, coma, respiratory depression (rare)

It is common for patients taking lithium to be inadequately monitored, which has prompted NICE and the National Patient Safety Agency (NPSA) to issue guidance on the matter. This topic is often tested in exams. According to NICE (CKS), lithium blood levels should be checked weekly until they become stable, and then every 3 months once they are stable. The levels should be taken 12 hours after the dose. Maudsley (13th) recommends checking levels every 6 months, but more frequent monitoring is necessary for those taking interacting drugs, the elderly, and those with established renal impairment of other relevant physical illness. The BNF recommends weekly monitoring until stable, and then every 3 months for the first year, followed by every 6 months thereafter. Patients should have their thyroid and renal function checked every 6 months, and they should be provided with an information booklet, alert card, and record book.

Lithium – Pharmacology

Pharmacokinetics:
Lithium salts are rapidly absorbed following oral administration and are almost exclusively excreted by the kidneys unchanged. Blood samples for lithium should be taken 12 hours post-dose.

Ebstein’s:
Ebstein’s anomaly is a congenital malformation consisting of a prolapse of the tricuspid valve into the right ventricle. It occurs in 1:20,000 of the general population. Initial data suggested it was more common in those using lithium but this had not held to be true.

Contraindications:
Addison’s disease, Brugada syndrome, cardiac disease associated with rhythm disorders, clinically significant renal impairment, untreated of untreatable hypothyroidism, low sodium levels.

Side-effects:
Common side effects include nausea, tremor, polyuria/polydipsia, rash/dermatitis, blurred vision, dizziness, decreased appetite, drowsiness, metallic taste, and diarrhea. Side-effects are often dose-related.

Long-term use is associated with hypothyroidism, hyperthyroidism, hypercalcemia/hyperparathyroidism, irreversible nephrogenic diabetes insipidus, and reduced GFR.

Lithium-induced diabetes insipidus:
Treatment options include stopping lithium (if feasible), keeping levels within 0.4-0.8 mmol/L, once-daily dose of the drug taken at bedtime, amiloride, thiazide diuretics, indomethacin, and desmopressin.

Toxicity:
Lithium salts have a narrow therapeutic/toxic ratio. Risk factors for lithium toxicity include drugs altering renal function, decreased circulating volume, infections, fever, decreased oral intake of water, renal insufficiency, and nephrogenic diabetes insipidus. Features of lithium toxicity include GI symptoms and neuro symptoms.

Pre-prescribing:
Before prescribing lithium, renal function, cardiac function, thyroid function, FBC, and BMI should be checked. Women of childbearing age should be advised regarding contraception, and information about toxicity should be provided.

Monitoring:
Lithium blood levels should be checked weekly until stable, and then every 3-6 months once stable. Thyroid and renal function should be checked every 6 months. Patients should be issued with an information booklet, alert card, and record book.

There exist two primary opioid antagonists.

Mechanisms of Action of Different Drugs

Understanding the mechanisms of action of different drugs is crucial for medical professionals. It is a common topic in exams and can earn easy marks if studied well. This article provides a list of drugs and their mechanisms of action in different categories such as antidepressants, anti dementia drugs, mood stabilizers, anxiolytic/hypnotic drugs, antipsychotics, drugs of abuse, and other drugs. For example, mirtazapine is a noradrenaline and serotonin specific antidepressant that works as a 5HT2 antagonist, 5HT3 antagonist, H1 antagonist, alpha 1 and alpha 2 antagonist, and moderate muscarinic antagonist. Similarly, donepezil is a reversible acetylcholinesterase inhibitor used as an anti dementia drug, while valproate is a GABA agonist and NMDA antagonist used as a mood stabilizer. The article also explains the mechanisms of action of drugs such as ketamine, phencyclidine, buprenorphine, naloxone, atomoxetine, varenicline, disulfiram, acamprosate, and sildenafil.

Antipsychotics are commonly used to treat various mental health conditions. Most atypical antipsychotics require twice daily administration due to their short half-lives, except for olanzapine, aripiprazole, and risperidone. These medications have longer half-lives and can be administered once daily. A recent randomized controlled trial compared once versus twice daily dosing of risperidone and olanzapine and found no significant difference in effectiveness and efficacy outcomes. However, the study suggests that once-daily dosing may be preferable due to lower mean dose and better side effect profile, especially for olanzapine.

Diphenhydramine is a type of antihistamine that belongs to the first generation. It is commonly used to alleviate extrapyramidal side effects (EPSE). Unlike second generation antihistamines, first generation antihistamines have anticholinergic properties and can penetrate the blood-brain barrier, resulting in sedative effects. The anticholinergic effects of first generation antihistamines are beneficial for treating EPSE, which is believed to be caused by excessive acetylcholine due to reduced dopamine activity. Dopamine normally inhibits acetylcholine, but when dopamine activity is reduced, acetylcholine levels increase, leading to EPSE.

Extrapyramidal side-effects (EPSE’s) are a group of side effects that affect voluntary motor control, commonly seen in patients taking antipsychotic drugs. EPSE’s include dystonias, parkinsonism, akathisia, and tardive dyskinesia. They can be frightening and uncomfortable, leading to problems with non-compliance and can even be life-threatening in the case of laryngeal dystonia. EPSE’s are thought to be due to antagonism of dopaminergic D2 receptors in the basal ganglia. Symptoms generally occur within the first few days of treatment, with dystonias appearing quickly, within a few hours of administration of the first dose. Newer antipsychotics tend to produce less EPSE’s, with clozapine carrying the lowest risk and haloperidol carrying the highest risk. Akathisia is the most resistant EPSE to treat. EPSE’s can also occur when antipsychotics are discontinued (withdrawal dystonia).

Debrisoquine hydroxylase is the primary enzyme responsible for metabolizing several antidepressants, such as tricyclics, selective serotonin reuptake inhibitors (SSRIs), venlafaxine, and others. Approximately 5 out of 100 individuals are poor metabolisers, which can lead to increased side effects from medications that rely on CYP2D6 for metabolism. Conversely, ultra-rapid metabolisers may require higher than average doses of these medications due to their highly active forms of the enzyme.

The Cytochrome P450 system is a group of enzymes that metabolize drugs by altering their functional groups. The system is located in the liver and small intestine and is involved in drug interactions through enzyme induction of inhibition. Notable inducers include smoking, alcohol, and St John’s Wort, while notable inhibitors include grapefruit juice and some SSRIs. CYP2D6 is important due to genetic polymorphism, and CYP3A4 is the most abundant subfamily and is commonly involved in interactions. Grapefruit juice inhibits both CYP1A2 and CYP3A4, while tobacco smoking induces CYP1A2. The table summarizes the main substrates, inhibitors, and inducers for each CYP enzyme.

Intravenous formulations bypass the initial metabolism in the liver, resulting in increased concentrations of the drug in the bloodstream.

Alternative Routes of Administration for Antidepressants

While most antidepressants are taken orally, there are a few alternative routes of administration available. However, it is important to note that these non-oral preparations should only be used when absolutely necessary, as they may not have a UK licence.

One effective alternative route is sublingual administration of fluoxetine liquid. Buccal administration of selegiline is also available. Crushed amitriptyline has been shown to be effective when administered via this route.

Intravenous administration is another option, with several antidepressants available in IV preparations, including citalopram, escitalopram, mirtazapine, amitriptyline, clomipramine, and allopregnanolone (which is licensed in the US for postpartum depression). Ketamine has also been shown to be effective when administered intravenously.

Intramuscular administration of flupentixol has been shown to have a mood elevating effect, but amitriptyline was discontinued as an IM preparation due to the high volumes required.

Transdermal administration of selegiline is available, and suppositories containing amitriptyline, clomipramine, imipramine, and trazodone have been manufactured by pharmacies, although there is no clear data on their effectiveness. Sertraline tablets and doxepin capsules have also been given rectally.

Serotonin syndrome may sometimes result in increased levels of CPK.

Serotonin Syndrome and Neuroleptic Malignant Syndrome are two conditions that can be difficult to differentiate. Serotonin Syndrome is caused by excess serotonergic activity in the CNS and is characterized by neuromuscular abnormalities, altered mental state, and autonomic dysfunction. On the other hand, Neuroleptic Malignant Syndrome is a rare acute disorder of thermoregulation and neuromotor control that is almost exclusively caused by antipsychotics. The symptoms of both syndromes can overlap, but there are some distinguishing clinical features. Hyper-reflexia, ocular clonus, and tremors are more prominent in Serotonin Syndrome, while Neuroleptic Malignant Syndrome is characterized by uniform ‘lead-pipe’ rigidity and hyporeflexia. Symptoms of Serotonin Syndrome usually resolve within a few days of stopping the medication, while Neuroleptic Malignant Syndrome can take up to 14 days to remit with appropriate treatment. The following table provides a useful guide to the main differentials of Serotonin Syndrome and Neuroleptic Malignant Syndrome.

ADHD medications can be classified into stimulant and non-stimulant drugs. The therapeutic effects of these drugs are believed to be mediated through the action of noradrenaline in the prefrontal cortex. Common side effects of these drugs include decreased appetite, insomnia, nervousness, headache, and nausea. Stimulant drugs like dexamphetamine, methylphenidate, and lisdexamfetamine inhibit the reuptake of dopamine and noradrenaline. Non-stimulant drugs like atomoxetine, guanfacine, and clonidine work by increasing noradrenaline levels in the synaptic cleft through different mechanisms. The most common side effects of these drugs are decreased appetite, somnolence, headache, and abdominal pain.

Tricyclic Antidepressants: First and Second Generation

Tricyclic antidepressants are classified into two generations: first generation of tertiary amines, and second generation of secondary amines. The secondary amines are known to have fewer side effects and primarily affect noradrenaline, while the tertiary amines are believed to enhance both serotonin and noradrenaline.

Secondary amines include Desipramine, Nortriptyline, Protriptyline, and Amoxapine. On the other hand, tertiary amines include Amitriptyline, Lofepramine, Imipramine, Clomipramine, Dosulepin (Dothiepin), Doxepin, Trimipramine, and Butriptyline.

By understanding the differences between the two generations of tricyclic antidepressants, healthcare professionals can better tailor their treatment plans to their patients’ needs.

The ‘Z drugs’ (zopiclone, zolpidem, zaleplon) are beneficial for nighttime sedation due to their relatively brief half-lives.

Benzodiazepines are a class of drugs commonly used to treat anxiety and sleep disorders. It is important to have a working knowledge of the more common benzodiazepines and their half-life. Half-life refers to the amount of time it takes for half of the drug to be eliminated from the body.

Some of the more common benzodiazepines and their half-life include diazepam with a half-life of 20-100 hours, clonazepam with a half-life of 18-50 hours, chlordiazepoxide with a half-life of 5-30 hours, nitrazepam with a half-life of 15-38 hours, temazepam with a half-life of 8-22 hours, lorazepam with a half-life of 10-20 hours, alprazolam with a half-life of 10-15 hours, oxazepam with a half-life of 6-10 hours, zopiclone with a half-life of 5-6 hours, zolpidem with a half-life of 2 hours, and zaleplon with a half-life of 2 hours. Understanding the half-life of these drugs is important for determining dosages and timing of administration.

Gabapentin, lithium, and topiramate require minimal of no hepatic metabolism, allowing them to be excreted without undergoing significant liver alteration.

Drug Clearance: Understanding the Rate of Drug Removal from the Body

Drug clearance refers to the efficiency of drug removal from the plasma, and is measured as the volume of plasma cleared of a drug over a specific time period. The unit of measurement for drug clearance is volume per time. Clearance of a drug involves both metabolism and excretion. When drug intake equals clearance, it is referred to as a steady state, which is usually achieved by 4.5 half-lives. The time taken to reach steady state depends on the half-life of the drug.

There are two main types of clearance: hepatic and renal. Hepatic clearance involves the conversion of the parent drug into a different chemical entity by the liver enzymes, while renal clearance involves the removal of the drug from the plasma into the urine. The clearance of a drug can take one of two forms: zero and first-order kinetics. In zero-order reactions, the clearance of a drug is constant and not related to the concentration of the drug in the plasma. This type of reaction is typically found when the material needed for the reaction to proceed (e.g. enzyme) is saturated. Ethanol and Phenytoin are good examples of this.

Most drugs tend to follow first-order reactions, where the clearance is related to the concentration of the drug in the plasma. The half-life of a drug is the time taken for its concentration to fall by half. In first-order reactions, this is constant. In zero-order reactions, it gets progressively shorter.

It is important to note that elimination and clearance are not the same. Elimination is the irreversible removal of the drug from the body, while clearance is a theoretical volume of blood that is cleared of the drug per unit of time, which is independent of the drug dose of concentration. Understanding drug clearance is crucial in determining the appropriate dosing regimen for a drug.

Hypnotic Drugs and Their Side Effects

Hypnotic drugs are medications that act on GABA receptors, specifically the BZ1, BZ2, and BZ3 receptors. The BZ1 receptor is responsible for sedative effects, while the BZ2 receptor is responsible for myorelaxant and anticonvulsant effects. The BZ3 receptor is responsible for anxiolytic effects.

Older benzodiazepines bind to all three types of receptors, while newer drugs like Z-drugs primarily bind to the BZ1 receptor. Zopiclone is a cyclopyrrolone drug that was marketed as a non-benzodiazepine sleep aid, but it can produce hangover effects and dependence. It is contraindicated in patients with marked neuromuscular respiratory weakness, respiratory failure, and severe sleep apnea syndrome. Zopiclone can cause alterations in EEG readings and sleep architecture similar to benzodiazepines. It should not be used by breastfeeding women as it passes through to the milk in high quantities. Side effects of zopiclone include metallic taste, heartburn, and lightening of sleep on withdrawal.

Zolpidem is another hypnotic drug that acts on the BZ1 receptor. Side effects of zolpidem include drowsiness, fatigue, depression, falls, and amnesia. It is important to be aware of the potential side effects of hypnotic drugs and to use them only as directed by a healthcare provider.

Lithium – Pharmacology

Pharmacokinetics:
Lithium salts are rapidly absorbed following oral administration and are almost exclusively excreted by the kidneys unchanged. Blood samples for lithium should be taken 12 hours post-dose.

Ebstein’s:
Ebstein’s anomaly is a congenital malformation consisting of a prolapse of the tricuspid valve into the right ventricle. It occurs in 1:20,000 of the general population. Initial data suggested it was more common in those using lithium but this had not held to be true.

Contraindications:
Addison’s disease, Brugada syndrome, cardiac disease associated with rhythm disorders, clinically significant renal impairment, untreated of untreatable hypothyroidism, low sodium levels.

Side-effects:
Common side effects include nausea, tremor, polyuria/polydipsia, rash/dermatitis, blurred vision, dizziness, decreased appetite, drowsiness, metallic taste, and diarrhea. Side-effects are often dose-related.

Long-term use is associated with hypothyroidism, hyperthyroidism, hypercalcemia/hyperparathyroidism, irreversible nephrogenic diabetes insipidus, and reduced GFR.

Lithium-induced diabetes insipidus:
Treatment options include stopping lithium (if feasible), keeping levels within 0.4-0.8 mmol/L, once-daily dose of the drug taken at bedtime, amiloride, thiazide diuretics, indomethacin, and desmopressin.

Toxicity:
Lithium salts have a narrow therapeutic/toxic ratio. Risk factors for lithium toxicity include drugs altering renal function, decreased circulating volume, infections, fever, decreased oral intake of water, renal insufficiency, and nephrogenic diabetes insipidus. Features of lithium toxicity include GI symptoms and neuro symptoms.

Pre-prescribing:
Before prescribing lithium, renal function, cardiac function, thyroid function, FBC, and BMI should be checked. Women of childbearing age should be advised regarding contraception, and information about toxicity should be provided.

Monitoring:
Lithium blood levels should be checked weekly until stable, and then every 3-6 months once stable. Thyroid and renal function should be checked every 6 months. Patients should be issued with an information booklet, alert card, and record book.

Lamotrigine is prescribed to enhance the effectiveness of clozapine in treating schizophrenia that is resistant to clozapine. However, it is important to note that lamotrigine can cause Stevens-Johnson syndrome, a serious skin condition that requires immediate medical attention. Therefore, if a rash appears, treatment with lamotrigine should be discontinued promptly.

Benzodiazepines have been found to suppress REM sleep and can lead to intense dreams and severe nightmares when discontinued due to a rebound effect. Additionally, they can cause anterograde amnesia, which is the inability to create new memories. While benzodiazepines do not directly induce of inhibit liver enzymes, they are metabolized by CYP3A4, which can be inhibited by certain medications such as SSRIs, erythromycin, and ketoconazole. Flumazenil, a medication used to manage benzodiazepine overdose, has a short half-life and may require repeated doses. However, benzodiazepines are not recommended for the treatment of depression of panic disorder.

Benzodiazepines: Effective but Addictive

Benzodiazepines are a class of drugs that are commonly used to treat anxiety. They are divided into two categories: hypnotics, which have a short half-life, and anxiolytics, which have a long half-life. While they can be effective in reducing anxiety symptoms, they are also highly addictive and should not be prescribed for more than one month at a time.

Benzodiazepines are particularly effective as hypnotics, but they do have some negative effects on sleep. They suppress REM sleep, and when they are discontinued, a rebound effect is often seen. This means that people may experience more vivid dreams and nightmares when they stop taking the medication. It is important for doctors to carefully monitor patients who are taking benzodiazepines to ensure that they are not becoming addicted and that they are not experiencing any negative side effects.

While the majority of SSRIs are believed to have minimal impact on the QTc interval, studies have demonstrated that citalopram and escitalopram can lead to QTc prolongation.

Antidepressants and Their Cardiac Effects

SSRIs are generally recommended for patients with cardiac disease as they may protect against myocardial infarction (MI). Untreated depression worsens prognosis in cardiovascular disease. Post MI, SSRIs and mirtazapine have either a neutral of beneficial effect on mortality. Sertraline is recommended post MI, but other SSRIs and mirtazapine are also likely to be safe. However, citalopram is associated with Torsades de pointes (mainly in overdose). Bupropion, citalopram, escitalopram, moclobemide, lofepramine, and venlafaxine should be used with caution of avoided in those at risk of serious arrhythmia (those with heart failure, left ventricular hypertrophy, previous arrhythmia, of MI).

Tricyclic antidepressants (TCAs) have established arrhythmogenic activity which arises as a result of potent blockade of cardiac sodium channels and variable activity at potassium channels. ECG changes produced include PR, QRS, and QT prolongation and the Brugada syndrome. Lofepramine is less cardiotoxic than other TCAs and seems to lack the overdose arrhythmogenicity of other TCAs. QT changes are not usually seen at normal clinical doses of antidepressants (but can occur, particularly with citalopram/escitalopram). The arrhythmogenic potential of TCAs and other antidepressants is dose-related.

Overall, SSRIs are recommended for patients with cardiac disease, while caution should be exercised when prescribing TCAs and other antidepressants, especially in those at risk of serious arrhythmia. It is important to monitor patients closely for any cardiac effects when prescribing antidepressants.

NMS is a potential side effect of antipsychotics.

Serotonin Syndrome and Neuroleptic Malignant Syndrome are two conditions that can be difficult to differentiate. Serotonin Syndrome is caused by excess serotonergic activity in the CNS and is characterized by neuromuscular abnormalities, altered mental state, and autonomic dysfunction. On the other hand, Neuroleptic Malignant Syndrome is a rare acute disorder of thermoregulation and neuromotor control that is almost exclusively caused by antipsychotics. The symptoms of both syndromes can overlap, but there are some distinguishing clinical features. Hyperreflexia, ocular clonus, and tremors are more prominent in Serotonin Syndrome, while Neuroleptic Malignant Syndrome is characterized by uniform ‘lead-pipe’ rigidity and hyporeflexia. Symptoms of Serotonin Syndrome usually resolve within a few days of stopping the medication, while Neuroleptic Malignant Syndrome can take up to 14 days to remit with appropriate treatment. The following table provides a useful guide to the main differentials of Serotonin Syndrome and Neuroleptic Malignant Syndrome.

The MHRA categorizes adverse drug reactions into five types. Type A reactions occur when a drug’s usual pharmacological actions are amplified at the normal therapeutic dose, and are typically dose-dependent. Type B reactions are unexpected and not related to the drug’s known pharmacological actions. Type C reactions persist for a prolonged period of time, while Type D reactions become apparent after a delay. Type E reactions are associated with the withdrawal of a medication.

Antipsychotics can be classified in different ways, with the most common being typical (first generation) and atypical (second generation) types. Typical antipsychotics block dopamine (D2) receptors and have varying degrees of M1, Alpha-1, and H1 receptor blockade. Atypical antipsychotics have a lower propensity for extrapyramidal side-effects and are attributed to the combination of relatively lower D2 antagonism with 5HT2A antagonism. They are also classified by structure, with examples including phenothiazines, butyrophenones, thioxanthenes, diphenylbutylpiperidine, dibenzodiazepines, benzoxazoles, thienobenzodiazepine, substituted benzamides, and arylpiperidylindole (quinolone). Studies have found little evidence to support the superiority of atypicals over typicals in terms of efficacy, discontinuation rates, of adherence, with the main difference being the side-effect profile. The Royal College also favors classification by structure.

Duloxetine is also licensed for the treatment of generalised anxiety disorder.

Antidepressants (Licensed Indications)

The following table outlines the specific licensed indications for antidepressants in adults, as per the Maudsley Guidelines and the British National Formulary. It is important to note that all antidepressants are indicated for depression.

– Nocturnal enuresis in children: Amitriptyline, Imipramine, Nortriptyline
– Phobic and obsessional states: Clomipramine
– Adjunctive treatment of cataplexy associated with narcolepsy: Clomipramine
– Panic disorder and agoraphobia: Citalopram, Escitalopram, Sertraline, Paroxetine, Venlafaxine
– Social anxiety/phobia: Escitalopram, Paroxetine, Sertraline, Moclobemide, Venlafaxine
– Generalised anxiety disorder: Escitalopram, Paroxetine, Duloxetine, Venlafaxine
– OCD: Escitalopram, Fluoxetine, Fluvoxamine, Paroxetine, Sertraline, Clomipramine
– Bulimia nervosa: Fluoxetine
– PTSD: Paroxetine, Sertraline

The half life of fluoxetine, the longest lasting SSRI, is four to six days, while its active metabolite, norfluoxetine, has a half life of four to 16 days. Citalopram has a half life of 33 hours, escitalopram has a half life of 30 hours, paroxetine has a half life of 24 hours, and sertraline has a half life of 26 hours.

Pharmacokinetics includes the study of drug metabolism.

Receptor Binding

Receptor binding is a crucial aspect of pharmacodynamics, which involves the study of how drugs affect the body. Receptors are specialized proteins located on the surface of inside cells that interact with specific molecules, such as neurotransmitters, hormones, of drugs. When a drug binds to a receptor, it can either activate or inhibit its function, leading to various biological effects. The affinity and efficacy of a drug for a receptor depend on its chemical structure, concentration, and the properties of the receptor. Understanding receptor binding is essential for developing safe and effective drugs, as well as for predicting drug interactions and side effects.

The half-life of a drug is the time taken for its concentration to fall to one half of its value. Drugs with long half-lives may require a loading dose to achieve therapeutic plasma concentrations rapidly. It takes about 4.5 half-lives to reach steady state plasma levels. Most drugs follow first order kinetics, where a constant fraction of the drug in the body is eliminated per unit time. However, some drugs may follow zero order kinetics, where the plasma concentration of the drug decreases at a constant rate, despite the concentration of the drug. For drugs with nonlinear kinetics of dose-dependent kinetics, the relationship between the AUC of CSS and dose is not linear, and the kinetic parameters may vary depending on the administered dose.

According to Gillman (1998), it is recommended to avoid using the antihistamines brompheniramine and chlorpheniramine as they act as serotonin reuptake inhibitors (SRIs). However, all other antihistamines are considered safe for use. Gillman’s study focused on the history and risk of serotonin syndrome.

MAOIs: A Guide to Mechanism of Action, Adverse Effects, and Dietary Restrictions

First introduced in the 1950s, MAOIs were the first antidepressants introduced. However, they are not the first choice in treating mental health disorders due to several dietary restrictions and safety concerns. They are only a treatment option when all other medications are unsuccessful. MAOIs may be particularly useful in atypical depression (over eating / over sleeping, mood reactivity).

MAOIs block the monoamine oxidase enzyme, which breaks down different types of neurotransmitters from the brain: norepinephrine, serotonin, dopamine, as well as tyramine. There are two types of monoamine oxidase, A and B. The MOA A are mostly distributed in the placenta, gut, and liver, but MOA B is present in the brain, liver, and platelets. Selegiline and rasagiline are irreversible and selective inhibitors of MAO type B, but safinamide is a reversible and selective MAO B inhibitor.

The most common adverse effects of MAOIs occurring early in treatment are orthostatic hypotension, daytime sleepiness, insomnia, and nausea; later common effects include weight gain, muscle pain, myoclonus, paraesthesia, and sexual dysfunction.

Pharmacodynamic interactions with MAOIs can cause two types of problem: serotonin syndrome (mainly due to SSRIs) and elevated blood pressure (caused by indirectly acting sympathomimetic amines releasers, like pseudoephedrine and phenylephrine). The combination of MAOIs and some TCAs appears safe. Only those TCAs with significant serotonin reuptake inhibition (clomipramine and imipramine) are likely to increase the risk of serotonin syndrome.

Tyramine is a monoamine found in various foods, and is an indirect sympathomimetic that can cause a hypertensive reaction in patients receiving MAOI therapy. For this reason, dietary restrictions are required for patients receiving MAOIs. These restrictions include avoiding matured/aged cheese, fermented sausage, improperly stored meat, fava of broad bean pods, and certain drinks such as on-tap beer. Allowed foods include fresh cottage cheese, processed cheese slices, fresh packaged of processed meat, and other alcohol (no more than two bottled or canned beers of two standard glasses of wine, per day).

The ‘cheese reaction’ is a potential adverse effect of phenelzine, a type of medication known as a monoamine oxidase inhibitor (MAOI). When a person takes phenelzine, foods that contain high levels of tyramine are not broken down properly due to the inhibition of MAO. This causes tyramine to enter the bloodstream and trigger the release of noradrenaline, which can lead to dangerous spikes in blood pressure.

The term ‘cheese reaction’ comes from the fact that many types of cheese are particularly high in tyramine. While early MAOIs irreversibly inhibit monoamine oxidase, newer medications like moclobemide are reversible and considered to be safer.

Studies have demonstrated that memantine possesses neuroprotective properties for individuals with Alzheimer’s disease and those who have suffered from traumatic brain injury.

Pharmacological management of dementia involves the use of acetylcholinesterase inhibitors (AChE inhibitors) and memantine. AChE inhibitors prevent the breakdown of acetylcholine, which is deficient in Alzheimer’s due to the loss of cholinergic neurons. Donepezil, galantamine, and rivastigmine are commonly used AChE inhibitors in the management of Alzheimer’s. However, gastrointestinal side effects such as nausea and vomiting are common with these drugs.

Memantine, on the other hand, is an NMDA receptor antagonist that blocks the effects of pathologically elevated levels of glutamate that may lead to neuronal dysfunction. It has a half-life of 60-100 hours and is primarily renally eliminated. Common adverse effects of memantine include somnolence, dizziness, hypertension, dyspnea, constipation, headache, and elevated liver function tests.

Overall, pharmacological management of dementia aims to improve cognitive function and slow down the progression of the disease. However, it is important to note that these drugs do not cure dementia and may only provide temporary relief of symptoms.

In the treatment of Alzheimer’s disease, acetylcholinesterase inhibitors such as galantamine are utilized to enhance central acetylcholine levels. Although they share this common mechanism of action, there are variations in how they function. Unlike galantamine, rivastigmine has the ability to inhibit butyrylcholinesterase.

Amantadine and QTc Prolongation

Amantadine is a medication used to treat Parkinson’s disease and influenza. It has been associated with QTc prolongation, which can increase the risk of Torsades de points. Therefore, caution should be exercised when prescribing amantadine to patients with risk factors for QT prolongation. If a patient is already taking amantadine and develops a prolonged QTc interval, the medication should be discontinued and an alternative treatment considered. It is important to monitor the QTc interval in patients taking amantadine, especially those with risk factors for QT prolongation.

Carbamazepine use can result in leucopenia, which is a reduction in white blood cell count, affecting 1 in 10 individuals. Although other side effects can occur with carbamazepine, they are rare of very rare. The decrease in WBC is believed to be due to the inhibition of colony-stimulating factor in the bone marrow. However, the co-administration of lithium, which stimulates colony-stimulating factor, may potentially reverse the effects of carbamazepine (Daughton, 2006).

Carbamazepine: Uses, Mechanism of Action, Contraindications, Warnings, and Side-Effects

Carbamazepine, also known as Tegretol, is a medication commonly used in the treatment of epilepsy, particularly partial seizures. It is also used for neuropathic pain, bipolar disorder, and other conditions. The drug works by binding to sodium channels and increasing their refractory period.

However, carbamazepine has notable contraindications, including a history of bone marrow depression and combination with monoamine oxidase inhibitors (MAOIs). It also carries warnings for serious dermatological reactions such as toxic epidermal necrolysis (TEN) and Stevens Johnson syndrome.

Common side-effects of carbamazepine include leucopenia, ataxia, dizziness, somnolence, vomiting, nausea, urticaria, and fatigue. Other side-effects include thrombocytopenia, eosinophilia, oedema, fluid retention, weight increase, hyponatraemia, and blood osmolarity decreased due to an antidiuretic hormone (ADH)-like effect, leading in rare cases to water intoxication accompanied by lethargy, vomiting, headache, confusional state, neurological disorders, diplopia, accommodation disorders (e.g. blurred vision), and dry mouth.

In summary, carbamazepine is a medication with multiple uses, but it also carries significant contraindications, warnings, and side-effects that should be carefully considered before use.