---

BDS 3rd Year General Medicine - University Examination Answers

---

Q1. Acute Myocardial Infarction (AMI) in a 70-Year-Old Patient on Dental Chair - Clinical Features and Management (10 Marks)

Introduction

---

A. CLINICAL FEATURES

1. Symptoms

• Sudden onset, severe, crushing, squeezing, or constricting pain
• Located in the centre of the chest (retrosternal), may radiate to:
  • Left arm (most common)
  • Jaw, neck, and teeth (of great dental relevance)
  • Left shoulder, epigastrium, back
• Pain lasts >30 minutes (unlike angina which resolves in <15 min with rest or nitrates)
• NOT relieved by sublingual nitrates

• The elderly commonly present without chest pain (silent MI)
• May present with:
  • Sudden breathlessness (dyspnoea)
  • Confusion, disorientation, or loss of consciousness
  • Profound weakness or fatigue
  • Nausea, vomiting, epigastric discomfort
  • Syncope or collapse
  • Sudden onset of heart failure

2. Associated Symptoms

• Profuse sweating (diaphoresis) - cold, clammy skin
• Nausea and vomiting
• Severe anxiety, feeling of impending doom ("angor animi")
• Palpitations (due to arrhythmias)
• Breathlessness / dyspnoea

3. Signs on Examination

• Patient is pale, ashen, cold and clammy
• Appears severely distressed and anxious
• Breathless

• Pulse: rapid and weak (tachycardia); may be irregular if arrhythmia present
• Blood pressure: may fall (cardiogenic shock) or initially elevated
• Temperature: mild fever may develop after 24-48 hours
• Respiratory rate: increased

• Heart sounds may be faint
• S3 gallop (indicates LV failure)
• Soft systolic murmur (mitral regurgitation due to papillary muscle dysfunction)
• Pericardial friction rub (in transmural MI, day 2-3)

• Fine basal crepitations in lungs
• Raised JVP (if RV involved)
• Central cyanosis in severe cases

---

B. IMMEDIATE MANAGEMENT IN THE DENTAL CHAIR

Step 1: Stop the Dental Procedure

• Stop all dental work immediately
• Remove instruments from the patient's mouth
• Keep the patient calm and reassured

Step 2: Position

• If conscious: Semi-reclined position (45 degrees) - do NOT lay flat (worsens breathlessness)
• If unconscious: Lay flat and begin BLS (Basic Life Support)

Step 3: Call for Help - ACTIVATE EMERGENCY SERVICES

• Call 108 / Emergency Medical Services immediately
• Inform them of suspected cardiac emergency

Step 4: Oxygen

• Administer high-flow oxygen 4-6 L/min by face mask
• Maintain SpO2 >94%

Step 5: Aspirin (MONA Protocol - used in dental settings)

• Aspirin 300 mg (chewed) - give immediately if not contraindicated
  • Chewing is important (faster absorption than swallowing)
  • Do not give if known aspirin allergy or active GI bleed

Step 6: Nitroglycerine (if available)

• Sublingual Glyceryl Trinitrate (GTN) 0.4 mg - if BP >90 mmHg systolic
• Repeat every 5 minutes x 3 doses if pain persists

Step 7: Monitor

• Monitor pulse, BP, and consciousness continuously
• Do NOT leave the patient alone

Step 8: Prepare for CPR

• If patient loses consciousness and has no pulse, begin:
  • CPR: 30 chest compressions : 2 rescue breaths
  • Use AED (Automated External Defibrillator) if available

---

C. MANAGEMENT IN HOSPITAL

A. Initial Assessment

• 12-Lead ECG - within 10 minutes of arrival
• Blood tests: Serum Troponin I/T (gold standard), CK-MB, CBC, RFT, serum electrolytes, blood glucose, lipid profile
• Chest X-ray
• Echocardiography

ECG Changes in AMI:

B. Reperfusion Therapy (Most Important)

• Balloon angioplasty + stenting of occluded artery
• Should be done within 90 minutes of first medical contact ("door to balloon time")
• Superior to thrombolysis

• Streptokinase 1.5 million units IV over 60 min (older drug)
• Alteplase (tPA) - more clot specific, preferred
• Contraindicated in: recent surgery, active bleeding, stroke, uncontrolled hypertension

C. Medical Treatment

D. Management of Complications

• Arrhythmias: Lidocaine (VT/VF); atropine (bradycardia)
• Cardiogenic shock: Dopamine/dobutamine; IABP (intra-aortic balloon pump)
• Cardiac failure: Diuretics (frusemide IV)
• VF: Immediate DC defibrillation

---

Q2. Hyperthyroidism and Hypothyroidism - Clinical Features, Diagnosis, and Treatment of Hyperthyroidism (10 Marks)

HYPERTHYROIDISM (THYROTOXICOSIS)

• Graves' disease (most common - autoimmune, TSI antibodies stimulate TSH receptor)
• Toxic multinodular goitre
• Toxic adenoma
• Thyroiditis (subacute)
• Excess iodine (Jod-Basedow effect)

A. CLINICAL FEATURES OF HYPERTHYROIDISM

• Goitre (enlarged thyroid gland) - diffuse in Graves', nodular in MNG
• Bruit over thyroid (in Graves')
• Pretibial myxoedema (Graves' - skin thickening over shins)
• Thyroid acropachy (Graves' - clubbing + soft tissue swelling)
• Fine tremor on outstretched hands
• Warm, moist skin
• Tachycardia, hyperdynamic circulation

---

HYPOTHYROIDISM

• Hashimoto's thyroiditis (autoimmune - most common in adults)
• Iodine deficiency (most common worldwide)
• Post-thyroidectomy / post-radioiodine
• Drugs: amiodarone, lithium
• Pituitary/hypothalamic disease (secondary/tertiary)
• Congenital (Cretinism in neonates)

B. CLINICAL FEATURES OF HYPOTHYROIDISM

• Mental retardation, short stature, pot belly
• Protruding tongue, umbilical hernia
• Delayed milestones, deafness

---

C. DIAGNOSIS OF THYROID DISORDERS

• TSH is the single best screening test for thyroid dysfunction
• Low TSH = Hyperthyroidism; High TSH = Hypothyroidism

---

D. TREATMENT OF HYPERTHYROIDISM

1. Anti-thyroid Drugs (Thionamides) - First Line

• Carbimazole: Initial dose 10-20 mg every 12 hours; maintenance 5-10 mg/day
• Methimazole: Active metabolite of carbimazole; once-daily dosing possible
• Propylthiouracil (PTU): 100-200 mg every 6-8 hours; preferred in pregnancy (first trimester) and thyroid storm
• Mechanism: Inhibit thyroid peroxidase (TPO), reducing oxidation and organification of iodide; PTU also inhibits peripheral conversion of T4 to T3
• Course: 12-18 months for maximum remission (30-60%)
• Titration regimen: Gradually reduce dose as euthyroidism achieved
• Side effects: Agranulocytosis (monitor WBC if fever/sore throat), hepatotoxicity (PTU)

2. Beta-blockers (Symptomatic Relief)

• Propranolol 40-80 mg 3-4 times daily
• Reduces tachycardia, tremor, anxiety, sweating
• Does not reduce thyroid hormone levels
• Used until antithyroid drugs take effect (6-8 weeks)

3. Radioiodine Therapy (¹³¹I)

• Oral dose of radioactive iodine
• Destroys thyroid tissue permanently
• Preferred in: Adults >45 years, relapse after antithyroid drugs, toxic nodular goitre
• Contraindicated in: Pregnancy, breastfeeding, active Graves' ophthalmopathy
• Eventually leads to hypothyroidism (requires lifelong thyroxine replacement)

4. Surgery (Thyroidectomy)

• Total or near-total thyroidectomy
• Indicated in: Large goitre with compressive symptoms, suspected malignancy, failed medical/radioiodine therapy, pregnant women in 2nd trimester who fail drugs
• Must make patient euthyroid before surgery (with antithyroid drugs for 6-8 weeks + Lugol's iodine for 10 days pre-op)

5. Treatment of Graves' Ophthalmopathy

• Mild: Lubricating eye drops, dark glasses
• Moderate-severe: IV methylprednisolone pulses, teprotumumab (IGF-1R antibody)
• Severe (optic nerve compression): Orbital decompression surgery

6. Thyroid Storm Management (Emergency)

• PTU 600 mg orally, then 200-300 mg every 4 h
• Propranolol IV
• Lugol's iodine (after PTU) 1 hour later
• Hydrocortisone 100 mg IV 8-hourly
• IV fluids, paracetamol (not aspirin), ICU care

---

Q3. SHORT NOTES (10 x 5 = 50 Marks)

---

I. TENDER HEPATOMEGALY

1. Infective:
   • Amoebic liver abscess (most common cause of painful hepatomegaly in India)
   • Pyogenic liver abscess
   • Acute viral hepatitis (A, B, E)
   • Infective mononucleosis
2. Vascular:
   • Congestive cardiac failure (CCF) - acute - hepatic congestion stretches Glisson's capsule
   • Budd-Chiari syndrome
3. Inflammatory:
   • Cholangitis
   • Acute alcoholic hepatitis
4. Malignant:
   • Rapid hepatic metastases (capsule stretch)
   • Hepatocellular carcinoma

• Right hypochondrial pain, sometimes referred to right shoulder
• Liver enlarged, tender, smooth
• In CCF: Hepatojugular reflux positive; pulsatile liver (TR)
• In amoebic abscess: fever, leukocytosis, diarrhoea history

• LFTs, Serum amylase, SGOT/SGPT
• Ultrasound abdomen (abscess, vascular lesion)
• CT scan, Liver biopsy if needed
• Serology (amoebic abscess: indirect haemagglutination test)

• Directed at the cause
• Amoebic abscess: Metronidazole 800 mg TDS x 5-10 days
• CCF: Diuretics, ACE inhibitors, treat primary cause

---

II. ACUTE GASTRITIS

1. NSAIDs / Aspirin (most common - inhibit prostaglandin synthesis, reduce mucosal defence)
2. Alcohol
3. H. pylori infection (acute phase)
4. Stress - critically ill patients (ICU), burns (Curling's ulcer), brain injury (Cushing's ulcer)
5. Corticosteroids
6. Bile reflux
7. Radiation

• Erosions, petechial haemorrhages, mucosal oedema
• Loss of surface epithelium
• May progress to frank ulceration

• Epigastric pain, burning, discomfort
• Nausea, vomiting
• Anorexia
• Haematemesis or melaena (if bleeding erosion)
• Often asymptomatic (especially NSAID-induced)

• Upper GI endoscopy (OGD) - gold standard (erythema, erosions, haemorrhagic areas)
• Biopsy for H. pylori (rapid urease test, histology)
• H. pylori: Urea breath test, stool antigen test

1. Stop the causative agent (NSAIDs, alcohol)
2. Proton Pump Inhibitors (PPIs): Omeprazole 20-40 mg BD - reduce acid secretion (mainstay)
3. H2 blockers: Ranitidine/Famotidine
4. Antacids: Symptomatic relief
5. Sucralfate / Misoprostol: Mucosal protection
6. H. pylori eradication: Triple therapy - PPI + Amoxicillin + Clarithromycin x 14 days
7. Stress ulcer prophylaxis in ICU: IV PPI or H2 blockers

---

III. BELL'S PALSY

• Reactivation of Herpes Simplex Virus (HSV-1) in geniculate ganglion is the most accepted cause
• Results in oedema and entrapment of facial nerve in stylomastoid foramen

• Sudden onset weakness/paralysis of all muscles of one side of face
• Inability to close eye (lagophthalmos) - corneal exposure risk
• Loss of forehead wrinkling (differentiates from UMN palsy - in UMN, forehead spared)
• Drooping of angle of mouth
• Bell's phenomenon: on attempting to close eye, eyeball rolls up (white sclera visible)
• Obliteration of nasolabial fold
• Food/liquid trapping in cheek
• Hyperacusis (if nerve to stapedius affected)
• Loss of taste on anterior 2/3 of tongue (chorda tympani affected)
• Decreased lacrimation (greater petrosal nerve affected)

• Clinical diagnosis
• EMG/NCS: To assess nerve injury severity
• MRI: Rule out central cause, acoustic neuroma

1. Prednisolone 60 mg/day for 5 days, then taper over 10 days (must start within 72 hours) - reduces inflammation
2. Acyclovir 400 mg 5 times daily x 10 days (antiviral - for HSV)
3. Eye care: Artificial tear drops, eye pad at night, glasses during day (prevent corneal exposure)
4. Physiotherapy, facial exercises
5. Most cases resolve within 3-6 months (85% full recovery)

---

IV. SCURVY

• Clinical (mainly)
• Serum/leucocyte vitamin C levels (low)
• X-ray (children): Ground glass appearance, cortical thinning

• Vitamin C 500-1000 mg/day orally for 1 month; maintenance 75-90 mg/day
• Dietary: Fresh fruits (amla, lemon, orange), green vegetables
• Resolution of symptoms usually within days to weeks

---

V. ANTITUBERCULAR TREATMENT (ATT)

• Pulmonary TB: 6 months (2 + 4)
• TB meningitis, bone/joint TB, miliary TB: 9-12 months
• All treatment under DOTS (Directly Observed Treatment Short course)

---

VI. INSULIN

• Binds to insulin receptor (tyrosine kinase receptor)
• Promotes glucose uptake in muscle and fat (GLUT-4)
• Inhibits gluconeogenesis and glycogenolysis in liver
• Promotes lipogenesis, inhibits lipolysis
• Anabolic: promotes protein synthesis

• Type 1 Diabetes Mellitus (mandatory)
• Type 2 DM: When oral drugs fail, during illness/surgery/pregnancy, DKA, HHS
• Gestational diabetes mellitus (GDM)
• Diabetic ketoacidosis (DKA) - IV regular insulin
• Hyperkalaemia (drives K+ into cells)

• Hypoglycaemia (most common and dangerous)
• Lipodystrophy at injection sites
• Weight gain
• Oedema
• Local allergic reactions
• Insulin resistance

• Diabetics on insulin are at risk of hypoglycaemia during dental procedures
• Never operate on a fasting diabetic on insulin
• Have glucose (juice/sugar) ready in dental clinic

---

VII. ANAPHYLACTIC REACTION

• Local anaesthetics (most common in dentistry - especially ester type)
• Penicillin / antibiotics
• NSAIDs (aspirin, ibuprofen)
• Latex gloves
• Contrast media

• Antigen binds to IgE on mast cells and basophils
• Releases histamine, leukotrienes, prostaglandins, tryptase
• Massive vasodilation, increased capillary permeability, bronchoconstriction

1. STOP the causative agent immediately
2. Call for emergency help (108)
3. Position: Lay patient flat with legs elevated (Trendelenburg); if breathing difficulty, sit up
4. Adrenaline (Epinephrine) - FIRST AND MOST IMPORTANT DRUG:
   • 0.5 mg (0.5 mL of 1:1000) IM into outer thigh (vastus lateralis)
   • May repeat every 5-15 minutes
   • Mechanism: alpha-1 vasoconstriction (raises BP), beta-2 bronchodilation, prevents further mediator release
5. Oxygen: High flow 10-15 L/min
6. IV access + IV fluids: Normal saline 500-1000 mL rapid infusion
7. Antihistamine: Chlorpheniramine 10 mg IM/slow IV
8. Corticosteroids: Hydrocortisone 200 mg IV (prevents late-phase reaction)
9. Bronchodilator: Salbutamol inhaler / nebulizer if bronchospasm persists
10. If cardiac arrest: CPR + ALS

---

VIII. COMPLICATIONS OF ENTERIC FEVER (TYPHOID)

1. Intestinal Perforation - Most serious; Peyer's patches in terminal ileum perforate; presents with acute abdomen, guarding, peritonitis, free gas under diaphragm on X-ray
2. Intestinal Haemorrhage - Due to sloughing of Peyer's patches; melaena/haematochezia
3. Paralytic Ileus

---

IX. NEPHROTIC SYNDROME

1. Heavy proteinuria (>3.5 g/day in adults; >40 mg/m²/hr in children)
2. Hypoalbuminaemia (<3.5 g/dL)
3. Generalised oedema (anasarca)
4. Hyperlipidaemia and lipiduria

• Primary (Idiopathic): Minimal Change Disease (MCD - most common in children), FSGS, Membranous nephropathy (most common in adults), Membranoproliferative GN
• Secondary: Diabetes mellitus (diabetic nephropathy), SLE (lupus nephritis), Amyloidosis, Malaria, HIV, drugs (gold, penicillamine)

• Loss of negative charge on glomerular basement membrane (GBM) and/or structural damage
• Allows proteins (mainly albumin) to pass into urine
• Low albumin → low oncotic pressure → oedema
• Liver compensates by increasing VLDL production → hyperlipidaemia

• Oedema: Periorbital (early morning, most characteristic), dependent oedema, ascites, pleural effusion, scrotal/labial oedema
• Frothy urine (lipiduria, proteinuria)
• Pallor
• Anorexia, fatigue
• Possible hypertension (especially in secondary forms)

• Infections (bacterial - Streptococcus pneumoniae, peritonitis) - due to loss of immunoglobulins
• Thromboembolism (renal vein thrombosis, DVT, PE) - loss of antithrombin III, protein C and S
• Hyperlipidaemia → accelerated atherosclerosis
• AKI
• Protein malnutrition, vitamin D deficiency, anaemia

• Urine: 24-hour protein, urine protein:creatinine ratio, lipid casts
• Serum albumin (low), serum cholesterol (high), TG (high)
• Serum creatinine and urea
• Renal biopsy (gold standard for definitive diagnosis - except typical MCD in children)
• Complement levels (C3, C4 - low in MPGN, SLE)
• ANA, anti-dsDNA (SLE), HBsAg, HCV, blood glucose

1. Specific: Based on histology - Steroids (MCD: prednisolone 60 mg/day - excellent response), cyclophosphamide, cyclosporine
2. Salt restriction, fluid restriction if severe oedema
3. Diuretics: Frusemide (loop diuretic)
4. ACE inhibitors/ARBs: Reduce proteinuria (e.g., ramipril, losartan)
5. Statins: Manage hyperlipidaemia
6. Anticoagulation if thromboembolism
7. Antibiotics/prophylaxis for infections (penicillin V in children)
8. Dietary protein intake: 0.8-1 g/kg/day of high-quality protein

---

X. HERPES ZOSTER (SHINGLES)

• Burning, stabbing pain, hyperalgesia, itching along the dermatome
• Malaise, fever, headache
• No visible rash yet (often misdiagnosed)

• Unilateral, dermatomal distribution (does NOT cross midline)
• Maculopapular rash → vesicles (clear fluid) → pustules → crusting
• Thoracic dermatomes most common (T3-T11)
• Intense pain (may persist as postherpetic neuralgia)

• Herpes Zoster Ophthalmicus (V1 - ophthalmic branch of trigeminal): Vesicles on forehead, tip of nose (Hutchinson's sign), risk of corneal ulceration and blindness
• Ramsay Hunt Syndrome (VII nerve - geniculate ganglion): Facial palsy + vesicles in external auditory canal/pinna + ipsilateral tinnitus, vertigo, deafness
• Oral Herpes Zoster (V2/V3 - maxillary/mandibular branch): Unilateral vesicles and ulcers on oral mucosa, palate, gingiva; extreme dental pain - relevant to dentists as it can mimic pulpitis or periapical abscess
• Zoster sine herpete: pain without rash

• Pain persisting >3 months after rash heals
• Most common complication; seen in >50% patients above 60 years
• Burning, lancinating, allodynia (light touch causes pain)

• Mainly clinical diagnosis
• Tzanck smear: Multinucleated giant cells (also seen in HSV)
• PCR for VZV DNA (gold standard)
• VZV-specific IgM (acute), IgG (past infection)

1. Antiviral drugs (must start within 72 hours of rash onset):
   • Acyclovir 800 mg 5 times daily x 7-10 days (standard)
   • Valacyclovir 1 g TDS x 7 days (better oral bioavailability, preferred)
   • Famciclovir 500 mg TDS x 7 days
2. Pain management:
   • Paracetamol, NSAIDs (mild)
   • Gabapentin / Pregabalin (neuropathic pain, postherpetic neuralgia)
   • Amitriptyline (tricyclic antidepressant - for postherpetic neuralgia)
   • Opioids (severe pain)
3. Topical: Calamine lotion, antiviral cream
4. Corticosteroids: Prednisolone may reduce acute pain and risk of postherpetic neuralgia (adjunct)
5. Eye care: Topical acyclovir eye ointment, ophthalmology referral (Zoster ophthalmicus)
6. Prevention: VZV vaccine (Shingrix - recombinant adjuvanted vaccine) - recommended for adults >50 years; 90% effective at preventing shingles

---

SUMMARY TABLE FOR QUICK REVISION

---

---

TREATMENT OF HYPOTHYROIDISM

---

INTRODUCTION

---

1. DRUG OF CHOICE: LEVOTHYROXINE (L-T4)

• Longer half-life (~7 days) - allows once-daily dosing and stable blood levels
• Peripheral tissues convert T4 to the active T3 as needed (physiological)
• Better tolerated than T3 preparations
• Steady state achieved in 6-8 weeks
• The American Thyroid Association (ATA) recommends against routine T3/T4 combination therapy as evidence of superiority over L-T4 alone is not consistent

---

2. DOSING

Standard Dosing (Full Replacement)

Key Rule: Never start full dose in elderly or cardiac patients - risk of precipitating angina, MI, or arrhythmia.

How to Take

• Take on an empty stomach, 30-60 minutes before breakfast OR at bedtime
• Food, caffeine, and certain drugs reduce absorption - must be taken consistently

---

3. MONITORING TREATMENT

• Primary hypothyroidism: TSH within the normal reference range (0.5-4.5 mIU/L)
• Central (secondary/tertiary) hypothyroidism: Monitor free T4 (fT4) - target upper third of reference range (TSH unreliable)
• Elderly: TSH target can be slightly higher than in younger adults

---

4. CAUSES OF TREATMENT FAILURE (Persistent High TSH Despite Therapy)

---

5. DRUG INTERACTIONS - IMPORTANT FOR BDS

---

6. ADVERSE EFFECTS OF OVER-TREATMENT (EXCESS L-T4)

• Palpitations, tachycardia, atrial fibrillation
• Tremor, nervousness, anxiety, insomnia
• Heat intolerance, excessive sweating
• Weight loss
• Long-term: Osteoporosis (especially post-menopausal women), atrial arrhythmias

---

7. SPECIAL SITUATIONS

A. Subclinical Hypothyroidism (SCH)

• Definition: Elevated TSH with normal fT4 and no/minimal symptoms
• Treat if:
  • TSH >10 mIU/L (all ages) - treat with L-T4
  • TSH 5-10 mIU/L with symptoms of hypothyroidism - consider treatment
  • Younger patients (<65-70 yrs) with TSH >10 - treat
  • Very elderly (>80-85 yrs) with TSH ≤10 - "watch and wait" strategy (mildly elevated TSH may be physiological in old age)
• Meta-analyses have not consistently shown reduction in MI or mortality with treating SCH

B. Hypothyroidism in Pregnancy

• TSH should be measured every 4 weeks until 20 weeks of gestation, then once in second half
• Levothyroxine dose typically increases by 25-30% early in pregnancy (often from week 4-6)
• Even mild maternal hypothyroidism can affect fetal neurological development
• Return dose to pre-pregnancy level immediately after delivery
• Target TSH: <2.5 mIU/L in first trimester

C. Congenital Hypothyroidism (Cretinism)

• Must be treated immediately after birth (neonatal screening - Guthrie test/heel prick)
• L-T4: 10-15 mcg/kg/day in neonates (higher dose per kg due to high metabolic demand)
• Early treatment prevents irreversible intellectual disability

D. Central (Secondary/Tertiary) Hypothyroidism

• Due to pituitary or hypothalamic disease
• IMPORTANT: Always exclude co-existing adrenal insufficiency BEFORE starting L-T4
  • Starting T4 first can precipitate an adrenal crisis (T4 increases cortisol clearance)
  • Give hydrocortisone first, then start L-T4
• Monitor with fT4, not TSH

---

8. MYXOEDEMA COMA - EMERGENCY TREATMENT

Emergency Management:

Why hydrocortisone? Myxoedema coma may be accompanied by adrenal insufficiency (Schmidt's syndrome - autoimmune polyglandular failure). Starting T4 without covering adrenals can be fatal.

---

9. SUMMARY TABLE

---

---

D. TREATMENT OF HYPOTHYROIDISM

1. Levothyroxine (L-T4) - Drug of Choice

• Synthetic T4 given orally, once daily
• Preferred over T3 (liothyronine) or combination T3/T4 because of its longer half-life (7 days), stable blood levels, and better tolerability
• Peripheral tissues convert T4 → active T3 as needed (physiological)
• Steady state achieved in 6-8 weeks; symptoms improve over weeks to months
• Full replacement dose: 1.5-1.7 mcg/kg/day (e.g., 75-150 mcg/day in average adult)
• Take 30-60 minutes before breakfast on an empty stomach (food reduces absorption)

2. Dosing by Patient Type

Never start full dose in elderly or cardiac patients - risk of precipitating angina or arrhythmia

3. Monitoring

• Check serum TSH at 4-6 weeks after starting or changing dose (do NOT check earlier - TSH lags)
• Repeat at 4-6 months, then annually once stable
• Target: TSH within normal range (0.5-4.5 mIU/L) in primary hypothyroidism
• In central hypothyroidism (pituitary/hypothalamic): monitor fT4, not TSH

4. Special Situations

• Pregnancy: Increase L-T4 dose by ~25-30% from early pregnancy; check TSH every 4 weeks up to 20 weeks; target TSH <2.5 mIU/L
• Congenital hypothyroidism (Cretinism): Treat immediately after birth with 10-15 mcg/kg/day to prevent irreversible intellectual disability
• Central hypothyroidism: Always exclude adrenal insufficiency first before starting L-T4 - otherwise adrenal crisis can be precipitated

5. Important Drug Interactions

• Rifampicin, phenytoin, carbamazepine - induce CYP450, increase T4 metabolism - dose may need to be increased
• Iron tablets, calcium carbonate, cholestyramine - reduce L-T4 absorption - take 4 hours apart

6. Adverse Effects of Over-Treatment (Excess L-T4)

• Palpitations, tachycardia, tremor, anxiety
• Long-term: Osteoporosis and atrial fibrillation

7. Myxoedema Coma (Emergency)

• IV Levothyroxine: Loading dose 200-400 mcg IV, then 50-100 mcg IV daily
• IV Hydrocortisone: 50-100 mg every 8 hours (to cover possible adrenal insufficiency)
• Supportive: ICU, ventilatory support, passive warming, IV fluids
• Treat the precipitant (infection, cold exposure, drugs)

---