книга / MasterPass _ Pharmacology in 7 Days for Medical Students

PHARMACOLOGY IN 7 DAYS FOR MEDICAL STUDENTS

Table 5.3 Differences between morphine and pethidine

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DRUG DIFFERENCES

Table 5.4 Differences between heparin and warfarin

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PHARMACOLOGY IN 7 DAYS FOR MEDICAL STUDENTS

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PHARMACOLOGY IN 7 DAYS FOR MEDICAL STUDENTS

Table 5.6 Differences between adrenaline and noradrenaline

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DRUG DIFFERENCES

Table 5.7 Differences between methyl dopa and clonidine

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6

Miscellaneous

Halothane

Advantages

1Good physical properties.

2Used to produce controlled hypotension and bloodless field during plastic/vascular surgery.

3Potent anaesthetic.

4Produces bronchodilatation (useful in asthmatic patients).

5Potent relaxant of masseter muscles.

6Potent inhibitor of laryngeal and pharyngeal reflexes.

7Does not cause bronchospasm, laryngospasm and coughing.

Disadvantages

1Poor analgesic.

2Poor muscle relaxant.

3Profound hypotension, if given in more than 2% concentration.

4Increases para-sympathetic tone, leading to bradycardia.

5Sensitises ventricular muscle and conduction tissue to adrenaline, causing arrhythmias.

6Hepatotoxic and respiratory depressant.

7Expensive, and special apparatus is needed for administration.

8Can cause malignant hyperthermia (ryanodine receptors).

9Genetic mutations → more binding of Ca++ with the receptors.

Nitrous oxide

Advantages

1Rapid induction and recovery.

2Non-inflammable, non-irritating and non-explosive (however supports combustion).

3Very potent analgesic (30–40% analgesia; 65–70% loss of consciousness; and 80% plane 1 of surgical anaesthesia).

4Used in procedures of short duration (tooth-extraction, obstetrical analgesia, cleansing and debridement of wounds and cauterisation).

5Induction and maintenance of anaesthesia, along with I/V thiopentone-gas- oxygen-halothane technique called balanced-anaesthesia.

6Safe. No organ toxicity (respiratory, renal, CVS, or hepatic).

7Measurement of cerebral and coronary blood flow by Fick’s Principle.

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8Decreases the dose of general anaesthetic. When combined → decreased complications and decreased recovery period from anaesthesia.

Disadvantages

1Not a potent anaesthetic and muscle relaxant, so violent excitement can occur.

2Second gas effect leading to transient hypoxia.

3CO2 accumulation and hypoxia→ cardiac irregularities during anaesthesia.

4Specialised apparatus to control its administration.

5Administration for more than 7 hours, leads to bone-marrow depression (leukopenia and anaemia).

6Prolonged administration → peripheral neuropathy, megaloblastic anaemia (due to interference with vitamin B12 metabolism) and abortion.

Ketamine

Advantages

1Effective by both intravenous and intramuscular routes.

2Anaesthesia is accompanied by profound analgesia.

3Does not produce vomiting, hypotension and bronchospasm.

4Less respiratory complications, due to less impairment of laryngeal/pharyngeal reflexes.

5Useful for poor risk geriatric/elderly and unstable patients.

6Used in low doses, as outpatient anaesthesia.

Disadvantages

1No muscle relaxation.

2Tends to raise heart rate, intraocular and intracranial pressures.

3Cannot be used for surgery on larynx, pharynx and bronchi.

4Poor in relieving visceral pain.

5Emergence phenomenon (characterised by bad dreams, post-op disorientation and sensory/perceptual delusions). Its Rx is diazepam, before the operation.

Thiopentone sodium

Advantages

1Ease of administration.

2Non-explosive.

3Induction and recovery is rapid and pleasant.

4No irritation of mucous membranes.

5No sensitisation of myocardium to adrenaline.

6No/less incidence of post-op vomiting and excitement.

7Low incidence of post-anaesthetic complications.

Disadvantages

1Stages of anaesthesia cannot be recognised.

2Pupils remain normal or constricted.

3During induction, unpleasant and fatal reactions (like apnea, coughing, hiccough, laryngospasm and bronchospasm) may develop.

4Depression of myocardium, respiratory and vasomotor centres.

5Rapid injection can lead to hypotension and cardiac arrhythmias.

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MISCELLANEOUS

6Intra-arterial injection→ severe pain and gangrene.

7Inadequate muscle relaxation.

8Laryngeal and pharyngeal reflexes are not abolished.

9Regurgitation due to relaxation of gastro-esophageal sphincter.

10Injury to surrounding nerves and tissues.

11Thromboembolism.

12Can precipitate porphyria in susceptible individuals.

Preference of benzodiazepines over barbiturates

1High margin of safety (i.e. 10 times the normal dose can be given without harmful effects).

2Least drug interactions, since no effect on the drug metabolising cytochrome P450 enzyme system in the liver.

3Selectivity of action (i.e. like barbiturates, benzodiazepines are not a general CNS depressant – they act mainly on limbic system).

4Lack of interactions (i.e. neither enzyme inhibitors nor enzyme inducers).

5Do not cause hyperalgesia.

6Fewer incidences of drug dependence/addiction.

7Less severe withdrawal syndrome.

8Less severe tolerance.

9Least alteration in sleep pattern.

Digoxin toxicity: features

1Arrhythmias (especially AV block).

2Nausea, vomiting, diarrhoea.

3Headache; dizziness.

4Seizures.

5Xanthopsia (yellow vision).

6Skin reactions.

7Impotence.

Digoxin toxicity: causes

1Electrolyte disturbances (↓ K+; ↓ Mg++; ↑ Ca++).

2Renal impairment.

3Hypothyroidism.

4Drug-induced (ACEI7; Ca-channel blockers; amiodarone8; quinidine; cyclosporine).

Digoxin toxicity: management

•Prevent absorption: gastric lavage; activated charcoal (if patient comes within 6–8hrs of ingestion).

•Correct electrolyte disturbances (↓ K+; ↓ Mg++; ↑ Ca++). K+ should not be raised above the level of 5 mEq/L.

•For bradyarrhythmia: Atropine.

•For symptomatic bradycardia that has failed to respond to atropine: Temporary pacemaker.

7 ACEI reduce renal clearance of digoxin → digoxin toxicity.

8 Amiodarone displaces digoxin from the binding proteins → digoxin toxicity.

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