Transdermal routes

The nurse observes the following points when administering drugs by die transdermal route ... 

The use of the transdermal route in the elderly is questionable because the amount of subcutaneous tissue is reduced in the aging process... 

Promoting an Optimal Response to Therapy N URATES The nitrates may be administered by die sublingual (under die tongue), buccal (between the cheek and gum), oral, IV, or transdermal route Nitroglycerin may be administered by die sublingual, buccal, to peal, transdermal, oral, or IV route If die buccal form of nitroglycerin has been prescribed, die nurse instructs die patient to place die buccal tablet between die cheek and gum or between die upper lip and gum above die incisors and allow it to dissolve The nurse shows the patient how and where to place die tablet in die mouth. Absorption of sublingual and buccal forms is dependent on salivary secretion. Dry mouth decreases absorption. 

Opioids maybe administered in a variety of routes including oral (tablet and liquid), sublingual, rectal, transdermal, transmucosal, intravenous, subcutaneous, and intraspinal. While the oral and transdermal routes are most common, the method of administration is based on patient needs (severity of pain) and characteristics (swallowing difficulty and preference). Oral opioids have an onset of effect of 45 minutes, so intravenous or subcutaneous administration maybe preferred if more rapid relief is desired. Intramuscular injections are not recommended because of pain at the injection site and wide fluctuations in drug absorption and peak plasma concentrations achieved. More invasive routes of administration such as PCA and intraspinal (epidural and intrathecal) are primarily used postoperatively, but may also be used in refractory chronic pain situations. PCA delivers a self-administered dose via an infusion pump with a preprogrammed dose, minimum dosing interval, and maximum hourly dose. Morphine, fentanyl, and hydromorphone are commonly administered via PCA pumps by the intravenous route, but less frequently by the subcutaneous or epidural route. 

The transdermal route of drug administration offers several advantages over other methods of delivery. For some cases, oral delivery may be contraindicated, or the drug may be poorly absorbed. This would also include situations for which the drug undergoes a substantial first-pass effect [173] and systemic therapy is desired. 

Preparations suitable for replacement therapy are shown in Table 31-1. The oral and transdermal routes are used most frequently. There is no evidence that one estrogen compound is more effective than another in relieving menopausal symptoms or preventing osteoporosis. 

Nitrates are required for symptomatic relief of chest pain they are not proven to improve hard outcomes such as MI or death. Nitrates should be given initially sublingually or by spray, followed by oral or transdermal routes if pain is relieved. Lack of pain relief mandates i.v. administration. Beta-blockers such as metoprolol are used and may reduce the risk of subsequent MI. Calcium channel blockers such as dilfiazem, verapamil, or long-acting di-hydropyridines can be added for symptom control if nitrates and beta-blockers do not suffice they do not improve outcomes. In fact, they may worsen outcomes in the presence of left ventricular dysfunction or CHF in acute coronary syndrome. 

The transdermal route (drug delivered through the skin into the systemic circulation), using trandermal patches, creams, ointments, gels. 

The hepatic first-pass effect can be avoided to a great extent by use of sublingual tablets and transdermal preparations and to a lesser extent by use of rectal suppositories. Sublingual absorption provides direct access to systemic—not portal—veins. The transdermal route offers the same advantage. Drugs absorbed from suppositories in the lower rectum enter vessels that drain into the inferior vena cava, thus bypassing the liver. However, suppositories tend to move upward in the rectum into a region where veins that lead to the liver predominate. Thus, only about 50% of a rectal dose can be assumed to bypass the liver. 

Natural alkaloids and most tertiary antimuscarinic drugs are well absorbed from the gut and conjunctival membranes. When applied in a suitable vehicle, some (eg, scopolamine) are even absorbed across the skin (transdermal route). In contrast, only 10-30% of a dose of a quaternary antimuscarinic drug is absorbed after oral administration, reflecting the decreased lipid solubility of the charged molecule. 

The route of entry for chemicals into the body differs in different exposure situations. In the industrial setting, inhalation is the major route of entry. The transdermal route is also quite important, but oral ingestion is a relatively minor route. 

While opioid peptides have been very useful for investigating the pharmacology of different opioid receptor subtypes, pharmacological investigations have established that no pharmacodynamic advantage is to be expected from opioid peptides with respect to analgesic activity or side-effects. Furthermore, they have their own shortcomings with respect to potential clinical applications. Most importantly their peptidic structure usually prohibits administration by the oral or transdermal route, which are the routes of choice for pain treatment. 

Clonidine can also be effective and tolerable when administered by the oral or transdermal route (Zeigler et al., 1992). 

In a case-control study 155 postmenopausal women who had had venous thromboembolism were compared with 381 matched controls (91). In all, 32 cases and 27 controls were current users of oral replacement therapy, whereas 30 cases and 93 controls were current users of transdermal products. After adjustment for potential confounding variables, the estimated risk ratio for venous thromboembolism in current users of the oral products compared with the transdermal users was 4.0 (1.9-8.3). This is strong evidence that the transdermal route was considerably safer. However, the conclusions of different studies continue to conflict with one another, no doubt in part because of variations in the formulations and patterns of use of the products. 

Therapeutically used types of estrogens and prog-estins are listed in Tables 30-4 and 30-5. Both types of hormones can be administered in their natural form (estradiol and progesterone), and several synthetic derivatives of each type are also available. Most of the drugs listed in Tables 30-4 and 30-5 are available as oral preparations, and many conditions can be conveniently treated by oral administration. These hormones may also be administered transdermally via patches, creams, or gels the transdermal route may offer certain advantages, such as decreased side effects and liver problems.86,130 Certain preparations can be... 

The route of entry for chemicals into the body differs in different exposure situations. In the industrial setting, inhalation is the major route of entry. The transdermal route is also quite important, but oral ingestion is a relatively minor route. Consequently, preventive measures are largely designed to eliminate absorption by inhalation or by topical contact. Atmospheric pollutants gain entry by inhalation, whereas for pollutants of water and soil, oral ingestion is the principal route of exposure for humans. 

Since nitroglycerin has been one of the most widely studied drugs which have been delivered by the transdermal route, the utility of the model will be illustrated for this compound. One membrane moderated device releases drug with well defined characteristics that have been measured in vitro [27]. There is an initial first order release of GTN (2mg) from the adhesive with an estimated rate constant of 1.3 h-1 over a surface area 10 cm. The zero order release from this device has been determined as 36yg/cm2/h. The... 

In contrast, Absolute Bioavailability involves comparison of the chug s bioavailability with respect to the corresponding bioavailability after iv administration. Absolute bioavailability may be calculated by comparing the total area under the Cp vs T curve obtained from the absorption route in question (often the oral route, although the approach can be used for other routes, such as the nasal, buccal, transdermal routes etc ), with that of the Cp vs T curve following iv administration ... 

The seven dmgs and the combination estrogen-progestin product presently approved in the US for delivery by the transdermal route were all well known and available in more conventional dosage forms before their formulation into skin patches . All of these dmgs are extremely potent, none requiring more than about 20 mg per day (and some, much less) for effective therapy. 

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