Obesity has been called the number one public health problem in America. Up to 40% of the adult population in some states is obese. Different medical options have been on the for decades, and two of the most common medications used for weight reduction are fenfluramine and phentermine, which together make up the famous fen-phen.
Fenfluramine is what we call a sympathomimetic. In other words, this medication affects the sympathetic systems that control many aspects of your body. It increases serotonin and also glucose utilization. Phentermine is an appetite suppressant, very similar to amphetamine. It is also a sympathomimetic medication. Phentermine stimulates the hypothalamus, which decreases appetite, and significantly reduces hunger and food intake in overweight individuals. Phentermine is more of a stimulant than fenfluramine, which tends to be a body depressant. Because of the way these medications work in the body, fen-phen can increase heart rate and pulmonary arterial pressure as well as overall body blood pressure. In addition, it can lower your blood sugar. Also, there is an aesthetic consideration with both medications that needs to be taken into consideration, as well as other reasons why it is not a good idea to be on this medication before having cosmetic surgery.
Patients on fen-phen, when put under anesthesia, can develop persistent or prolonged hypotension or low blood pressure that is unresponsive to medications like ephedrine. This creates a problem for the anesthesiologist because the patient can actually die even if the low blood pressure is treated with medication used to increase blood pressure. In addition, fen-phen can cause the stomach to empty too slowly, which can lead to aspiration during or after surgery. In addition, if you are diabetic, fenfluramine can increase the insulin effect by increasing the uptake of glucose and decreasing the liver production of glucose, which makes it problematic to monitor your blood sugar during surgery. In noninsulin-dependent diabetes, fenfluramine produced a significant fall in fasting blood glucose levels and increased insulin sensitivity, without affecting insulin secretion. Although it is rare, pulmonary artery blood pressure can increase, which, again, can be very difficult to manage and cause progressive shortness of breath, chest pain, and palpitations, among others. Finally, phentermine can induce heat tolerance by increasing endogenous heat production as a result of central nervous system stimulation, which prevents heat dissipating from the body.
So, those are the anesthetic systemic effects related to fen-phen; you can also have other systemic effects when taking this medication, like arrhythmia, which is the heart beating in a very irregular way, high blood pressure, and death. It is very important that during your consultation, you are extremely honest with your surgeon regarding the medications that you are using. Informing your surgeon and stopping this medication at least two to three weeks before surgery will help to prevent serious complications, including death.