Topical applications, transdermal drug

Transdermal and Topical Administration Transdermal administration is used to apply the drug on the skin surface. The drug is absorbed and transported by blood to receptors, which may be remote from the part of the skin where the transdermal patch is. The flrst pass metabohsm is circumvented. Topical administration is used to apply the drug for local effects. The typical areas for topical application are the skin, eyes, throat, nose, and vagina. 

The solubilization of a drug substance in monophasic liquid crystalline vehicles gives semisolid formulations which are preferably used for topical application (see Surfactant Gels and Transdermal Patches above). 

Some pharmacokinetic properties of the commonly used amide local anesthetics are summarized in Table 26-2. The pharmacokinetics of the ester-based local anesthetics have not been extensively studied owing to their rapid breakdown in plasma (elimination half-life < 1 minute). Local anesthetics are usually administered by injection into dermis and soft tissues around nerves. Thus, absorption and distribution are not as important in controlling the onset of effect as in determining the rate of offset of local analgesia and the likelihood of CNS and cardiac toxicity. Topical application of local anesthetics (eg, transmucosal or transdermal) requires drug diffusion for both onset and offset of anesthetic effect. However, intracavitary (eg, intra-articular, intraperitoneal) administration is associated with a more rapid onset and shorter duration of local anesthetic effect. 

The objective of this chapter is to show how the concepts of chemical kinetics can be applied to the passage of molecules across the skin. The barrier function of the skin is still not totally understood but application of kinetic principles has allowed us to gain a better understanding of the barrier and how penetration enhancers may modulate it. The application of kinetics has allowed a mechanistic interpretation and therefore the development of predictive models. These can assist in the identification and design of novel transdermal drugs, and in the optimal design of topical formulations. 

Excipients can influence delivery from topical and transdermal medications. The propensity of the drug to migrate from the formulation to the application surface is affected by factors such as lipophilicity of the vehicle, drug solubility in the formulation, and effects of additives on the barrier properties of the skin or mucosal surface. 

Wang D-P, Lin C-Y, Chu D-L, Chang L-C. Effect of various physical/chemical properties on the transdermal delivery of ciclosporin through topical application. Drug Dev Ind Pharm 1997 23(1) 99-106. 

RNase (RNAse ribonuclease) An enzyme that cleaves RNA. routes of administration of drugs There are many different routes but common ones include intravascular injection or infusion (into the blood vessels, e.g. by drip, mainly intravenous (into veins) but sometimes intra-arterial (into arteries) intramuscular (injection into muscles) subcutaneous (injection beneath the dermis of the skin) intradermal (injection into the skin) transdermal (across the skin. e.g. from skin patches) topical (application to the skin or mucous membranes) per rectum (by an ointment or suppository into the rectum) intravaginally (by an ointment or pessary into the vagina) intrathecal (by injection into the subarachnoid space of the spinal cord) intranasally (often as a spray) orally (by mouth) inhalation. rRNA ribosomal RNA. 

One of the earlier studies demonstrating the role of blood flow on percutaneous absorption in humans used comparison dermal concentrations after topical application in vitro and in vivo (Schaefer and Stuttgen, 1978). Perfusion caused by cutaneous microcirculation also affected responses after the topical penetration of the vasodilator methyl nicotinate in humans (Guy et al., 1983). Altered transdermal drug absorption of the vasoactive nonsteroidal antiinflammatory drug (NSAID) methyl salicylate (MeSA) has also been attributed to changes in in vivo cutaneous perfusion. Exercise, heat exposure, or both increased MeSA absorption more than three times the control levels in six volunteers (Danon etal., 1986). A later case study reported that skin necrosis and other toxic symptoms occurred when a heating pad was used with a topical MeSA and menthol formulation meant to treat arthritic pain (Heng, 1987). 

Clonidine hydrochloride is readily absorbed by oral route with an absorption time of 2 to 4 hours (9). Drug is well absorbed from the gastro-intestinal tract. It may also be absorbed when applied topically to the eye, clonidine is well absorbed percutaneously following topical application of a transdermal system to the arm or chest. Plasma clonidine concentrations of 2 ng/mL have been detected one hour after administration of a single 0.39 mg oral dose of radiolabeled drug. Peak plasma concentrations following oral administration occur in approximately 3-5 hours (1). 

The advancement of different polymers has enabled the production of materials for medical purpose, which can be used above all as drug carriers or materials without an active substance, which are designed for topical application. In the case of transdermal... 

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