6 VerduÁ EF, Fraser R, Armstrong D, et al. Effects of omeprazole

and lansoprazole on 24-hour intragastric pH in Helicobacter

pylori-positive volunteers. Scand J Gastroenterol 1994; 29:

1065±9.

7 Hatlebakk JG, Katz PO, Kuo B, Castell DO. Nocturnal gastric

acidity and acid breakthrough on different regimens of ome-

prazole 40 mg daily. Aliment Pharmacol Ther 1998; 12:

1235±40.

8 Mela GS, Savarino V, Moretti M, Bonifacino G, Zentilin P.

Mean and median of pH values, characterizing average in-

tragastric acidity. Am J Gastroenterol 1989; 84: 444±5.

9 Mela GS, Savarino V, Caputo E, Sumberaz A, Bonifacino G,

Zentilin P. 24-hour gastric pH-metry analysis: in¯uence of

arbitrarily prede®ned time intervals on the reliability of acidity

indexes. Am J Gastroenterol 1990; 85: 381±4.

10 Mela GS, Savarino V, Vigneri S. Optimizing the information

obtained from continuous 24-hour gastric pH monitoring. Am

J Gastroenterol 1992; 87: 961±6.

ReplyÐnocturnal gastric acid breakthrough on proton

pump inhibitors

Sirs, We appreciate Drs, Savarino and Mela's interest

and comments regarding our manuscript. Our ®rst

study1 investigated retrospectively the frequency of

oesophageal acid exposure during nocturnal gastric

acid breakthrough on proton pump inhibitors. We

concur that the frequency of nocturnal acid break-

through is affected by the presence of Helicobacter pylori.

In fact we have shown in a recent study that the

frequency of nocturnal gastric acid breakthrough is

more frequent in H. pylori-negative patients on a proton

pump inhibitor.2 Regardless of H. pylori status, oeso-

phageal acid re¯ux is present in 30±50% of patients

who have nocturnal gastric acid breakthrough while on

a proton pump inhibitor. This is the major conclusion of

our study and is unaffected by H. pylori status.

The two studies commented upon in the letter are

separate.1, 3 The ®rst was designed only to evaluate the

frequency of gastro-oesophageal re¯ux during noctur-

nal gastric acid breakthrough and did not address total

time pH < 4 in either the upright or recumbent

position. The second was designed to study the ef®cacy

of three different dosing regimens of omeprazole, as well

as to establish the frequency of nocturnal gastric acid

breakthrough on these dosing regimens. The de®nition

of nocturnal gastric acid breakthrough is similar

regardless of methodology; greater than 60 continuous

minutes of gastric pH < 4 in the nocturnal period.

There is no inconsistency in our de®nition of this

phenomenon.

P. O. K A T Z A N D D. O. C A S T E L L

Department of Medicine, Graduate Hospital,

Philadelphia, Pennsylvania

REFERENCES

1 Katz PO, Anderson C, Khoury R, Castell DO. Gastro-oeso-

phageal re¯ux associated with nocturnal gastric acid break-

through on proton pump inhibitors. Aliment Pharmacol Ther

1998; 12: 1231±4.

2 Katz PO, Silman J, Katzka D, et al. H. pylori (HP) infection in-

creases nocturnal acid control on proton pump inhibitors (PPI).

Am J Gastroenterol 1998; 93: A1641(Abstract).

3 Hatlebakk J, Katz PO, Kuo B, Castell DO. Nocturnal gastric

acidity and acid breakthrough on different regimens of ome-

prazole 40 mg daily. Aliment Pharmacol Ther 1998; 12:

1235±40.

978 LETTERS TO EDITORS

Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 977±978