Pharmacokinetics and pharmacodynamics of ritodrine after intramuscular administration to pregnant women

Article Abstract:

Ritodrine is the only tocolytic agent approved by the Food and Drug Administration to control premature labor. Ritodrine is traditionally given orally, which may not achieve labor-inhibiting concentrations, or else intravenously, which may induce serious side effects. The action and dynamics of ritodrine administered intramuscularly (IM, in the muscle) were evaluated in a total of 12 women, six receiving 5 milligrams and six receiving 10 milligrams of ritodrine. Two injections were given on different days, one in the gluteus muscle in the buttocks and one in the deltoid muscle, in the shoulder. Blood samples were removed before administration and 12 times in the next six hours following IM administration. The peak concentration obtained with the 5 mg dose of ritodrine was 38 nanograms (ng) per milliliter (ml) when given in the deltoid muscle and 26 ng per ml when given in the gluteus muscle. The difference was not statistically significant. A 22 percent increase in heart rate, a 10 percent increase in systolic blood pressure (pressure during contractions) and a 19 percent decrease in diastolic pressure (pressure in between heart contractions) accompanied the increase from 5 mg to 10 mg doses. The average blood pressure did not differ between the two dosages. The intramuscular administration of ritodrine can control premature labor with one 5 or 10 mg dose without affecting the heart. (Consumer Summary produced by Reliance Medical Information, Inc.)

Physiological aspects, Drug therapy

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Neuromuscular blockade with magnesium sulfate and nifedipine

Article Abstract:

Nifedipine and magnesium sulfate are drugs used in treating complications of preterm labor. Nifedipine is used to treat pregnancy-induced high blood pressure, while magnesium sulfate prevents associated convulsions. Both of these drugs are calcium channel blockers (a class of drug which inhibits the flow of calcium to relax smooth muscle tone and decrease uterine contractions) and were found, in one patient, to cause jerky movements, swallowing difficulties, breathing difficulties, and the inability to lift her head off a pillow. This neuromuscular blockade reaction suggests that nifedipine may have the effect of increasing the strength of magnesium sulfate, and thus the two drugs should not be used in combination. Other combinations of drugs should be considered when treating preterm labor patients.

Usage, Evaluation, Nifedipine, Calcium channel blockers, Magnesium sulphate

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Pharmacokinetics of orally administered ritodrine

Article Abstract:

Ritodrine is a drug used to prevent preterm (early) labor. Studies of the action of oral ritodrine were done on 10 pregnant and 10 nonpregnant women. Both groups were given oral doses (20 mg) of ritodrine in fasting and non-fasting states to determine absorption rates (the rate at which the drug is taken up into the bloodstream). Pregnant women had lower concentrations of the drug in their blood and slower absorption rates than non-pregnant women. The presence of food in the intestines (where absorption takes place) did not increase absorption. Therefore, the current recommended ritodrine concentration of 20 mg is too low. The dose recommended for effective use should be increased to prevent preterm labor.

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