How Molecular Properties will Determine Drug Stability


Fluoxetine is a drug used to treat people suffering from depression and obsessive behaviors by taking in a component called serotonin which is an inhibitor for reuptake. The drug is also referred to as IUPAC its chemical formula is C17H18F3NO. Fluoxetine is unique from other drugs because the amine group is located near the end of methyl as shown in the structural formula in the table. As observed in the structural formula, benzene rings are separated by an amine. The carbon chain with an amine group is connected to benzene along with hydrogen and ether. Fluoxetine assumes the smell of mint and dissolves in water to form a colorless solution while it exists as a solid at room temperature. It has a melting point of approximately 180 degrees Celsius and its solubility in water range from 49-51 mg/ml at room temperature. A method to determine hydrolysis in fluoxetine is by using an acidic medium to determine its continuous or discontinuous systems. The result is usually a spectrum and emission of excited ions. This method is used to determine the presence of fluoxetine in drugs. In research to determine the reactions of the drug, five thousand patients were given the drug and closely monitored. Twenty patients were found to suffer adverse effects of extrapyramidal events. The conclusion was that patients using the drug are likely to have increased reactions to psychotropic medication. The half-life of fluoxetine is approximately between one to three days because it has been observed to disappear from the plasma within the same period. From the year of manufacture, the drug can be kept on the shelves for a maximum period of six years implying that the drug’s lifetime is six years. The functional component in fluoxetine is the ethereal oxygen and the present amide components (Litvoc, 2009).


Bupropion which was earlier referred to as amfebutamone has strong properties of depression and a ceasing smoking aid. People suffering from anxiety are also advised to use this drug. Bauer (2008), the drug has the characteristics of emphatics and contrave which have been analyzed to have issues with stability. The procedures required in the manufacture of this drug have to do with the control of oxidation and moistening. The drug is not very stable and efforts are being done to ensure that the drug has the confidence of customers. Concerning aging, Bupropion decreases the skin aging process. Bupropion has a chemical formula C13H18ClNO·HCl. The molecular Protonated ion of bupropion is generated by collision rely on the ionization method used to form [M+H]+ ions. The energy of decomposition does not depend on the daughter ion but on the ratio of balancing of keto-enol. Bupropion has a molecular weight of approximately 276.2, soluble in water, and is stable under ordinary conditions. When its half-life is taken, it is approximately twenty-five hours after being taken into the system while steady-state plasma concentrations are achieved after eight days. The drug is administered orally and the expected achievement of full plasma concentration is expected to fully happen after three hours. Bupropion does not affect food because it has been found to increase food Cmax. After manufacture, the drug is immediately sold because its stability is greatly affected by environmental and storage conditions. Bupropion is effectively mixed with other compounds to achieve a stabilizing effect. The shelf life of bupropion is two years when it is maintained at room temperature conditions. Smokers who were subjected to use bupropion had the following reactions; the rate of abstinence was approximately twenty percent for one year, the users gained by 2.1 kilograms. The drug is used to minimize seizure given they are used under the following conditions: the daily dose does not exceed 400mg, the drug is administered two times a day according to the recommended dose, the drug is administered in ascending proportions, and that the patient should not take more than 200gm of the drug in a single dose. The functional group of bupropion is carbonyl which makes it different from other stimulants.


Amitriptyline is an anti-depressant that has a direct effect on unbalanced brain chemicals causing depression characterized by lack of appetite, sadness, malaise, and fatigue. Amitriptyline interacts with the receptors in the body such as the Na+ ions. Its chemical formula is C20H23N. it has an approximate molecular weight of 277.41and its ionization constant is 9.42. The rate of oxidation of Amitriptyline is very high in its metabolism. This drug degrades through demethylation with a high rate in phenobarbital treatment compared to hydroxylation of nortriptyline. Amitriptyline has a shelf life of up to three months when stored at a temperature of eighty degrees. The drug’s pharmacological effects include uptake of serotonin and norepinephrine but do not affect the absorption of dopamine. The average half-life of this drug is approximately fifteen hours. The functional group of this drug is the salt which makes it to be very active.


Phenelzine is an inhibitor that is used as an antidepressant and reduction of anxiety. Phenelzine is a strong inhibitor of monoamine oxidase. Its chemical formula is C8 H12 N2 • H2SO4 with a molecular weight of 234.3 and its structural formula is in the table. Each tablet contains phenelzine contains active ingredients of phenelzine and other dormant ingredients. They include magnesium stearate. Unlike other inhibitors that activate the absorption of serotonin, it is considered to be the most effective but given as the last option due to its dangerous side effects. Regarding pharmacology, it prevents the actions of isoforms. This prevention of monoamine oxidase leads to increased reactions in the extracellular cells. It is administered orally and quickly absorbed in the gastrointestinal tract. The maximum time for concentration is forty-three minutes while its half-life is approximately twelve hours. Unlike other antidepressants, phenelzine does not have to be in the blood for it to act because of the enzyme monoamine. Its effects are felt for three weeks. Metabolism of this drug takes place in the liver and its wastes are released with urine. Oxidation of this drug takes place during metabolism in the liver with a resultant release of phenelzine acid. Over ninety-three percent of the doses taken are released for one hundred hours. Gonzalez (2006) wrote, “The manufacture of phenelzine is done by chemical reaction of hydrazine and phenyl-ethyl bromide 2. Phenelzine reacts with vitamin B2 through enzymatic reactions to form non-reactive metabolites. In this case, both the drug and vitamin B2 become inactive. The amide group is the functional group in this case.


Venlafaxine is an inhibitor that absorbs serotonin and was first introduced by Wyeth in 1993 which was meant to treat depressive disorders and anxiety. The chemical formula of venlafaxine is C17H27NO2·HCl. The molecular has an atom labeling and an 01-H..N1 which is intermolecular as observed in its structural formula. It has a molecular weight of approximately 313.9 and its stability is high under ordinary conditions. Its average boiling point is 216 degrees Celsius while the solubility in water is good. An experiment was conducted to determine oxidation of this drug using various solutions with different ranges of PH and the results showed that boric acid and tetrahydroxoborate indicated analytic signals. Venlafaxine has a short life of approximately five hours and should be administered in separate doses twice a day. Venlafaxine slightly reacts with cimetidine to increase active metabolites of venlafaxine. It also reacts with fluoxetine to increase its concentration which might lead to severe side effects. According to scientists Venlaflaxineis more stable when exposed to oxidative conditions (Gonzalez, 2006).

The table below represents the names and structural formulas of the drugs.

Fluoxetine Formula
Bupropion Formula
Amitriptyline Formula
Phenelzine Formula
Venlafaxine Formula
Carbamazeine H H
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H – C – C – O – H
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Carbamazepine is used for the medication of epilepsy and bipolar diseases and hypersensitive disorders. Carbamazepine works by blocking the chain of sodium, therefore, bringing stability to the sodium channel (52, 53). The drug has a molecular weight of 236.3 and the chemical formula C15H 12N2O. It has a melting point of approximately 191 degrees Celcius and its solubility in substances varies. It is hardly soluble in water and ether but the solubility in chloroform is excellent. Carbamazepine exhibits different half-lives for different patients with a stability range within five to seven days of dose administration. Carbamazepine has the potential to stabilize non-active sodium making cells in the brain non-excitable. When Carbamazepine is used together with other drugs, it can cause reactions that can be harmful. For instance, it can react when a patient combines its use with antiepileptics and drugs used to stabilize mood. It may eliminate other drugs from the blood system thereby reducing the level of blood. After taking a single dose, carbamazepine can induce its metabolism so that the overall half-life is approximately eighteen to sixty hours depending on the age of the recipient (Granger, 1995). The final products of this drug when it has been administered are released via urine and feces. Hydroxyl ions are the functional group of carbamazepine.

Antidepressants vary in different ways and only a few of them can allow a patient to use another for the same treatment. These drugs do not provide accurate medication but they provide medics with appropriate alternatives to treat patients suffering from depression. It is therefore important to know the drugs that can have positive results on the patients.


Bauer, A (2008) Applied pharmacokinetics. New Yolk: Mc Grawhill.

Gonzalez, J (2006) Drug Metabolism. New York: Mc Graw Hill.

Granger, P. (1995) Modulation of the gamma-aminobutyric acid type A receptor by the antiepileptic drugs carbamazeine and phenytoin. London: Oxford University Press.

Litvoc, D (2009) Comparison of carbamazeine and lithium in treatment of bipolar disorder: a systematic review of randomized controlled trials. Califonia: Hum Psychopharmacol.