Читать книгу The Dentist's Drug and Prescription Guide - Mea A. Weinberg - Страница 18

1 Q. What is the difference between dose and dosage form?

2 A. The dose of a drug is a specified quantity of a drug – the size or frequency at which the drug doses are administered. The dosage form of a drug is the drug formulation such as a tablet, capsule, syrup, liquid suspension, solution, ointment, or cream that generally contains the active drug substance in association with one or more inactive ingredients. The FDA has stated that a dosage form is the way of identifying the drug by its physical form, which is linked both to physical appearance of the drug product and to the way it is administered (www.fdalawblog.net/fda_law_blog_hyman_phelps/2009/05/fda‐petition‐response‐reaffirms‐fda‐orange‐book‐dosage‐form‐nomenclature‐policy.html).If a patient is instructed to take one 500 mg capsule po (orally) qid (four times a day), the total dose is calculated from the dose multiplied by the number of times a day the dose is administered; one tablet (500 mg) qid is 2000 mg or 2 g.

3 Q. Why are some tablets “candy coated”?

4 A. These “candy‐coated” tablets are what is known as enteric coated. Some drugs are either irritating to the stomach lining or are inactivated, to different degrees, by acid in the stomach. To prevent the drug from being inactivated or destroyed in the stomach and allow it to travel to the intestine where it will ultimately be absorbed, enteric‐coated buffered tablets protect the drugs from gastric juices. Examples include erythromycin base, ibuprofen, and aspirin.

5 Q. Is it important to know the patient's baseline hepatic and renal function when deciding on the proper dosage?

6 A. Yes. Most drugs require adequate hepatic function for metabolism and adequate renal function for elimination. It is important to review the medical history and specifically ask the patient if they have any liver or kidney problems.

7 Q. What is the principle of selection of a therapeutic regimen?

8 A. Since the outcome of drug therapy is the product of a multifaceted interaction between drug and patient, the selection of an appropriate drug and dosing regimen is dependent on a thorough evaluation of the patient's medical and dental status and the actions and effects of the drugs to be used in treatment.

9 Q. What are the variabilities in drug dosage requirements?

10 A. There are many variabilities relating to alterations in drug dosing. The age of the patient, their renal and liver function, and pregnancy status can change the way the body reacts to medications.

11 Q. What are loading doses and maintenance doses of drugs?

12 A. Most drugs are not administered as a single dose. Rather, repeated doses resulting in an accumulation of the drug in the blood are needed to reach a plateau whereby the level of drug in the plasma is maintained constantly within the therapeutic range and there are no fluctuations in the concentration‐time profile. A steady state is achieved when the amount of drug absorbed into the body equals the amount of the drug leaving the body. To keep a proper steady state, the drug dosing must be consistent and the drug must be taken at the same time every day. Not achieving and maintaining steady state may make the drug therapy ineffective. It must be emphasized to the patient that the drug must be taken as prescribed. The drug should be taken at the same time every day and without any missed doses. In order to reach steady state, a loading dose is first administered on day 1, which is a higher amount of drug needed to quickly reach a therapeutic plasma drug concentration. Without a loading dose, it takes longer to reach steady state. After the loading dose is administered and before the plasma levels drop, a maintenance dose is given to maintain plasma drug levels within the therapeutic range. This maintenance dose is given in lower doses after the loading dose. For example, penicillin V is usually given as “1000 mg initially, followed by 500 mg every 6 hours.” Doxycycline is given as “100 mg every 12 hours on day 1, then 100 mg every day afterward.”

13 Q. How much loading dose is administered?

14 A. The loading dose is usually twice the regular dose.

15 Q. What drugs are given as an initial loading dose followed by a maintenance dose?

16 A. Antibiotics that are administered every 6–8 hours (including azithromycin, which is dosed once every 24 hours) usually require a loading dose in order to rapidly achieve a high tissue concentration for acute dental infections.

17 Q. How is a loading dose, followed by a maintenance dose, administered?

18 A. The loading dose is given on day 1, followed by the maintenance dose on day 1, day 2 etc….

19 Q. What is the proper duration of antibiotic treatment for dental infections?

20 A. Generally, the duration of antibiotic therapy has been variable and not evidence based. The current theory focuses on shortening the course of antibiotics, which might limit antibiotic resistance. Generally, most private practice and hospital‐based dentists empirically prescribe antibiotics for 7–10 days. However, high‐dose, short‐term therapy has also been advocated in medical guidelines. Prescribing antibiotics for three days has been shown to reduce the incidence of antibiotic resistance (Paterson et al. 2016). It is also important to take the antibiotic for the full course prescribed, even if the patient is clinically responding, in order to minimize the chance of the resistant bacteria not being targeted, thus preventing a relapse. However, there are no specific guidelines or recommendations regarding the duration of dental antibiotic therapy.

21 Q. What is the importance of knowing the peak concentration of a drug?

22 A. Peak concentration is the maximum plasma concentration of a drug which is seen during dosing intervals. At the time (usually hours) of peak concentration, the drug has the highest concentration in the plasma. Knowing the peak concentration of a drug is important because this is the time required if antibiotic prophylaxis is to be achieved. Antibiotic prophylaxis is defined as prevention of development of an infection at the surgical site (Munckoff 2005). For example, antibiotic prophylaxis is recommended by the American Heart Association (AHA) before a sinus graft is performed in anticipation of possible perforation of the Schneiderian membrane (creating signs and symptoms of sinusitis). Having the antibiotic already in the systemic circulation before the surgical procedure is performed is ideal for optimum therapeutic effects. Thus, before performing surgical procedures, the antibiotic needs to be administered only during the peak hours before the surgery and not days before.

23 Q. What are the peak blood levels of antibiotics used in dentistry?

24 A. See Table 3.1.Table 3.1 Peak blood levels of antibioticsDrugTime to peakAmoxicillin1–2 hoursAzithromycin (Zithromax®)2.5–4 hoursClindamycin45–60 minutesDoxycycline1–2 hoursPenicillin VK30–60 minutesTetracycline2–4 hours

25 Q. What are the peak levels of common analgesics used in dentistry?

26 A. See Table 3.2Table 3.2 Peak levels of common analgesicsDrugTime to peakAcetaminophen0.5–2 hoursCodeine1–1.5 hoursDiflunisal (Dolobid®)2–3 hoursIbuprofen1–2 hoursMeperidine (Demerol®)1 hourNaproxen sodium (Aleve, Anaprox®)1 hourOxycodone30–60 minutes

27 Q. What is the difference in prescribing capsules or tablets (e.g., doxycycline 100 mg comes in tablets and capsules)?

28 A. If a patient has difficulty swallowing capsules, prescribe tablets. To be absorbed, capsules need to undergo dissolution or to be opened (usually takes about four minutes) and tablets need to undergo disintegration or to break up (takes slightly longer than a capsule) to release the active ingredient that will be absorbed. Both processes take time and absorption will occur in the duodenum (small intestine). A liquid gel capsule (Aleve®, Advil®) is formulated to dissolve quickly which allows the liquid inside the capsule to be absorbed fast. A gel capsule is a capsule‐shaped tablet coated with gelatin for easy swallowing. Basically, it is a tablet and not a capsule. That means it will be absorbed like a tablet, but it may take longer to disintegrate because the gelatin must disintegrate first and then the tablet. Liquid drug (e.g., solution) is absorbed most rapidly, followed by liquid gel capsule, capsule, tablet, and then gel capsule.

29 Q. What happens if a patient misses a dose of an antibiotic?

30 A. It is important not to miss doses because drugs that require daily administration are only effective when they achieve steady state in the blood, which is required for a medication to reach therapeutic and effective levels. This means that steady state occurs when the amount of drug entering the blood equals the amount of drug being eliminated from the body. Ideally, doses should be equally spaced throughout the day and taken at the same times each day. This will help to maintain a constant level of antibiotic in the bloodstream. If the patient misses a dose of an antibiotic, it is best not to double the next dose because this could increase the incidence of adverse effects. If you miss a dose, take it as soon as remembered; do not take if it is almost time for the next dose. Instead, skip the missed dose and resume your usual dosing schedule. Do not “double up” the doses.

31 Q. What does first‐pass effect have to do with drug dosing?

32 A. First‐pass effect is defined as the biotransformation of a drug in the liver that occurs before the drug enters the systemic circulation. For example, sublingual nitroglycerin has a high first‐pass metabolism because 90% of it is inactivated by the liver before it enters the blood. Morphine and lidocaine are other drugs with high first‐pass effect when administered orally. Because this, they cannot be given orally because they would be totally inactivated before reaching the target site.

33 Q. How does age affect drug metabolism?

34 A. Age often affects drug metabolism and drug dosages may need to be adjusted in children and the elderly. Years ago, pediatric dosing was determined using pediatric formulas such as Clark's Rule, Young's Rule and Fried's Rule, which were based on the weight of the child in pounds or on their age in months. Today, these formulations are not used but rather the dose is based on body surface area or weight of the infant/child. In order to calculate the proper dosage, the manufacturer's safe dose (in mg/kg) of the prescribed drug must be known. This dose is predetermined by the manufacturer.Children and the elderly require lower drug doses due to differences in their response to drugs.