The cytochrome p450 3A4 enzyme system in the liver is affected by grapefruit juice. Patients taking antihistamines should be advised to avoid drinking grapefruit juice. This is because constituents of grapefruit juice such as naringin and bergamottin inhibit CYP3A4 in the liver, particularly at high doses, leading to decreased drug elimination via hepatic metabolism and can increase potential drug toxicities. Inhibition of this enzyme system leads to reduced metabolism of antihistamines leading to an increased incidence of side effects like excessive drowsiness and nausea as in this patient.

Bradycardia and miosis should be anticipated following the administration of anticholinesterases.Anticholinesterase agents include the following medications:- Pyridostigmine, neostigmine, and edrophonium which play a significant role in the diagnosis and the management of myasthenia gravis.- Rivastigmine, galantamine and donepezil are cholinesterase inhibitors found to be significantly useful in the management of Alzheimer’s disease.Mechanism of action and pharmacological effects:Inhibition of cholinesterase increases the level and the duration of action of acetylcholine within the synaptic cleft. Thus, cholinergic effects such as a reduction in heart rate (bradycardia), miosis (pupillary constriction), increased secretions, increased gastrointestinal motility and reduction in BP may occur with anticholinesterases.Toxins such as organophosphates and carbamates also are primarily anticholinergic and cause the following typical SLUDGE symptoms:- Salivation- Lacrimation- Urination- Diaphoresis- Gastrointestinal upset- Emesis

Among the give options, reactivation of tuberculosis may occur in a patient under treatment with etanercept.Etanercept is a biological TNF inhibit commonly used to control ankylosing spondylitis, juvenile idiopathic arthritis, plaque psoriasis, psoriatic arthritis, and rheumatoid arthritis.Etanercept is a soluble receptor that binds both TNF-alpha and TNF-beta to inhibit the inflammatory response in joints and skin that is characteristic of these autoimmune disorders.The most common adverse effects include infections (viral, bacterial, and fungal – mostly upper respiratory tract infections) and injection site reaction (erythema, itching, pain, swelling, bleeding, bruising).Rarely it can also cause, reactivation of hepatitis B and TB, pneumocystis pneumonia, congestive cardiac failure, Steven-Johnson syndrome, toxic epidermal necrolysis, etc.

Carbimazole is used to treat hyperthyroidism. Carbimazole is a pro-drug as after absorption it is converted to the active form, methimazole. Methimazole prevents thyroid peroxidase enzyme from coupling and iodinating the tyrosine residues on thyroglobulin, hence reducing the production of the thyroid hormones T3 and T4 (thyroxine).

Confusion and pink mucosae are typical features of CO poisoning.The patient often presents, most commonly with headaches, and other symptoms like malaise, nausea, and dizziness.Carbon monoxide (CO) poisoning, considered as the great imitator of other diseases as the patients present with a myriad of symptoms. The carbon monoxide diffuses rapidly across the pulmonary capillary membrane binding to the haem molecule with a very high affinity (240 times that of oxygen) forming carboxy-haemoglobin (COHb). Non-smokers have a baseline COHb of ,3% while smokers have a baseline COHb of 10-15%.Features of carbon monoxide toxicity- Headache: 90% of cases- Nausea and vomiting: 50%- Vertigo: 50%- Confusion: 30%- Subjective weakness: 20%- Severe toxicity: ‘pink’ skin and mucosae, hyperpyrexia, arrhythmias, extrapyramidal features, coma, deathTreatment:Use of Hyperbaric oxygen therapy (HBOT) for treating mild to moderate CO poisoning is not routine.The selection criteria for HBOT in cases of CO poisoning include:• COHb levels > 20-25%• COHb levels > 20% in pregnant patient • Loss of consciousness• Severe metabolic acidosis (pH <7.1)• Evidence of end-organ ischemia (e.g., ECG changes, chest pain, or altered mental status)

The next step in managing this patient is to give 10 mg and continue administering in 10 mg increments each hour until symptoms are under control.Methadone alleviates opioid withdrawal symptoms and reduces cravings. Methadone is useful for detoxification from longer-acting opioids such as morphine or methadone itself.Methadone should be used with caution if the patient has:Respiratory deficiencyAcute alcohol dependenceHead injuryTreatment with monoamine oxidase inhibitors (MAOIs)Ulcerating colitis or Crohn’s diseaseSevere hepatic impairmentThe dose must be reviewed on a daily basis and adjusted based upon how well the symptoms are controlled and the presence of side effects. The greater the dose of opioids used by the patient, the greater the dose of methadone required to control withdrawal symptoms. To avoid the risk of overdose in the first days of treatment The recommended dosing of methadone is 30mg in two doses of 15mg morning and evening.It is important to note that a methadone dose equivalent to what the patient reports they are taking should never be given. It is rare to need more than 40 mg per 24 hours: beware of overdosing which can lead to respiratory arrest.

The presence of tinnitus, fever and hyperventilation are clues for aspirin (salicylate) toxicity. Clinical Presentation of salicylate toxicity can include:• Pulmonary manifestations include: Hyperventilation, hyperpnea, severe dyspnoea due to noncardiogenic pulmonary oedema, fever and dyspnoea due to aspiration pneumonitis• Auditory symptoms caused by the ototoxicity of salicylate poisoning include: Hard of hearing and deafness, and tinnitus (commonly encountered when serum salicylate concentrations exceed 30 mg/dL).• Cardiovascular manifestations include: Tachycardia, hypotension, dysrhythmias – E.g., ventricular tachycardia, ventricular fibrillation, multiple premature ventricular contractions, asystole – with severe intoxication, Electrocardiogram (ECG) abnormalities – E.g., U waves, flattened T waves, QT prolongation may reflect hypokalaemia.• Neurologic manifestations include: CNS depression, with manifestations ranging from somnolence and lethargy to seizures and coma, tremors, blurring of vision, seizures, cerebral oedema – With severe intoxication, encephalopathy• GI manifestations include: Nausea and vomiting, which are very common with acute toxicity, epigastric pain, GI haemorrhage – More common with chronic intoxication, intestinal perforation, pancreatitis, hepatitis – Generally in chronic toxicity; rare in acute toxicity, Oesophageal strictures – Reported as a very rare delayed complication• Genitourinary manifestations include: Acute kidney injury (NSAID induced Nephropathy) is an uncommon complication of salicylate toxicity, renal failure may be secondary to multisystem organ failure.• Hematologic effects may include prolongation of the prothrombin and bleeding times and decreased platelet adhesiveness. Disseminated intravascular coagulation (DIC) may be noted with multisystem organ failure in association with chronic salicylate toxicity.• Electrolyte imbalances like: Dehydration, hypocalcaemia, acidaemia, Syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypokalaemiaManagement of these patients should be done in the following manner:• Secure Airway, Breathing, and Circulation• Supportive therapy• GI decontamination• Urinary excretion and alkalization• Haemodialysis

Renal elimination of a drug has no role in altering the bioavailability of a drug.The bioavailability of a drug is the proportion of the drug which reaches systemic circulation. Mathematically, bioavailability is the AUCoral/AUCiv x 100%, where AUC = area under the concentration-time curve following a single (oral or iv) dose. Other options are true:By definition, the bioavailability of a drug given intravenously is 100%.Drugs given orally that undergo high pre-systemic (first-pass) metabolism in the liver or gut wall have a low bioavailability e.g. lidocaine. Bioavailability is also affected by the degree of absorption from the gut and this can change depending on gut motility and administration of other drugs.

Different Oral Hypoglycaemic Agents (OHAs) and their respective mechanism(s) of action include:• Sulfonylureas (such as, glipizide, gliclazide, glimepiride) – bind to ATP sensitive Potassium channels (K – ATP channels) in the 𝝱 cells of the islets of the pancreas. Inhibition of these channels lead to an altered resting membrane potential in these cells causing an influx of calcium which increases insulin secretion.• Meglitinides (like Repaglinide) through a different receptor, they similarly regulate K – ATP channels thereby causing an increase in insulin secretion.• Biguanides (e.g., Metformin) increase the hepatic AMP-activated protein kinase activity leading to reduced gluconeogenesis and lipogenesis and increased insulin-mediated uptake of glucose in muscles. (it doesn’t increase insulin secretion)• Thiazolidinediones (rosiglitazone, pioglitazone) bind to PPAR-𝝲 and increase peripheral uptake of glucose and decrease hepatic glucose production.• α-Glucosidase inhibitors (such as acarbose, miglitol, voglibose) competitively inhibit α-glucosidase enzymes in the intestine that digest the dietary starch thus, inhibiting the polysaccharide reabsorption as well as metabolism of sucrose to glucose and fructose.• DPP-4 inhibitors (sitagliptin, saxagliptin, vildagliptin, linagliptin, alogliptin) prolong the action of glucagon-like peptide. This leads to inhibition of glucagon release, increase in insulin secretion and a decrease in gastric emptying leading to a decrease in blood glucose levels.• SGLT2 inhibitors (dapagliflozin and canagliflozin) inhibit glucose reabsorption in the proximal tubules of the renal glomeruli leading to glycosuria which in-turn reduces blood glucose levels.Note: Side effects of pioglitazone are weight gain, pedal oedema, bone loss and precipitation of congestive cardiac failure.

Triptans are specific 5-HT1 agonists used in the acute treatment of migraine. They are generally used as first-line therapy in combination with an NSAID or paracetamol.

Sumatriptan acts as an agonist on 5-HT1B/1D receptors by inducing vasoconstriction in the basilar artery and blood vessels within the dura mater. The drug reduces peripheral nociception either by selective cranial vasoconstriction or by affecting trigeminovascular nerves.

The total daily morphine dose is 30 x 2 = 60 mg. Therefore, the breakthrough dose should be one-sixth of this, 10 mg.

The blood gas analysis provided above is suggestive of a mixed respiratory alkalosis and metabolic acidosis characteristic of salicylate overdose.Pathophysiology:The direct stimulation of the cerebral medulla causes hyperventilation and respiratory alkalosis.As it is metabolized, it causes an uncoupling of oxidative phosphorylation in the mitochondria. Lactate levels then increase due to the increase in anaerobic metabolism. This, along with a slight contribution from the salicylate metabolites result in metabolic acidosis.Tinnitus is characteristic and salicylate ototoxicity may produce deafness. Other neurological sequelae include encephalopathy and agitation, seizures and CNS depression and coma. Cardiovascular complications include tachycardia, hypotension, and dysrhythmias (VT, VF, and asystole).

Memantine is an antagonist of the NMDA (N-Methyl-D-Aspartate)-receptor subtype of glutamate receptor. It is used to slow the neurotoxicity thought to be involved in Alzheimer’s disease and other neurodegenerative diseases.

Drug interactions:

• When given concomitantly with other NMDA-receptor antagonists (e.g., ketamine, amantadine) there is increased risk of psychosis.
• Dopamine agonists, L-dopa, and anticholinergics enhance effects of memantine.
• Antispasmodics (e.g., baclofen) enhance effects, as memantine has some antispasmodic effects.
• Drugs excreted by cationic transporters in the kidney (e.g. quinine, cimetidine, ranitidine) reduce excretion.
• Common adverse effects include dizziness, headache, confusion, diarrhoea, and constipation.

In such a clinical scenario, NICE guidelines support initiating treatment with bisphosphonates without waiting for a DEXA scan.Osteoporosis is defined as low bone mineral density caused by altered bone microstructure ultimately predisposing patients to low-impact, fragility fractures.Management:Vitamin D and calcium supplementation should be offered to all women unless the clinician is confident they have adequate calcium intake and are vitamin D repleteAlendronate is the first-line treatment. Around 25% of patients cannot tolerate alendronate, usually due to upper gastrointestinal problems. These patients should be offered risedronate or etidronate.Strontium ranelate and raloxifene are recommended if patients cannot tolerate bisphosphonates.Other medications that are useful in the treatment of osteoporosis are denosumab, teriparatide, raloxifene, etc.

Tumour lysis syndrome (TLS) occurs most notably in patients with haematological malignancies including, Non-Hodgkin’s Lymphoma (NHL) and Acute Lymphocytic Leukaemia (ALL).Risk factors for TLS include:• Large tumour burden• Sensitivity of the tumour to chemotherapy• Rapid tumour growth rateTLS is characterized by:• Hyperuricemia• Hyperkalaemia• Hyperphosphatemia• HypocalcaemiaTreatment of TLS:• Allopurinol: It is a xanthine oxidase inhibitor, it reduces the conversion of nucleic acid by-products to uric acid. Thus, it prevents urate nephropathy and subsequent oliguric renal failure. Note: dose reduction is essential in renal failure or if given along with mercaptopurine or azathioprine.Alternatives to Allopurinol: Febuxostat; Rasburicase are useful in patients with hyperuricemia.• Hydration• Diuresis: Should be considered in well hydrated patients with insufficient urine output. Furosemide to be considered in normo-volemic patients with hyperkalaemia. Urine alkalization can be considered for promoting alkaline diuresis.• Treatment of electrolyte imbalances including hyperkalaemia, hyperphosphatemia, and hypocalcaemia.• Dialysis can be considered in refractory cases.

Temazepam is an orally available benzodiazepine used in the therapy of insomnia. The soporific activity of the benzodiazepines is mediated by their ability to enhance gamma-aminobutyric acid (GABA) mediated inhibition of synaptic transmission through binding to the GABA-A receptor.The recommended initial dose for insomnia is 7.5 mg before bedtime, increasing as needed to a maximum dose of 30 mg. The most common side effects of temazepam are dose-related and include daytime drowsiness, lethargy, ataxia, dysarthria, and dizziness.Tolerance develops to these side effects, but tolerance may also develop to the effects on insomnia.

Spironolactone is an aldosterone antagonist which acts in the distal convoluted tubule. It is a potassium-sparing diuretic that prevents the body from absorbing too much salt and keeps the potassium levels from getting too low. Spironolactone is used to treat heart failure, high blood pressure (hypertension), or hypokalaemia (low potassium levels in the blood).

Sildenafil (Viagra) is a phosphodiesterase type V inhibitor used in the treatment of impotence.Contraindications:- Patients taking nitrates and related drugs such as nicorandil- Hypotension- Recent stroke or myocardial infarction (NICE recommend waiting 6 months)Side-effects:Visual disturbances e.g. cyanopsia, non-arthritic anterior ischaemic NeuropathyNasal congestionFlushingGastrointestinal side-effectsHeadache

The most likely complaint of this patient would be hot flushes.

Alopecia and cataracts are listed as possible side-effects, however they are not as prevalent as hot flushes, which are very common in pre-menopausal women.

Tamoxifen is a Selective Oestrogen Receptor Modulator (SERM) which acts as an oestrogen receptor antagonist and partial agonist. It is used in the management of oestrogen receptor-positive breast cancer

Adverse effects:

• Menstrual disturbance: vaginal bleeding, amenorrhoea
• Hot flushes – 3% of patients stop taking tamoxifen due to climacteric side-effects.
• Venous thromboembolism.
• Endometrial cancer (although antagonistic with respects to breast tissue, tamoxifen may serve as an agonist at other sites. Therefore the risk of endometrial cancer is increased). Raloxifene is a pure oestrogen receptor antagonist and carries a lower risk of endometrial cancer.

Tamoxifen is typically used for 5 years following the removal of the tumour.

The patient (known case of acromegaly) seems to have developed cholelithiasis (presenting with right upper quadrant pain) probably due to octreotide.It is a long-acting analogue of somatostatin which is released from D cells of the pancreas and inhibits the release of growth hormone, glucagon, and insulin.Uses- Acute treatment of variceal haemorrhage- Acromegaly- Carcinoid syndrome- Prevent complications following pancreatic surgery- VIPomas- Refractory diarrhoeaAdverse effectsGallstones (secondary to biliary stasis)Other options:- Bromocriptine – a dopamine agonist with side effects arising from its stimulation of the brain vomiting centre.- Desmopressin – predominantly used in patients with diabetes insipidus by increasing the presence of aquaporin channels in the distal collecting duct to increase water reabsorption from the kidneys. The main side effects include headache and facial flushing due to hypertension.- Metformin – mainly reduces hepatic gluconeogenesis in patients with type 2 diabetes, common side effects include diarrhoea, vomiting, and lactic acidosis- Levothyroxine – synthetic thyroxine used in patients with hypothyroidism, common side effects result from incorrect dosing and mimic the symptoms of hyperthyroidism.

Sarin acts by inhibiting acetylcholinesterase.Sarin gas is a highly toxic synthetic organophosphorus compound which causes inhibition of the enzyme acetylcholinesteraseSarin gas is a highly toxic synthetic organophosphorus compound which causes inhibition of the enzyme acetylcholinesterase. This results in high levels of acetylcholine (ACh).The effects of excessive ACh can be remembered by the mnemonic DUMBELLS:DiarrhoeaUrinationMiosis/muscle weaknessBronchorrhea/BradycardiaEmesisLacrimationSalivation/sweatingOrganophosphate insecticide poisoning:One of the effects of organophosphate poisoning is inhibition of acetylcholinesteraseFeatures can be predicted by the accumulation of acetylcholine (mnemonic = SLUD)SalivationLacrimationUrinationDefecation/diarrhoeacardiovascular: hypotension, bradycardiamiosis, muscle fasciculation.Organophosphate poisoning is treated with the anti-muscarinic atropine.

Tacrolimus is a calcineurin inhibitor used as an immunosuppressive agent used for prophylaxis of organ rejection post-transplant.Pharmacology: Calcineurin inhibition leads to reduced T-lymphocyte signal transduction and IL-2 expression. It has a half-life of 12 hours (average).Other off-label indications for the use of tacrolimus include Crohn disease, graft-versus-host disease (GVHD), myasthenia gravis, rheumatoid arthritis.Adverse effects of tacrolimus includes: Cardiovascular: Angina pectoris, cardiac arrhythmias, hypertensionCentral nervous system: Abnormal dreams, headaches, insomnia, tremors.Dermatologic: Acne vulgaris, alopecia, pruritis, rashEndocrine and metabolic: Decreased serum bicarbonate, decreased serum iron, new-onset diabetes mellitus after transplant (NODAT), electrolyte disturbances.Gastrointestinal: Abdominal pain, nausea, vomiting, diarrhoeaGenitourinary: Urinary tract infectionHepatic: Abnormal hepatic function testsNeuromuscular and skeletal: Arthralgia, muscle crampsOphthalmic: Blurred vision, visual disturbanceOtic: Otalgia, otitis media, tinnitusRenal: Acute renal failureOther options:Sirolimus (a macrolide) is an mTOR inhibitor that blocks the response to IL-2 and has a half-life of 12–15 hours. Azathioprine inhibits purine synthesis, an essential step in the proliferation of white cells and has a half-life of around 5 hours.

Although rare, ocular toxicity in the form of optic neuritis (most commonly retrobulbar neuritis) has been well documented as a side effect of ethambutol. It is renally excreted and not associated with hepatitis.

Blue tinge of vision/cyanopsia is caused due to the intake of sildenafil citrate.Sildenafil citrate (Viagra) is the first oral drug to be widely approved for the treatment of erectile dysfunction. It is a potent and selective inhibitor of type-V phosphodiesterase, the primary form of the enzyme found in human penile erectile tissue, thereby preventing the breakdown of cyclic guanosine monophosphate (cGMP), the intracellular second messenger of nitric oxide.Uses:It is used for the treatment of erectile dysfunction, idiopathic pulmonary hypertension, premature ejaculation, high altitude illness, penile rehabilitation after radical prostatectomy, angina pectoris, and lower urinary tract symptoms.Adverse effects:Mild headache, flushing, dyspepsia, cyanopsia, back pain, and myalgias – due to a high concentration of PDE11 enzyme in skeletal muscle, which shows significant cross-reactivity with the use of tadalafil.It can also cause hypotension, dizziness, and rhinitis.Note: Xanthopsia (yellow-green vision) may occur secondary to treatment with digoxin.

Lead can be absorbed through the skin and by inhalation. It is associated with iron deficiency and a microcytic anaemia. The most common gastrointestinal symptoms are abdominal colic and constipation.

Among the given options the most appropriate management in this patient would be ethanol and haemodialysis.Ethanol competes with ethylene glycol for alcohol dehydrogenase and thus, helps manage a patient with ethylene glycol toxicity.Ethylene glycol is a type of alcohol used as a coolant or antifreezeFeatures of toxicity are divided into 3 stages:Stage 1: (30 min to 12 hours after exposure) Symptoms similar to alcohol intoxication: confusion, slurred speech, dizziness (CNS depression)Stage 2: (12 – 48 hours after exposure) Metabolic acidosis with a high anion gap and high osmolar gap. Also tachycardia, hypertensionStage 3: (24 – 72 hours after exposure) Acute renal failureManagement has changed in recent times:Fomepizole, an inhibitor of alcohol dehydrogenase, is now used first-line in preference to ethanol.Ethanol has been used for many years works by competing with ethylene glycol for the enzyme alcohol dehydrogenase this limits the formation of toxic metabolites (e.g. glycolaldehyde and glycolic acid) which are responsible for the hemodynamic/metabolic features of poisoning.Haemodialysis has a role in refractory cases.

Metoclopramide causes extrapyramidal effects (especially in children and young adults), hyperprolactinaemia, and occasionally tardive dyskinesia on prolonged administration. Also reported are drowsiness, restlessness, diarrhoea, depression, neuroleptic malignant syndrome, rashes, pruritus, oedema.

Vestibular damage is a neurological side effect of streptomycin.Streptomycin is an aminoglycoside bactericidal antibiotic. It is used in the treatment of tularaemia and resistant mycobacterial infections.The most common neurological side-effect is vestibular damage leading to vertigo and vomiting. Cochlear damage is less frequent and results in deafness. Other side-effects include rashes, angioneurotic oedema, and nephrotoxicity.

Both fibrates and nicotinic acid have been associated with myositis, especially when combined with a statin. However, the Committee on Safety of Medicines has produced guidance which specifically warns about the concomitant prescription of fibrates with statins concerning muscle toxicity.Bezafibrate: It is a fibric acid derivative (fibrate) that has been used as a class of agents known to decrease triglyceride levels while substantially increasing HDL-C levels.Pharmacological effects:- Increases VLDL catabolism by increasing lipoprotein and hepatic triglyceride lipase.- Decreases triglyceride synthesis by inhibiting acetyl-CoA reductase.- Decreases cholesterol synthesis by inhibiting HMG-CoA reductase.Side effects:- Hypersensitivity- Primary biliary cirrhosis- Pre-existing gallbladder disease- Concurrent use with HMG-CoA inhibitors (statins) can produce myopathy- Hepatic/renal impairment in a patient warrants dose adjustment as this drug is primarily excreted via the renal mechanism.Contraindications: Concurrent use of MAO inhibitors, hypersensitivity, pre-existing cholestasis, and pregnancy.Use: It can be used to treat Barth syndrome (characterized by dilated cardiomyopathy, neutropenia (presenting with recurrent infections), skeletal myopathy and short stature)

Benign Prostatic Enlargement or Hyperplasia (BPE/BPH) is the most probable diagnosis of the patient in question. It is a histological diagnosis characterized by proliferation of the cellular elements of the prostate. The initial treatment modality of choice is selective alpha 1 antagonists (such as Prazosin, Alfuzosin and Indoramin, and long acting agents like, Terazosin, Doxazosin, etc.) as they provide immediate relief from the bothersome lower urinary tract symptoms (LUTS).Other treatment modalities include:• Non-selective alpha blockers: no longer used due to severe adverse effects and the availability of selective alpha 1 blockers.• 5 alpha reductase inhibitors: Finasteride and Dutasteride, they target the underlying disease process and reduce the overall prostate volume. Thus, reduce the urinary retention and the lower urinary tract symptoms. (They do not provide immediate relief from LUTS and thus are not preferred as first line drugs over alpha 1 antagonists)• PDE-5 Inhibitors: The long-acting tadalafil has proven to be useful.• Surgical Treatment modalities: TURP, Prostatectomy, etc.