Injection prolonged action

Parasitic pressure drops, 15 823t, 824 Para- substituents, 9 371, 372 Paratacamite, 7 769 Parathion, 13 524-525 Paratungstates, 25 383 demand for, 24 276 Parcel charter, 25 330 Parenteral drug dosage forms, IS 713-716 Parenteral drug injections, prolonged action, 18 715-716 Parenteral formulations,... 

Prolonged Action Parenterals Injections. Intramuscular injections have been developed to achieve prolonged therapeutic effects. This can be accompHshed by suspension of dmg particles in oils or flowable gels, from which the dmg slowly diffuses. Aqueous suspensions can also provide such therapeutic response. In these cases, the soHd dmg crystals generally are quite water insoluble and of a controlled particle size and crystallized form. 

Ester and amide local anaesthetics differ in the manner, site and rate of metabolism. There is little relation between the elimination of local anaesthetics and their duration of action. Amethocaine has a prolonged action due to its high affinity for nerve tissue despite being rapidly removed from plasma. Bupivacaine can be detected in the plasma many hours after its effects have worn off due to continuing absorption from the site of injection. The renal excretion of unchanged local anaesthetics is minimal. 

After local anaesthetic injection, onset of nerve block and duration depends mainly on lipid solubility and on the region in where the diug is injected. In some formulations adrenaline is added to prolong the blocking action by inducing regional vasoconstriction and hereby reduce absorption and metabolisation. 

The mineralocorticosteroid activity of methyl-prednisolone is even less than that of prednisone/ prednisolone. It has a comparable duration of action. It is less suitable for substitution therapy in patients with adrenal hypofunctional states. Methyl-prednisolone sodium succinate is formulated for parental administration while methylprednisolone acetate is used for intra-articularly or peri-articularly injections. It can also be administered IM and then has prolonged systemic effects, lasting 1 weeks as the acetate is absorbed slowly from the site of injection. Oral absorption is rapid with peak effects within 1-2 hours. The duration of action is then about 1.5 days. 

The vasoconstrictor actions of epinephrine and norepinephrine have been used to prolong the action of local anesthetics by reducing local blood flow in the region of the injection. Epinephrine has been used as a topical hemostatic agent for the control of local hemorrhage. Norepinephrine is infused intravenously to combat systemic hypotension during spinal anesthesia or other hypotensive conditions in which peripheral resistance is low, but it is not used to combat the hypotension due to most types of shock. In shock, marked sympathetic activity is already present, and perfusion of organs, such as the kidneys, may be jeopardized by norepinephrine administration. 

Diazoxide lowers blood pressure within 3 to 5 minutes after rapid intravenous injection, and its duration of action may be 4 to 12 hours. Interestingly, if diazoxide is either injected slowly or infused its hypotensive action is quite modest. This is believed to be due to a rapid and extensive binding of the drug to plasma proteins. Both the liver and kidney contribute to its metabolism and excretion. The plasma half-life is therefore prolonged in patients with chronic renal failure. 

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