ROUTES OF DRUG ADMINISTRATION
In attempting to create a state of tranquility, we must get a certain concentration of agent to the appropriate location in the central nervous system (CNS). The effect can be altered by varying the agent. Some agents are more therapeutic than others. In gaining access to the appropriate areas of the CNS, a variety of routes of administration can be used.
Ultimately, this access depends on getting the drug into the circulation of arterial blood going to the brain. Since we are treating apprehensive patients, it is important to gain this access with as little pain as possible. Through inhalation, gaseous agents gain access via the lungs; liquid agents may be injected into the venous circulation, sprayed on nasal mucosa, absorbed sublingually, and injected under the skin into underlying muscle or swallowed and absorbed from the stomach and small intestine. Some agents have been administered rectally.
When considering routes, we should consider patient comfort, time to achieve effect, control of the effect, ease of administration, the skill needed for administration of the drug, necessary equipment for administration and monitoring of the patient. Unfortunately, we must also consider medical-legal questions of insurance and regulation by governmental organizations.
In general, the faster the drug reaches the CNS and has an effect the better control we have of the sedation. By titrating for effect, we can give just that amount of drug that is necessary to control apprehension. Both intravenous and inhalation agents can be readily controlled in this manner. Other routes of administration require administering an appropriate dose and waiting up to an hour to see the desired effect. It is obvious that it is impractical to titrate when we must wait for an hour to see the effect. These routes require very specific dosages usually associated with body size. They require conservative dosages as hypersensitivity to a medication will not be obvious until it is much too late to adjust the dosage. It is imperative that a drug with a very wide range of safety be used when these slower routes of uptake are utilized. Ideally, we will have reversal agents that can deactivate the drug in the case of overdose when using these routes.
We in dentistry have used and continue to use a variety of agents and combinations of agents. Multiple agents often complicate the treatment as each has side effects which may be addictive. They all are CNS depressants and some have unwanted depressing effects on respiratory and the cardiovascular systems. The combination of all these effects can lead to problems that are hard to predict and even more difficult to control. However, if only one agent is used, the side effects are often more predictable.
In general terms, it is easier (safer) to use a single agent as we then only have one set of side effects to contend with. This, of course, assumes a single agent will provide the needed effect at a concentration where few side effects are present. When Dione looked at combinations used by 264 dentists he found 82 distinct combinations. "The scientific basis for the use of such a diverse group of agents and combinations is unclear."
Inhalation sedation
The inhalation route of administration offers a major advantage when we consider an overdose. By removing the source of the drug (having the patient breathe room air or 100% oxygen), they will excrete most inhalation agents via the lungs, thus reversing the overdose. A practitioner must assure that the patient's respiratory system is functioning normally and that their tidal volume is adequate to provide the oxygen they need and remove their carbon dioxide both for their safety and to remove the inhalation agent. It should be remembered that all agents depress the respiratory system to some extent and it is important to have monitors that assure that an adequate exchange is taking place. It is necessary that the practitioner be skilled in assisting respiration should significant depression take place.
Intravenous sedation
With the regulations that are now in place in many states, it is nearly impossible to use intravenous sedation. Many states require a 60 hour course in addition to any training that was received in dental school. These courses have not been taught for a number of years and do not seem to be coming back. The cost of malpractice insurance to do intravenous sedation is another problem. If the added cost of malpractice insurance is passed on to the patient, it can increase the cost of each appointment $100 to $200.
Intravenous sedation has several advantages to the oral route of administering medication. When giving a drug IV, one slowly titrates the concentration of a drug to the level of sedation desired. For most drugs, these effects began to diminish in a short period of time - first, due to redistribution to other tissues (primarily fat stores) and then more slowly as the drug is metabolized into inactive forms (in some cases less active forms) or eliminated in the urine or feces.
Oral Sedation
Several factors come to light when we consider oral sedatives. The time from ingestion to sedation becomes very important. For any effect to take place, the drug must be absorbed into the blood stream and delivered to the site of action, usually thought to be in the central nervous system, in sufficient quantities to be effective. Some drugs can be absorbed sublingually, others must be swallowed and absorbed from either the stomach or small intestine. Depending on the time necessary for absorption, it may be necessary to have the patient take the drug at home before coming to the office. However, I prefer to administer the drug in the office because then I know how much was taken, when it was taken, and by whom it was taken. Also, I don't have to worry about the patient trying to drive to the appointment as the drug starts to take effect. Last but not least, should there be a reaction to the drug, the patient is in the office where aid can be administered.
We need a predictable means of determining dosage. Because it will take 45 minutes to one (1) hour to get the desired sedation, we can not easily titrate or alter the dose if a patient is not adequately sedated. Because of the length of time necessary to get sedation, we can not depend on redistribution of the drug to counter its effect. With some intravenous drugs you can give a dose necessary for sedation and within a few minutes have the patient nearly back to normal because the drug concentration in the blood stream has been reduced as the drug is redistributed to other tissues of the body.