Provide an approximate value of ED50 for both acetylcholine and pilocarpine or carbachol. Analyse the effect of the antagonists on the dose-response curves for both drugs. How would you describe the mechanism of action of the antagonist on the muscarinic receptors?

Applied Pharmacology Coursework

Part 1: Data analysis and interpretation

Using the Virtual Organ Bath 2.8 software, you’ll study the effects of two different agonists (for example: acetylcholine & pilocarpine or carbachol) on the contraction of smooth muscle from guinea pig small intestine.

The effect of both drugs should be evaluated without and in the presence of one antagonist.

Set a list of concentrations for both acetylcholine and pilocarpine. With the help of dilution formula in the virtual organ bath software, work out the volumes required from the appropriate stock solutions.

Progressively increasing doses of the agonist should be added to the bath (use a range between 1×10-10 – 1×10-6 M) and contraction of the tissue (in gms) will be measured and recorded.

Afterwards, the appropriate antagonist (concentration in the reservoir 5×10-8 M) should be added, and the experiment is repeated using higher concentrations of the agonists (up to 1×10-4 M)

These tables are just an example of how you could record your data:
Dose used (without antagonist) Contraction Response in gms
(unit) Acetylcholine Pilocarpine

Dose used (with antagonist 5×10-8 M) Contraction Response in gms
(unit) Acetylcholine Pilocarpine

Your submitted work should include the following:
• A brief description of the design of the experiment and how the data was collected.
• Your data recorded in tables with concentration of both agonists and the corresponding antagonist.
• Answer the following questions:

1. Discuss
• What is Acetylcholine and how does it produce contraction of the smooth muscle (dynamics: receptors, type and drug-receptor interaction)?
• What is pilocarpine (or carbachol if it was chosen in the experiment) ? what is its mechanism of action? discuss briefly its therapeutic applications
• Identify two drugs that can be used for their effect on smooth muscles within the body (urinary tract, blood vessels, or respiratory system) and briefly discuss the following:
– the mechanism of action
– drug-drug interaction
– therapeutic application

2. Using Excel, or Graphpad Prism:

• Convert the contraction values into %response and the dose into log10 for each drug
• Plot the following graphs :

o the %response vs. log10 dose for acetylcholine (with and without the antagonist, 2 curves in the same graph)
o the %response vs. log10 dose for pilocarpine or carbachol (with and without the antagonist, 2 curves in the same graph)

• Describe both graphs:

o Compare the 2 dose-response curves (without antagonists): which agonist is the most potent? And which one is the most effective? provide evidence from your data.

o Provide an approximate value of ED50 for both acetylcholine and pilocarpine or carbachol.

o Analyse the effect of the antagonists on the dose-response curves for both drugs. How would you describe the mechanism of action of the antagonist on the muscarinic receptors?

Part 2: Case Studies

Read the following three case studies and answer all questions:

1. A patient is taking Paroxetine and presents to A&E with tremor, tachycardia, hypertension and high temperature. After a genetic screening, the variant CYP2D6*4 is identified. Discuss:

• What is Paroxetine and how does it work (mechanism and clinical use)?
• What is the role of the CYP2D6 in the drugs’ metabolism in general?
• What is the metabolic pathway of Paroxetine and how is it affected by the genetic variant described in this case study?
• What is the resulting alteration in the blood levels of Paroxetine?
• What is the link between the altered blood levels of Paroxetine and the signs and symptoms reported (can you identify the syndrome)?

2. A 20 yo woman with history of poorly controlled asthma presents to the A&E with severe shortness of breath and audible respiratory wheezing. She has normal blood pressure but she is pale. She uses terbutaline inhaler when needed but now the inhaler isn’t helping
• What emergency drug should be administered?
• Discuss: the indications, side-effects and mechanism of action of the proposed drug
• What long-term therapy should follow, after she is stabilized?
• Discuss: the indications, side-effects and mechanism of action of the proposed therapy for long-term management

3. A 57 year old female presents to the GP with palpitations on and off for 4 months. The patient describes the palpitations as feeling like missed beats, flutters, and a racing heart usually of sudden onset. Her medical/health history reveals that she has hypertension (BP 152/94 mmHg), she is a mild diabetic, and also suffers from gastro-oesophageal reflux disease (GORD). She has a BMI of 38. Her medications include Cilazapril and Hydrochlorothiazide, and Omeprazole.

A blood test revealed the following:
Test Result
FBC (full blood count) Normal
TFTs (Thyroid function tests) TSH 3.2 (0.6-4.5)
U+E (urea & electrolytes) K+ 3.2 mmol/l (3.5-5.0 mmol/l)
Magnesium 0.68 mmol/l (0.75-1.25 mmol/l)
Urea 7.8 mmol/l (3.6-7.1 mmol/l)
Creatinine 118 mcmol/l (52.2-91.9 mcmol/l)
Random glucose 9.8 mmol/l (3.0-7.8 mmol/l)
Normal ranges are shown in the table between brackets.
Analyse this case using a critical thinking approach as outlined below:

Gather, analyse and interpret the relevant medical and pharmacological information the clinician needs before treating this patient. (Assessment)

What are the relevant assumptions you have about this case, and what investigations would you undertake to confirm these assumptions? Would you check the levels of any other electrolytes?

Devise a care plan – what are the possible interventions/drugs that could be used to treat this patient? Consider the implications and consequences of the possible interventions and devise a ‘complete’ care plan (short & long term).