Barbiturates are derived from barbituric acid, which itself is nondepressant, but appropriate side-chain substitutions result in CNS depressant activity that varies in potency and duration with carbon chain length, branching, and saturation.

Oxybarbiturates retain an oxygen atom on number 2-carbon atom of the barbituric acid ring.

Thiobarbiturates replace this oxygen atom with a sulphur atom, which confers greater lipid solubility. Generally speaking, a substitution such as sulphuration that increases lipid solubility is associated with greater hypnotic potency and more rapid onset, but shorter duration of action.

Addition of a methyl group to the nitrogen atom of the barbituric acid ring, as with oxybarbiturate methohexital, also results in a compound with a short duration of action.

Adenosine is the first line for AV nodal re-entry tachycardia. An initial dose of 6 mg is given, and a consequent second dose or third dose of 12 mg is administered if the initial dose fails to terminate the arrhythmia.

Aside from Adenosine, a vagal manoeuvre (e.g. carotid massage) is done to help terminate the supraventricular arrhythmia.

Amiodarone is not a first-line drug for supraventricular tachycardias. Digoxin and Propranolol can be considered if the arrhythmia is of a narrow complex irregular type. Verapamil is an alternative to Adenosine if the latter is contraindicated.

After ingestion of more than 150 mg/kg paracetamol within 24 hours, hepatotoxicity can occur but can also develop rarely after ingestion of doses as low as 75 mg/kg within 24 hours. Hepatocellular damage will not occur in this patient and therefore no need to engage management pathway for paracetamol overdose. If his weight was <33 kg or he already had a history of impaired liver function, then the management would bde different. Subsequent post-operative doses will be a standard dose of 1 g 6 hourly. This is a drug administration error and should be reported as an incident even though the patient will not be harmed.

Daptomycin alters the curvature of the membrane, which creates holes that leak ions. This causes rapid depolarization, resulting in loss of membrane potential. Thus it interferes with the outer membrane of gram-positive bacteria resulting in cell death.

The statement Epinephrine is formulated as 1 in 1000 solution means 1 gm epinephrine is present in 1000 ml of solution.

Ketamine is primarily used for the induction and maintenance of anaesthesia. It induces dissociative anaesthesia. But it is contraindicated in cardiovascular diseases such as unstable angina or poorly controlled hypertension.

Tricyclic antidepressants (TCA) are primarily used as antidepressants which is important for the management of depression. These are second-line drugs next to SSRI. They work by competitively preventing re-uptake of amines (noradrenaline and serotonin) from the synaptic cleft so increasing their concentration. But TCA overdoses are toxic and have cardiovascular effects, central effects, and anticholinergics effects. Cardiovascular effects like prolonged QT and widened QRS at lower doses progressing to ventricular arrhythmias and refractory hypotension at higher doses can be life-threatening. When used in the perioperative period, it can lead to increased sensitivity to circulating catecholamines therefore care is needed perioperatively.

Cephalosporin belongs to a family of beta-lactam antibiotics. All ?-lactam antibiotics interfere with the synthesis of the bacterial cell walls. The ?-lactam antibiotics inhibit the transpeptidases so that cross-linking (which maintains the close-knit structure of the cell wall) does not take place i.e. they inhibit bacterial cell wall formation.

When responsiveness diminishes rapidly after administration of a drug, the response is said to be subject to tachyphylaxis. This may be due to frequent or continuous exposure to agonists, which often results in short-term diminution of the receptor response.

Many mechanisms may be responsible, such as blocking access of G protein to activated receptor, or receptor molecules internalized by endocytosis to prevent exposure to extracellular molecules.

Tolerance occurs when larger doses are required to produce the same effect. This may be due to changes in receptor number or function due to exposure to the drug.

Desensitization refers to the common situation where the biological response to a drug diminishes when it is given continuously or repeatedly. It is a chronic loss of response, occurring over a longer period than tachyphylaxis. It may be possible to restore the response by increasing the dose (or concentration) of the drug but, in some cases, the tissues may become completely refractory to its effect.

Drug dependence is defined as a psychic and physical state of the person characterized by behavioural and other responses resulting in compulsions to take a drug, on a continuous or periodic basis in order to experience its psychic effect and at times to avoid the discomfort of its absence.

The mechanism of action of macrolides is inhibition of bacterial protein synthesis by preventing peptidyltransferase from adding to the growing peptide which is attached to tRNA to the next amino acid.

Staphylococcus aureus colonizes the nasopharynx in >20% of the general population.

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to flucloxacillin.

Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.

All ?-lactam antibiotics like penicillin interfere with the synthesis of the bacterial cell walls. The ?-lactam antibiotics inhibit the transpeptidases so that cross-linking (which maintains the close-knit structure of the cell wall) does not take place