Phentermine can be classified as an oral sympathomimetic amine that is used as a complementary therapy for the short-term treatment of exogenous obesity of 8-12 weeks. It has the same effects and characteristic properties as amphetamines. The FDA approved its resin complex in 1959 but its marketing was stopped in the U.S. Phentermine hydrochloride was later approved in 1973. Phentermine relinquished its fame in the mid 90’s as a treatment for obesity and substance abuse. It was presumed to be more effective when combined with other anorectic, fenfluramine, but there was very little evidence to support these claims. On 8th July 1997, the FDA warned physicians against the combination of phentermine with fenfluramine with reasons that women on this treatment were likely to develop pulmonary hypertension and heart disease. Fenfluramine was consequently withdrawn from the U.S markets after this. On may 2011, a phentermine hydrochloride orally disintegrating tablet was approved by the FDA for the treatment of exogenous obesity. The use of phentermine in conjunction with other anorectic agents is not advisable because their effects have not been clearly established.
Phentermine is analogous to methamphetamine, just as these compounds, phentermine also reacts to facilitate the release of dopamine and norepinephrine in the nerve terminals and inhibit their re-absorption. Because of this reason, it is classified as an indirect sympathomimetic. Phentermine has the ability to raise serotonin levels although its effect is much weaker compared to methamphetamine. Its clinical effects include the stimulation of the central nervous systems and the elevation of the blood pressure.
After a few weeks of beginning this treatment, some individuals can develop a tolerance to the effects of this medication. This tolerance is thought to be pharmacodynamic in nature. It can be relieved by the administration of higher doses of phentermine but this is not recommended. It is advisable to discontinue this treatment immediately.
Phentermine is in the form of capsules so it is administered orally. It has a half-life ranging from 19-24 hours then it is excreted by the kidneys. It is influenced by the pH of the urine because its pKa is 9.84. Under acidic urinary conditions, its half-life can decrease to 7-8 hours.
Route specific pharmacokinetics.
After the oral administration, most of the absorption of phentermine occurs in the small intestines. 8 Mg capsules become reactive after about 4 hours while the 30 mg and the 37.5 mg capsules become reactive after about 12-14 hours. Phentermine oral disintegrating tablets can be taken with or without food. Its action is not affected by water.
Phentermine is used to treat and manage exogenous obesity as a short-term complementary treatment in conjunction with a weight reduction method that cuts down or restricts your calorie intake. It is a stimulant that is similar to most amphetamines. It suppresses your appetite by stimulating various branches of the sympathetic nervous system which are located within the central nervous systems. Phentermine works best if incorporated with the practice of a healthy lifestyle.
You should always make sure that you use phentermine in the correct amounts and dosage as prescribed by your medical service provider. Phentermine can react adversely if mixed with other substances or lead to some adverse effects. The following are some of its contraindications.
Phentermine products are contraindicated in patients with cardiac disease or a history of cardiac disease. These can include, heart failure, cardiac arrhythmias, coronary artery disease, stroke and uncontrolled hypertension. It is also contraindicated in patients with hyperthyroidism.
It should never be combined with fenfluramine as various reports indicate that it can lead to the development of valvular heart diseases in women. The effects of the combination of phentermine with other weight loss products have not been clearly established but it is advisable to avoid this completely. Treatment should be discontinued in any patient who develops unexplainable symptoms of dyspnea, syncope, lower extremity oedema and angina pectoris.
Phentermine is contraindicated for use within 2 weeks following the use of MAO inhibiting drugs. Monoamine oxidase inhibitors can intensify or prolong the vasopressor effects and cardiac stimulation of phentermine.
It is contraindicated in patients who exhibit states of agitated behavior e.g. psychosis and severe anxiety since it can intensify these mental conditions.
Phentermine should not be taken by people who regularly operate machinery or perform tasks that require prolonged mental alertness because it can affect mental and motor performance.
Patients with diabetes Mellitus should use this drug very cautiously and always monitor their glucose levels regularly while on this treatment. Diabetic patients are more susceptible to the sympathomimetic side effects of phentermine. It is not recommended for patients with eating disorders and a patient with a history of drug and substance abuse.
It is contraindicated during pregnancy and breastfeeding because of the probable negative side effects that it can have on a foetus or an infant.
There has been much controversy and speculation over the safety of phentermine when used with other substances like benzphetamine, amphetamine, dexfenfluramine, diethylpropion, dextroamphetamine, sibutramine, ephedrine and fenfluramine. The effects of these compounds, when used with phentermine, have not been clearly established so their combinations should always be avoided. They have the potential to cause the development of various serious side effects.
You should never use phentermine concurrently with bromocriptine and cabergoline since it can result in adverse effects such as a worsening headache, ventricular tachycardia, hypertension, cerebral vasospasm, loss of vision and seizures.
It should never be used together with dronabinol, nabilone and THC. It can cause cardiotoxicity, hypertension and tachycardia.
Phentermine can limit the action and decrease the beneficial effects of antihypertensive agents like guanadrel, guanethidine, reserpine and methyldopa. These substances should not interact.
You should be very cautious when using phentermine in conjunction with serotonin, norepinephrine reuptake inhibitors and vortioxetine. These may cause negative cardiovascular and pulmonary effects. If you have to do this, ensure that you are on a stable antidepressant and make sure you receive close monitoring and periodic medical evaluation.
This medicine can be addictive following long-term use and it may not mix well with other substances. Whenever you are on this medication, limit your intake of caffeine and chocolate. Inform your physician of any history of drug abuse or alcohol since these may lead to very serious heart-related side effects.
If you experience any signs of hypersensitivity or a probable overdose, contact your health service provider immediately. Some signs of an adverse reaction can include; chest pains, headaches dizziness, passing out, rashes and deterioration of your medical condition.
Other side effects can include; insomnia, nervousness and an abnormal drying of the mouth. This list does not mention all the possible effects so if you experience any negative or life-threatening conditions, contact your physician and seek medical advice immediately.
This medication should be administered orally. It should be stored at room temperature and away from children.
Phentermine is commonly prescribed for the treatment of obesity.
Our Pharmacy’s capsules are compounded under stringent USP-795 guidelines. Our quality assurance processes ensure the potency, uniformity, consistency, and beyond-use-dating (BUD) of each and every capsule we dispense. For more information on this medication, please contact us.