Dicyclomine hydrochloride is used in the treatment of functional disturbances of GI motility such as irritable bowel syndrome. As with other antispasmodics, dicyclomine has limited efficacy in the treatment of these disorders and should be used only if other measures (e.g., diet, sedation, counseling, amelioration of environmental factors) have been of little or no benefit. Although dicyclomine has also been used in combination with phenobarbital in the treatment of irritable bowel syndrome, attempts to substantiate claims of efficacy for fixed combinations that include an antispasmodic and phenobarbital have generally failed and these combinations are generally considered as lacking substantial evidence of efficacy in the treatment of this condition.
Dicyclomine has been used alone and in combination with phenobarbital in the treatment of infant colic and acute enterocolitis, but the drug alone and the combination are generally considered as lacking substantial evidence of efficacy in the treatment of these conditions. Infant colic is considered a benign, self-limiting condition that tends to resolve spontaneously and not require medical treatment.
Dosage and Administration
Dicyclomine hydrochloride is usually administered orally. When oral therapy is not feasible, the drug may be administered by IM injection. IM injection of the drug may produce local irritation and/or transient sensation of lightheadedness. Oral therapy should replace IM therapy as soon as possible, and IM therapy should not be used for longer than 1 or 2 days. Dicyclomine should not be administered by IV or subcutaneous injection. The oral solutions should be diluted with an equal volume of water just prior to administration.
The only oral dosage of dicyclomine hydrochloride clearly shown to be effective in adults is 40 mg 4 times daily. Because this dosage is associated with a substantial incidence of adverse effects, the usual initial dosage should be 20 mg 4 times daily. Depending on the patient's response, dosage should be increased during the first week of therapy to 40 mg 4 times daily unless adverse effects limit upward titration. If an adequate response is not obtained within 2 weeks or adverse effects limit dosage to less than 80 mg daily, the drug should be discontinued.
The safety of dosages of 80-160 mg daily for longer than 2 weeks has not been established. Abuse and/or dependence on dicyclomine for its anticholinergic effects has been reported rarely.
The recommended IM dosage of dicyclomine hydrochloride for adults is 20 mg 4 times daily.
The pharmacokinetics of dicyclomine hydrochloride have not been fully determined.
Dicyclomine hydrochloride is absorbed rapidly from the GI tract, achieving peak plasma concentrations within 1-1.5 hours after oral administration of the drug (about 1, 1.1, and 1.5 hours for the solution, capsules, and tablets, respectively). Comparison of the areas under the plasma concentration-time curves (AUCs) for single, 40-mg doses of dicyclomine hydrochloride oral solution and IM injection indicates that the relative oral bioavailability of the drug is about 67% of that following IM injection. The drug is absorbed slightly faster following IM injection than after oral administration. The bioavailabilities (as determined by AUC) of dicyclomine hydrochloride oral solution, capsules, and tablets are equivalent.
The apparent volume of distribution of dicyclomine is reportedly 3.65 L/kg.
Plasma concentrations of dicyclomine hydrochloride appear to decline in a biphasic manner. The half-life of the drug in the initial distribution phase (t½α) is about 1.8 hours and the half-life in the terminal elimination phase (t½β) is about 9-10 hours. Although the metabolic fate of dicyclomine has not been determined, about 80% of a dose is eliminated in urine and about 10% in feces.