Methyldopa dosage

Information is limited, but this interaetion appears to be established and clinically important. Monitor the effeets of eoneurrent use and increase the methyldopa dosage as neeessary. Separating the dosages by up to 2 hours apparently only partially reduees the effeets of this interaction. Ferrous gluconate appears to internet like ferrous sulfate, and all iron compounds would be expeeted to internet similarly. 

Diuretics and alcohol increase the hypotensive action of methyldopa (37 ). Ox-prenolol too is said to augment the hypotensive action, rendering it possible to reduce methyldopa dosage and thereby lowering the incidence of side effects (54< ). Interaction between methyldopa and haloperidol, both of which affect dopamine in the CNS, was found to result in an acute dementia in 2 patients who received the drugs simultaneously. The condition was reversible, and the mental condition was again normal 3 days after withdrawal of the haloperidol (148 ). 

The use of a tubular carbon electrode (TCE) for the electrochemical oxidative determination of ascorbic acid [159], L-dopa [160], and methyldopa [161] in dosage forms has been described. The flow system, electrode assembly, and electrochemical instrumentation required for these assays are shown in Figure 26.11. The method is based on continuous analysis in flowing streams... 

Dose Usual, initial dose, oral 250 mg of anhydrous methyldopa 2 or 3 times per day for 2 days usual maintenance dosage is 0.5 to 2 g of anhydrous methyldopa everyday. 

Methyldopa can increase the effects of levodopa and permit a reduction in the dosage in some patients taking levodopa alone, but it can aiso worsen dyskinesias in others. This interaction would not be expected to be significant in a patient taking levodopa with benserazide or carbidopa but this does not appear to have been studied. A small increase in the hypotensive actions of methyldopa may also occur. 

Other reports in patients taking levodopa alone describe reductions in the levodopa dosage of up to 30% and 70% during concurrent treatment with methyldopa. Another report states that the control of Parkinson s disease improved during the concurrent use of methyldopa in some patients taking levodopa alone, hut the dyskinesias were worsened in others. Methyldopa on its own can cause a reversihle parkinsonian-like syn-drome. " ... 

Well documented. Concurrent use need not be avoided but the outcome should be well monitored. In patients on levodopa alone, the use of methyldopa may allow a reduction in the dosage of the levodopa (the reports cited " quote figures of between 30 and 70%) and may enhance the control ofParkinson s disease, but it should also be borne in mind that in some patients dyskinesias may be worsened. However, in the presence of carbidopa or benserazide the dopa decarboxylase effects of methyldopa would be expected to be less significant and so it seems unlikely that a dose reduction of levodopa would be required. The increased hypotensive effects seem to be small, but they too should be checked. 

The increased hypotension and orthostasis that can occur if chlorpromazine or other phenothiazines are used with antihypertensive drugs such as methyldopa is established. Note that, of the phenothiazines, levome-promazine is particularly associated with postural hypotension. Warn patients that they may feel faint and dizzy particularly during the initial stages of concurrent use, and that if this occurs they should lie down, and that they should remain lying down until symptoms abate completely. Dosage adjustments may be necessary. 

An active substance, although initially released from its dosage form (and dissolved), may become unavailable for absorption due to reactimis with other medicines or food components [4]. An example is the formation of insoluble complexes of tetracycline with calcium or aluminium ions from antacids or milk products. Interaction (chelation or binding) with iron ions leads to a reduced absorption for a variety of active substances such as doxycycline, penicillamine, methyldopa and ciprofloxacin. The absorption of active substances showing pH-dependent dissolution behaviour may be influenced by medicines that influence the gastric pH, such as H2-antagonists, proton pump inhibitors and antacids. Antimycotic active substances such as ketoconazole or itraconazole dissolve better in acidic fluids. Therefore their bioavailability may be increased by the concomitant use of an acidic drink like cola, whereas the concomitant use of antacids or proton pump inhibitors is likely to reduce the bioavailability. Concomitant use of milk may increase the dissolution of acidic active substances, whereas fats from food may increase the bioavailability of lipophilic active substances like albendazole and griseofulvin. 

In between 5 and 30% of cases treated with a-methyldopa for more than 6 months a positive Coombs test can be found. High dosage favours its development. In only 0.5—3% of these cases does a haemolytic anaemia develop at any time, the clinical picture often being precipitated by an intercurrent illness (3, 7 IF, 12, 18, 3V). In such cases, besides the positive Coombs test, typical warm reactive IgG antibodies are found which react with normal red cells in the absence of the drug. As in idiopathic IgG-induced warm reactive haemolysis the antibody is directed against the rhesus nucleus substance and the principal site of haemolysis is the spleen (38, 39, 40 ). 

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