USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 31-year-old woman comes to the obstetrics and gynecology office because of excessive vaginal bleeding for the past 7 days. The patient's past medical history is significant for menarche at the age of 13. She reports irregular and heavy menses occurring every 4 to 6 months. Her temperature is 37°C (98.6°F); pulse is 80/min; respirations are 16/min, and blood pressure is 135/80 mm Hg. On physical examination, the patient is obese and hirsute. The uterine fundus is difficult to palpate due to body habitus. Pelvic exam is otherwise unremarkable. Laboratory results reveal an elevated testosterone level and fasting blood glucose of 130 mg/dL. The patient mentions that she currently has no partner, but desires future fertility. In addition to oral contraceptives, which of the following medication should be also be added to her regimen?
Hypoglycemics are used to treat high blood sugar, a condition commonly known as diabetes mellitus.
As a quick review, Type 1 diabetes mellitus, which most commonly affects children and adolescents, arises when certain cells of the pancreas known as beta cells are unable to produce enough insulin to maintain normal blood glucose levels.
This is in contrast to Type 2 diabetes mellitus where the body is able to produce insulin, but the tissues don’t respond as well to it, or in other words, these individuals are insulin resistant.
Many hypoglycemics, like sulfonylureas, promote the release of insulin from the beta cells of the pancreas and therefore are known as insulin secretagogues.
In this video, however, we’ll be focusing specifically on the use of non-secretagogues in the treatment of Type 2 diabetes.
These medications include multiple classes of medications such as biguanides, thiazolidinediones, alpha glucosidase inhibitors, amylin analogues, and sodium glucose transporter 2 inhibitors.
It’s important to note, however, that diet and exercise should always be the first step in managing diabetes before initiating medications, and should generally be continued while on medication as well.
There are two classes of medications that increase insulin sensitivity and decrease the production of new glucose and they include biguanides and thiazolidinediones. Let's start with the biguanides.
Biguanides are the first line of therapy for the treatment of type 2 diabetes. There is one main medication in the biguanide class and that is metFORMIN.
It's main mechanism of action is to decrease the production of new glucose from the liver, or to inhibit hepatic gluconeogenesis.
Although the exact mechanism remains unknown, it’s believed that metFORMIN does this by increasing the activity of a liver enzyme known as AMP-dependent protein kinase (or AMPK).
AMPK has many complex functions, namely it plays a role in insulin signaling, as well as helping to regulate the metabolism of glucose and lipids.
Activated AMPK inhibits certain genes that promote gluconeogenesis such as phosphoenolpyruvate carboxykinase and glucose-6-phosphatase. Thus, via AMPK activation, metFORMIN results in the reduction of gluconeogenesis.
In addition, activation of AMPK causes the glucose transporter protein GLUT4, stored within adipose and muscle tissue, to embed into the plasma membrane, allowing glucose to enter.
Thus, metFORMIN increases insulin sensitivity in these tissues and promotes peripheral glucose uptake, and this reduces the overall levels of glucose in the blood.
A third mechanism of action of metFORMIN is that it decreases the intestinal absorption of glucose, and again, causes less glucose to enter the bloodstream.
MetFORMIN also reduces plasma glucagon levels, which is a hormone that stimulates glycogenolysis in the liver.
Glycogenolysis is the breakdown of glycogen molecules into glucose, therefore, less glycogen means less glucose in the blood.
As a result, metFORMIN lowers fasting and postprandial, or post-meal, glucose levels; but it’s important to note that metFORMIN is not associated with hypoglycemia!
Finally, besides diabetes type II, this medication can be used to treat polycystic ovarian syndrome, or short PCOS, and antipsychotic-induced weight gain in individuals with schizophrenia or schizoaffective disorder.
The most common side effects of metFORMIN are gastrointestinal disturbances such as diarrhea, nausea, vomiting, and abdominal cramps.
It is also associated with weight loss, and therefore metFORMIN is particularly useful in overweight or obese diabetic patients.
Furthermore, long-term use of metFORMIN is linked to vitamin B12 deficiency, therefore these individuals should consider B12 supplementation.
Although rare, one of the most well-known side effects of metFORMIN is lactic acidosis.
Typically, lactate is taken up by the liver and utilized in the process of hepatic gluconeogenesis.
However, since metFORMIN inhibits gluconeogenesis, the lactate builds up in the blood.
In healthy individuals this excess lactate usually does not become problematic because the kidneys are able to excrete it in the urine.
In addition, since it can cause lactic acidosis, metformin is also contraindicated in individuals with liver impairment, alcoholism, and conditions that are associated with tissue anoxia and increased lactic acid production, such as heart failure, respiratory failure, or shock.
Metformin treatment must be stopped before the administration of intravenous iodinated contrast medium, which is just like metformin, excreted by the kidneys.
Therefore, iodinated contrast can reduce metformin’s elimination and cause lactic acidosis!
Similar to the biguanides, thiazolidinediones are insulin sensitizers, meaning they make peripheral tissues more sensitive to the insulin that the body has already produced.
But, in contrast to metFORMIN, these medications have a slow onset of action, meaning they might require several weeks to develop their therapeutic effect.
They work as agonists at a receptor known as the peroxisome proliferator activated receptor gamma, or PPAR gamma.
Normally, this receptor is activated when ligands such as free fatty acids bind to it, after which, it binds to DNA and another receptor known as a retinoid X receptor.
The medications rosiglitazone and pioglitazone are synthetic ligands that can bind to PPAR gamma receptors in the same way as the natural ligands, which leads to increased insulin sensitivity.
In fact, these medications have been shown to increase insulin sensitivity or glucose uptake in peripheral tissues by 30-50%.
In addition, thiazolidinediones increase adiponectin levels, which is a hormone that inhibits hepatic gluconeogenesis; and stimulates glucose uptake by skeletal muscles, consequently decreasing blood glucose levels.
As a result, just like metFORMIN, these medications lower fasting and postprandial glucose levels.
Furthermore, the thiazolidinediones also increase the synthesis of proteins involved in lipid metabolism.
The end result is a decrease in triglycerides, and increase in both high density lipoprotein or HDL and low density lipoprotein or LDL.
In terms of side effects, when used as monotherapy, these medications are rarely associated with hypoglycemia.
But, it’s important to note that they can cause fluid retention and edema, which can further increase the risk of heart failure; therefore, they are contraindicated in individuals with NYHA class III or IV heart failure.
Next, thiazolidinediones are associated with weight gain and increased risk of osteopenia and fractures.
There is also some concern that these medications can increase the risk of hepatitis and liver failure, and therefore liver enzymes must be monitored closely, particularly during the first few months of initiating therapy.
Now the next two classes of medications, the alpha glucosidase inhibitors and amylin analogues act directly upon the GI tract by delaying the breakdown of food and its excretion from the body.
Alpha glucosidase is an enzyme that is found in the brush border of the intestines and it breaks down oligosaccharides and disaccharides into simpler monosaccharide units, like glucose, which is eventually absorbed through the lining of the intestine and into the blood.
Alpha glucosidase inhibitors prevent this process and reduce intestinal glucose absorption; thus they should be taken just before meals.
This ultimately lowers postprandial glucose levels; but in contrast to the previous two groups, these medications lack an effect on fasting glucose!
Now, as far as the side effects go, the undigested carbohydrates remain within the colon and are digested by intestinal bacteria.
This results in increased bacterial fermentation and gastrointestinal disturbances like gas, bloating, and diarrhea.
Therefore, if individuals on alpha-glucosidase inhibitors experience hypoglycemia, they should not be treated with sucrose since it will promote gastrointestinal side effects; instead, they should be treated with dextrose whose absorption is not inhibited.
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- "Rang and Dale's Pharmacology" Elsevier (2019)
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- "Thiazolidinediones: the Forgotten Diabetes Medications" Current Diabetes Reports (2019)
- "The mechanisms of action of metformin" Diabetologia (2017)