994). Mothers on antiepileptic drugs, for example, are at high risk of delivering an infant with manifest vitamin K deficiency (Cornelissen et al. Hypoprothrombinaemia may be caused by some cephalosporins, especially those containing an N-methylthiotetrazole side-chain, and may require vitamin K supple- mentation (Breen & St Peter, 1997). A tendency to bleed is also increased by individual susceptibility to one of these anticoagulants, interference with other drugs or poor dietary intake of vitamin K.