pharmacology and contrast agents

PHARMACOLOGY AND CONTRAST AGENTS

BY: MOHAMAD YUSRI AMRI BIN GHZALI

A substance placed in the body to increase image differentiation of anatomical structures.

It increases the differentiation between the areas containing contrast media and the areas not containing contrast media.

WHAT IS CONTRAST AGENT?

TYPE OF THE CONTRAST AGENTS

POSITIVE CONTRAST AGENTS

High Osmolar Contrast Media (HOCM) Composed of salts which dissociate in water

into anions (radiopaque) and cations (osmotically active).

Osmolality up to 5x serum -toxicity. Non-intravascular route – oral / rectal. Not for use in subarachnoid space. E.g. Gastrografin, Urografin, Isteropac

IONIC

Low Osmolar Contrast Media (LOCM) -Non-dissociating. -Only about 2x serum osmolality. -Less side effects, less nephrotoxic. E.g. Ultravist, OmnipaqueIso-osmolar Contrast Media -Osmolality approximately serum osmolality. -Preferred in renal impaired patients. E.g. Visipaque

NON IONIC

1.Iodine concentration the change that more x-ray photons will be

absorbed therefore that particular CM maybe more radiopaque than a comparative low iodine concentrated CM. The higher the iodine concentration, the greater the risk of an adverse reaction .

QUALITIES OF IODINATED CONTRAST AGENTS THAT CONTRIBUTE TO DISCOMFORT, SIDE EFFECT AND REACTION

2.Viscosity◦ Describes the THICKNESS or RESISTANCE to flow

of contrast agent.◦ Related to the concentration, the size of the molecules

in a specific contrast agent and the temperature of the contrast agent.

◦ Determine the force that is required to inject it through a needle or catheter into a patient.

◦ Viscosity can be reduced by lowering the concentration of the contrast medium BUT reducing the iodine concentration may also result in unsatisfactory opacification.

3.Osmolality (related to blood plasma)◦ Measurement of the number of MOLECULES

and PARTICLES in a solution per kilogram of water.

◦ May also be described as a measurement of the number of molecules that can crowd out or displaced water molecules in a kilogram of water.

◦ Osmolality of contrast media solution is being simply a function of the concentration of particles within it.

◦ Concentration of particles (osmoles) per unit weight (kilograms) of solvent (mOsm/kg H2O)

4. Miscibility Contrast agents should be readily miscible with

blood. 5. Toxicity Potential toxicity is greater with higher-

concentration agents and ionic agents, viscosity also increase as room temperature decrease.

Barium CM are used to diagnose abnormalities of the gastrointestinal tract, such as tumors, ulcers and other inflammatory conditions, polyps, hernias, and strictures. With the use of barium sulfate, a metallic chemical that x-rays cannot pass through, x-rays are taken of the area under examination.

BARIUM CONTRAST MEDIA

1.AIR As in the picture on the right where both air and barium are

used together air can be used as a contrast material because it is less radio-opaque than the tissues it is defining. In the picture it highlights the interior of the colon.

2. CARBON DIOXIDE Carbon dioxide also has a role in angiography. It is low-risk as

it is a natural product with no risk of allergic potential. However, it can be used only below the diaphragm as there is a risk of embolism in neurovascular procedures. It must be used carefully to avoid contamination with room air when injected.

NEGATIVE CONTRAST AGENTS:AIR AND CARBON DIOXIDE

Proven/suspected hypersensitivity to iodine Previous severe reaction to contrast media Asthma/significant allergy history Heart disease Infants/children/elderly Liver failure Renal impairment (moderate-severe) – NIDDM on Metformin Myelomatosis Poor hydration Sickle cell anaemia Thyrotoxicosis Pregnancy Phaeochromocytoma

CONTRAINDICATIONS

1 Adults: 50mg Prednisone PO 13, 7 and 1 hour before the

injection. 50mg Benadryl (Diphenhydramine) IV/PO within 1

hour of the injection. 2. In an emergency setting an alternative faster (but

less proven) regime is: 200mg Hydrocortisone IV 4 hours before injection. 50mg Benadryl (Diphenhydramine) IV/PO within 1

hour of the injection.

PREMEDICATION

50mg Benadryl (Diphenhydramine) IV/PO within 1 hour of the injection.

3. Pediatrics (For patients less than 50kg): Prednisone 0.7mg/kg (not to exceed 50mg) PO 13, 7 and 1

hour before the injection. Benadryl (Diphenhydramine) 1mg/kg IV/PO (not to exceed

50mg) within 1 hour of the injection. 4. In an emergency setting an alternative faster (but less

proven) regime is: Hydrocortisone 1mg/kg (not to exceed 200mg) IV 4 hours

before injection. Benadryl (Diphenhydramine) 1mg/kg IV/PO (not to exceed

50mg) within 1 hour of the injection.

1.Fasting 4-6 hrs2.Steroid cover  – allergy, asthma T. prednisolone 50 mg 13, 7, 1 hr before

examination IV hydrocortisone 200mg stat3. Renal impairment N-acetyl cysteine 600mg the day before and 1

day after examination

SCHEDULING DIAGNOSTIC IMAGING EXAMINATIONS

1.Hypersensitivity reaction2.Nephrogenic systemic fibrosis -Recently reported serious late adverse

reaction of gadolinium-based contrast. -Seen in patients with renal failure and on

dialysis. Fibrosis of skin and organs.

COMPLICATIONS

Clinical symptoms developed 2-8 weeks after exposure to gadodiamide.

Avoid in patient with creatinine clearance <15mL/min