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Bella 1 Capsule (Bupropion HCl / Phentermine HCl / Topiramate / Naltrexone HCl / Methylcobalamin) (Slow Release) (Each)
Bella 2 Capsule (Bupropion HCl / Phentermine HCl / Topiramate / Naltrexone HCl / Methylcobalamin) (Slow Release) (Each)
Bella 3 Capsule (Bupropion HCl / Caffeine / Oxytocin / Topiramate / Naltrexone HCl / Methylcobalamin) (Each)
Bella 4 Capsule (Bupropion HCl / Phentermine HCl / Topiramate / Naltrexone HCl / Methylcobalamin) (Slow Release) (Each)
Bella 5 Capsule (Bupropion HCl / Naltrexone HCl / Topiramate)(Each)
Bella Decaf Capsule (Bupropion HCl / Oxytocin / Topiramate / Naltrexone HCl / Methylcobalamin) (Each)
Bella Plus Capsule (Bupropion HCl / Caffeine / Metformin / Oxytocin / Topiramate / Naltrexone HCl / Methylcobalamin) (Each)
Bella Plus Decaf Capsule (Bupropion HCl / Metformin / Oxytocin / Topiramate / Naltrexone HCl / Methylcobalamin) (Each)
Bupropion HCl
The aminoketone class of oral antidepressants includes bupropion. It has no relation to other recognized antidepressants and is not a tricyclic antidepressant. Bupropion has been well tolerated in individuals using tricyclic antidepressants for orthostatic hypotension; nonetheless, it has a higher risk of producing seizures than other antidepressants. Bupropion is also indicated for use as an aide to smoking cessation, and is used off-label for addiction to smokeless tobacco. The drug has been shown to help people with COPD quit smoking when combined with behavior modification. Bupropion is also used off-label for multiple neurological/psychological uses, including ADHD and neuropathic pain. Bupropion hydrochloride was originally approved by the FDA in December 1985 but was removed from marketing for several years due to concern over drug-induced seizures. It was reintroduced in July 1989 as an antidepressant (i.e., Wellbutrin), and later in a sustained-release formulation (i.e., Wellbutrin SR). Another sustained-release oral dosage form, Zyban, was approved for the management of smoking cessation in May 1997. Zyban received an additional indication for use in combination with nicotine transdermal systems (NTS) for treating the symptoms of smoking cessation in 1999. A controlled-release formulation (Wellbutrin XL) was approved in August 2003 as a once-daily formulation for major depression in adults. In June 2006, Wellbutrin XL was FDA-approved for prevention of major depressive episodes in patients with a history of seasonal affective disorder (SAD). Wellbutrin XL is the first prescription product approved for patients with a history of SAD. In April 2008, a once-daily formulation of bupropion hydrobromide (Aplenzin) was approved by the FDA for depression, and in August 2012 Aplenzin was approved for the prevention of seasonal major depressive episodes in patients with SAD. Aplenzin differs from all previously marketed formulations which are the hydrochloride salt of bupropion.
Phentermine HCl
Phentermine is an oral sympathomimetic amine used as an adjunct for short-term (e.g., 8—12 weeks) treatment of exogenous obesity. The pharmacologic effects of phentermine are similar to amphetamines. Phentermine resin complex was approved by the FDA in 1959, but is no longer marketed in the US. Phentermine hydrochloride was FDA approved in 1973. In the mid-90s, there was renewed interest in phentermine in combination with another anorectic, fenfluramine, for the treatment of obesity and substance abuse, however, little scientific data support this practice. On July 8, 1997, the FDA issued a ‘Dear Health Care Professional’ letter warning physicians about the development of valvular heart disease and pulmonary hypertension in women receiving the combination of fenfluramine and phentermine; fenfluramine was subsequently withdrawn from the US market in fall of 1997. Use of phentermine with other anorectic agents for obesity has not been evaluated and is not recommended. In May 2011, the FDA approved a phentermine hydrochloride orally disintegrating tablet (Suprenza) for the treatment of exogenous obesity.
Topiramate
Topiramate is an oral antiepileptic drug (AED) used for partial-onset, generalized primary tonic-clonic seizures, and as an adjunct therapy in Lennox-Gastaut syndrome. It is derived from the naturally occurring monosaccharide D-fructose and is structurally different from other AEDs. Unlike other AEDs, topiramate appears to block the spread of seizures rather than raise the seizure threshold. Topiramate possesses more than one mechanism of action, which may explain why it can be effective in patients with various seizures that are refractory to other agents. Topiramate continues to be studied as both add-on therapy and monotherapy in various refractory epilepsies in children and adults, including infantile spasms associated with West syndrome. It is also used for migraine prophylaxis in adult and pediatric patients. There is some evidence of a role for topiramate treatment ‘off-label’ for eating disorders such as binge-eating disorder, for tics due to Tourette’s syndrome or other chronic tic disorders, or for substance abuse disorders such as alcohol dependence.
Naltrexone HCl
Naltrexone is an oral opiate receptor antagonist. It is derived from thebaine and is very similar in structure to oxymorphone. Like parenteral naloxone, naltrexone is a pure antagonist (i.e., agonist actions are not apparent), but naltrexone has better oral bioavailability and a much longer duration of action than naloxone. Clinically, naltrexone is used to help maintain an opiate-free state in patients who are known opiate abusers. Naltrexone is of greatest benefit in patients who take the drug as part of a comprehensive occupational rehabilitative program or other compliance-enhancing program. Unlike methadone or LAAM, naltrexone does not reinforce medication compliance and will not prevent withdrawal. Naltrexone has been used as part of rapid and ultrarapid detoxification techniques. These techniques are designed to precipitate withdrawal by administering opiate antagonists. These approaches are thought to minimize the risk of relapse and allow quick initiation of naltrexone maintenance and psychosocial supports. Ultrarapid detoxification is performed under general anesthesia or heavy sedation. While numerous studies have been performed examining the role of these detoxification techniques, a standardized procedure including appropriate medications and dose, safety, and effectiveness have not been determined in relation to standard detoxification techniques. Naltrexone supports abstinence, prevents relapse, and decreases alcohol consumption in patients treated for alcoholism. Naltrexone is not beneficial in all alcoholic patients and may only provide a small improvement in outcome when added to conventional therapy. The FDA approved naltrexone in 1984 for the adjuvant treatment of patients dependent on opiate agonists. FDA approval of naltrexone for the treatment of alcoholism was granted January 1995. The FDA approved Vivitrol, a once-monthly intramuscular naltrexone formulation used to help control cravings for alcohol in April 2006, and then in October 2010, the FDA approved Vivitrol for the prevention of relapse to opioid dependence after opioid detoxification.
Methylcobalamin
Methylcobalamin, or vitamin B12, is a B-vitamin. It is found in a variety of foods such as fish, shellfish, meats, and dairy products. Although methylcobalamin and vitamin B12 are terms used interchangeably, vitamin B12 is also available as hydroxocobalamin, a less commonly prescribed drug product (see Hydroxocobalamin monograph), and methylcobalamin. Methylcobalamin is used to treat pernicious anemia and vitamin B12 deficiency, as well as to determine vitamin B12 absorption in the Schilling test. Vitamin B12 is an essential vitamin found in the foods such as meat, eggs, and dairy products. Deficiency in healthy individuals is rare; the elderly, strict vegetarians (i.e., vegan), and patients with malabsorption problems are more likely to become deficient. If vitamin B12 deficiency is not treated with a vitamin B12 supplement, then anemia, intestinal problems, and irreversible nerve damage may occur.
The most chemically complex of all the vitamins, methylcobalamin is a water-soluble, organometallic compound with a trivalent cobalt ion bound inside a corrin ring which, although similar to the porphyrin ring found in heme, chlorophyll, and cytochrome, has two of the pyrrole rings directly bonded. The central metal ion is Co (cobalt). Methylcobalamin cannot be made by plants or by animals; the only type of organisms that have the enzymes required for the synthesis of methylcobalamin are bacteria and archaea. Higher plants do not concentrate methylcobalamin from the soil, making them a poor source of the substance as compared with animal tissues.
Caffeine
Caffeine is a naturally occurring xanthine derivative used as a CNS and respiratory stimulant, or as a mild diuretic. Other xanthine derivatives include the bronchodilator theophylline and theobromine, a compound found in cocoa and chocolate. Caffeine is found in many beverages and soft drinks. Caffeine is often combined with analgesics or with ergot alkaloids for the treatment of migraine and other types of headache. Caffeine is also sold without a prescription in products marketed to treat drowsiness, or in products for mild water-weight gain. Caffeine was first approved by the FDA for use in a drug product in 1938. Clinically, it is used both orally and parenterally as a respiratory stimulant in neonates with apnea of prematurity. Caffeine reduces the frequency of apneic episodes by 30—50% within 24 hours of administration. Caffeine is preferred over theophylline in neonates due to the ease of once per day administration, reliable oral absorption, and a wide therapeutic window. A commercial preparation of parenteral caffeine, Cafcit®, was FDA approved for the treatment of apnea of prematurity in October 1999, after years of availability only under orphan drug status (e.g., Neocaf). The FDA has continued the orphan drug status of the approved prescription formulation.
Oxytocin
Endogenous oxytocin is a hormone secreted by the supraoptic and paraventricular nuclei of the hypothalamus and stored in the posterior pituitary. It stimulates contraction of uterine smooth muscle during gestation and causes milk ejection after milk has been produced in the breast. Oxytocin has been associated with mating, parental, and social behaviors. Oxytocin is released during intercourse in both men and women, which has led to the belief that it is involved in sexual bonding. There is speculation that in addition to facilitating lactation and the birthing process, the hormone facilitates the emotional bond between mother and child. Oxytocin has also been studied in autism and have some sort of relation to the social and developmental impairments associated with the disease. Clinically, oxytocin is used most often to induce and strengthen labor and control postpartum bleeding. Intranasal preparations of oxytocin, used to stimulate postpartum milk ejection, are no longer manufactured in the U.S. Oxytocin was approved by the FDA in 1962.
Metformin
Metformin is an oral biguanide antidiabetic agent similar to phenformin, a drug that was withdrawn from US marketing in 1977 due to the development of lactic acidosis. The risk for this adverse reaction is considerably lower with metformin, however. The actions of metformin differ from, yet complement, those of the sulfonylureas and other antidiabetic therapies. Compared to glyburide in type 2 diabetes, metformin was found to achieve similar glycemic control. although it lead to a higher incidence of digestive complaints. Metformin has been found useful in the treatment of polycystic ovary syndrome (PCOS); it lowers serum androgens and restores normal menstrual cycles and ovulation, and may improve pregnancy rates. Additionally, limited data indicate that it may delay puberty onset in females with precocious puberty and delay menarche onset in females with early-normal onset of puberty. The use of metformin versus intensive lifestyle modification in patients with impaired glucose tolerance has been investigated, and while both reduce the incidence of diabetes, lifestyle intervention has the greater effect. Although lifestyle intervention is highly effective, most patients fail lifestyle modifications when used alone within the first year of diagnosis. Therefore, a joint consensus algorithm for the treatment of type 2 diabetes mellitus, developed by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes, suggests that the combination of metformin with lifestyle interventions should be initiated at the time of diagnosis. Metformin was chosen as the initial drug therapy based on its efficacy, safety, and cost. Additionally, in a follow-up study to the UKPDS, researchers found that after 10-years of resuming typical care, patients originally randomized to metformin therapy had a 33% relative reduction (RR 0.67, 95% CI 0.51—0.89; p=0.005) in the risk of myocardial infarction and a 27% relative reduction (RR 0.73, 95% CI 0.59—0.89; p=0.002) in the risk of death from any cause as compared to patients originally randomized to conventional therapy; it should be noted that these reductions in cardiovascular risks persisted even though HbA1c concentrations were similar in the 2 groups after 1 year of follow-up. Metformin was introduced in Europe in the 1950’s but was not approved by the FDA until December 1994. It is approved for type 2 diabetes either as monotherapy or in combination with sulfonylureas, alpha-glucosidase inhibitors, or insulin. The regular-release tablets were approved for use in children >= 10 years in January 2001. An oral solution (Riomet) was approved in September 2003. Three extended-release formulations have been approved, Glucophage XR in October 2000, Fortamet in April 2004, and Glumetza in June 2005, each with a unique drug delivery system (see Pharmacokinetics section). The extended-release formulations provide similar glycemic control compared to regular-release metformin, but have the advantage of once-daily administration. Another advantage is a claim of decreased adverse events, specifically gastrointestinal-related adverse events (i.e., flatulence, diarrhea); however, larger trials comparing regular-release to extended-release metformin are needed to confirm these claims as current trial results are conflicting.
Bupropion HCl
The action of bupropion is not fully understood. Bupropion selectively inhibits the neuronal reuptake of dopamine and is significantly more potent than either imipramine or amitriptyline in this regard. Actions on dopaminergic systems, however, require doses higher than those needed for a clinical antidepressant effect. The blockade of norepinephrine reuptake at the neuronal membrane is weaker for bupropion than for tricyclic antidepressants. CNS-stimulant effects are dose-related. Bupropion does not inhibit monoamine oxidase or the reuptake of serotonin. Bupropion does exhibit moderate anticholinergic effects, and produces a sensation of mild local anesthesia on the oral mucosa. Antidepressant activity is usually noted within 1—3 weeks of initiation of bupropion treatment; full effects may not be seen until 4 weeks of therapy.
The mechanism by which bupropion enhances the ability to abstain from tobacco smoking is unknown, but is probably related to inhibition of noradrenergic or dopaminergic neuronal uptake. The resultant increase in norepinephrine may attenuate nicotine withdrawal symptoms. Increased dopamine at neuronal sites may reduce nicotine cravings and the urge to smoke. Because the onset of activity is usually after 1 week of treatment, patients should start bupropion 1—2 weeks prior to their chosen smoking ‘quit-day’. In smoking cessation, the ability to abstain from smoking continuously through the seventh week of bupropion therapy is associated with maintenance of long-term abstinence. Patients who have not stopped smoking by the seventh week of treatment are generally considered non-responsive to bupropion treatment.
Phentermine HCl
Limited data are available in reference texts regarding the mechanism of action of this drug. Phentermine is an analog of methamphetamine. Similar to the amphetamines, phentermine increases the release of norepinephrine and dopamine from nerve terminals and inhibits their reuptake. Thus, phentermine is classified as an indirect sympathomimetic. Other effects include a weak ability to dose-dependently raise serotonin levels, although the effect on serotonin occurs is less potent than that of methamphetamine itself. Clinical effects include CNS stimulation and elevation of blood pressure. Appetite suppression is believed to occur through direct stimulation of the satiety center in the hypothalamic and limbic region.
Tolerance to the anorexiant effects of phentermine usually develops within a few weeks of starting therapy. The mechanism of tolerance appears to be pharmacodynamic in nature; higher doses of phentermine are required to produce the same response. When tolerance develops to the anorexiant effects, it is generally recommended that phentermine be discontinued rather than the dose increased.
Topiramate
The exact mechanism of topiramate’s anticonvulsant and migraine prophylaxis effects is unknown. It appears that topiramate may block the spread of seizures rather than raise the seizure threshold like other AEDs. The drug appears to have several mechanisms of action. First, topiramate reduces the duration of abnormal discharges and the number of action potentials within each discharge. This is probably secondary to its ability to block voltage-sensitive sodium channels. Second, topiramate enhances the activity of the inhibitory neurotransmitter gamma-aminobutyrate (GABA) at GABA-A receptors by increasing the frequency at which GABA activates GABA-A receptors. Third, topiramate inhibits excitatory transmission by antagonizing some types of glutamate receptors. Specifically, topiramate antagonizes the ability of kainate to activate the kainate/AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid; non-NMDA) subtype of excitatory amino acid (glutamate) receptor. There is no apparent effect on the activity of N-methyl-D-aspartate (NMDA) at the NMDA receptor subtype. Topiramate is also a weak carbonic anhydrase inhibitor (isozymes II and IV); however, while this action can cause a risk for metabolic acidosis, this mechanism does not appear to be involved in the anticonvulsant action of the drug.
In addition to its efficacy in epilepsy and migraine prophylaxis, topiramate has also demonstrated neuroprotective effects against hypoxic-ischemic brain damage in both in vitro and animal models. The cerebral damage of hypoxic-ischemic encephalopathy occurs in part due to an increased release of excitatory neurotransmitters, including glutamate. Glutamate activates AMPA receptors, depolarizes the cell, and promotes the removal of the voltage-sensitive magnesium block on NMDA receptors. This, in turn, promotes the entry of calcium into the cell, stimulating a series of reactions that lead to cell necrosis and apoptosis. The neuroprotective properties of topiramate appear to be primarily related to its inhibition of the kainate/AMPA subtype of glutamate receptors. In addition, blockade of sodium channels, high-voltage calcium currents, carbonic anhydrase isoenzymes, and mitochondrial permeability transition pore (MPTP) may also contribute to its neuroprotective effects.
Naltrexone HCl
Like naloxone, naltrexone is a competitive antagonist at opiate receptors mu, kappa, and delta. Opiate receptors have been reclassified by an International Union of Pharmacology subcommittee as OP1 (delta), OP2 (kappa), and OP3 (mu). Naltrexone can either displace opiate agonists from binding at these receptors or prevent opiate binding. Naltrexone does not antagonize the effects of non-opiates such as cocaine, ethanol, amphetamines, barbiturates, or benzodiazepines. Blockade of opiate receptors by naltrexone is a competitive phenomenon and results in elimination of the euphoric effect of opiates. At usual opiate concentrations, naltrexone’s greater affinity for the receptor prevents the binding of the opiate agonist to the receptor. However, when opiate concentrations are extremely high, the opiate can displace naltrexone, and respiratory depression and/or death is possible. Although naltrexone itself may possess some agonistic properties, these are minor compared to its potent antagonistic actions. Naltrexone is 17-times more potent than nalmorphine and twice as potent as naloxone. In patients who are physically dependent on opiates, naltrexone will precipitate an opiate withdrawal syndrome. Naltrexone use is not associated with tolerance or dependence, therefore, withdrawal from naltrexone does not occur. When co-administered with opiate agonists, naltrexone blocks the physical dependence to morphine, heroin, and other opiate agonists. Depending on the dose, the clinical effects of naltrexone can persist for up to 72 hours.
Endogenous opiods such as beta-endorphins and enkephalins may play an important role in alcoholism. An opioid reward system mediated by mu- and delta-receptors and an opposing aversions system mediated by kappa-receptors must be in balance to maintain a neutral state in regards to the development of addiction. Several therories regarding alcohol addiction and the function of endongeous opioids exist. All of these therories are based on an imbalance in favor of the endongenous reward pathways due to alcohol. Naltrexone inhibits the effects of endogenous opioids and decreases the positive or reward pathways associated with alcoholism. Naltrexone is not aversive therapy and will not produce a disulfiram-like reaction if opiates or ethanol are ingested while receiving naltrexone.
Methylcobalamin
Vitamin B12 is used in the body in two forms, methylcobalamin and 5-deoxyadenosyl cobalamin. The enzyme methionine synthase needs methylcobalamin as a cofactor. This enzyme is involved in the conversion of the amino acid homocysteine into methionine which is, in turn, required for DNA methylation. The other form, 5-deoxyadenosylcobalamin, is a cofactor needed by the enzyme that converts L-methylmalonyl-CoA to succinyl-CoA. This conversion is an important step in the extraction of energy from proteins and fats. Furthermore, succinyl CoA is necessary for the production of hemoglobin, the substance that carries oxygen in red blood cells.
Vitamin B12, or methylcobalamin, is essential to growth, cell reproduction, hematopoiesis, and nucleoprotein and myelin synthesis. Cells characterized by rapid division (epithelial cells, bone marrow, myeloid cells) appear to have the greatest requirement for methylcobalamin. Vitamin B12 can be converted to coenzyme B12 in tissues; in this form it is essential for conversion of methylmalonate to succinate and synthesis of methionine from homocysteine (a reaction which also requires folate). In the absence of coenzyme B12, tetrahydrofolate cannot be regenerated from its inactive storage form, 5-methyl tetrahydrofolate, resulting in functional folate deficiency. Vitamin B12 also may be involved in maintaining sulfhydryl (SH) groups in the reduced form required by many SH-activated enzyme systems. Through these reactions, vitamin B12 is associated with fat and carbohydrate metabolism and protein synthesis. Vitamin B12 deficiency results in megaloblastic anemia, GI lesions, and neurologic damage (which begins with an inability to produce myelin and is followed by gradual degeneration of the axon and nerve head). Vitamin B12 requires an intrinsic factor-mediated active transport for absorption, therefore, lack of or inhibition of intrinsic factor results in pernicious anemia.
Caffeine
Caffeine is a mild, direct stimulant at all levels of the CNS and also stimulates the heart and cardiovascular system. The related xanthine, theophylline, shares these properties and is widely used in the treatment of pulmonary disease. Both caffeine and theophylline are CNS stimulants, with theophylline exerting more dramatic effects than caffeine at higher concentrations. Caffeine also stimulates the medullary respiratory center and relaxes bronchial smooth muscle. Caffeine stimulates voluntary muscle and gastric acid secretion, increases renal blood flow, and is a mild diuretic.
While the clinical responses to caffeine are well known, the cellular mechanism of action is uncertain. Several theories have been proposed. At high concentrations, caffeine interferes with the uptake and storage of calcium by sarcoplasmic reticulum of striated muscle. While this action would explain the effects of caffeine on cardiac and skeletal muscle, it does not appear to occur at clinically achievable concentrations. Inhibition of phosphodiesterases (and subsequent accumulation of cyclic nucleotides) also does not appear to occur at clinically achievable concentrations.
Currently, it is believed that xanthines act as adenosine-receptor antagonists. Adenosine acts as an autocoid, and virtually every cell contains adenosine receptors within the plasma membrane. Adenosine exerts complex actions. It inhibits the release of neurotransmitters from presynaptic sites but works in concert with norepinephrine or angiotensin to augment their actions. Antagonism of adenosine receptors by caffeine would appear to promote neurotransmitter release, thus explaining the stimulatory effects of caffeine.Recently, a distinct syndrome has been associated with caffeine withdrawal. It is possible that the manifestations of caffeine withdrawal may be secondary to catecholamine or neurotransmitter depletion.
The following mechanisms of action are hypothesized for caffeine’s action in apnea of prematurity: 1) stimulation of the respiratory center, 2) increased minute ventilation, 3) decreased threshold to hypercapnia, 4) increased response to hypercapnia, 5) increased skeletal muscle tone, 6) decreased diaphragmatic fatigue, 7) increased metabolic rate, and 8) increased oxygen consumption. All of these actions are thought to be related to adenosine receptor antagonism.
Oxytocin
Synthetic oxytocin elicits the same pharmacological response produced by endogenous oxytocin, with cervical dilation, parity, and gestational age as predictors of the dose response to oxytocin administration for labor stimulation. Oxytocin increases the sodium permeability of uterine myofibrils, indirectly stimulating contraction of the uterine smooth muscle. The uterus responds to oxytocin more readily in the presence of high estrogen concentrations and with the increased duration of pregnancy. There is a gradual increase in uterine response to oxytocin for 20 to 30 weeks gestation, followed by a plateau from 34 weeks of gestation until term, when sensitivity increases. Women who are in labor have a greater response to oxytocin compared to women who are not in labor; only very large doses will elicit contractions in early pregnancy. In the term uterus, contractions produced by exogenous oxytocin are similar to those that would occur during spontaneous labor. Oxytocin increases the amplitude and frequency of uterine contractions, which transiently impede uterine blood flow and decrease cervical activity, causing dilation and effacement of the cervix.
Oxytocin causes contraction of the myoepithelial cells surrounding the alveolar ducts of the of the breast. This forces milk from the alveolar channels into the larger sinuses, and thus facilitates milk ejection. While oxytocin possesses no galactopoietic properties, if it is absent the milk-ejection reflex in the breast fails.
Oxytocin causes dilation of vascular smooth muscle, thus increasing renal, coronary, and cerebral blood flow. Blood pressure usually remains unaffected, but with the administration of very large doses or high concentration solutions blood pressure may decrease transiently. This transient decrease in blood pressure leads to reflex tachycardia and an increase in cardiac output; any fall in blood pressure is usually followed by a small, but sustained, increase in blood pressure.
Oxytocin does possess antidiuretic effects, but they are minimal. If oxytocin is administered with an excessive volume of electrolyte-free IV solution and/or at too rapid a rate, the antidiuretic effects are more apparent and water intoxication can result.
Metformin
Metformin is an antihyperglycemic agent that improves glucose tolerance, lowering both basal and postprandial plasma glucose with mechanisms different from other classes of oral antidiabetic agents. Metformin decreases hepatic gluconeogenesis production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization. With metformin therapy, insulin secretion remains unchanged while fasting insulin levels and day-long plasma insulin response may actually decrease. Metformin improve glucose utilization in skeletal muscle and adipose tissue by increasing cell membrane glucose transport. This effect may be due to improved binding of insulin to insulin receptors since metformin is not effective in diabetics without some residual functioning pancreatic islet cells. Unlike the sulfonylureas, metformin rarely causes hypoglycemia since it does not significantly change insulin concentrations. An important distinction is that sulfonylureas increase insulin secretion thus making them useful in non-obese patients with type 2 diabetes while metformin improves insulin resistance, a common pathophysiologic finding in obese patients with type 2 diabetes. Metformin causes a 10—20% decrease in fatty-acid oxidation and a slight increase in glucose oxidation. Unlike phenformin, metformin does not inhibit the mitochondrial oxidation of lactate unless plasma concentrations of metformin become excessive (i.e., in patients with renal failure) and/or hypoxia is present.
Clinically, metformin lowers fasting and postprandial hyperglycemia. The decrease in fasting plasma glucose is approximately 25—30%. Unlike oral sulfonylureas, metformin rarely causes hypoglycemia. Thus, metformin demonstrates more of an antihyperglycemic action than a hypoglycemic action. Metformin does not cause weight gain and in fact, may cause a modest weight loss due to drug-induced anorexia. Metformin also decreases plasma VLDL triglycerides resulting in modest decreases in plasma triglycerides and total cholesterol. Patients receiving metformin show a significant improvement in hemoglobin A1c, and a tendency toward improvement in the lipid profile, especially when baseline values are abnormally elevated.
Insulin resistance is a primary cause of polycystic ovarian syndrome (PCOS). In PCOS patients, metformin reduces insulin resistance and lowers insulin levels, which lowers serum androgen concentrations, restores normal menstrual cycles and ovulation, and may help to resolve PCOS-associated infertility. Metformin, when administered to lean, overweight, and moderately obese women with PCOS, has been found to significantly reduce serum leuteinizing hormone (LH) and increase follicle stimulating hormone (FSH) and sex hormone binding globulin (SHBG). Serum testosterone concentrations were also found to decrease by approximately 50%.
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