Pseudoephedrine, absorption

Lucarotti RL, Colaizzi JL, Baity H, Poust RI. Enhanced pseudoephedrine absorption by concurrent administration of aluminium hydroxide gel in humans. JP/iawi-S d (1972) 61,903-5. 

Actifed is a medicinal preparation in which the effective components are the two drugs pseudoephedrine hydrochloride and triprolidine hydrochloride. The absorption spectrum of Actifed tablets dissolved in 0.1M hydrochloric acid is similar to that shown in Fig. 17.14(a) which is clearly of no value for quantitative determinations. A second derivative spectrum however is similar in character to that shown in Fig. 17.14(6) in which peak C corresponds to the pseudoephedrine hydrochloride and D to the triprolidine hydrochloride and from which it is possible to make quantitative measurements. Experience showed that it is advisable to use different response times for the two peaks with the instrument used a response setting of 3 was found to give the best results for pseudoephedrine hydrochloride, whilst a setting of 4 was best for the triprolidine hydrochloride. 

The ultraviolet spectrum of pseudoephedrine hydrochloride in ethanol was obtained with a Beckman ACTA CIII ultraviolet spectrophotometer and is shown in Figure 3.4 Pseudoephedrine hydrochloride exhibits absorption maxima at 208, 251, 257, and 264 nm with extinction coefficients of 8300, 161, 201, and 161, respectively. 

Commercial samples containing approximately 400 mg of ephedra per capsule yield roughly 5 mg of ephedrine, 1 mg of pseudoephedrine, and less than 1 mg of methylephedrine (White et al. 1997). For a dose of four capsules, yielding approximately 20 mg of ephedrine, the elimination half-life is 5.2 hours. The time to reach maxium concentration is 3.9 hours. Compared to pure ephedrine tablets, the elimination kinetics of ephedra are comparable. However, ephedra showed somewhat different absorption kinetics (e.g., lag time, area under the concentration-time curve, and maximum plasma concentration). So, ephedra tablets may vary from pure ephedrine in the onset of action, but the durations of action are grossly equivalent. 

Following the ingestion of a large dose of pseudoephedrine, dogs and cats may exhibit hyperactivity, mydriasis, depression, vomiting, hyperthermia, disorientation, bradycardia, and tachycardia. Therapy is directed at prevention of absorption and control of tachyarrhythmias with lidocaine (dogs only) or procainamide (dogs only). Diazepam may be used for symptoms associated with central nervous system (CNS) stimulation. 

In a single-dose crossover study in 6 healthy subjects, 30 inL of aluminium hydroxide gel did not affect the total amount of pseudoephedrine absorbed from a single 60-mg dose over 24 hours, but the rate of absorption was significantly increased during the first 3 hours. Conversely, 30 rriL of a 30% suspension of kaolin redueed the amount of pseudoephedrine absorbed from a single 60-mg dose by just 10%. The rate of absorption was also decreased. ... 

The increased rate of absorption of pseudoephedrine seen with aluminium hydroxide is probably also due to pH rises, which favour the formation of the lipid-soluble absorbable form of pseudoephedrine. The reduced absorption with kaolin is probably due to adsorption of the pseudoephedrine onto the surface of the kaolin. 

Aluminium hydroxide may possibly cause a more rapid onset of pseudoephedrine activity (but this needs confirmation). Any interaction seems unlikely to be clinically significant. Similarly, the effects of kaolin on absorption are small and unlikely to be clinically important. For the effect of sodium bicarbonate on pseudoephedrine and ephedrine, see urinary alka-Iinisers%(p.l277). 

Lippstone, M. B., Grath, E. K., and Sherma, J. (1996). Analysis of decongestant pharmaceutical tablets containing pseudoephedrine hydrochloride and guaifenesin by HPTLC with UV absorption densitometry. J. Planar Chromatogr.—Mod. TLC 9 456-458. 

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