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  • Anti Depressant Drugs Free Pharmacology Note – 2021

    Anti Depressant Drugs are used to treat Depression. Depression is a disorder of mood and it is classified as an affective disorder. Anti Depressant Drugs are classified into two major types of depression: unipolar depression and bipolar depression. In this note, we will describe the Classification, Mechanism of Action, Adverse Effects, Therapeutic Uses, and Drug Interactions of Anti Depressants.

    Anti Depressant Drugs Free Pharmacology Note – 2021
    Anti Depressant Drugs Free Pharmacology Note – 2021

    Introduction

    Depression is a disorder of mood and hence it is classified as an affective disorder. There are two major types of depression: unipolar depression and bipolar depression. Unipolar depression is further sub-divided into reactive depression and endogenous depression. About 80% of depressed patients experience unipolar depression in which the mood swings in one direction only i.e. either depression with a feeling of worthlessness or depression with irritability. About 60% of unipolar depressed patients show reactive depression manifested by feelings of sadness or grief and anxiety due to reasons like the death of a loved one, unemployment, physical illness, or social problems. It is self-limiting and responds to antianxiety drugs. About 25% of unipolar patients are having endogenous depression with suicidal thoughts. It is not self-limiting unless treated with an antidepressant drug or by electroconvulsive therapy (ECT). It results either due to genetic causes or due to disturbed neurotransmission of NE, 5-HT, or DA in certain areas of the brain.

    Symptoms of Depression

    Symptoms of Depression includes:

    • Sleep disturbance
    • Feeling of guilt
    • Ugliness, and
    • Loss of Libido

    Classification of Anti Depressant Drugs

    Classification of anti depressants on the basis of Mechanism of Action is given below:

    • Tricyclic antidepressants (TCAs): These drugs block NE and 5-HT
      • NA + 5-HT reuptake inhibitors: Imipramine, Clomipramine, Amitriptyline, Doxepin
      • Predominantly NA reuptake inhibitors: Desipramine, Nortriptyline, Amoxapine, Reboxetine
    • Selective serotonin reuptake inhibitors (SSRIs): Sertraline, Fluoxetine, Fluvoxamine, Paroxetine, Citalopram, Escitalopram
    • Atypical antidepressants: Trazodone, Nefazodone, Bupropion, Mirtazapine, Mianserin
    • Antidepressants of natural origin: St. John’s wort (Active principle: Hyperforin)
    • MAO inhibitors:
      • Non-selective: Tranylcypromine;
      • Selective: Moclobemide

    Mechanism of Action of Different Anti Depressant Drugs

    Mechanism of Action of different types of Anti Depressants are discussed below:

    • Drugs that block NE and 5-HT reuptake: These are tricyclic antidepressants. They block the reuptake of NE and 5-HT into their neuron by inhibiting respective transporters. It leads to more availability and a longer stay of NE and 5-HT at their respective receptor sites.
    • SNRIs: Besides the effects shown by tricyclic antidepressants, SNRIs lack α1- adrenergic, histamine H1 and cholinergic receptor blocking properties of TCAs. Hence, they have fewer side effects.
    • Drugs blocking NE reuptake: These drugs predominantly inhibit NE reuptake which results in increased concentration of NE in the synaptic cleft.
    • SSRIs: They selectively increase levels of serotonin in the synaptic cleft. They are most commonly prescribed antidepressant drugs. All antidepressants described above exhibit a lag of 2-3 weeks to produce desirable clinical effects.
    • Atypical antidepressants: Atypical antidepressants have different mechanisms of action. Trazodone/ Nefazodone inhibits the uptake of 5-HT, blocks the 5-HT2A receptor, and desensitizes the presynaptic 5-HT receptor. Mianserin blocks presynaptic α1-receptors and increases the release of NE in the brain. Mirtazapine acts by increasing both NE and 5-HT release. Bupropion is a weak inhibitor of neuronal reuptake of 5-HT, NE, and DA.
    • Antidepressants of Natural Origin: Active ingredients of St. John’s wort (Hypericum perforatum) are monoamine reuptake inhibitors, mild MAO inhibitors, and stimulants at GABA receptors.
    • MAO Inhibitors: MAO inhibitors increase brain amine levels by inhibiting their metabolism, resulting in the increase of NE and 5-HT. There are two isoforms of MAO: MAO-A and MAO-B.MAO inhibitors need a biological lag of 2-3 weeks to exert clinical effects.

    Pharmacokinetics of Anti Depressant Drugs

    Oral absorption of most antidepressant drugs is good; still, the bioavailability is uncertain because of their first-pass metabolism. Bioavailability of Citalopram and Protryptyline is90%. The plasma half-life of most antidepressants is long, hence plasma concentration is built up slowly. After reaching steady-state, one daily dose at bedtime is enough. Plasma half-life for some antidepressants is low. Amoxapine (8 hours), Nefazodone (2-4 hours), Trazodone (4-8 hours), and Venlafaxine (4-9 hours) are some examples. The half-life is longer due to their metabolites except for Fluvoxamine, Paroxetine, and Protriptyline. Among MAO inhibitors, Moclobemide is readily absorbed but its first-pass metabolism reduces
    bioavailability; its half-life is 1-3 hours.

    Therapeutic Uses of Anti Depressant Drugs

    Therapeutics uses of different anti depressants are given below:

    Tricyclic Antidepressants

    • Nocturnal Enuresis: It is the condition of bed wetting which occurs to the children of ages of 2-3 year due to inadequate control over bladder. The treatment involves bladder training and correction of psycho pathological factors.
    • Bulimia Nervosa: It is a behavioral disorder in which the patient over eats then vomits or fasts to undo the threat of weight gain.
    • Other Uses: Tricyclic Antidepressants are also used in Migraine. They are also widely used in panic disorder, and for relieve from headache.

    MAO Inhibitors

    • MAO inhibitors are widely used in the treatment of endogenous unipolar depression. They are also used in panic disorder, bulimia nervosa, and post traumatic reaction. They are also used as a second line when TCAs are fail to work. The Selective MAO B inhibitor selegiline is used significantly for treating Parkinsonism.

    SSRIs

    • SSRIs like Fluoxamine and Fluoxetine are useful in treating bulimia nervosa.
    • SSRIs like Paroxetine or reversible MAO-A inhibitor Moclobemide are preferred for school phobia and social phobia. Paroxetine with Alprazolam are preferred for posttraumatic stress disorder. SSRIs are helpful in controlling impulse control disorder like gambling.

    Atypical Depressants

    • Bupropion is used to treat nicotine dependence and smoking caessation.
    • Citalopram is used to treat ethanol abuse syndrome.

    Adverse Effects of Anti Depressant Drugs

    Adverse effects are dependent on the type of anti-depressant based on its mechanism
    of action.

    • TCAs which block uptake of NE or NE + 5-HT: TCAs with histamine H1 receptor blocking actions (Amitriptyline, Doxepin and Trimipramine) cause more sedation. Drugs like Maprotiline, Bupropion and Clomipramine lower seizure threshold and precipitate epileptic seizures. Drug like Amoxapine can induce extrapyarmidal effects, gynacomastia (in males) and galactorrhoea (in females).
    • SNRIs: These drugs have serotonergic side effects like discontinuation syndrome.
    • SSRIs: Some patients complain of agitation, anxiety and insomnia. Few others complain of sexual dysfunction including decreased libido and delayed ejaculaton. Nausea and loose stools are also experienced by few patients. Sudden withdrawal causes discontinuation syndrome leading to dizziness, paresthesias and headache.
    • MAO Inhibitors: Their adverse effects include postural hypotension (in elders), weight gain, dizziness and sexual dysfunction.
    • Atypical Antidepressants: Trazodone causes nausea, sedation, postural hypotension and priapism leading to impotence. Bupropion causes agitation and insomnia. Mirtazapine and Mianserin cause sedation due to histamine H1-blockade. Hepatotoxicity and blood dyscrasias have also been reported.

    Drug Interection of Anti Depressant Drugs

    They are classified under three categories:

    • Interactions with TCAs and related Drugs
      • TCAs potentiate effects of directly acting sympathomimetics causing rise in BP and arrhythmias; but inhibit effects of indirectly acting sympathomimetics.
      • Anticholinergic drugs aggravate toxicity of TCAs.
      • Phenytoin, Chlorpromazine and Aspirine displace TCAs from their protein binding sites leading to increased effect of TCAs.
      • MAO inhibitors have synergistic action with TCAs causing hypertension, arrhythmiasand seizures.
    • Interactions with MAO inhibitors
      • Food articles containing tyramine, like cheese, beer, red wine, banana, yoghurt and pickled meat when used with MAO inhibitors can cause hypertensive crisis.
      • MAO inhibitors with TCAs or with directly/indirectly acting sympathomimetics can cause hypertension, arrhythmias and seizures.
      • MAO inhibitors inhibit degradation of DA. This can result in hypertension.
      • MAO inhibitors retard metabolism of drugs like morphine causing severe respiratory depression. It also retards metabolism of sulfonylureas causing hypoglycaemia and that of chloroquinine causing toxicity of chloroquine.
    • Interactions with SSRIs
      • SSRIs inhibit metabolising enzymes like CYP2D6 and CYP3A4. As a result, plasma levels and toxicity of TCAs, Haloperidol, Clozapine, Warfarin, Dextromethorphan, Terfenadine, Astemizole and Cisapride are increased. Elevated levels of Terfenadine, Astemizole and Cisapride can precipitate arrhythmias.
      • SSRIs with MAO inhibitors result in elevated levels of 5-HT causing “serotonin syndrome” leading to hyperthermia, muscle rigidity, tremors and rapid changes in mental status along wirth cardiovascular collapse.

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    Conclusion

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  • Route Of Drug Administration Free Pharmacology Note – 2021

    In this topic “Route of Drug Administration” we are going to discuss the different types of Routes from where we can administrate the drugs. There are many ways to administrate a drug like the Parenteral route, Oral route, Local route, systemic route, and many other routes. In this post, we will do a detailed discussion on these routes and the advantages, disadvantages of these routes.

    Routes of Drug Administration
    Routes of Drug Administration

    What is Route of Drug Administration

    Route of drug administrations refers to the starting point of the body from where the drug will be introduced to the body and will be reached the target organ or system to show its effects. Most of these drugs can be administrated via different routes and they also depend on different factors

    Factors Affecting Route of Drug Administration

    There are many routes of drug administration and it is depend on many factors also. The factors that effect on the route of drug administration are given below:

    • The physical and chemical properties of drug molecules affect the routes for drug administration.
    • The site for the desired action also affects the routes
    • The route for administration of the drug also depends upon the condition of the patient. The route can change for unconscious, vomiting, diarrhea patients.
    • The age of the patient is also an important factor.
    • The route also depends on the usage type of the drug. This can be changed on emergency usages or routine usages.
    • Effects of gastric pH, digestive enzymes, and first-pass metabolism also affect the route of drug administration.

    Different Routes of Drug Administrations

    There are different type of routes for drug administration. There are mainly two different routes 1. Local Route and 2. Systemic Route.

    Different routes of drug administrations
    Different routes of drug administrations

    Oral Routes

    Drugs absorption via oral administration can be quite variable. Dosage form design may also be used modify the rate of absorption.

    Advantages of Oral Drug Administration

    • Drugs administrated via Oral routes are safe, cheap and easy to take.
    • Drug administration via oral routes are very convenient.
    • Variety of dosage forms are available for oral administration.

    Disadvantages of Oral Drug Administration

    • Sometimes inefficient – high dose or low solubility drugs may suffer poor availability, only part of the dose may be absorbed. Griseofulvin was reformulated about 1970 to include the drug as a micronized powder. The recommended dose at that time was decreased by a factor of two because of the improved bioavailability.
    • First-pass effect – drugs absorbed orally are transported to the general circulation via the liver. Thus drugs that are extensively metabolized will be metabolized in the liver during absorption.
    • Food – Food and G-I motility can affect drug absorption. Often patient instructions include a direction to take with food or take on an empty stomach. Absorption is slower with food for tetracyclines and penicillins, etc. However, for propranolol bioavailability is higher after food, and for griseofulvin, absorption is higher after a fatty meal.
    • Local effect – Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties. Thus, antifungal agents may be included with an antibiotic.
    • Unconscious patient – The patient must be able to swallow solid dosage forms. Liquids may be given by tube

    Buccal and Sublingual

    Some of the drugs are taken as smaller tablets that are held in the mouth or under the tongue. These are buccal or sublingual dosage forms. Buccal tablets are usually harder tablets [4 hour disintegration time], designed to dissolve slowly. Nitroglycerin, as a softer sublingual tablet [2 min disintegration time], may be used for the rapid relief of angina. This Route of Administration is also used for some steroids such as testosterone and oxytocin. Nicotine-containing chewing gum may be used for cigarette smoking replacement.

    Advantages

    • First pass – In this route, the Liver is bypassed so there is no loss of drug by the first-pass effect like the Oral administration route for buccal or sublingual administration. Bioavailability is higher also.
    • Rapid absorption – Because of the good blood supply to the area of absorption is usually quite rapid, especially for drugs with good lipid solubility.
    • Drug stability – pH in mouth relatively neutral (cf. stomach – acidic). Thus the drug may be more stable.

    Disadvantages

    • Holding the dose in the mouth is somewhat difficult. If any part of the dose is swallowed mistakenly then that portion must be treated as an oral dose and it will be then subject to first pass metabolism.
    • Usually Buccal and Sublingual routes more suitable for drugs with small doses.
    • Drug taste may need to be masked

    Rectal

    Drugs are given by the rectal route of drug administration are most commonly given as suppository or enema. Some of the drugs that are given by this route include aspirin, theophylline, chlorpromazine, and some barbiturates.

    Advantages

    • By-pass liver – Some (but not all) of the veins draining the rectum lead directly to the general circulation thus bypassing the liver. Therefore there may be a reduced first-pass effect.
    • Useful – This route may be most useful for patients unable to take drugs orally or with younger children.

    Disadvantages

    • Erratic absorption – Drug absorption from a suppository is often incomplete and erratic. However, for some drugs, it is quite useful. There is research being conducted to look at methods of improving the extent and variability of rectal administration. Absorption from solutions used as an enema may be more reliable.

    Intravenous

    Drugs that are given via Intravenous are usually given into a peripheral vein. Rapid injections are used to treat epileptic seizures, acute asthma, or cardiac arrhythmias.

    Advantages

    • Rapid – A quick response is possible for the drugs that are given via the Intravenous route. Plasma concentration can be precisely controlled using IV infusion administration.
    • Total dose – The whole dose is delivered to the bloodstream that is given via the Intravenous route. That is the bioavailability is generally considered to 100% after IV administration.

    Disadvantages

    • Finding Suitable vein – It may be difficult to find a suitable vein to give the drug via the Intravenous route. There may be also some tissue damage at the site of injection if it is not given carefully.
    • Maybe toxic – As the drugs administrated via the Intravenous show the rapid response, toxicity can be a problem with rapid drug administrations.
    • Requires trained personnel – Trained personnel are required to give intravenous injections.
    • Expensive – Sterility, pyrogen testing, and larger volume of solvent mean greater cost for preparation, transport, and storage.

    Subcutaneous

    By Subcutaneous method the drugs are given under the skin. Insulin Injection is given to the patients via this route of administration.

    Advantages

    • Drugs of this route can be given by the patient.
    • Absorption can be fast from an aqueous solution but slower with depot formulations. Absorption is usually complete. Improved by massage or heat. Vasoconstrictor may be added to reduce the absorption of a local anesthetic agent, thereby prolonging its effect at the site of interest.

    Disadvantages

    • Can be painful. Finding suitable sites for repeat injection can be a problem.
    • Irritant drugs can cause local tissue damage.
    • Maximum of 2 ml injection thus often small doses limit use.

    Intramuscular

    Advantages

    • A larger volume than Subcutaneous can be given by Intramuscular. They may be easier to administer than intravenous injections.
    • A depot or sustained release effect is possible with the intramuscular injections, e.g. procaine penicillin

    Disadvantages

    • Trained personnel required to give injections via Intramuscular routes.
    • Absorption can be rapid from an aqueous solution. Absorption is sometimes erratic, especially for poorly soluble drugs,e.g. diazepam, phenytoin. The solvent may be absorbed faster than the drug causing precipitation of the drug at the site of injection.
    • Sometime this method can be painful

    Inhalation

    Inhalation may be used for local effects like bronchodilators. Inhalation can also be use for systemic effects like general anesthesia. Drugs taken via Inhalation shows rapid absorption as it by pass the liver.

    Topical

    • Local effect – ear drops, eye drops or ointment, antiseptic creams and ointments, sunscreens, callous removal products, etc.
    • Systemic effect – e.g., nitroglycerin ointment
    • Generally, absorption is quite slow. Absorption through the skin especially via cuts and abrasions or from sites where the skin is quite thin can be quite marked. This can be a real problem in handling toxic materials in the laboratory or pharmacy. This can also be a serious problem with garden chemicals.

    Effect of Route of Drug Administration on Initiation of Effect of Drugs

    Route of administrationTime
    Intravenous30 – 60 sec
    Intraosseous30 – 60 sec
    Endotracheal2 – 3 min
    Inhalation2 – 3 min
    Sublingual3 – 5 min
    Intramuscular10 – 20 min
    Subcutaneous15 – 30 min
    Rectal5 – 3 min
    Oral39 – 90 min
    Transdermal or Topicalmins to hours

    Conclusion

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