Pharmacodynamics

Pharmacodynamics is the study of what drugs do to the body and how they do it.

Dose-Response Relationships

- Basic Features of the Dose-Response Relationship:  The dose-response relationship is graded instead of all-or-nothing (as dose increases, response becomes progressively larger).

- Maximal Efficacy and Relative Potency

- Maximal Efficacy: the largest effects that a drug can produce

- Relative Potency:  Potency refers to the amount of drug that must be given to elicit an effect.

- Potency is rarely an important characteristic of a drug.

- Potency of a drug implies nothing about its maximal efficacy.
 

Prostaglandines:

Every cell in the body is capable of synthesizing one or more types of PGS. The four major group of PGs are E, F, A, and B.

Pharmacological actions:

stimulation of cyclicAMP production and calcium use by various cells

CVS
PGE2 acts as vasodilator; it is more potent hypotensive than Ach and histamine

Uterous
PGE2 and PGF2α Contract human uterus

Bronchial muscle

PGF2α and thromboxan A2 cause bronchial muscle contraction.

PGE2 & PGI2 cause bronchial muscle dilatation

GIT: PGE2 and PGF2α cause colic and watery diarrhoea

Platelets

Thromboxan A2 is potent induce of platelets aggregation

Kidney

PGE2 and PGI2 increase water, Na ion and K ion excretion (act as diuresis) that cause renal vasodilatation and inhibit
tubular reabsorption

USE
PGI2: Epoprostenol (inhibits platelets aggregation)
PGE1: Alprostadil (used to maintain the potency of arterioles in neonates with congenital heart defects).
PGE2: Dinoproste (used as pessaries to induce labor)
Synthetic analogue of PGE1: Misoprostol (inhibit the secretion of HCl).

Macrolide

The macrolides are a group of  drugs (typically antibiotics) whose activity stems from the presence of a macrolide ring, a large  lactone ring to which one or more deoxy sugars, usually cladinose and desosamine, are attached. The lactone ring can be either 14, 15 or 16-membered. Macrolides belong to the polyketide class of natural products.

The most commonly-prescribed macrolide antibiotics are:  

Erythromycin,  Clarithromycin, Azithromycin, roxithromycin,

Others are: spiramycin (used for treating  toxoplasmosis), ansamycin, oleandomycin, carbomycin and tylocine.

There is also a new class of antibiotics called ketolides that is structurally related to the macrolides. Ketolides such as telithromycin are used to fight respiratory tract infections caused by macrolide-resistant bacteria.

Non-antibiotic macrolides :The drug Tacrolimus, which is used as an

immunosuppressant, is also a macrolide. It has similar activity to  cyclosporine.

Uses : respiratory tract infections and soft tissue infections.

Beta-hemolytic  streptococci,  pneumococci, staphylococci and enterococci are usually susceptible to macrolides. Unlike penicillin, macrolides have shown effective against mycoplasma, mycobacteria, some rickettsia and chlamydia.

Mechanism of action: Inhibition of bacterial protein synthesis by binding reversibly to the subunit 50S of the bacterial ribosome, thereby inhibiting translocation of peptidyl-tRNA. This action is mainly bacteriostatic, but can also be bactericidal in high concentrations

Resistance : Bacterial resistance to macrolides occurs by alteration of the structure of the bacterial ribosome.

Beta-Adrenergic blocking Agents 

• Prototype - Propranolol 
• Prevent or inhibit sympathetic stimulation
– Reduces heart rate
– Myocardial contractility 
– Reduce BP - decreases myocardial workload and O2 demand 
• In long-term management used to decrease frequency and severity of anginal attacks 
• Added when nitrates do not prevent anginal episodes 
• Prevents exercise induced tachycardia
• Onset of action 30 min after oral dose. 1-2 min IV

Therapeutic Actions
• Block Beta adrenergic receptors in the heart and juxtaglomerular apparatus 
• Decrease the influence of the sympathetic nervous system decreasing excitability of the heart 
• Decrease cardiac output. 
• Indicated for long term management of anginal pectoris caused by atherosclerosis 

Atenolol, metoprolol, and nadolol have the same actions, uses, and adverse effects as propranolol, but they have long half-lives and can be given once daily. They are excreted by the kidneys, and dosage must be reduced in clients with renal impairment.

Needle selection

Nerve blocks:

Inferior alveolar- 25 G short (LLU technique)

PSA- 25 G short

Mental/Incisive- 25 G short

Palatal- 27/30 G short/ultrashort

Gow-Gates/Akinosi- 25 G long

Infraorbital- 25 G long

Field Block:

ASA 25/27 short

Infiltration:

Infiltration/SP 25/27 short

PDL/Intraosseous

PDL 27/30 short

Intraosseous 30 short/ultrashort

Characteristics of Opioid Receptors

mu₁

Agonists : morphine phenylpiperidines

Actions:  analgesia bradycardia sedation

mu₂

Agonists : morphine phenylpiperidines

Actions:  respiratory depression euphoria physical dependence  

delta

Actions:  analgesia-weak,  respiratory depression

kappa

Agonists: ketocyclazocine dynorphin nalbuphine butorphanol

Actions:  analgesia-weak respiratory depression sedation

Sigma

Agonists: pentazocine

Action: dysphoria -delerium hallucinations tachycardia hypertension

epsilon:

Agonists: endorphin

Actions: stress response acupuncture