Methyldopa

Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Neuroscience · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology (Index, Outline)

Methyldopa chemical structure Methyldopa
(2S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methyl-propanoic acid IUPAC name
CAS number 555-30-6	ATC code C02 AB01
PubChem 4138	DrugBank APRD01106
Chemical formula	{{{chemical_formula}}}
Molecular weight	211.215 g/mol
Bioavailability	approximately 50%
Metabolism	Hepatic
Elimination half-life	105 minutes
Excretion	Renal for metabolites
Pregnancy category	a drug of choice in PIH
Legal status	Rx-only
Routes of administration	Oral, IV

Methyldopa or alpha-methyldopa (brand names Aldomet, Apo-Methyldopa, Dopamet, Novomedopa) is a centrally-acting adrenergic antihypertensive medication. Its use is now deprecated following introduction of alternative safer classes of agents. However it continues to have a role in otherwise difficult to treat hypertension and pregnancy-induced hypertension.

Pharmacokinetics[edit | edit source]

Methyldopa has variable absorption from the gut of approximately 50%. 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.

Mechanism of action[edit | edit source]

Methyldopa, in its active metabolite form, is a central alpha-2 receptor agonist. Using methyldopa leads to alpha-2 receptor-negative feedback to sympathetic nervous system (SNS) (centrally and peripherally), allowing peripheral sympathetic nervous system (PSNS) tone to decrease. Such activity leads to a decrease in total peripheral resistance (TPR) and cardiac output.

Rebound effect[edit | edit source]

Rebound hypertension has been reported in some cases when methyldopa has been abruptly withdrawn after extended use^[1]. This results because the long term use of methyldopa lowers the sensitivity of presynaptic alpha 2 receptors: the release of norepinephrine (NE) from sympathetic nerve endings is modulated by NE itself acting on the presynaptic alpha 2 autoreceptors thus inhibiting its own release. The discontinuation of methyldopa removes the inhibition on NE release leading to excessive NE release from the SNS and the rebound hypertension.

History[edit | edit source]

When introduced it was a mainstay of antihypertensive therapy, but its use has declined, with increased use of other safer 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[edit | edit source]

There are many possible reported side-effects with some, whilst rare, being serious. Side effects are usually fewer if the dose is less than 1 g per day:^[2]

Gastro-intestinal disturbances
Dry mouth
Bradycardia (slow pulse rate)
Worsening of angina
Orthostatic hypotension (Postural hypotension)
Sedation, headaches, dizziness
Myalgia (muscle pain), arthralgia (joint pain) or paraesthesia (numbness)
Nightmares, mild psychosis, depression
Parkinsonism
Bell's palsy
Abnormal liver functions tests and hepatitis
Pancreatitis
Haemolytic anaemia
Bone marrow suppresion leading to thrombocytopenia (low platelets) or leucopenia(low white blood cells)
Hypersensitivity reactions including lupus erythematosus-like syndrome, myocarditis (heart muscle inflammation), pericarditis and rashes
Ejaculatory failure, Impotence, decreased libido, gynecomastia (breast enlargement in men), hyperprolactinaemia and amenorrhoea
Note that if used in pregnant women, it may cause a positive Coombs test