NAVLE Qs Pharmacology

BETA 1 Adrenergic (Location)

Heart and Kindey

Beta1 Adrenergic ( Action)

Increase HR And Contractility

Role in fat metabolism

Beta 2 Adrenergic ( Location)

Loungs, Blood Vessels, and Uterus

Beta2 Adrenergic (Action)

Bronchodilation

Vasodilation

Uterine relaxation

A synthetic, direct-acting catecholamine and positive inotrope

Dobutamine (Drug Class)

Dobutrex, Posijec

Dobutamine (Trade Names)

Predominantly a strong, direct Beta-1 (β
1
​
) adrenergic agonist, with only mild Beta-2 (β
2
​
) and Alpha-1 (α
1
​
) adrenergic effects at standard doses

Dobutamine (Mechanism of Action)

Short-term inotropic support for heart failure (e.g., DCM, septic shock) and hypotension during anaesthesia

Dobutamine (Primary Indications)

Tachycardia, proarrhythmia, hypotension, and hypokalaemia (with prolonged use); seizures are possible, especially in cats

Dobutamine (Adverse Effects)

Patients with a cardiac outflow obstruction, such as aortic stenosis

Dobutamine (Contraindications)

Increased risk of arrhythmias when used with halothane, doxapram, or MAOIs; diabetic patients may require increased insulin

Dobutamine (Drug Interactions)

Must be given as a dilute continuous rate infusion (CRI) with careful monitoring of blood pressure and ECG; dose is titrated to effect

Dobutamine (Administration)

Dogs and Cats

Dobutamine (Species)

A selective beta-2 (β
2
​
) adrenergic agonist and bronchodilator

Salbutamol (Drug Class)

Ventolin

Salbutamol (Trade Name)

Selective stimulation of beta-2 (β
2
​
) adrenergic receptors, which causes smooth muscle relaxation and bronchodilation

Salbutamol (Mechanism of Action)

Treatment of bronchospasm associated with inflammatory airway disease (e.g., feline asthma) and irritation

Salbutamol (Primary Indications)

In cats, chronic use can exacerbate airway inflammation; it should be reserved for acute or short-term management only

Salbutamol (Feline Use)

Tachycardia, arrhythmias, muscle cramps, palpitations, and peripheral vasodilation; shivering and agitation may be seen in dogs

Salbutamol (Adverse Effects)

Increased risk of side effects if used with diuretics, digoxin, theophylline, or corticosteroids (based on human data)

Salbutamol (Drug Interactions)

Administered via a metered-dose inhaler (100 µg per inhalation)

Salbutamol (Administration)

A non-selective beta-adrenergic antagonist (beta-blocker)

Propranolol (Drug Class)

Blocks beta-1 (β
1
​
) receptors in the heart (reducing rate/contractility) and beta-2 (β
2
​
) receptors in the vasculature and bronchi (causing vasoconstriction/bronchoconstriction)

Propranolol (Mechanism of Action)

Management of cardiac arrhythmias (tachycardias), hypertrophic cardiomyopathy (HCM), systemic hypertension, and situational anxiety

Propranolol (Primary Indications)

Used to reverse some of the clinical features of thyrotoxicosis (hyperthyroidism), particularly prior to surgery

Propranolol (Thyroid-Related Use)

Bradycardia, AV block, hypotension, myocardial depression, and bronchospasm; sudden withdrawal can cause rebound arrhythmias

Propranolol (Adverse Effects)

Patients with bradyarrhythmias or decompensated congestive heart failure; use with extreme caution in animals with airway disease (e.g., feline asthma)

Propranolol (Contraindications)

Increased bradycardia risk with calcium-channel blockers or digoxin; blocks the bronchodilatory effects of theophylline; its metabolism is affected by many drugs

Propranolol (Drug Interactions)

Alpha-1 Receptors:

• Location:

• Primarily found on vascular smooth muscle, where they mediate vasoconstriction. 

Alpha-1 Receptors: Mechanism

When activated, they lead to increased intracellular calcium, causing smooth muscle contraction. 

Alpha-1 Receptors: Effect

• Stimulation of alpha-1 receptors results in vasoconstriction, increased blood pressure, and increased peripheral resistance. 

Alpha-2 Receptors:

• Location:

• Found in the brain and periphery. 

Alpha-2 Receptors: Mechanism

Activation of alpha-2 receptors in the brain can reduce sympathetic outflow, leading to decreased norepinephrine release and lower blood pressure. In the periphery, their function is not fully understood but may contribute to blood flow control

Alpha-2 Receptors: Effect

• Can cause vasoconstriction in some tissues, but also inhibit norepinephrine release, potentially leading to vasodilation in others. 

A selective alpha-1 (α
1
​
) adrenergic agonist

Phenylephrine (Drug Class)

Stimulates alpha-1 (α
1
​
) adrenergic receptors, causing peripheral vasoconstriction (if given IV) and contraction of the iris dilator muscle (if given topically)

Phenylephrine (Mechanism of Action)

As an IV infusion in conjunction with fluid therapy to treat hypotension caused by drugs or vascular failure

Phenylephrine (Systemic Indications)

To produce mydriasis for intraocular surgery, differentiate conjunctival vs. episcleral vessels, and reduce conjunctival haemorrhage

Phenylephrine (Ophthalmic Indications)

Used to diagnose Horner's syndrome via a denervation hypersensitivity test. The time to mydriasis after topical application helps locate the lesion; rapid dilation (

Phenylephrine (Horner's Diagnosis)

Hypertension, tachycardia, and reflex bradycardia; serious tissue necrosis can occur with extravasation of the IV infusion

Phenylephrine (Adverse Effects)

Increased risk of arrhythmias when used with digoxin or volatile anaesthetics; pressor effects are enhanced by oxytocic agents

Phenylephrine (Drug Interactions)

Use with care in cats and small dogs (use lower concentrations); do not apply topically once ophthalmic surgery has started due to risk of absorption

Phenylephrine (Contraindications / Cautions)

It is ineffective for producing mydriasis in cats when used as a sole agent

Phenylephrine (Feline Use)

An anticholinergic (parasympatholytic) agent

Atropine (Drug Class)

Atrocare

Atropine (Trade Name)

Blocks the action of acetylcholine at muscarinic cholinergic receptors in the parasympathetic nervous system (parasympathicolytic)

Atropine (Mechanism of Action)

Increased heart rate, pupillary dilation (mydriasis), bronchodilation, and decreased GI motility, salivation, and tear production

Atropine (Primary Effects)

To treat bradycardia/bradyarrhythmias, for management of organophosphate/carbamate toxicity, and as a mydriatic for ophthalmic use

Atropine (Clinical Indications)

Sinus tachycardia, decreased tear production (potentially worsening KCS), increased intraocular pressure, and drying of bronchial secretions

Atropine (Adverse Effects)

Glaucoma, lens luxation, and keratoconjunctivitis sicca (KCS)

Atropine (Contraindications)

Low doses can cause a paradoxical exacerbation of bradycardia before the heart rate increases

Atropine (Dosing Precaution)

Combining with alpha-2 agonists is not recommended; its effects are enhanced by many drugs like antihistamines, benzodiazepines, and phenothiazaines

Atropine (Drug Interactions)

Dogs and Cats

Atropine (Species)

amitraz poisoning

Pesticide, antidote: alpha-2 antagonist such as yohimbine or atipamezole, used in veterinary medicine primarily for treating tick infestations.

yohimbine ( class)

alpha-2 antagonist

atipamezole (class)

alpha-2 antagonist

A non-selective adrenergic agonist (sympathomimetic)

Adrenaline (Drug Class)

Directly stimulates alpha-1 ($α_1$), beta-1 ($β_1$), and beta-2 ($β_2$) adrenergic receptors

Adrenaline (Mechanism of Action)

Low doses cause mainly beta-effects (increased cardiac output, vasodilation), while high doses cause predominantly alpha-effects (vasoconstriction)

Adrenaline (Dose-Dependent Effects)

Treatment of cardiopulmonary arrest (CPA), status asthmaticus, bronchoconstriction, and severe anaphylactoid reactions

Adrenaline (Primary Indications)

Can produce arrhythmias (including ventricular fibrillation), tachycardia, and increases myocardial oxygen demand; necrosis may occur at the injection site

Adrenaline (Adverse Effects)

Propranolol can cause unopposed alpha-effects (hypertension); risk of arrhythmias is increased with agents like halothane or digoxin

Adrenaline (Drug Interactions)

Use with caution in animals with diabetes mellitus, hyperthyroidism, or hypovolaemia

Adrenaline (Cautions)

For CPA, give IV or intraosseously every 3-5 mins, followed by a fluid bolus to push the drug into central circulation

Adrenaline (CPA Administration)

A pure mu-opioid receptor agonist; the prototypical opiate analgesic

Morphine (Drug Class)

Provides analgesia through its action as a full agonist at the mu-opioid receptor

Morphine (Mechanism of Action)

Management of moderate to severe pain, particularly in the perioperative period, and as a component of premedication protocols

Morphine (Primary Indications)

Respiratory depression, vomiting, decreased GI motility, and histamine release (causing vasodilation/hypotension) if injected too rapidly IV

Morphine (Adverse Effects)

Inject slowly intravenously to avoid rapid histamine release, which can cause vomiting and hypotension

Morphine (Administration Precaution)

Has a short duration of action (especially in dogs) requiring frequent dosing or CRI; metabolized by the liver with a high first-pass effect for oral route

Morphine (Pharmacokinetics)

Its CNS and respiratory depressant effects are potentiated when used with other CNS depressants like anaesthetics, phenothiazines, or tranquilizers

Morphine (Drug Interactions)

Naloxone

Morphine (Reversal Agent)