VivaCast 14 : Pharmacokinetics, Hypoglycaemics & Clinical Studies

Key Topics Covered:

• The four pillars of pharmacokinetics: absorption, distribution, metabolism, and excretion.
  • + Bioavailability and first-pass metabolism.
• Hypoglycaemic medications: insulin, metformin, sulfonylureas, and newer agents like GLP-1 receptor agonists.
• Clinical trials: phases, methodologies, and the importance of randomized controlled trials (RCTs).

Pharmacokinetics: How Drugs Move Through the Body

Pharmacokinetics describes what the body does to a drug, categorised into:

Absorption – The route by which a drug enters the bloodstream.

• Routes of administration (oral, intravenous, parenteral, topical, intranasal, intrathecal, epidural, subcutaenous, intramuscular, intraocular ).
• First-pass metabolism and its impact on drug delivered to target site.

Distribution – How drugs are transported through the body.

• Lipid vs. water solubility and their effects on drug movement.
• Protein Binding
• Volume of distribution
• Dis-association activity
• Factors influencing tissue penetration and therapeutic effects.

Metabolism – The body’s method of transforming drugs.

• Liver metabolism: Phase I and Phase II reactions.
• Active vs. inactive metabolites and their clinical significance.

Excretion – The removal of drugs from the body.

• Renal (kidneys), hepatic (bile), and pulmonary (exhalation) excretion pathways.
• Drug accumulation risks in patients with organ dysfunction.

Example: Paracetamol is well absorbed with minimal first-pass metabolism, making it highly bioavailable. In contrast, vancomycin has poor oral absorption, requiring IV administration for systemic effects, but has the convenience of treating intra-luminal bacteria with high drug concentrations (think clostridium difficile)

Hypoglycaemic Medications: Mechanisms and Clinical Considerations

Hypoglycaemic agents are crucial in diabetes management. They can be categorized into:

• Insulin:
  • Acts on peripheral tissues (liver, muscle, CNS) via tyrosine kinase receptors.
  • Different types:
    • Long-acting (e.g. Lantus) – Provides basal insulin coverage.
    • Short-acting (e.g. Novorapid) – Matches postprandial glucose spikes.
• Metformin (Biguanide):
  • Enhances insulin sensitivity rather than increasing secretion.
  • Does not cause hypoglycemia but carries a risk of lactic acidosis in critically unwell patients.
• Sulfonylureas (Gliclazide):
  • Stimulates insulin release from beta cells of the pancreas.
  • Major side effect: Hypoglycemia, especially in elderly or renal-impaired patients.
• SGLT2 Inhibitors (Flozins):
  • Increase urinary glucose excretion.
  • Also beneficial for heart failure (disease modifying) and weight loss.
  • Cause a Euglycaemic Ketoacidosis in poorly folk.
• GLP-1 Receptor Agonists (e.g. Semaglutide, Liraglutide):
  • Enhance insulin secretion, suppress appetite.
  • Recently used for weight loss therapy.
• Incretins – DPP4 inhiibitors (SitaGLIPTINS)
  • Inhibits DPP-4 increasing the availability of GLP-1 receptor agonists/GIP
• GIP analogs (gastric inhibitory peptide)
  • Tirzepatide (MOUNJARO) – also acts as a GLP-1 Receptor Antagonist

Key Clinical Consideration:
Which drugs cause hypoglycemia?

• Insulin and Sulfonylureas are most associated with low blood sugar.
• Metformin, SGLT2 inhibitors, and GLP-1 agonists generally do not cause hypoglycemia.

⠀

Clinical Trials

A clinical trial is a structured investigation to test medical interventions using scientific principles.

Phases of a Clinical Trial

Phase 1: Safety and dosage testing in a small group.

Phase 2: Efficacy assessment in a controlled population.

Phase 3: Large-scale trials to confirm effectiveness and monitor side effects.

Phase 4: Post-marketing surveillance to detect rare adverse effects.

⠀Gold Standard: Randomized Controlled Trials (RCTs)

• Patients randomly assigned to treatment vs. placebo/control groups.
• Often double-blinded to eliminate bias.
• Used to determine true cause-and-effect relationships in medicine.

⠀Meta-Analysis: Combining Trial Data

• Systematic review of multiple trials to generate stronger evidence.
• Helps determine if a treatment truly works across different studies and populations.
• Classically produces a scatter plot of the data from each trial, with confidence intervals, once the data has been processed / variances accounted for with weightings

⠀

Final Thoughts & Takeaways

• Understanding pharmacokinetics is crucial for effective drug dosing and administration, robust knowledge of this is expected in the FRCA Primary Exam
• Hypoglycaemic medications have varying mechanisms of action, and their side effects should be carefully considered in clinical practice. The question could be in an OSCE where you’re discussing when to stop such agents / VRII plans.
• Clinical trials, particularly RCTs, form the foundation of evidence-based medicine, and this is easy marks in an exam if you’ve covered it!

References

Peck and Hill is the hero of the hour yet again (read it) – don’t leave it till a week before your primary to open it…..

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“Thanks for listening guys… Every day you are getting better at this. Take it day by day, don’t overcook yourself, don’t freak out, and keep studying!”

Podcast Information

Transcript GasGasGas Podcast – Episode 014: Pharmacokinetics, Hypoglycaemic Drugs & Clinical Trials

Introduction

00:00-00:28 Hello and welcome to Gas Gas Gas, the podcast that covers the FRCA primary exam. We’re going to fit into your day and give you as much of your life back as you could possibly imagine. Listen to us on your commute, in the gym, in the shower, or when ironing your scrubs. Expect facts, concepts, model answers and the odd tangent. Check out the show notes for all the detail and remember to follow the show so that you never miss an episode.

Pharmacology Viva Session

01:12-01:26 This is Tom’s pharmacology viva session, with improved timing discipline. We’re setting a timer to keep this structured and focused.

Pharmacokinetics Definition

01:26-03:51

The Four Pillars of Pharmacokinetics

Pharmacokinetics encompasses all the processes that the body performs on a drug, broken down into four main areas:

1. Absorption

Non-intravenous routes:

• Drug absorption varies significantly by route
• Gastric absorption: Some drugs absorbed well in stomach, others poorly
• Intestinal absorption: Alternative absorption site for many medications
• Parenteral routes: Less absorption concern

⠀First-pass metabolism:

• Drugs absorbed in gut → portal circulation → liver
• Significant proportion metabolised before reaching systemic circulation
• Must account for this when determining dosing

⠀2. Distribution

Tissue affinity variations:

• Different drugs have different tissue preferences
• Lipid-soluble drugs: Travel freely across cell membranes, reach distant body parts
• Water-soluble drugs: More retained in vascular compartments, slower target site arrival

⠀3. Metabolism

Modification reactions:

• Usually occurs before excretion
• Some drugs excreted unchanged
• Active metabolites: May be therapeutically active or toxic
• Inactive metabolites: Modified into excretable forms
• Important consideration for drug action duration and safety

⠀4. Excretion

Elimination routes:

• Renal: Via kidneys
• Hepatic: Via bowel
• Pulmonary: Via exhalation
• Route affects drug accumulation and duration in different patient populations

⠀Bioavailability Factors

04:00-05:37

Route of Administration

Intravenous administration:

• 100% bioavailability (by definition)
• Circulates via heart into systemic circulation without significant liver metabolism

⠀Enteral administration:

• Portal venous system → direct liver passage
• First-pass metabolism reduces bioavailability
• Percentage bioavailable = percentage surviving initial liver passage

⠀Examples

High bioavailability: Paracetamol

• Well absorbed, minimal first-pass metabolism

⠀Zero bioavailability: Vancomycin (oral)

• Not absorbed from GI tract (not due to liver metabolism)

⠀Hepatic Enzyme Factors

Enzyme induction/inhibition:

• Other drugs can activate or inactivate drug-metabolising enzymes
• Affects rate of hepatic drug processing
• Important drug interaction mechanism

⠀Diabetes Mellitus Medications

06:10-10:30

Classification by Mechanism

Direct action on liver and peripheral tissues:

• Insulin: Acts directly on target tissues

⠀Insulin sensitivity enhancers:

• Metformin: Increases body’s sensitivity to insulin effects

⠀Insulin secretion modulators:

• Incretins: Affect insulin secretion and appetite control, reducing dietary sugar intake

⠀Renal glucose management:

• SGLT2 inhibitors (flozins): Increase glucose excretion via kidneys

⠀Insulin Details

Source and function:

• Produced: Beta cells of pancreatic islets of Langerhans
• Primary function: Controls peripheral glucose uptake into tissues (skeletal muscle, liver, CNS)
• Mechanism: Binds to tyrosine kinase-coupled receptors on cell surfaces
• Result: Downstream signalling promotes cellular glucose uptake for energy production

⠀Insulin Preparations

Duration categories:

1 Long-acting: Provides basal insulin levels (essential in Type 1 diabetes to prevent hyperglycaemia/DKA)

2 Short-acting: Coincides with dietary glucose spikes

3 Rapid-acting: NovoRapid – peak effect matches meal glucose absorption

4 Intermediate-acting: Part of insulin regimens matching individual patient glucose patterns

⠀Hypoglycaemia Risk

High-risk medications:

• Gliclazide: Promotes insulin action → blood glucose reduction
• Insulin: Primary action reduces plasma glucose concentration

⠀Lower-risk medications:

• Metformin: Sensitises tissues to insulin without causing hypoglycaemia

⠀Other Antidiabetic Agents

GLP-1 agonists:

• Semaglutide, liraglutide: Incretin hormones affecting appetite and insulin secretion
• Used for weight loss as well as diabetes treatment

⠀Metformin vs. Gliclazide

Metformin mechanism: Sensitises peripheral tissues to insulin action (does not promote insulin secretion) Gliclazide mechanism: Promotes insulin secretion

Metformin in Unwell Patients

Lactic acidosis risk:

• Mild form: No clinical significance in well patients
• Critically unwell patients: Worsening acidosis and lactataemia could have significant negative effects
• Important consideration for perioperative management

⠀Clinical Trials

11:07-15:40

Definition

Clinical trial: Research process testing medical interventions via scientific method by systematically selecting patients and testing intervention effects on specific groups.

Types of Clinical Trials

Gold standard: Randomised Controlled Trial (RCT)

• Control group: No intervention given
• Blinding: Participants and sometimes administrators blinded to intervention status
• Comparison: Intervention effects measured against predetermined outcomes

⠀Other study types:

• Prospective studies: Forward-looking intervention analysis
• Retrospective studies: Historical intervention effect analysis using regression analysis to control confounders

⠀Pharmaceutical Development Phases

Phase I: Safety study

• Small group testing
• Dose-finding study – range of doses tested
• Establishes medication safety for administration
• Not randomised

⠀Phase II: Efficacy study

• Different regimens to determine optimal potency
• Begins investigating specific therapeutic effects
• Tests whether intervention produces desired outcome (e.g., reduced heart attack rate)
• Not randomised

⠀Phase III: Large-scale RCT

• Optimal dose and frequency established from earlier phases
• Proper randomised controlled trial
• Statistically powered for meaningful conclusions
• Most rigorous testing phase

⠀Phase IV: Post-market surveillance

• Large population use after public availability
• Identifies rare adverse effects not detected in smaller studies
• Confirms Phase II findings in broader population

⠀Meta-Analysis

Purpose: Combines results of multiple trials examining the same intervention when well-designed individual RCT unavailable

Requirements:

• Relevant trial identification: Finding all applicable studies
• Quality assessment: Effective trial performance evaluation
• Outcome comparison: Same or comparable endpoints
• Population similarity: Comparable study populations
• Intervention consistency: Actually the same treatment

⠀Analysis method: Forest plot showing combined effect with uncertainty range – determines positive, neutral, or negative effects on outcomes of interest

Post-Viva Reflection

15:40-17:33

Timing Improvements

Better time management: Successfully completed three 5-minute sections within 15-minute timeframe, unlike previous meandering sessions

Phase Trial Clarification

Correction noted:

• Phase I & II: Not randomised
• Phase III: Proper randomised controlled trial after optimal dosing established
• Phase IV: Post-market surveillance

⠀Clinical Trial Definition Challenge

Reflection: First time considering formal definition of clinical trial – good practice for unexpected question approaches

Learning point: Importance of practicing verbal explanations for fundamental concepts, even when they seem obvious