Find information on thousands of medical conditions and prescription drugs.

Methyldopa

Methyldopa or alpha-methyldopa (brand names Aldomet, Apo-Methyldopa, Dopamet, Novomedopa) is a centrally-acting antiadrenergic antihypertensive medication. more...

Home
Diseases
Medicines
A
B
C
D
E
F
G
H
I
J
K
L
M
Macrodantin
Maprotiline
Marcaine
Marezine
Marijuana
Marinol
Marplan
Matulane
Maxair
Maxalt
Maxolon
MDMA
Measurin
Mebendazole
Mebendazole
Meclofenoxate
Medrol
Mefenamic acid
Mefloquine
Melagatran
Melarsoprol
Meloxicam
Melphalan
Memantine
Metadate
Metamfetamine
Metamizole sodium
Metandienone
Metaxalone
Metenolone
Metformin
Methadone
Methamphetamine
Methaqualone
Metharbital
Methcathinone
Methenamine
Methionine
Methocarbamol
Methohexital
Methotrexate
Methotrexate
Methoxsalen
Methylcellulose
Methyldopa
Methylergometrine
Methylin
Methylphenidate
Methylphenobarbital
Methylprednisolone
Methyltestosterone
Methysergide
Metiamide
Metoclopramide
Metohexal
Metoprolol
Metrogel
Metronidazole
Metyrapone
Mobic
Moclobemide
Modafinil
Modicon
Monopril
Montelukast
Motrin
Moxidectin
Moxifloxacin
Moxonidine
MS Contin
Mucinex
Mucomyst
Mupirocin
Mupirocin
Muse
Mycitracin
Mycostatin
Myfortic
Mykacet
Mykinac
Myleran
Mylotarg
Mysoline
Phentermine
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

Methyldopa is approximately 50% absorbed from the gut; it is metabolized in the intestines and liver; its metabolite alpha-methylnorepineprine acts in the brain to stimulate alpha-adrenergic receptors decreasing total peripheral resistance. It is excreted in urine.

Methyldopa, in its active metabolite form, leads to increased alpha-2 receptor-mediated inhibition of SNS (centrally and peripherally), allowing PSNS tone to increase. Such activity leads to a decrease in total peripheral resistance (TPR) and cardiac output.

All drugs in this class can cause "rebound" hypertension due to an up-regulation of alpha-2 receptors while under the influence of the drug. If the drug is abruptly withdrawn, the "original" as well as "new" receptors become available and cause a severe reaction to the "normal" SNS activity (which is usually in excess). In other words, the SNS typically releases more norepinephrine (NE) than is needed to activate receptors (leading to a sustained response), and extra receptors leads to an over-response (in this case mediated by alfa-2 receptors leading to vascular smooth muscle constriction = rebound hypertension).

When introduced it was a mainstay of antihypertensive therapy, but its use has declined, with increased use of other classes of agents. One of its important present-day uses is in the management of pregnancy-induced hypertension, as it is relatively safe in pregnancy compared to other antihypertensive drugs.

Side effects (some of these are serious and need to be reported to a physician)
A possible side-effect of methyldopa is breast enlargement in men (gynecomastia). Hyper-prolactinaemia. Many patients report orthostatic hypotension, which tends to improve over time. Skin rashes. Bruising. Low white blood cells. Thrombocytopenia (Low platelets). Haemolytic anaemia: the direct Coombs test may become positive. Tiredness. Depression. Impotence.

This list is not complete.
Side effects are usually fewer if the dose is less than 1 gm per day.

Read more at Wikipedia.org


[List your site here Free!]


Coombs' tests
From Gale Encyclopedia of Medicine, 4/6/01 by J. Ricker Polsdorfer

Definition

Coombs' tests are blood tests that identify the causes of anemia.

Purpose

Anemia, which literally means no blood, refers to blood with abnormally low oxygen-carrying capacity. The hemoglobin in red blood cells carries oxygen. One of the many causes of anemia is destruction of red blood cells, a process called hemolysis (hemo means blood and lysis means disintegration). A simple blood count detects anemia. Even the test done before a blood donation can identify anemia. To detect hemolysis requires other tests. The Coombs' tests are conducted in order to determine the cause of anemia.

One characteristic of hemolysis is the autoimmune response against the body's red blood cells. Instead of protecting the body from outside agents, the immune system attacks parts of its own body with a deluge of antibodies. Autoimmunity is thought to be the cause of many collagen-vascular diseases, including rheumatoid arthritis and systemic lupus erythematosus. It is also the cause of the autoimmune hemolytic anemias. The Coombs' tests detect the antibodies responsible for the destruction of the red blood cells.

Causes of autoimmune hemolytic anemia include:

  • Drugs such as penicillin, methyldopa (lowers blood pressure), and quinidine (treats heart rhythm disturbances)
  • Cancers of the lymph system--Hodgkin's disease and lymphomas
  • Virus infections
  • Collagen-vascular diseases
  • Mismatched blood transfusions
  • Rh incompatibility between a mother and fetus. This disease is called erythroblastosis fetalis

Many times the cause cannot be identified.

Description

There are two Coombs' tests. A direct Coombs' test detects the two different antigens that might induce hemolysis in the patient's red blood cells. An indirect Coombs' test looks for antibodies to someone else's red blood cells in the patient's serum (the blood without the cells). Combining the two tests gives clues to the origin of the hemolysis.

Preparation

No preparation is needed for this test. It will probably be among the second or third set of blood tests done after anemia is diagnosed and there is a suspicion that its cause is hemolysis.

Aftercare

Coombs' tests are done on blood that is drawn from the arm.

Risks

Taking blood for testing is the most common medical procedure performed. The worst complication is a bruise at the site of the puncture or punctures. It is extremely rare for the needle to injure an important structure such as an artery or a nerve.

Normal results

If the Coombs' tests are negative, the anemia is unlikely to be autoimmune, and the hematologist will have to search elsewhere for a cause.

Abnormal results

If the test is positive, the antigens that react will narrow the search for a cause. Coombs' tests are also done for blood transfusion reactions to determine why the transfused blood did not match, and when there is a chance a newborn may have an Rh problem.

Key Terms

Antibody
A protein made by the immune system and used as a weapon against foreign invaders in the body.
Antigen
The chemical that stimulates an immune response.
Anemia
Reduced oxygen-carrying capacity of the blood, due to too little hemoglobin or too few red blood cells.
Collagen-vascular disease
Various diseases inflaming and destroying connective tissue.
Hematologist
Physician who specializes in diseases of the blood.
Hemoglobin
The red pigment in blood that carries oxygen.
Hemolysis
Breaking apart red blood cells.
Rh
A blood typing group, like the ABO system. When a mother is Rh negative and her baby is Rh positive, she may develop antibodies to the baby's blood that will cause it to hemolyze.

Further Reading

For Your Information

    Books

  • Rosse, Wendell and H. Franklin Bunn. "Hemolytic Anemias and Acute Blood Loss." In Harrison's Principles of Internal Medicine, edited by Kurt Isselbacher, et al. New York: McGraw-Hill, 1998.
  • Schreiber, Alan D. "Autoimmune Hemolytic Anemia." In Cecil Textbook of Medicine, edited by J. Claude Bennett and Fred Plum. Philadelphia: W. B. Saunders, 1996.

Gale Encyclopedia of Medicine. Gale Research, 1999.

Return to Methyldopa
Home Contact Resources Exchange Links ebay