Pharmacology Study Set 4
Quiz 28 :
Review of the Cardiovascular System
The proteins in the plasma are albumin, globulin, and fibrinogen. Albumin comprises of 54%, globulin 38%, and fibrinogen 7% of total plasma proteins. Plasma proteins play vital role in the transportation of the lipids, hormones, vitamins and minerals. Pharmacokinetics is the branch of pharmacology which deals with the distribution of the drugs in the body. Drug distribution comprises of the movement of the drug from the plasma to the interstitial of the target cells. The binding of the drug to the plasma proteins is the major determinant of the drug distribution. A drug in the blood exists as bound and unbound form. The unbound form is the active form of the drug which gives pharmacological effects and the bound form of the drug acts as the reservoir of the drug. Thus the efficiency of the drug is measured by the degree to which the drug binds to the plasma proteins. The drug more bound is less in unbound form and thus less efficient. The drug less bound is more in unbound form and is more efficient. The most common plasma proteins that the drugs bound to are the albumin, lipoprotein, and the glycoprotein. When two drugs are administered at a time there are chances for both the drugs to compete for the binding site on the plasma proteins which affects each other. This depends on the affinity and the concentration of the drugs. Thus the plasma proteins play a vital role in the distribution of the drug through protein drug binding.
Sympathomimetic drugs are also known as adrenergic drugs. As the name suggests, the main action of them are to mimic the effects of the sympathetic nervous system on heart and vascular system. These drugs are significant during heart failure and shock (cardiogenic, hypovolemic, and septic). The effects of these drugs on heart are to increase the heart rate , increase the cardiac output, and to increase the heart conduction. Parasympathomimetics are also known as cholinergic drugs. These drugs mimic the effects of the parasympathetic nervous system. They stimulate the acetylcholine receptors. These are administered during tachycardia. These drugs are effective to decrease the heart rate. Adrenergic agonists are the drugs that stimulate the response of the adrenergic receptors. These drugs are a kind of Sympathomimetic drugs and cause the stimulation of the sympathetic nervous system. These drugs increase the rate of contraction of heart and increases heart rate. Anticholinergic are the drugs that block the neurotransmitter acetylcholine. These drugs bind to the receptors of the acetylcholine and inhibit the parasympathetic nervous system. Thus anticholinergics when administered results in increased heart rate by inhibiting the parasympathetic nervous system.
Autonomic drugs are the drugs that either imitate or inhibit the normal function of the autonomic nervous system (sympathetic nervous system and parasympathetic nervous system). They are further divided into cholinergic and adrenergic drugs. Adrenergic antagonists are the class of drugs that are prescribed for hypertension but preferable not as first line of drugs. Adrenergic antagonists are the drugs that inhibit the action of catacholamines at the adrenergic receptors. Based on the receptors on which they act, they are divided into alpha blockers and beta blockers. Alpha blockers are the drugs that block alpha receptors and the beta blockers are the drugs that block the beta receptors. Alpha blockers are classified into alpha1-antagonists and alpha2- antagonists. • Alpha1 adrenergic antagonists lower the blood pressure directly by blocking receptors on the arterioles causing the vessels to dilate. Prazosin (Minipress) and terazosin (Hytrin) are the alpha1 - adrenergic antagonists used for hypertension. • Alpha2 adrenergic antagonists are mainly used in research. In clinical use they are reserved for treating resistant hypertension that cannot be managed by safer medications. Methyldopa (Aldomet) and clonidine (Catapres) are the two drugs of this type. Beta blockers are either cardio selective beta blockers (beta1) or nonspecific beta blockers (beta1 and beta2). Propranolol (Inderal), metoprolol (Lopressor), atenolol (Tenormin), and timolol (Betimol) are the beta adrenergic antagonists used for hypertension. At low doses beta blockers are well tolerated but when dosage is increased, adverse effects can become numerous and potentially serious. While discontinuing these drugs, drug doses should be tapered over a several week period to avoid rebound hypertension.