Multiple Choice Questions (MCQ) on Veterinary Pharmacology (Part- 3)

ANSWERS & EXPLANATIONS

1.

c. (Benzoic acid)
Food preservatives employed in commercial pet foods – Benzoic acid
Benzoic acid is a commonly used antimicrobial preservatives in food and beverages, especially in carbonated beverages, as it presents it’s highest antibacterial activity at pH 2.5 – 4.
Benzoic acid has inhibitory effects on the proliferations of bacteria and yeast, a major causes of food spoilage. 

2.

d. (after a day or week)
The pharmacological response to drug acting through nuclear receptor normally occurs after a day or weeks.
Nuclear receptors are a class of protein responsible for sensing steroids, thyroid hormones, vitamins and certain other molecules.

3.

c. (Antagonist)
A drug interacting with receptors and elicit response is called Agonist
A drug interacting with receptor but does not elicit response – Antagonist.
Drug doesn’t have receptor – Orphan drug.
Placebo: Non- therapeutics agents e.g., Nutritive agents) but elicit response.

4.

a. (1st pass effect)
The pre- systemic metabolism of drugs before reaching systemic circulation is called 1st pass effect.
1st pass effects include:
-Hepatic metabolism
-Metabolism by intestinal wall enzymes
-Metabolism by Intestinal flora
If a drug is subject to Hepatic 1st pass effect:
-It may be effective orally if given in high dosage
-A chemical analogue resistant to hepatic metabolism may be given orally
-Response to the oral drug is more in the presence of hepatic dysfunction.
-1st pass effects decreases the bioavailability of drug
Note:
-Enzyme induction by a drug is only of a specific isoenzyme.
-Hepatic cytochrome p-450 activity is inhibited by the continuous use of Cimetidine, spironolactone, Ethyl estradiol
- In the presence of severe hepatic disease, Ionizable drugs can be prescribed normally.

5.

c. (Decreased by drugs which sterilize the gut)
Enterohepatic circulation refers to the process whereby a drug or a metastable metabolite thereof in the liver is secreted into the bile, stored in the gall bladder, and subsequently released into the small intestine, where the drug can be reabsorbed back into circulation and subsequently returned to the liver, leads to increases the half- life of the drug.

6.

d. (Urinary excretion is primary mode of clearance)
1st order of kinetics of drug Elimination: It states that the amount of drug eliminated per unit time changes with the concentration of the drug in the blood.
1st order of kinetics of drug elimination depends on the concentration of only one reactant and a constant fraction of the drug in the body is eliminated per unit time.
While, In zero order kinetics (Also called Saturation kinetics), in which metabolizing enzymes get saturated where the rate of a n elimination of drug is independent of plasma concentration of drug.

7.

c. (Respiratory arrest)
Death due to Cobra envenomation is due to respiratory arrest.

8.

b. (Relative safe)
If therapeutics index of a given drug (X) = 8, then it means the drug (X) is relative safe, because it implies Lethal dose of drug is 8th times of the effective dose of the drug.
Therapeutics index = (Toxic Dose 50) / (Effective Dose 50).

9.

d. (Lungs)
Prostaglandins are essentially metabolized in Lungs.
Once secreted into the peripheral circulation, most prostaglandins (with exception of prostacyclin and TXA2) are rapidly metabolized in the lungs by an enzyme called 15- hydroxy prostaglandins dehydrogenase (15-OH-PGDH). This enzyme selectively oxidizes the hydroxyl group at carbon 15 into a 15- keto moiety.

10.

a. (u receptors)
The analgesics effects of opioids mediated via u- receptors.
Opioid receptors are a group of inhibitory G- protein coupled receptors (GPCRs), with opioid as ligands.
The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins, and nociception.

Classification of opioid receptors

Receptors	Functions	Endogenous opioids
Mu receptor	Supraspinal and spinal analgesia; sedation; inhibition of respiration; slowed gastrointestinal transit; modulation of hormones and neurotransmitter release	Endorphins >Enkephalin > Dynorphins
Delta receptors	Supraspinal and spinal analgesia; modulation of hormones and neurotransmitter release	Encephalins> Endorphins> Dynorphins
Kappa receptors	Supraspinal and spinal analgesia; psychomimetic effects; slowed gastrointestinal transits	Dynorphins> Endorphins> encephalins

11.

c. (Botulinum)
Botulinum prevents the release of Acetylcholine at neuromuscular junctions.
Botulinum toxin, the most potent neurotoxins, produces paralysis by blocking presynaptic release of neurotransmitter (Acetylcholine) at the neuromuscular junction, with reversible chemical denervation of the muscle fibre, thereby inducing partial paralysis and atrophy.
Chlorpromazine (antiemetic drug) block the histamine (H1), Dopamine (D2) and Muscarinic (M1) receptor in the vomiting centre.
Strychnine, competitive glycine antagonist at the brainstem and spinal postsynaptic receptors. Glycine is normally an inhibitory neurotransmitter, once antagonized, there is loss of normal descending inhibitory motor tone resulting in muscle spasm.
Nicotine: Nicotine stimulates presynaptic acetylcholine receptors thereby enhancing Ach release and metabolism.

12.

d. (Ketamine)

• N- methyl D-aspartate (NMDA) receptor are ligand- gated cation channels activated by an excitatory neurotransmitter, glutamate.
• These receptors are located mostly at excitatory synapses, and thereby, participate in excitatory neurotransmission in CNS.
• NMDA receptors agonist: Glutamate, Morphine, N-methyl- D Asparate, Cycloserine
• NMDA receptor antagonist: Ketamine, Dextromethorphan, Memantine and amantadine

13.

c. (Ketoconazole)
-Drugs inhibits Cytochrome P450 metabolic enzymes: Amitriptyline, aprepitant, Carvedilol, Chloramphenicol, cimetidine, Ciprofloxacin, clarithromycin, Codeine, donepezil, fluvoxamine, haloperidol, imatinib, ketoconazole, metoprolol, Paroxetine, risperidone, ritonavir, tramadol, verapamil etc.
Drugs induces Cytochrome P450 activity: Carbamazepine, griseofulvin, phenobarbital, phenytoin, rifampicin, St. John’s wort.

14.

b. (Vancomycin)

• Drug of Choice for treatment of MRSA – Vancomycin
• DOC for trichomoniasis : Metronidazole
• DOC for E. canis : Doxycycline
• Antithielerial drugs: Buparvaquone, halofuginine lactate

15.

b. (Kidney)
-Drug metabolism in fish essentially occurs in Kidney.

16.  

a. (Tetracycline)
Tetracycline serve as an excellent example of the phototoxic hazards of antibacterial agents. Among them, Chlorderivatives are the most frequently reported to cause phototoxicity. Chlortetracycline and doxycycline are more photoactive than tetracycline, OTC, Methacycline or minocycline.

17.  

a. (Enalapril)

• Enalapril is an example of Prodrug.
• Prodrug are medications that turns into an active form once they enter the body.
• Examples of prodrugs that exists naturally or were produced unintentionally during drug development includes Enalapril, Aspirin, Psilocybin, parathion, irinotecan, codeine, Heroin, L-dopa and various antiviral nucleoside. 

18.

a. (Blocking Na+ channel)

• Lignocaine acts by blocking Na+ channels.
• Lignocaine/ lidocaine reversibly blocks Na+ and K+ ion channels and regulates intracellular and extracellular Calcium concentration through other ligand –gated ions channels.
• Lidocaine was 1st sodium channel blocker to be identified.

19.

d. (facilitate glucose entry into RBCs)

• Two hormones responsible for regulation of glucose level in blood
• Insulin ( Decrease glucose level in blood by promoting glycogenesis in liver (Glucose storage) and uptake of glucose by cells)
• Glucagon ( Increase glucose level in blood by promoting gluconeogenesis )
• Both the hormones are produced by Pancreas ( Glucagon – alpha cells of Pancreas while Insulin –Beta cells of Pancreas).

20.

c. (phytomenadione)
Antagonist of Warfarin is phytomenadione (Vitamin K1), a naturally occurring compound, promotes hepatic synthesis of clotting factors (II, VII, IX, X) , used to prevent and treat haemorrhage related to Vitamin K deficiency.
Note:
Ethamsylate acts on 1st step of haemostasis by improving platelets adhesiveness and restoring capillary resistance.
Clopidogrel selectively inhibits the binding of ADP to it’s platelets P2Y12 receptor and the subsequent ADP- mediated activation of the glycoprotein GPIIb/IIIa complex, thereby inhibiting platelets aggregations. This action is irreversible.
Protamine sulfate: Highly cationic peptide that binds to either heparin or low molecular weight heparin to form stable ion pair, which does not have anticoagulant activity. The ionic complex is then removed and broken down by the reticuloendothelial systems.

21.

b. (Docusate sodium)
Laxative that promotes defecation without increasing peristalsis : Docusate sodium
Classification of Laxatives or purgatives:

• Bulk : Increase volume of non absorbable solid residue. Polysaccharides and cellulose derivatives e.g. psyllium, agar, alginates, guar gum, methylcellulose, carboxymethyl cellulose sodium, Calcium polycarbophil , malt soup extract.
• Osmotic: Increase water content in large intestine. Organic (Sugars): lactulose, Polyethylene glycol; Non- organic (Saline purgatives): Magnesium salts, sodium or potassium salts.
• Stimulant: Increase motility and secretion. Diphenylmethane (Phenolphthalein, Bisacodyl, sodium picosulfate); Anthraquinone (Senna, cascara sagrada); Serotonin agonist (tegaserod); Fixed oil (Castor oil).
• Fecal softeners (Lubricants): Alter the consistency of feces –easier to pass. Docusates and liquid paraffin.

22.

c. (Log Dose –response curve is sigmoid)

• Log Dose – response curve, describes the magnitude of the response of an organism, as a functions of exposure or dose to a stimulus or chemical after a certain exposure time.
• Log Dose- response curve is sigmoidal in shape.

23.

c. (Both a and b)
Spare receptors:

• Determine the efficiency of receptor- effector interaction
• If present in large number, increases the sensitivity of the tissue to the drug
• Receptors may be considered spare when the maximal response is elicited by an agonist at a concentration that does not produce full occupancy of the available receptors. Spare receptors exist when maximum drug response is achieved prior to saturation of all receptors.
• They are not hidden receptors
• When they are occupied, they can be coupled to response
• Can be demonstrated by using irreversible antagonist. Experimentally, the spare receptor concept can be shown when the agonist can still produce an undiminished maximal response in presence of an irreversible antagonist.

24.

d. (All of the above)
Facts related to ligand- gated plasma membrane channels are:

• The ligand receptors that controlling membrane channels are on the cell surface
• The ligands regulates the flow of ions through membrane channels
• Several amino acids neurotransmitters act by this mechanism.

25.

d. (All of the above)

Facts are true:

• Potency refers to the concentration of drug required to produce a given effects
• ‘Efficacy’ refers to the maximal response that can be achieved in high dose.
• “Clinical effectiveness’ of the drug depends not on it’s potency but on it’s maximal efficacy

26.

a. (Vidarabine)

Classification of Antiviral drugs

• Antiviral drugs acts on DNA polymerase enzymes: Nucleoside( Vidarabine, Acyclovir, Gancyclovir, Cidofovir, Famciclovir, Idoxuridine, Penciclovir, Trifluridine, Valaciclovir, Valganciclovir); Non – Nucleoside (Phosphonoacetic acid)
• Antiviral drugs acts on reverse transcriptase: Nucleoside ( Zidovudine, Zalcitabine, Tenovir, Telbivudine, Lamivudine, Entecavir, Emtricitabine, Didanosine, Adeflovir); Non – nucleoside (Delavirdine, Efavirenz, Etravirine, Nevirapine, Rimatadine)
• Antiviral drugs which is (protease inhibitors): (Afazanavir, Amprenavir, Darunavir, Indinavir, Nelfinavir, Oseltamivir, Ritonavir, Saquinavir, Tipranavir, Zanamivir)
• Integrase inhibitors: Raltegravir
• Fusion inhibitors: Cyclosporine, Docosanol, Enfuviritide, Maraviroc
• Signaling inhibitors: Resveratrol, Ribavirin

27.

d. (Both b and c)

• Idiosyncratic drug response is usually caused by the genetic differences, may be by the immunologic mechanism.
• Idiosyncratic drug reactions may be defined as the adverse effects that cannot be explained by the known mechanism of action of offending agents.
• Examples of some drugs, causing idiosyncratic reactions includes troglitazone, valproate, amiodarone, ketoconazole, disulfiram, and isoniazid.

28.

a. (Smooth muscles of gut, bronchus and urinary bladder)
Smooth muscles of gut, bronchus and urinary bladder are innervated by both sympathetic and parasympathetic nerve.

29.

d. (All)
Denervation super sensitivity occurs in:

• In the skeletal muscles after denervation
• In the blood vessel after sympathetectomy
• Due to upregulation of receptors.

30.

b. (They are not sensitive to the transmitters released by the neuron)
Features of the presynaptic nerve terminals of ANS:

• They synthesize, store and release transmitters in response to nerve impulse
• The presynaptic inhibition may be homotropic as well as heterotropic
• They release more than one transmitter in response to nerve impulse

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