ANTITHYROIDAGENTS (Systemic)
Some commonly used brand names are:
In the U.S.?
In Canada?
- Propyl-Thyracil 2
- Tapazole 1
Another commonly used name for methimazole is thiamazole.
Note: | For quick reference, the following antithyroid agents are numberedto match the corresponding brand names. |
Category
- Antihyperthyroid agent? Methimazole; Propylthiouracil
Description
Methimazoleand propylthiouracil are used to treat conditions in which the thyroid glandproduces too much thyroid hormone.
These medicines work by making it harder for the body to use iodine tomake thyroid hormone. They do not block the effects of thyroid hormone thatwas made by the body before their use was begun.
Methimazole and propylthiouracil are available only with your doctor'sprescription, in the following dosage forms:
Oral- Methimazole
- Tablets (U.S. and Canada)
- Propylthiouracil
- Tablets (U.S. and Canada)
Before Using This Medicine
In deciding to use a medicine,the risks of taking the medicine must be weighed against the good it willdo. This is a decision you and your doctor will make. For antithyroid agents,the following should be considered:
Allergies?Tell your doctor if you have ever had any unusual orallergic reaction to methimazole or propylthiouracil. Also tell your healthcare professional if you are allergic to any other substances, such as foods,preservatives, or dyes.
Pregnancy?Use of too large a dose during pregnancy may causeproblems in the fetus. However, use of the proper dose, with careful monitoringby the doctor, is not likely to cause problems.
Breast-feeding?These medicines pass into breast milk. (Methimazolepasses into breast milk more freely and in higher amounts than propylthiouracil.)However, your doctor may allow you to continue to breast-feed, if your doseis low and the infant gets frequent check-ups. If you are taking a large dose,it may be necessary for you to stop breast-feeding during treatment.
Children?This medicine has been used in children and, in effectivedoses, has not been shown to cause different side effects or problems in childrenthan it does in adults.
Adolescents?This medicine has been used in teenagers and, ineffective doses, has not been shown to cause different side effects or problemsin teenagers than it does in adults.
Older adults?Elderly people may have an increased chance of certainside effects during treatment. Your doctor may need to take special precautionswhile you are taking this medicine.
Other medicines?Although certain medicines should not be usedtogether at all, in other cases two different medicines may be used togethereven if an interaction might occur. In these cases, your doctor may want tochange the dose, or other precautions may be necessary. When you are takingantithyroid agents, it is especially important that your health care professionalknow if you are taking any of the following:
- Amiodarone or
- Iodinated glycerol or
- Potassium iodide (e.g., Pima)?The use of these medicines maychange the effect of antithyroid agents
- Anticoagulants (blood thinners)?The use of antithyroid agentsmay affect the way anticoagulants work in your body
- Beta-adrenergic blocking agents (e.g., Inderal, Metoprolol, Sotalol)?Theuse of antithyroid agents may change the amount of beta-blockers you needto take.
- Digitalis glycosides?The use of antithyroid agents may affectthe amount of digitalis glycosides in the bloodstream
Other medical problems?The presence of other medicalproblems may affect the use of antithyroid agents. Make sure you tell yourdoctor if you have any other medical problems, especially:
- Liver disease?The body may not get this medicine out of thebloodstream at the usual rate, which may increase the chance of side effects
Proper Use of This Medicine
Use this medicine only as directed by your doctor. Do not use moreor less of it and do not use it more often or for a longer time than yourdoctor ordered. To do so may increase the chance of side effects.
This medicine works best when there is a constant amount in the blood. To help keep the amount constant, do not miss any doses.Also, if you are taking more than one dose a day, it is best to take the dosesat evenly spaced times day and night. For example, if you are to take3 doses a day, the doses should be spaced about 8 hours apart. If this interfereswith your sleep or other daily activities, or if you need help in planningthe best times to take your medicine, check with your health care professional.
Food in your stomach may change the amount of methimazole that is ableto enter the bloodstream. To make sure that you always get the same effects,try to take methimazole at the same time in relation to meals every day. Thatis, always take it with meals or always take it on an empty stomach.
Dosing?The dose of these medicines will be differentfor different patients. Follow your doctor's orders orthe directions on the label. The following information includes onlythe average doses of these medicines. If your dose isdifferent, do not change it unless your doctor tells you to do so.
The number of tablets that you take or the number of suppositories thatyou use depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, andthe length of time you take the medicine depend on the medical problem forwhich you are taking antithyroid agents.
For methimazole- For oral dosage form (tablets):
- For treatment of hyperthyroidism (overactive thyroid):
- Adults and teenagers?At first, 15 to 60 milligrams (mg) a dayfor up to six to eight weeks. Later, your doctor may want to lower your doseto 5 to 30 mg a day. This may be taken once a day or it may be divided intotwo doses a day.
- Children?Dose is based on body weight and must be determinedby your doctor. The usual dose is 0.4 mg per kilogram (kg) (0.18 mg per pound)of body weight a day. Later, your doctor may want to lower the dose to 0.2mg per kg (0.09 mg per pound) of body weight a day. The dose may be takenonce a day or it may be divided into two doses a day.
- For treatment of thyrotoxicosis (a thyroid emergency):
- Adults and teenagers?15 to 20 mg every four hours.
- For rectal dosage form (suppositories):
- For treatment of thyrotoxicosis (a thyroid emergency):
- Adults and teenagers?15 to 20 mg inserted into the rectum everyfour hours. Your doctor may change your dose as needed.
- Children?The dose is based on body weight and must be determinedby your doctor. The usual dose is 0.4 mg per kg (0.18 mg per pound) of bodyweight inserted into the rectum a day. This may be used as a single dose orit may be divided into two doses a day.
For propylthiouracil- For oral dosage form (tablets):
- For treatment of hyperthyroidism (overactive thyroid):
- Adults and teenagers?At first, 300 to 900 milligrams (mg) aday. Some people may need up to 1200 mg a day. This may be taken as a singledose or it may be divided into two to four doses in a day. Later, your doctormay lower your dose to 50 to 600 mg a day.
- Children 6 to 10 years of age?At first, 50 to 150 mg a day.This may be taken as a single dose or it may be divided into two to four dosesin a day. Later, your doctor may change your dose as needed.
- Children 10 years of age and older?At first, 50 to 300 mg aday. This may be taken as a single dose or it may be divided into two to fourdoses in a day. Then, your doctor may change your dose as needed.
- For treatment of thyrotoxicosis (a thyroid emergency):
- Adults and teenagers?200 to 400 mg every four hours. Your doctorwill lower your dose as needed.
- Newborn infants?Dose is based on body weight and must be determinedby your doctor. The usual dose is 10 mg per kilogram (kg) (4.5 mg per pound)of body weight a day. This is usually divided into more than one dose a day.
- For rectal dosage forms (enemas or suppositories):
- For treatment of thyrotoxicosis (a thyroid emergency):
- Adults and teenagers?200 to 400 mg inserted into the rectumevery four hours. Your doctor may change your dose as needed.
- Children 6 to 10 years of age?50 to 150 mg inserted into therectum a day. This dose may be used as a single dose or it may be dividedinto two to four doses in a day. Your doctor may change your dose as needed.
- Children 10 years of age and older?50 to 300 mg inserted intothe rectum a day. This dose may be used as a single dose or it may be dividedinto two to four doses in a day. Your doctor may change your dose as needed.
- Newborn infants?Dose is based on body weight and must be determinedby your doctor. The usual dose is 10 mg per kg (4.5 mg per pound) of bodyweight inserted into the rectum. This is usually divided into more than onedose a day. Your doctor may change your dose as needed.
Missed dose?If you miss a dose of this medicine, take it assoon as possible. If it is almost time for your next dose, take both dosestogether. Then go back to your regular dosing schedule. If you miss more thanone dose or if you have any questions about this, check with your doctor.
Storage?To store this medicine:
- Keep out of the reach of children.
- Store away from heat and direct light.
- Do not store in the bathroom, near the kitchen sink, or in otherhigh-moisture areas. Heat or moisture may cause the medicine to break down.
- Do not keep outdated medicine or medicine no longer needed. Be surethat any discarded medicine is out of the reach of children.
Precautions While Using This Medicine
It is very important that your doctor check your progress atregular visits to make sure that this medicine is working properlyand to check for unwanted effects.
It may take several days or weeks for this medicine to work. However, do not stop taking this medicine without first checking withyour doctor. Some medical problems may require several years of continuoustreatment.
Before having any kind of surgery (including dental surgery) or emergencytreatment, tell the medical doctor or dentist in chargethat you are taking this medicine.
Check with your doctor right away if you get an injury,infection, or illness of any kind. Your doctor may want you to stoptaking this medicine or change the amount you are taking.
While you are being treated with antithyroid agents, and after you stoptreatment with it, do not have any immunizations (vaccinations)without your doctor's approval. Antithyroid agents may lower your body'sresistance and there is a chance you might get the infection the immunizationis meant to prevent. In addition, other persons living in your household shouldnot take or have recently taken oral polio vaccine since there is a chancethey could pass the polio virus on to you. Also, avoid other persons who havetaken oral polio vaccine. Do not get close to them, and do not stay in thesame room with them for very long. If you cannot take these precautions, youshould consider wearing a protective face mask that covers the nose and mouth.
Before you have any medical tests, tell the doctor in charge that you aretaking this medicine. The results of some tests may be affected by this medicine.
Side Effects of This Medicine
Along with its needed effects,a medicine may cause some unwanted effects. Although not all of these sideeffects may occur, if they do occur they may need medical attention.
Check with your doctorimmediately if any of the following side effects occur:
Less common
Cough; fever or chills (continuing orsevere); general feeling of discomfort, illness orweakness; hoarseness; mouthsores; pain, swelling, or redness in joints; throat infection
Check with your doctor as soon as possibleif any of the following side effects occur:
Rare
Backache; black, tarry stools; blood in urine or stools; shortnessof breath; increase in bleeding or bruising; increase or decrease in urination; numbness or tingling of fingers, toes, or face; pinpoint red spots on skin; swelling of feet or lowerlegs; swollen lymph nodes; swollen salivary glands
Otherside effects may occur that usually do not need medical attention. These sideeffects may go away during treatment as your body adjusts to the medicine.However, check with your doctor if any of the following side effects continueor are bothersome:
Other side effects not listed above may also occur in some patients. If younotice any other effects, check with your doctor.
Revised: 07/19/2001
