Adrenaline, with chemical name “Epinephrine” is an endogenous catecholamine which acts as one of the three signal molecules for Adrenergic sympathetic autonomic nervous system (ANS).
Adrenaline (Adr) works as a direct sympathomimetic agonist drug on α or β or on both α and β adrenoreceptors.
It helps to treat various emergency life-threatening allergic reactions (anaphylaxis), sudden asthma, life-threatening hypotension linked to septic shock, swelling of face, lips, and throat.
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The action of epinephrine includes widening or relaxing the muscles or constricting blood vessels. Epinephrine helps the body to prepare for fight and flight response.
Mechanism of action
Adrenaline causes conformational change by binding to beta-adrenergic receptors on cell surface And then interacts with G-protein binding with stimulatory G-protein which binds with GTP, which then activates enzyme adenylyl cyclase (AC).
ATP is hydrolysed and converted to cAMP which activates cAMP dependent protein kinase after phosphorylation. This protein kinase phosphorylates troponin and phospholamban which combines with calcium ions which finally causes contraction and faster relaxation.
GIT (Gastrointestinal Tract)
It activates alpha- and beta- receptors in the gut causing relaxation but causes constriction of human peristalsis with no clinical import.
- Uterus: Adrenaline causes both contraction and relaxation of uterine muscles depending on the alpha- and beta- receptors. It causes relaxation at the time of pregnancy but at other times causes contraction.
- Skeletal muscles: It causes activation of alpha-1 receptors causing acetylcholine release from autonomic nerve endings, on the other side, it has direct effect on beta- receptors present in muscle fibres.
- CNS (Central Nervous system): It does not have any direct effect on the CNS system because of poor penetration across BBB (blood brain barrier). But it can cause some minimal effects like restlessness, apprehension, and tremor. But because of activation of alpha-1 receptors, it results in fall in blood pressure and bradycardia.
- Metabolic effects: It causes glycogenolysis resulting in hyperglycemia, hyperlactacidemia, lipolysis, and calorigenesis because of direct activity on liver, muscles and adipose tissues. It also occurs due to reduction of insulin and augmentation of glucagon secretion.
Overview Adrenaline Injection
Heart
Adrenaline helps to increase heart rate by enhancing working of SA nodes in the heart, which is popularly known as pacemaker.
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It also acts on other parts of the heart known as instant pacemaker- AV node and his Purkinje fibres, which results in steep increase in blood pressure.
This marked increase in BP can also cause arrhythmias. Adr help in following points:
- Increase in idioventricular rate in patients complaining of complete heart block.
- Increase in cardiac contraction force
- Accelerated rate of relaxation and development tension in heart muscles.
- Increased cardiac output and oxygen consumption of heart
Blood vessel
The activity depends on the α and β receptors present in the tissue, dose of drug, and vascular bed across the organ.
For example, adrenaline causes constriction in minute network blood vessels whereas it causes vasodilation in skeletal muscles and liver blood vessels.
By causing vasodilation, it causes breakdown of glycogen into glucose molecules and circulation of free fatty acids which are used in stress responses causing increased alertness and exertion.
Blood pressure
The effect on blood pressure depends on the dose of drug and rate of administration.
Adrenaline if given slowly through i.v (intravenous) infusion or by subcutaneous injection results in rise in systolic BP and decrease in diastolic BP.
There is also a decrease in vascular peripheral resistance. This implies that there is a rise in BP as well in pulse rate.
Respiratory system
Adrenaline is the potent bronchodilator by acting on β2 receptors by acting on constricted bronchi. It acts by decongesting bronchial mucosa by acting on α receptors.
Other than this, adrenaline works directly on the respiratory centre (RC). If infused intravenously will cause transient apnoea and also causes pulmonary edema in toxic doses.
Eye
Adrenaline causes minimal contraction of iris’ radial muscles resulting in mydriasis because of presence of α1 receptors.
Benefits and Side-effects of Adrenaline Injection
- Transient restlessness
- Headache
- Palpitations
- Anxiety
- Tremor
- Pallor
- Marked rise in BP
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- Cerebral haemorrhage
- Ventricular tachycardia
- Ventricular fibrillation
- Myocardial infarction
- Sweating
- Dizziness
Consider reading about –
- Irregular heartbeat
- Skin redness
- Nausea
- Vomiting
- Pale skin
- Uncontrollable shaking
- Vision loss
- Blurred vision
- Eye pain
- Swelling
- Stiff muscles
- Confusion
- Slurred speech
- Trouble walking
- Loss of coordination
- Unsteady feeling
- Chest fluttering
- Tunnel vision
- Buzzing in ears
Composition of Adrenaline Injection
Adrenaline/ epinephrine 1mg/mL in 1:1000
For kids concentration is 0.3 – 0.5 mg/ml.
Contraindications
- General anaesthetics like isoflurane, desflurane
- Antidepressants like MAOIs for example’ Nardil
- Oxytocin
- Phenothiazines includes chlorpromazine, thioridazine
- Steroidal medications (prednisone, cortisone, prednisolone)
- Diuretics
- Digoxin
- Ergot alkaloids for example dihydroergotamine, ergonovine, ergotamine, methylergonovine
- Anti- Parkinson drugs (Entacapone)
- Anti- histamines (chlorpheniramine, diphenhydramine)
- Medications used for BP, heart diseases
- Theophylline
- Thyroid treating drugs (levothyroxine)
- Antipsychotic drugs
- Beta-blockers
- OTC sleep medications
Safety Advice for Adrenaline Injection
Before proceeding with this medication, one should tell the prescriber if they have any conditions like diabetes, glaucoma, heart diseases, blood pressure, kidney problem, Parkinson’s disease, thyroid, allergic reactions, pregnancy, breast feeding.
