Comparison of 200 mg cimetidine with multiple doses of antacid on extent and duration of rise in gastric pH in volunteers

Crystal structure transformations and dissolution studies of cimetidine-piroxicam coprecipitates and physical mixtures

We have recently demonstrated that coprecipitation of cimetidine (C) and piroxicam (P) at a mole ratio of 1:1 results in the transformation of the crystalline forms of both drugs to an amorphous state. In this study, coprecipitates and physical mixtures of cimetidine and piroxicam were further investigated at C/P mole ratios of 1:10, 1:5, 1:4, 1:2, 10:1, 20:1, 30:1, 40:1, and 52.5:1, the latter being the composition of a clinically used dosage. The physicochemical properties of these samples were examined using X-ray diffraction and Fourier transform infrared spectroscopy. Additionally, dissolution of piroxicam in the samples at C/P mole ratios of 10:1, 20:1, 30:1, 40:1, and 52.5:1 was investigated at pH 1.2 and pH 4. In coprecipitates with C/P mole ratios of 10:1, 20:1, 30:1, and 40:1, crystalline forms of both drugs were transformed to amorphous states. A mixture of an amorphous state and cimetidine crystalline form A was observed for the coprecipitate with a C/P mole ratio of 52.5:1. For the coprecipitates with C/P mole ratios of 1:2, 1:4, 1:5, and 1:10, cimetidine form A was transformed to form C, whereas piroxicam form II was modified to form I. It is interesting that small molecules, instead of polymers or solvents, can cause such crystal structure transformations. The dissolution of piroxicam at pH 4 is lower than that at pH 1.2. Additionally, the coprecipitates and physical mixtures with C/P mole ratios of 10:1, 20:1, 30:1, 40:1, and 52.5:1 demonstrate substantially higher dissolution of piroxicam compared to that of drug alone.

Influence of cimetidine co-administration on the pharmacokinetics of acebutolol enantiomers and its metabolite diacetolol in a rat model: the effect of gastric pH on double-peak phenomena

Acebutolol (AC) is a chiral beta-adrenergic receptor-blocking agent, which has been shown to be clinically effective in hypertension. The plasma concentration-time profiles of AC exhibit two peaks following oral administration of racemate for both R- and S-enantiomers. In the present study, the absorption of AC after a single dose was studied as a function of gastric pH in male Sprague-Dawley rats. Furthermore, the effect of cimetidine (CIM) on pharmacokinetic parameters of AC and its metabolite diacetolol (DC) was evaluated. CIM (50 mg kg(-1)) was administered via jugular vein 30 min prior to AC administration to elevate the intragastric pH. AC (50 mg kg(-1)) was administered orally by gavage and serial blood samples were collected before and for 8h after AC administration. Plasma samples were assayed for AC and DC, pharmacokinetic parameters were estimated and compared with those of control. The concentration-time profiles and the pharmacokinetics of AC were unchanged after co-administration of CIM. The oral absorption of AC, as assessed by the area under the plasma concentration-time curve (AUC) and the amount of unchanged drug recovered in the urine were not affected by CIM. The amount of metabolite recovered in the urine and the rate of absorption, however, were significantly altered. These are unlikely to be of clinically importance as we have found that the extent of absorption was not changed. We, therefore, concluded that intragastric elevation of pH has no effect either on generation of multiple peaking or on pharmacokinetic parameters of AC.

Synergy between low-dose ranitidine and antacid in decreasing gastric and oesophageal acidity and relieving meal-induced heartburn

BACKGROUND

The pathophysiology of recurrent postprandial heartburn and the basis for the effectiveness of antacids or low doses of histamine H2-receptor antagonists have not been well studied.

METHODS

The selected subjects (n=26) had heartburn more than four times a week for at least 2 months, which was responsive to antacids. Gastric pH and oesophageal pH were measured for 1 h before, during, and 4.5 h after ingestion of a meal over 0.5 h. Heartburn severity was assessed at 15-min intervals beginning at the end of the meal. Each subject randomly received placebo, 75 mg ranitidine, 420 mg calcium carbonate, and ranitidine plus calcium carbonate. Values for pH were converted to acid concentration (mM) and integrated acidity was calculated from the cumulative, time-weighted means of the acid concentrations for every second of the postprandial recording period.

RESULTS

There was a close temporal relationship between heartburn and oesophageal acidity. Most oesophageal acid exposure occurred over a 90-min period that began approximately 45 min after the end of the meal. During this period the gastric acid concentration was less than 5% of maximal. Ranitidine significantly decreased gastric but not oesophageal acidity, whilst antacid significantly decreased oesophageal but not gastric acidity. Ranitidine plus antacid significantly decreased both gastric and oesophageal acidity. Antacid alone and ranitidine plus antacid significantly decreased heartburn severity.

CONCLUSIONS

Determining integrated gastric and oesophageal acidity provides novel information regarding the pathophysiology of meal-induced heartburn as well as the actions of low-dose ranitidine and antacid. For subjects with meal-induced heartburn, treatment with low-dose ranitidine plus antacid is particularly effective in decreasing gastric and oesophageal acidity as well as heartburn severity.